WERSITY OF ILLINOIS BULLETIN
ISSUED WEEKLY
I AUGUST 7, 1916 No. 49
-~=~«H-«>iiusj[ mailer Dec. 11, 1912. at the Post Office at Urbana. 111., under tbe Act ot Aug. 2i
RESULTING FROM MINING
BY
L. E. YOUNG
AND
H. H. STOEK
.UNOIS COAL MINING IV T*STIGATIONS
COOPERATIVE AGRt. CNT
Cooperative Agreement bet we -n the Engineering E.xperi-
t" Illinoi: . the Illinois State Geological
nd the U. S. Bureau of Mines.)
BULLETIN No. 91
ENGINEERING EXPERIMENT STATION
PUBLISHED BY THE t. DIVERSITY OF ILLINOI URT^NA
CHAPMAN AND HAT,* . LTD., LONDON
EUROI'
EXCHANGE
UNIVERSITY OF ILLINOIS
ENGINEERING EXPERIMENT STATION
BULLETIN No. 91 AUGUST, 1916
SUBSIDENCE KESULTING FEOM MINING
• BY
L. E. YOUNG
Mining Engineer for the Illinois Coal Mining Investigations,
and
H. H. STOEK
Professor of Mining Engineering, University of Illinois
CONTENTS
PAGE
[INTRODUCTION 5
CHAPTER I :
Nature and Extent of Subsidence Problem 7
Eecords of Damage to Surface 9
Nature of Damage Due to Disturbance of the Overlying
Material 41
Nature of Earth Movement 42
Surface Cracks 44
Pit-Holes or Caves 46
Effect of Underwatering Surficial Beds 47
Effect on Drainage '. 49
Effect on Water Supply. . > 49
Subaqueous Mining 50
Industries and Interests Affected by Subsidence 57
Agriculture 58
345921
2 • -U\J--* *.-iaa.ii j,^
„
* •* ' " *%* PAGE
Transportation 59
Municipalities 62
Injury to Streets, Sidewalks, and Transportation
Lines 62
Injury to Buildings, Towers, and Chimneys 63
Injury to Water, Gas, and Steam Lines 68
Injury to Sewers and Sewage Plants 68
CHAPTER II :
Geological Conditions Affecting Subsidence 70
Mineral Deposits 70
Physical Character 70
Extent and Dip of Deposit 74
Uniformity of Mineral Deposit 75
Underlying Rocks 75
Overlying Rocks 76
Cleavage 80
Fractures 81
Experiments to Determine Rock Fracture 83
CHAPTER III:
Theories of Subsidence — General Principles 85
Historical Review of Theories of Subsidence 86
Opinions of American Engineers 113
CHAPTER IV:
Engineering Data and Observations 122
Angle of Break and Draw 130
Time Factor in Subsidence 136
CHAPTER V:
Laboratory Experiments and Data 138
Tests and Experiments for Securing Data 138
Effects of Lateral Compression Upon Stratified Mate-
rials 142
Effect of Vertical Compression Upon Beds of Stratified
Materials 143
Effect of Lateral Tension Upon Stratified Material. . .143
General Experiments 144
The Behavior of Various Types of Artificial Supports. 144
Suggested Experiments and Tests 144
CONTENTS 3
CHAPTER VI : PAGE
Protection of Objects on the Surface 146
Shaft Pillars 147
Room Pillars 149
Strength of Eoof 153
Filling Methods 155
Griffith's Method of Filling. 156
Gob Stowage in Longwall Mines 156
Gob Piers 157
Concrete and Masonry Piers 157
Cogs 158
Special Types of Cogs and Piers 159
Iron Supports 159
Hydraulic Filling 159
Pneumatic Filling 163
Supporting Power of Filling 164
Construction Over Mined-Out Areas : 167
Restoring Damaged Lands 169
CHAPTER VII:
Legal Considerations 170
Eight of Support 170
Mining Under Municipalities 170
Exemption from Liability for Damage to Surface 173
Protection of Surface by Grants and by Legislation 175
Remedies 177
Bibliography * 180
4 CONTENTS
LIST OF FIGURES
PACK
1. Probable Effect of Removal of Pillar Coal 22
2. Relation of Surface Cracks to Underground Workings 23
3. Section Through Adamson Mine, Oklahoma 27
4. Sugar Notch Mine, Surface and Underground Before Accident
5. Surface and Underground Features After Accident
6. Supposed Conditions Along C-C Before Accident 35
7. Actual Conditions Along C-C After Accident i
8. Plan of Greentree Tunnel and Old Mine Working 39
9. Section Through Tunnel and Mine 39
10. Lateral Movement of Monuments 43
11. Tension as a Cause of Surface Cracks 44
12. Surface Cracks in Western Pennsylvania 44
13. Surface Cracks at Ashland, Pa 45
14. Cave in Soft Soil (Photo by H. I. Smith, U. S. Bureau of Mines) 47
15. Pond Formed by Subsidence. . . 58
16. Disturbance of Grade by Subsidence <
17. Break in Sidewalk Due to Subsidence <
18. Cracks in Brick Building 64
19. Effect of Subsidence on Stone Lintels and Sills 64
20a. Effect of Subsidence on Stone Lintels and Sills 65
20b. Effect of Subsidence on Stone Lintels and Sills 65
20c. Cracks in Long Walls 65
81. Cracks in Masonry Wall 67
22. Angle of Fracture of Stone 81
23. Diagram Illustrating the "Law of the Normal" 86
24. "The Law of the Normal" Not Applicable to Steeply Dipping Beds 87
25. Forces Acting on Rock in an Inclined Bed 88
26. Fracture Normal to Bedding Plane 89
27. Line of Break Between Normal and Vertical 90
28. Vertical Fracture of Dipping Beds of Shale !
29. Schultz's Idea of Fracture of Sandstone Beds 93
30. Fracture in Dipping Beds According to Von Sparre 94
31. Subsidence Beyond Angle of Break According to Wachsmann 95
32. Angles of Fracture in Rock and of Subsidence in Marl 96
33. Basse's Theory; Angle of Break Vertical and Sliding Angle 97
34. "Main Break" and "After Break" 98
35. "Zone of Falling" and "Zone of Tearing" 100
36. "Zone of Tearing" Extended to Surface 101
87. Subsidence Outside Undermined Area 101
38. Large Subsidence in Case of Bending of Rock 103
39. Small Subsidence in Case of Breaking of Rock 104
40. Stresses in Arch 116
41. Arch Stresses in Mine Roof 117
42. Space Shortened by Falling Roof 118
43. Subsidence at Commentry Mine 123
44. Subsidence at Commentry Mine 124
45. Angle of Fracture at Shirebrook Colliery 127
46. Fractures and Survey Stations, Shirebrook Colliery 128
47. Data Obtained by S, R. Kay 130
48. Data Obtained by S. R. Kay 130
49. Location of Shaft Pillar in Dipping Bed 132
50. Sagging of Iron Bars 138
51. Subsidence of Artficial Beds 140
52. Bending of Shale Under Pressure (Photo by H. I. Smith, U. S. Bureau of Mines) . 143
53. Sizes of Shaft Pillars According to Different Formulas 148
64. Effect of Extent of Excavation on Amount of Movement 150
LIST OF TABLES
PAGE
1. Accidents in Wyoming Field Due to Inrushes of Sand and Water 34
2. Particulars of Coal Seams Worked Under the Waters of Oceans, Rivers, and Lakes. 51
3. Dimensions of Rooms and Pillars, Dominion Coal Company 56
4. Compression Tests of Illinois Coal February 6, 1907. Laboratory of Applied
Mechanics, University of Illinois 72
5. Average Results of Tests on Anthracite Specimens , 74
6. Moduli of Rupture of Stones '.!"..'!.'!!! 78
7. Specific Gravity of Rocks 79
8. Observations at Bent Colliery '.'... 126
9. Dates of Leveling and Particulars of Subsidence at South Kirby Colliery 127
1 0. Subsidence at Stuffynwood Hall 129
11. Angle of Break „'...' 134
12. Amount of Subsidence Expressed in Percentage ..'.'.'.'. ! 134
13. Dimensions of Pillars and Rooms in Pillar-and-Room Mining in Illinois 152
14. Increase in Volume of Materials in Filling 164
15. Results of Tests of Compression Upon Crushed Material * | " 165
16. Supporting Strength of Various Forms of Dry Filling 166
17. Extent of Filling in Ruhr Coal District, Germany 167
SUBSIDENCE RESULTING FROM MINING
INTRODUCTION.
The subject of the subsidence of the earth's crust as a result of
underground excavation due to mining has attracted widespread attention
for some years past, but particularly during recent years. With the
extension of mining and the increased value of the surface above the
mines in many localities, the growth of towns in mining regions, and the
extension of railroads over mining properties, the subject is one that
will be of increasing interest as time goes on, not alone to those engaged
in mining coal and ores, but to the railroads, municipalities, and other
owners and users of the surface that may be 'affected by mining opera-
tions.
That the subject is not one of mere local interest is shown by the
widespread distribution of surface subsidence as described in the follow-
ing pages.
This bulletin has been prepared not with a view of bringing forward
any new theories in regard to the subject, but it is in the nature of a
reconnoissance and a statement of present knowledge of the subject,
based upon the literature available up to the present time. It and a com-
panion preliminary Cooperation bulletin on subsidence in Illinois by
Dr. Young, which will be issued by the Illinois Geological Survey, are
intended as studies upon which to base a detailed cooperative investiga-
tion of. subsidence conditions in Illinois.
This bulletin represents the result of a study of the literature on
the subject. Much of the text is an abstract of this literature, supple-
mented by extensive private correspondence by the writers, and by a
study of conditions in western Pennsylvania, in West Virginia, and in
Maryland as given by office data and by an intimate acquaintance with
the subsidence problem in the anthracite fields of Pennsylvania.
The authors are particularly indebted to the several anthracite sub-
sidence commissions for the use of unpublished reports, and to a number
of engineers for private data, for some of which it has been possible to
give due credit in the text, while other data of a confidential nature has
had to be incorporated without due credit.
This preliminary study of subsidence literature and of the conditions
in Illinois suggests the advisability of undertaking a detailed study of
the problem in Illinois. This study may extend over a number of years
6 ILLINOIS ENGINEERING EXPERIMENT STATION
in the future. To begin such a study, several groups of mines should be
selected; one group in northern Illinois, one in the central part of the
state, and another in the southern part. At each mine selected monuments
should be erected, and the elevation of these monuments taken at intervals.
In connection with these surface observations the conditions in the mine
should be noted as closely as possible, in the hope that gradually data
will be collected upon which it will be possible to determine the prob-
abilities of and the extent of subsidence upon the surface when under-
ground conditions are known, to determine the size of pillars which will
most effectively prevent loss of coal due to squeezes and will properly
protect a given surface area.
For the preparation of the extensive bibliography, for the prepara-
tion of the abstracts of literature, and for the detailed presentation of the
data collected, credit is due entirely to Dr. Young, the undersigned hav-
ing acted mainly by assisting in the gathering of data and in an advisory
capacity in the preparation of the manuscript.
H. H. STOEK.
CHAPTER I.
NATURE AND EXTENT OF SUBSIDENCE PROBLEM
The removal of solid minerals from the earth's crust produces
cavities, and thus the equilibrium which has previously existed is dis-
turbed. If the cavities caused by the mining operations are not of great
extent, or, even if long, are narrow, this disturbance may be apparent
only as a local movement and may cause only occasional falls of rock
from the roof. If the excavation is wide as well as long, the unsupported
strata above the excavation will tend to sag under their own weight and,
if their texture will not permit the bending movement necessary for the
strata to become adapted to the new conditions, cracks and fissures result-
ing in extensive falls of roof will occur. Successively, the overlying beds
may break and fall until the disturbance extends to the surface.
If the overlying measures bend without breaking and sag until
finally they are supported by the floor of the excavation, the strata at
greater height may sag successively and in a corresponding manner.
Eventually, this movement may extend to the surface, the disturbance
generally being less extensive as the vertical distance from the excavation
increases.
In estimating the weight upon any coal seam or other mineral de-
posit due to the overlying rock, it is customary to assume that this weight
is distributed more or less uniformly over the entire deposit. When a
portion of a bed of mineral is removed, the burden carried per unit of
area by the unmined portion becomes greater than the burden carried
before any portion of the deposit was mined, because the weight formerly
distributed over the deposit is now concentrated upon the pillars. The
extent of the increase of burden on the pillars depends upon the extent
of removal of the material of the bed, assuming that the overlying rock
does not break in such a way as to relieve the stress on the pillars. If the
pillars are not strong enough to support the increased load, or if the
underlying bed does not have sufficient bearing power to resist the in-
creased pressure, a movement will begin which is commonly called a
"squeeze"* or a "creep." Depending upon the depth of the mining
operations and the geological conditions, the "squeeze" may cause an
extensive vertical movement which may reach to the surface. The
*The Pennsylvania Mine Cave Commission gave the following definition: "A 'squeeze'
is _ caused by the general subsidence of the strata overlying the coal bed, due to a partial
failure of the pillars; when this subsidence radiates from origin it is calted a 'creep'." -An-
other meaning of "creep" is movement of the floor, due to pressure of pillars.
8 ILLINOIS ENGINEERING EXPERIMENT STATION
removal of coal or other bedded minerals from any considerable area,
therefore, at once develops the problem of the support of the surface
which involves certain factors requiring careful attention by the mine
operator before extensive excavations are made. If the operator, for
commercial reasons, meets these problems in a manner that is not in
harmony with the prevailing ideas of conservation, a remedy should be
sought which will secure for the public the greatest continuing benefit.
Upon the opening of a new mine, the following questions may well
be asked:
1. Is the owner of the surface, if other than the owner of the mine
or mining rights, legally entitled to surface support?
2. Is the material to me mined at such a depth that mining of all
of it will not disturb the surface ?
3. If the removal of all the deposit will cause surface subsidence,
what percentage of the deposit left in pillars will prevent subsidence?
4. What is the ratio between the value of the material in the pillars
necessary to prevent surface subsidence and the value of the surface?
What would be the charge per ton against this pillar material if the
surface were bought outright ?
5. What amount and what extent of subsidence may be expected
under the conditions of operation most economical at the time?
6. Upon what basis will it be possible to adjust claims for damages?
7. What will it cost to restore the surface for agricultural uses after
all the deposit has been removed ?
There are certain questions which the public and the state should
answer at an early date :
1. Shall the coal or other mineral now in the ground be brought to
the surface and used or. shall it be left in the ground, serving like worth-
less rock, only to support the surface?
2. Assuming that the removal of all the material will temporarily
prevent the use of that part of the surface overlying the area being mined,
will it be better policy for the state to see to it that all the merchantable
material is mined and then have the surface restored, or will it be wiser
to permit nearly one-half the material to be lost permanently in the
effort to avoid temporary injury to the surface?
3. If the mine operator is required by law to protect the surface,
shall anything be done to prevent his leaving a large percentage of the
deposit in the ground, never to be recovered and simply to support the
surface?
Scientists who have investigated the national resources have em-
YOUNG-STOEK — SUBSIDENCE RESTJTING FROM MINING 9
phasized the fact that the supply of minerals is not inexhaustible and
that at the present rate of increase in production the exhaustion of the
supply of some of the most important ones is not far off, as time is
measured in the life of a nation. In the case of coal, one of the means
by which the life of our supply may be extended is by recovering all, or at
least a much greater percentage than is recovered at present, of the coal
in the ground. If the extent of the entire area underlaid with workable
coal beds be compared with the extent of tillable land not underlaid with
coal, it will be noted that the actual area that might be affected by surface
subsidence is relatively small. When it is realized that land affected by
subsidence may in most cases be restored to service for agriculture after
all the deposit has been removed, it may be rightly urged that the mine
operators remove much more of the coal than is taken under present con-
ditions, when preservation of the surface is frequently the determining
factor in deciding the amount to be mined. Since mineral once lost by
improper mining or left in pillars in abandoned mines is lost forever,
the maximum recovery consistent with safe mining is of prime im-
portance and is fundamental. The problems, therefore, are to discover
what effect mining under the existing physical conditions will have upon
the surface, to anticipate and to reduce to a minimum possible surface
subsidence and finally to discover the best means of harmonizing and co-
ordinating the various industrial and commercial interests involved.
As will be noted in the discussion of the legal considerations involved
in the problem* the legal rights of the several parties interested in the
minerals, in the surface, and in the other forms of property in the com-
munity must be considered both relatively and absolutely. A study of
the subsidence problem from various angles shows the complexity of
"conservation" applied to mining, to agriculture, and to other interests
at the same time. The complexity seems to increase when efforts are
made to coordinate these various interests.
KECORDS OP DAMAGE TO SURFACE.
While the technical press contains many reports of surface sub-
sidence attributed to mining operations there are in America only a few
reliable records, available for study, showing the exact amount of sub-
sidence of the surface after the mineral deposit has been mined. How-
ever, there are a number of instances in which European engineers have
kept records of surface levels extending through long periods of years.
•See Ch. VI.
10 ILLINOIS ENGINEERING EXPERIMENT STATION
Surface movements have in many instances been disastrous; records
of damage to property being available both in Europe and in America.
In the following section a number of the most important instances of
damage to property resulting from mining operations are presented.
These instances show that the problem is of widespread interest and is
not a local one.
Belgium.
Although serious subsidence adjacent to salt mines was noted in
England in 1850* and instances of damage by coal mining are recorded
in British technical literature., the problem of surface subsidence due to
mining operations seems to have been studied first in Belgium. In the
early part of the nineteenth century it was claimed that coal mining
about Liege, Belgium, was causing damage to buildings, and in the year
1839 complaints were filed with the city officials on account of damages to
property. As a direct result of these complaints, the city appointed a
committee to report upon the problem and in filing its report the com-
mittee established the necessary restrictions required for the safety of
the city and determined the size of adequate safety pillars.
The Belgian engineer, Gonot, formulated a theory of subsidence in
1839 and some years later published a pamphlet dealing with the dam-
age to a row of houses adjacent to the mine of the D'Avroy Bovene Com-
pany, claiming the mining company was responsible for the damage done.
The mining company published a reply to Gonot in 1858. The Provincial
Government appointed two engineers to investigate the cause of the
damage to the houses and they reported that the houses were not dam-
aged by coal mining.
By a decree of May 31, 1858, the Minister of Public Works ap-
pointed a special committee to report on the influence of mining upon the
surface and also to review the rules of the committee appointed in 1839.
The committee of 1858 endorsed the recommendations of the committee
of 1839.
The disturbance of the surface about Liege continued and G. Dumont
was appointed to investigate the matter. In his reportf he supported the
fundamental principle of Gonot's theory but made certain reservations
in its application. He placed the responsibility for the surface disturb-
ances upon the mining companies. The Colliery Owners' Association
*Trans. I. M. E., Vol. 19, p. 249, 1899.
t"Des Affaisements Du Sol Produits par 1'Exploitation houillere." Liege, 1871.
YOUNG-STOEK — SUBSIDENCE RESITTING FROM MINING 11
published a statement* pointing out the fallibility of Gonot's theory but
admitted the applicability of the theory to relatively flat seams.
Since 1875 considerable attention has been given to the problem in
Belgium, and the situation has been complicated by the mining of coal
from superimposed beds.
England, Scotland, and Wales.
Considerable attention has been given to the subsidence problem in
England, Scotland, and Wales, owing to the extent of the coal and salt
measures, to the importance of the coal industry, and to the proximity of
the mines to centers -of population. In the early days of coal mining in
Great Britain it was customary to leave pillars, but as mining practice
improved a portion of the coal in the pillars was removed. In discuss-
ing early methods of working coal, Bulman and Eedmaynef refer to
surface subsidence resulting from the removal of pillar coal as follows :
"The date at which it became customary to remove pillars formed by a
previous working has been a point of some importance in determining
claims for damage to the surface, and many such claims in which the
point arose have led to legal proceedings. That damage of this kind was
done at an early date is proved by the records of the Halmote Court for
the County of Durham. Early in the fifteenth century there was an
inquiry before that court about a case which had occurred in the parish
of Whickham in which it is recorded : 'It is found by the jury that John
de Penrith is injured by a coal mine of Rogers de Thorton so that the
house of the said John is almost thrown down, to the damage of the said
John of 200 pounds, assessed by the jury ; therefore it is considered that
the said Eoger repair the said house to the value aforesaid, or satisfy the
said sum.' "$
Since the year- 1860 a number of British mining engineers and
operators have written upon the general subject of subsidence and sup-
port of excavations. Subsidence has resulted from salt mining operations,
as well as from coal mining, and owing to the nature and extent of the
salt deposits the effect upon the surface has been even more disastrous
than the effect of coal mining. Salt mining has been carried on in the
vicinity of Northwich, Cheshire, for many years. In a depth of 390
feet there i& a total thickness of almost 200 feet of salt in four beds, the
thinnest being 5 feet thick and two being each approximately 90 feet.
The shallowest bed is covered by 32 feet of soil and by 92 feet of salt
*"Des Affaisements Du Sol Attribues a 1'Exploitation houillere." Liege, 1875.
tBulman, H. F., and Redmayne, R. A. S. "Colliery Working and Management," p.~ 9.
^'History of Durham." Francis Whellan & Co.
12 ILLINOIS ENGINEERING EXPERIMENT STATION
marl. Shafts were sunk to the upper bed shortly after 1670 and the
pillar-and-room system was used. Pillars from 12 to 21 feet square were
left to support the surface, but these pillars were weakened in time by the
dissolving action of the water which seeped through the roof and was
pumped out as brine. Surface breaks occurred which were generally
marked by brine pools. In 1750 the first serious breaks occurred near
the main street of Northwich. These old breaks have been filled and
buildings have been erected directly over them. Since 1750 numerous
breaks have occurred throughout the salt district.* After 1781 all new
shafts were sunk to the second bed, which is nearly 92 feet thick and is
separated from the upper bed by about 28 feet of hard marl. The most
serious subsidence occurred in 1880, and the locality is now covered by a
lake about 30 acres in area and of considerable depth.
The drilling of brine wells has increased the rapidity with which
the pillars have become weakened and has hastened subsidence in the
•vicinity of the old mines. Brine streams or channels have been formed
underground between the wells and old shafts, and subsidence is greatest
near these underground streams.
Owing to the seriousness of the subsidence over an area of 600 acres,
frame buildings are used, as these may be blocked up and restored after
the most serious surface movement has abated.
The local Board of Trade was asked by the Salt Chamber of Com-
merce in 1871 to have a report made upon the local situation. This
request was referred by the Board of Trade to the Secretary of State,
who directed Mr. Joseph Dickinson, Inspector of Mines, to make a report.
In March, 1873, Mr. Dickinson presented to Parliament a report which
was published under the heading, "Landslips in the Salt Districts."
In 1881 there was introduced in Parliament a bill which proposed to
give relief to the owners of damaged property in the salt district. This
bill failed to pass, but in 1891 a bill was passed providing for Com-
pensation Boards to be formed in the salt districts. These boards were
empowered to levy a tax, not exceeding 3d. on every 1,000 gallons of
brine pumped, to form a fund to compensate owners of property dam-
aged. This act was put into force, and in 1896 a provision was added,
limiting such compensation to private holders of property and excluding
all local authorities, gas and water companies, railway and canal com-
panies, and all pumpers of brine, no compensation whatever being allowed
them if any of their property were injured by subsidence.
*Ward, T. "Subsidence In and Around the Town of North wich in Chethire." Trans.
Inst Min. Engrs,. Vol. 19, p. 841, 1889-1890.
YOUNG-STOEK — SUBSIDENCE RESUTINQ FROM MINING 13
The examples of surface subsidence due to coal mining in England
and Wales are very numerous. Much agricultural land has been dam-
aged and also various improvements, including buildings, railroads,
bridges, railroad tunnels, canals, reservoirs, and streets and highways.
In one district the Great Western Railway had to fill 60,000 to
70,000 cubic yards annually. A canal in South Staffordshire has been
raised 20 feet. Coal mining under the Merthyr tunnel, 1% miles long,
produced a total subsidence of 10 feet in part of the tunnel. The settle-
ment throughout the length of the tunnel was not uniform and part of
the line had to be cut down to make the grade uniform.*
In the South Staffordshire district there has been considerable dif-
ficulty in securing suitable reservoir sites owing to the fact that coal
mining has extended under most of the land and owing also to the fact
that the bed is thick and nearly all the coal has been removed. A
3,500,000-gallon reservoir was built on a site which had been under-
mined thirty-four years before. When the reservoir was filled, the sub-
sidence amounted to 1*4 to 2 inches. The cracks were filled with cement
and the reservoir has since given no trouble. Another 43,000,000-gallon
reservoir was constructed in the coal district in which there are three
workable beds of coal, one being 8 feet 3 inches thick and lying at a depth
of 1,200 feet, while 66 feet below it is a 6-foot 3-inch seam, and 80 feet
above it is a 6-foot seam. These have been worked and one end of the
reservoir has lowered 4 feet more than the other, the great difference in
elevation between the ends being attributed to a fault.
In order to reduce the damage to water mains the practice in the
English mining districts is to use lead joints instead of the "turned and
bored" pipes, f
In the Midland and South Yorkshire coal fields the measures over-
lying the coal are principally shales, and mining at a depth as great as
2,000 feet has caused some subsidence.^
In his address as President of the Institution of Mining Engineers,
W. T. Lewis called attention to the seriousness of subsidence in Wales,
stating that the surface sinks from 10 to 15 feet on account of mining at
1,800 to 2,400 feet.fi The removal of 4 feet 9 inches of coal and under-
day, constituting a shaft pillar, at a depth of 2,108 feet is reported to
have caused surface subsidence of 3 feet 6 inches at the South Kirby Col-
*Ingles, J. C. "Subsidence Due to Coal Workings." Proceedings, Inst. of Civ. Engi-
neers, Vol. 135, p. 131, 1898.
tProc. Inst. of Civil Engrs., Vol. 135, p. 156, 1898.
JEng. and Min. Jour., Vol. 84, p. 196, 1907.
flTrans. Inst. Min. Engrs., Vol. 22. p. 290. 190L
14 ILLINOIS ENGINEERING EXPERIMENT STATION
liery.* This amount of subsidence is unusual in the district and was
attributed to the crushing of a shaft pillar in the overlying Barnsley bed.
A maximum subsidence of 1.74 feet resulted from longwall mining of 5
feet of coal at a depth of 1,595 feet in Derby shi re. f Mr. James Barrow
cited an instance of mining coal 5 feet 6 inches to 6 feet 6 inches at a
depth of 2,400 feet. The longwall method was used and the debris re-
sulting from the working of the seam and the brushing of the roof was
stowed underground.^ Subsidence caused buildings on the surface to
crack, water and gas mains to be broken, and bridges to be squeezed and
distorted. Mr. J. Kirkup reported that the mining by longwall of a
seam 22 inches thick produced cracks in walls and caused damage in
pipes in workings in a seam 279 feet above. Moreover, a careful survey
showed that the movement in the upper seam extended in advance of the
workings in the lower seam.fl Mr. I. T. Eees has reported on subsidence
resulting from longwall mining in the coal field in South Wales. The
lower seam worked was from 3 to 4 feet thick and was well stowed.
"Three hundred sixty feet above this seam, workings had been prose-
cuted in another seam in advance of the seam below, and although there
were 360 feet of intervening strata, and the openings caused by working
the seams were well stowed, yet the workings of the seam above were
affected a distance of 150 feet in advance of the workings of the seam
below."§ In 1912 the Wearmouth Coal Company, Ltd. (Sunderland),
was forced to stop working the Hulton seam, which employed 400 men,
on account of the heavy charges for surface damage resulting from sub-
sidence. In one case the charge was $500,000.**
France.
In France subsidence has been noted in the salt mining district as
well as in the coal fields. In French-Lorraine, the salt measures extend
under an area approximately 9 by 19 miles. The thickness of the beds
varies from 33 to 230 feet and the beds lie at a depth of 300 feet or
more. The salt has been removed in part by solution methods, which
produce large chambers, and, owing to the great size of these chambers
and to the character of the roof, extensive falls of roof rock have oc-
curred. The subsidence has generally taken place slowly, but where the
*Snow, Charles "Removal of a Shaft Pillar at South Kirby Colliery." Trans. Inst.
Min. Engrs., Vol. 46, p. 8, 1913.
tHay, W. "Damage to Surface Buildings Caused by Underground Workings." Trans.
Inst. Min. Engrs.. Vol. 34, p. 427, 1908.
JProc. South Wales Inst. of Engrs., Vol. 20, p. 356, 1897.
JIKirkup, T. Discussion of paper on "The Absolute Roof of Mines." Trans. Inst.
Min. Engrs., Vol. 31, p. 180, 1905.
§Proc. South Wales Inst. of Engrs., Vol. 20, p. 359, 1897.
**Trans. Inst. Min. Eng., Vol. 44, p. 533. 1912.
YOUtfG-STOEK — SUBSIDENCE RESITTING FROM MINING 15
covering is limestone there have been sudden breaks which have caused
extensive damage. Among the serious surface movements reported are
one in 1879 at St. Nicholas and one at Ars-sur-Meurthe in 1876.*
Fayol made a number of observations of subsidence at the Com-
mentry Mines, as well as laboratory experiments, and published the
results of his observations, including the levels taken at these mines
from August, 1879, to May, 1885.f He advanced a theory of sub-
sidence which was essentially different from that formulated by the
Belgian engineer, Gonot.
Germany.
Probably the first important German publication on surface sub-
sidence in connection with mining was by A. Schulz, in 1867'4 He
investigated the dimensions of safety pillars and the angle of break in
the Saarbruck field. The problem was considered so important that in
1868 the Prussian government appointed a commission of four engineers
to investigate the effect upon the surface of mining operations in the
coal fields of Belgium, England, France, and Rhenish Prussia. In
1869 von Dechen wrote upon the subsidence in and about the city of
Essen. He had previously (in 1866) emphasized the importance of
studying the part played by the heavy marl beds overlying the coal
measures.
In 1867, von Sparre contributed a paper upon the "afterbreak."fl
In 1894, the project of a canal between Herne and Ruhrort aroused a
discussion in regard to the stability of the surface over which the pro-
posed canal was to run. The Board of Mines of Dortmund conducted
observations in the Dortmund district and the results were published in
1897.§
In the Dortmund district there have been a number of accidents**
due to thrust movements, and in the Ruhr coal fields miniature earth-
quakes, supposed to have been due to coal mining, have caused consid-
erable damage.
Methods of reducing surface subsidence by hydraulic stowing have
received much attention from the mining operators of Upper Silesia
and Westfalia.
The coal-beds under Zwickau, Saxony, are situated at a depth of
*Bailly, L. "Subsidence Due to Salt Workings in French-Lorraine." Annales des
Mines, Ser. 10, Vol. 5, pp. 403-494, 1904.
tBul. de la Societe de 1'Industrie Minerale, IIe serie, Vol. 14, p. 818, 1885.
JZeit. fur B.-, H.-, u. S.-W.. 1867.
UGliickauf, 1867.
§Zeit. fur B.-. H.-, u. S.-W., p. 372, 1897.
**Zeit. fur B.-, H.-, u. S.-W., Vol. 51, p. 439, 1903.
16 ILLINOIS ENGINEERING EXPERIMENT STATION
600 to 2,500 feet. Beginning in 1885, observations were made at eighty-
two points to determine the surface movement resulting from mining
operations. After twelve years it was noted that subsidence amounted
to 85.2 inches, due to mining at 600 to 900 feet. At 1,500 feet, the
subsidence was only 9.17 inches.
The town of Eisleben in the Mansfeld mining district was seriously
damaged by earth shocks, fissures, and subsidence during the years from
1892 to 1896. Various theories were advanced concerning the cause of
these disturbances. Some held that they were due to the dissolving of
various salt deposits by underground water thus producing caverns,
and that as these caverns became of great extent, large falls of overlying
rock caused the shocks and the subsidence. Others held that in addi-
tion to the solution of the salt, carbonated waters were leaching the
deeper lying dolomitic formations, and when these became honeycombed,
they were unable to support the load concentrated on the natural pillars
resulting from the solution of part of the overlying salt beds. At the
Mansfield Copper Mine copper bearing shale from 12 to 20 inches thick
was being mined by a longwall method at a depth of from 900 to 1,800
feet. Public opinion blamed the mining company and, as a result of
arbitration, the company paid $125,000 damages.*
Potash mining at Stassfurt in beds 50 feet thick and dipping 40
degrees has caused serious subsidence. Stone buildings have sunk as
much as 20 feet, rows of houses have been removed to firm ground, and
chimneys and towers are standing 5 degrees from the vertical.f
On June 10, 1910, surface subsidence, described as a local earth-
quake, occurred at the Consolidation Mine. "The part of the coal
measures most affected formed part of an undulation or 'saddle.' The
forces at work were of such intensity, and so irregular in their action,
that steel rails were twisted into corkscrew like shapes, and in a section
of the saddle 10 feet in length, two lines of rails, water-pipes, signal-
wires, and rope-way were found crushed together into a bundle of about
12 to 16 inches thick/?$
Austria.
The review of the theories of subsidence presented by Austrian en-
gineers, as given by Goldreich,!}. indicates that as early as 1859 there
*Lang, Otto "Subsidences at Eisleben." Bui. de la Societe Beige de Geologic, Vol.
11, p. 190, 1898.
t Private correspondence.
JZeit. f. B.-, H.-, u. S.-W., Vol. 59, p. 68, 1911. Abstracted in Trans. Inst. Min. Eng.,
Vol. 41, p. 587, 1910.
flGoldreich, A. H. "Die Theorie der Bodensenkungen in Kohlengebieten." Berlin, 1913.
YOUNG-STOEK — SUBSIDENCE RESUTING FROM MINING 17
were regulations controlling the mining of coal under railways in
Austria. Director W. Jicinsky published a treatise on "The Subsidences
and Breaks of the Surface in Consequence of Coal Mining."* The
publication by Ezihaf was the first contribution by an Austrian engineer
to the theories of subsidence. Most of the Austrian writings on sub-
sidence have been on the problems of the Ostrau-Karwin coal district.
Goldreich has studied the problem principally through years of ob-
servation in railway engineering.
One of the most serious disasters in Austria resulting from sur-
face subsidence occurred July 19, 1895, at Brux, Bohemia^ where the
brown-coal seams lie nearly horizontal at a depth of 325 feet, covered
by clay-shale interspersed with quicksand from 10 to 65 feet thick.
There are in all four seams having an average total thickness of 80 feet.
Some filling had been used, but sand broke into the mine, and it is
estimated that two million cubic feet of sand entered the workings.
Numerous holes were formed on the surface, rendering sixty-six houses
uninhabitable and making 2,000 people homeless.
Another serious disaster occurred at Eaibi, Bohemia, at a lead mine,
where an attempt was being made to secure an adequate water supply
through underground workings. Two short drifts were being driven
through the rock toward water-bearing sands, and though a borehole
was kept ahead of each drift, a blast so weakened the cover that the roof
broke and a rush of sand followed. A large hole was made on the sur-
face and without warning a small municipal hospital dropped forty
feet, causing the death of seven of the inmates.fl v
India.
Coal mining in the Bengal field has caused disturbance of the
surface along the outcrop. At the Khoira Colliery the mining of 10
feet 6 inches of coal dipping 30 degrees has caused complete subsidence
of the surface where the workings are shallow. At the Barrea Colliery,
owing to the value of the rice land, stowing has been used to reduce the
amount of subsidence. § In the same field mining of thick coal over-
laid by thick beds of sandstone has been attended by extensive falls of
roof which have produced fatal air-blasts.**
*Oestrr. Zeit. fur B.-, u. H.-W., p. 457, 1876.
tOestrr. Zeit. fur B.-, u. H.-W., 1882.
JHelmhacker, R. "Land Subsidence at Brux, Bohemia." Trans. Inst. Min. Engrs.,
Vol. 10, p. 583, 1895-96.
flOestrr. Zeit. fur B., u. H.-W., Vol. 58, p. 31, 1910.
§ Stonier, G. A. "Bengal Coal Fields." Trans. Inst. Min. Engrs., Vol. 28, p. 537. 1904.
**Adamson, T. Trans. Inst. Min. Engrs., Vol. 29, p. 425, 1905.
18 ILLINOIS ENGINEERING EXPERIMENT STATION
South Africa.
In the diamond mines of South Africa there have been rushes of
mud into the mines. These have been due to water softening the steep
walls of the open pits which then give way and fill the mine openings.*
In connection with the Rand gold mines there has been surface
subsidence similar to that caused by deep longwall coal mining, f The
maximum depth from which mining has affected the surface has been
710 feet on the Champ d'Or. Other depths from which subsidence has
extended to the surface are 566 feet at the Bonanza mine, 650 feet at the
May Consolidated, 480 feet at the Treasury, 340 feet at the New Klein-
fontein, 490 feet at the New Heriot, and 425 feet at the Windsor. At
the Gueldenhuis Deep an area 1,000 feet on the strike by 620 feet on
the dip, at depths of from 650 to 924 feet, with an average stoping width
of 15 feet caved suddenly but no sinking of the surface resulted. Similar
results at other mines have led South African engineers to conclude
that cavings of stopes below 1,000 feet in depth will not affect the
surface.
UNITED STATES.
Alabama.
In Alabama little attention has been given to the subsidence prob-
lem, owing to the fact that many of the coal mining companies have
been operating under land to which they hold the title and of which
the surface has relatively little value in comparison with the coal. At
least 90 per cent of the mining is at a depth of less than 400 feet. Some
cracks have extended to the surface and when damage has been caused
to property not owned by the mining companies, it has usually been
possible for the mining companies to make settlements not greatly out
of proportion to the damage done.J At the present time some mining
is being carried on where the cover is as much as from 800 to 1,200
feet and very little trouble is being experienced.
Idaho.
In the metal mines of the Coeur d'Alene district, disturbances
have been noted which apparently are due to causes similar to those
•Williams, G. F. "Diamond Mines of South Africa," pp 400-404.
tRichardson, A. "Subsidence in Underground Mines. Jour, of the Chem. Met. and
Min. Soc. of S. A.j Mar., 1907; Eng. and Min. Jour., Vol. 84, p. 196, 1907.
JPrivate correspondence.
YOTJNG-STOEK — SUBSIDENCE RESUTING FROM MINING 19
which have produced air-blasts in other ore mines.* Kecently at an
Idaho ore mine two men were killed and four seriously injured by an
air-blast.
Illinois.
Subsidence of the surface due to coal mining has attracted atten-
tion in Illinois for a number of years. In the early days of coal mining,
when only the shallow beds were mined, the surface was seriously dam-
aged, but in those days the price of farm lands was low and most of the
mining was conducted in sections not thickly populated. The first im-
portant suit for damages that was appealed to the higher courts in
Illinois was in Sangamon county in 1880 (Wilms vs. Jess, 94 111. 464).
Since that date but few subsidence cases have been tried in the higher
courts in Illinois, most of the claims for damages being settled by ar-
bitration or by decisions of the lower court.
An investigation in 1914 showed that there had been surface sub-
sidence in the most important coal producing counties of the state.
Twenty-four of the total of fifty-two counties in which coal is mined
produced 94 per cent of the coal mined in the state in 1913, and in
twenty-one of these counties, subsidence, in various stages and degrees
of intensity, was noted.
The reported damages include injury to farm lands and buildings,
to city buildings and streets, to railroads and highways, and to domestic
and municipal water supplies. Large tracts of farm land in northern
Illinois are reported to be damaged by disturbance of surface drainage
due to subsidence. There has been litigation to determine the extent
to which mining is responsible for the inundation of lands adjacent to
waterways and streams.
Few instances of injury to persons by subsidence of the surface
have been reported. Mining at shallow depths has permitted the move-
ment of large bodies of surficial material, at time resulting in a rush
of sand, clay, and water into the mine, causing serious damage to the
mine. Fortunately there have been but few such instances of personal
injury to miners from such rushes. This may be due largely to the pre-
cautionary steps which have been taken since the accident in the long-
wall field in 1883 at Braidwood. The disaster at Mine No. 2 of the
Diamond Coal Company near Braidwood, Illinois, was due to the inrush
of water through surface breaks caused by subsidence.f
*Sizer, F. L. "An Air-Blast or Earth Movement." Mines and Minerals Vol 33 o 87
1912.
tCoal Report of Illinois, p. 97, 1883. Roy, A. "History of the Coal Mines of the
U. S." Columbus, pp. 190-194, 3d Ed., 1907.
20 ILLINOIS ENGINEERING EXPERIMENT STATION
A horizontal bed, 3 feet thick, was being mined at a depth of about
100 feet. The overlying strata are largely shale and clay. Longwall
mining had permitted the surface to sink and, at various points at which
the rock cover was thin, cracks and breaks extended for some distance
up into the surficial material. In February, 1883, there had been a
heavy fall of snow followed by a thaw and rain. On February 15, vast
sheets of water were standing on the prairie and on the following day
a number of the miners did not go to work, as they feared that the water
would break through into the mine. At 11 a. m. on February 16 there
occurred a cave which permitted a great inrush of water from the sur-
face. The flow of water cut out a larger inlet to the mine and in a short
time all of the low points on the roadways were filled with water so
that escape was impossible. In three hours the entire mine was filled
and the water rose to the surface. Sixty-one men and boys failed to
escape before the mine was flooded.
A comprehensive report upon subsidence in Illinois has been pre-
pared by L. E. Young and will appear as a contribution of the Coopera-
tive Investigation by the Illinois Geological Survey.
Indiana.
The following data regarding subsidence in Indiana have been fur-
nished by H. I. Smith, mining engineer, U. S. Bureau of Mines :
A few squeezes have been reported in the mines near Evansville. At
one mine operated under the Ohio Kiver at a depth of 260 feet below
the river bottom no trouble from the overlying river was reported and at
another mine operated at a depth of about 300 feet no loss of coal due
to squeezes was reported when about 55 per cent of the coal was removed.
Local squeezes occurred but were stopped by a barrier pillar and the coal
was reached from the next set of parallel entries.
Probably the greatest damage from subsidence in Indiana has been
in Clay county over the upper and lower block coal beds. In one in-
stance in which there was from 20 to 40 feet of cover, consisting of shale
with 2 to 6 feet of clay and soil on top, the overlying material was so
yielding that an outline of each pillar or stump could be traced on the
surface. After a period of twenty years these sinks are said to have
evened up, leaving little or no trace upon the surface. Over recent work-
ings succeeding rooms can be traced on the surface by pit-holes or sinks.
In some cases the strata have broken through to the surface and the
depth of the hole is the same as the thickness of the coal, that is, about
five feet. Local residents state that within five years farm land again be-
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 21
comes tillable and in twenty years the depressions have disappeared.
This does not apply to large swags which cover a number of adjacent
rooms and which in some cases must be drained. A good example of
these swags is found at West Seeleyville in the field north of the inter-
urban stop and between the interurban stop and the Vandalia Eailroad.
These swags are said to have occurred one year before the mine was
abandoned, and the coal is said to lie at a depth of 110 feet.
In Vigo county, about 1% miles north of Miami, a number of small
sinks were observed in a cultivated field. On the opposite side of the
road, in Clay county, one of the sinks has broken through and is about
five feet deep. Other depressions were observed in the line of these work-
ings, but were not broken through.
A private correspondent reports that in Linton, about six years ago,
one side of a concrete block house dropped from 2~y2 to 3 feet. The break
extended from top to bottom and passed through the blocks instead of
following the joints. Two or three years ago one section of an L-shaped
school house was badly damaged and the front end of a store fell in.
The court records show five or six suits at Linton for recovery of dam-
ages due to mining. The coal is worked on the room-and-pillar system.
Longwall mining at shallow depths in Kansas in the vicinity of
Osage City has caused some subsidence, but no damage has been done
to sidewalks, brick buildings, etc. The coal is from 12 to 18 inches thick,
and lies at a depth of 70 to 80 feet.* Above the coal is a light limestone
and upon it rest the upper Pennsylvania strata of alternating shale and
limestone.f
It is reported that subsidence of surface has resulted from the re-
moval of salt by brine-pumping. The salt measures are about 400 feet
thick and are covered by a total thickness of 600 feet of beds of shale,
limestone, and sandstone.
In the southeastern part of the state mining is conducted on the
room-and-pillar system in coal dipping gently toward the west. There
have been subsidences, especially near the outcrop, but no extensive dam-
age has been done.
Near Leavenworth longwall mining is carried on at a depth of about
700 feet in a bed 19 to 24 inches thick. There are no published records
of subsidence. The surface is rolling and no damage would be likely
'Private correspondence.
t Kansas State Ceol. Survey, Vol. I, p. 70.
ILLINOIS ENGINEERING EXPERIMENT STATION
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING
23
except to buildings, paving, pipes or sewers. The numerous stone and
brick buildings of the State Penitentiary at Lansing have been under-
mined by the State Mine, but show no evidences of subsidence. Mines
extended under the Missouri Eiver show no seepage of river water.
Maryland.
In the George's Creek Eegion, Maryland, the coal seam varies from
6 feet 6 inches to 9 feet 10 inches in thickness and, when the pillar coal
is removed, falls occur which extend to the surface.* Fig. 1 indicates
the supposed effect of the removal of the pillars under the overlying strata
where the surface is 250 feet above the coal seam. Subsidence extends
FIG. 2. RELATION OF SURFACE CRACKS TO UNDERGROUND WORKINGS.
to the surface in such a case after the pillars have been drawn back
220 feet. After the first break occurs at B due to drawing the pillar at A,
the entire block of roof sinks and causes the cavity C. The distance from
A to B horizontally is 40 feet, or 40 feet of pillar have been taken out
when the first fall occurs. The second fall occurs at D and the fracture
line extends to the space E at the Redstone seam. This break occurs
*Reppert, A. E. "Pillar Falls and the Economical Recovering of Coal from Pillars "
Proc. West. Va, Coal Mining Institute, p. 110, 1911.
24 ILLINOIS ENGINEERING EXPERIMENT STATION
after 60 feet of pillar has been taken out and the break extends almost 40
feet above the floor of the Pittsburgh seam. The third fall extends to F
and the fourth to G, the line of fracture in the latter case extending to
the space H in the Lower Sewickley seam, 85 feet above the floor of the
Pittsburgh seam, the total length of pillars drawn up to this stage being
100 feet. The next break occurs when pillars have been drawn for 160
feet to K and the break extends to L. When the pillars are drawn back
a distance of 220 feet to M the fracture extends to the surface at N, a
height of 250 feet above the bottom of the Pittsburgh seam. This frac-
ture line is approximately correct as shown in Fig. 1 and is based on
actual survey and observation of a large number of surface breaks in rela-
tion to the mine workings. Fig. 2 indicates the position of surface breaks
due to the removal of pillars at a depth of 170 feet over an area 300 feet
by 350 feet, the thickness of coal averaging 8 feet. The first surface
break occurred between rooms No. 1 and 2 and was about 70 feet from
the barrier pillar. The average angle of fracture from the vertical is
22° 30'. The break along the barrier pillar at the top of the rooms was
at an angle of 14° from the vertical, while the break along the left hand
pillar of No. 4 room was nearly vertical. The conclusion has been drawn
that "until a pillar fall extends to the surface, the fracture is conical in
shape, but as the pillar line extends down the rooms beyond the first
surface break, the strata fracture on a nearly vertical line."*
Michigan.
Copper Mines. — In the deep copper mines of northern Michigan ex-
tensive falls of roof have produced air-blasts. At great depths the
pillars left to support the roof, or at times masses of poor rock left tin-
mined, show the effect of the tremendous weight upon them. The edges
of these pillars fail first and large slabs may burst off and fly some
distance. The pillars fail suddenly and the fall of rock may be extensive
enough to cause a jar that will be felt on the surface.f
Beginning in 1904 there were a number of caves at the Atlantic
mine. The stopes averaged 15 feet in width and extended for a mile
along the strike of the lode and for one-half mile down the dip. These
falls became so extensive and the pressure on the pillars became so great
that the shafts were ruined and the mine was put out of commission,
May, 1906.$
*Op. Cit, p. 118.
tMcNair, F. W. "Deep Mining in the Lake Superior District." Eng. and Min. Jour.,
Vol. 88, p. 822.
IStevens. H. J. Copper Handbook. VoL 10, p. 877.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 25
Extensive falls of the hanging-wall or roof have caused trouble at
the Quincy mine. Stoping averages 20 feet in width and in parts of
the mine has been carried on to a depth of more than 6,000 feet on the
dip of the lode. The sudden and violent compression of air by falls
in the mine has caused damage to the levels and shafts and has produced
miniature earthquakes.* The general manager of the Quincy mine, in
his report for the year 1914, writes as follows:
"On March 25 air-blasts occurred throughout the mine and con-
tinued intermittently for a week or ten days. As a consequence, various
cross-cuts and drifts were crushed and closed up. No. 6 shaft timbers
were seriously crushed between the 51st and 58th levels, and No. 2 shaft
was crushed and closed between the 40th and 50th levels. About 500
feet of the crushed section of No. 2 shaft had to be entirely recovered
and retimbered at an expense nearly as great as that of sinking a new
shaft. In the remaining portion of the damaged shaft about half of the
timbers were replaced.
"Below the 50th level the shaft was not damaged by the air-blasts,
though the cross-cuts at the 57th, 64th, 65th and 66th levels were en-
tirely closed, and the levels north were badly crushed.
"In earlier days, when air-blasts were little understood, it was the
custom to stope out the lode without reference to the shaft. Going
through the upper portions of No. 2 and No. 6 shafts is like going down
through open stopes, with practically no pillars left to protect the shafts.
It was in the lower part of these sections that the caving and crushing
took place with such serious results.
"At the present bottom of the mine, pillars are being left 200 feet
on each side of the shaft. The air-blasts have never caused any damage
to these sections of the shaft.
"Air-blasts have continued with more or less frequency since July,
though they have not damaged or retarded the work to any great extent.
In order to meet the air-blasts and prevent as far as possible the dam-
ages caused by them, as fast as the mining in each stope is finished, the
bottom of the stope along the back of the level is filled with poor rock,
constituting what is termed 'rib work.' Experience has taught that
these rock-packs are the most effective means yet employed to lessen the
damages caused by air-blasts. In order, however, that the highest effect-
iveness possible may be secured within the limits of profitable mining at
greater depth, this rib work should be still further strengthened. It is
'Ibid.. Vol. 10. p. 1444.
26 ILLINOIS ENGINEERING EXPERIMENT STATION
estimated that the voids in the rock give it a shrinkage of about 20 per
cent at the present depth of the mine. In order to lessen this shrink-
age and strengthen the rib work, the question of filling the voids with
bank sand, stamp sand, or crushed rock is receiving serious attention,
inasmuch as provision must be made for better and stronger supports
to the back of each level, as fast as stoping is finished. During the year
$57,190 was spent for the recovery of the shafts and levels that were
damaged by the air-blasts, and $21,487 has been expended in the fight
toward preventing damages by air-blasts."
These rock movements appear to be confined to the deeper portions
of the mines and no effect is noted at the surface except a vibration,
giving the effect of an earthquake. No subsidence is reported.
- Iron Mines. — At a number of points on the Lake Superior iron
ranges, in Michigan and in Minnesota, the mining of extensive bodies
of ore close to the surface has caused the subsidence of large areas. A
considerable portion of the iron ranges is covered with glacial deposits
and when the bedrock is shattered by mining rushes of sand into the
mine may follow.
At several important mines large caves have occurred under im-
portant railway lines. Owing to the inclination, volume, and extent
of the ore body it was thought that it would be more practical to bring
the track to grade by filling than to construct a new line entirely outside
the subsiding area. The continued development of the ore body and
deeper mining have caused the subsidence to continue from year to
year so that now the problem of filling has become a very expensive one
for the railroad company.
Missouri.
At Lexington, Missouri, the mining of 20 inches of coal at a depth
of 160 feet has caused subsidence amounting in places to the full thick-
ness of the coal. No serious damage has resulted.*
In the Joplin district extensive caves of the surface have resulted
from the mining of large bodies of zinc ore at shallow depths, but no
detailed study of subsidence has been made.
During the year 1915 a number of mills were damaged through the
tailings piles falling into the excavations. One cave-in resulted in the
death of several men in the mine by drowning and it seems inevitable
that there will be many more caves in the district, particularly in the
sheet deposits where small pillars are left.
'Private correspondence.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 27
In the Flat Eiver district large areas have been mined at depths up
to 700 feet. The beds are practically horizontal and have good roofs.
"In some mined-out areas where the pillars have been removed and
slabbed the back has come in, extended over an area of from one to
three acres. In two such caved areas that have been examined it has
been found that in each case a natural arch has been formed and the
caved material has nearly filled the opening to the back. The largest
of the caves of this type has run up about 100 feet into the back, which
leaves about 400 feet of undisturbed formation above it."*
Oklahoma.
Coal mining in Oklahoma has caused surface disturbance at a num-
ber of places. On September 4, 1914, a serious squeeze occurred in
Mine No. 1 of the Union Coal Company at Adamson, which resulted in
the death of thirteen miners, complete loss of the mine, and minor sur-
face damage. The mine was opened on the pillar-and-room system.
Fig. 3 shows a cross-section through the two thin seams that were
worked. The lower seam is 4 feet thick and 45 feet above it is a seam
Cmc/rs
Caved to arrow
Z'cracX be/owgrouncf.
None on surface
eoo' 400
FIG. 3. SECTION THROUGH ADAMSON MINE, OKLAHOMA.
2 feet 3 inches thick, not worked. The beds dip about 30 degrees.
Eooms were turned on 33-foot centers, the room pillars being not more
than 9 to 12 feet wide and in places much less. The roof was a sandy
shale, 28 feet thick, and above it an equal thickness of hard sandstone
and a little fireclay. The squeeze came comparatively quickly, completely
^Private correspondence.
28 ILLINOIS ENGINEERING EXPERIMENT STATION
closing the slope. A number of cracks appeared on the surface, but no
serious surface damage was done.*
There are no records available showing the amount of surface sub-
sidence, but the surface cracks have been located fairly accurately. As-
suming that the underground break extended to the tenth level, there
was about 700 feet of cover, and the angle of break may be calculated
for the cracks farthest from the mouth of the slope. It has been
assumed that the large crack over the east side resulted when the 7th
East entry was lost. Similarly cracks on the west may be correlated with
the underground movement on the 6th West and 9th West entries.
George S. Kice, Chief Mining Engineer, U. S. Bureau of Mines,
says in regard to this accident :
"What happened was almost inevitable with a strong roof and in-
creasing depth, where so large a percentage of the coal had been ex-
tracted in the advance work and the pillars left standing. Estimating
from the map, about 7'5 per cent of the coal had been taken out by the
entries and rooms. As a result, in the lowest level of the mine there was
a load of over 3,000 pounds per square inch on the 25 per cent of coal
which remained in the entry and room pillars. This is more than
bituminous coal can sustain. Therefore, I am inclined to think that the
main support of the overlying strata had been carried by arch stresses,
the arch being buttressed on one side by the strata near the outcrop and
on the other by the dipping strata. Then when the fracture occurred
at the latter buttress, it threw the entire weight on the mine pillars,
causing them to be crushed. The surface cracks, reported by reliable
witnesses to have occurred prior to the collapse, running parallel but in,
advance (horizontally) of the lowest level, indicated that a shear frac-
ture had occurred in a plane roughly at right angles to the plane of the
dipping beds, and when this fracture extended laterally to a- sufficient
distance, it formed a slip plane which permitted the entire weight ol
the overlying strata less friction to be thrown upon the pillars, resulting
in the collapse of the mine."
Pennsylvania.
Pennsylvania Anthracite Field. — In the United States surface sub-
sidence due to mining operations has received most attention in the an-
thracite field of Pennsylvania, and notably in the city of Scranton. Of
the total area of 176 square miles in the Wyoming region, incorporated
boroughs and cities cover 101 square miles.f The city of Scranton ex-
•Brown, G. M. "A Sudden Squeeze in an Oklahoma Mine/' Coal Age, Vol. 0,
p. 618, 1914.
tReport of Pa. State Anthracite Mine Cave Commission, 1918.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 29
tends entirely across the coal field, a distance of five miles, and for the
same distance along the valley. Beneath a portion of the city are eleven
important coal beds having an average aggregate thickness of 58 feet.
It has been estimated that during the seventy-five years of active mining
under the city 177,000,000 tons of coal have been produced. This
output represents a volume of 198,000,000 cubic yards, an amount in
excess of the total estimated excavation in connection with the Panama
Canal.* In the early years of mining accurate maps of the mines were
not made and preserved and a number of the coal companies made little
effort to columnize the pillars in the various coal beds that were worked.
These conditions have made it difficult to study the problem and to pro-
vide adequate and practical remedies.
While subsidence has occurred in many parts of the city, it was
estimated in 1912 that not more than 15 per cent of the area of the city
was threatened.
Although surface subsidence had damaged property within the
city limits prior to August 29, 1909, the public in general gave the matter
little connected attention. This was due largely to the fact that the
mining companies hold deeds which permit them to remove the coal
without liability for damage to the surface. On the date mentioned,
surface subsidence caused serious damage to a school building, which
fortunately was not in use at that season of the year.
Following this cave Honorable J. B. Dimmick, then Mayor of
Scranton, by approval of the City Council and the Board of Control of
the Scranton School District, created a Commission to investigate the
physical causes of mine caves and the legal responsibility therefor. The
report of this Commission, submitted March 20, 1911, was published in
1912 as Bulletin No. 25, U. S. Bureau of Mines. It was the result
largely of the investigations of Eli T. Conner and William Griffith and
reviews the existing mining conditions and discusses at length methods
for supporting the surface. Considerable attention was given to "flush-
ing" methods of filling and the report contains a chapter by N. H.
Darton, entitled "Notes on Sand for Mine Flushing in the Scranton
Region." An appendix includes the results of tests to determine the
compressive strength of anthracitef and of tests of various kinds of
materials for supporting the roof in mine workings.^
*Bul. 25, U. S. Bureau of Mines, Washington, 1912.
tThese tests were made for a committee of the Scranton Engineers' Club in 1900 in the
engineering laboratories at Cornell University, Lehigh University, and the Pennsylvania
State College.
^Fifteen tests on the compressive strength of materials for supporting roof were made
for this investigation at the Engineering Laboratory of Lehigh University.
30 ILLINOIS ENGINEERING EXPERIMENT STATION
The U. S. Bureau of Mines continued investigations along several
lines which were discussed in the report by Conner and Griffith and
subsequently published the results as bulletins. Bulletin No. 60 con-
tains the investigation by Charles Enzian entitled "Hydraulic Mine
Filling; Its Use in the Pennsylvania Anthracite Fields." Bulletin No.
45 by N. H. Barton is a report upon "Sand Available for Filling Mine
Workings in the Northern Anthracite Basin of Pennsylvania."
In 1911 Governor Tener appointed the Pennsylvania State An-
thracite Mine Cave Commission to investigate the physical conditions
and legal rights of surface support. This Commission consisted of:
W. J. Richards, Vice-President and General Manager, Philadelphia
and Reading Coal and Iron Co.
G. M. Davies, Mining Contractor.
J. Benjamin Dimmick, Mayor of Scranton.
E. G. Lynett, Editor, Scranton Truth.
W. L. Connell, Coal Operator, Ex-Mayor of Scranton.
R. A. Phillips, General Manager, Coal Department, Delaware,
Lackawanna and Western Railroad.
W. H. Lewis, Retired Coal Operator.
Charles Enzian, Mining Engineer, U. S. Bureau of Mines.
W. A. Lathrop, President, Lehigh Coal and Navigation Co.
(Owing to the death of W. A. Lathrop, he was succeeded by S. D.
Warriner, President, Lehigh Coal and Navigation Company.)
The investigation of this Commission covered the period from June
12, 1911, to March 1, 1913, when the report was submitted to the Gov-
ernor and Legislature, the text of the report being printed in the
Journal of the Pennsylvania Legislature for 1913, Volume 5, page 5947.
This Journal report contains none of the maps or illustrations essential
to an understanding of the report, which is available, therefore, only
in typewritten form. .In addition to the field investigations, the Com-
mission conducted a series of thirty-four tests upon supporting ma-
terials, the tests being made at the Bureau of Mines Laboratory in Pitts-
burgh, in cooperation with the U. S. Bureau of Standards, under the
supervision of Charles Enzian.
The 1913 session of the Pennsylvania General Assembly enacted
the Davis Mine Cave Law,* which provides for the protection of public
highways, streets, etc., and also provides for the creation by municipal-
ities of a Bureau of Mine Inspection and Surface Support, the duties
of which are to investigate the mine workings in their relation to the
*Act No. 857. Approved July 26, 1913.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 31
support of public highways. Thus far the City of Scranton is the only
municipality in Pennsylvania that has passed an ordinance for the
creation of such a bureau. The City of Scranton Bureau of Mine In-
spection and Surface Support has been in existence since August 5, 1913,
and has investigated a number of mines and made reports upon such
investigations. The reports of this Bureau are not in print.
The City Council of Scranton on October 24, 1913, appointed H. D.
Johnson and D. T. Williams to prepare a report upon the mine of the
Peoples Coal Company, and in their work they were assisted by Chas.
Enzian, Mining Engineer of the U. S. Bureau of Mines. The report
of these gentlemen, submitted December 12, 1913, was made under the
provisions of the Davis Mine Cave Act. It comprises ninety-three type-
written pages and, in addition to reviewing the mining conditions in
three city wards, contains much concise information of general applica-
tion in the study of the problem of surface subsidence.
The subsidence problem in the Pennsylvania anthracite field has
been further complicated by the glacial deposits which occasionally are
localized in upot-holes." These pot-holes may extend to a consider-
able depth below the glacial sheet, making it dangerous to carry on
any mining operations near them. When the subsidence of the coal
measures extends to a pot-hole filled with sand and water, the water
and some of the sand may seep into the mine, and if the subsidence has
shattered the intervening strata or if the roof has been thin and weak, a
rush of sand may fill the mine workings. The difficulties of mining
under such glacial deposits have been recently presented* to the mining
profession and fourteen accidents have been noted.
In most of these a large area of the workings has been filled by the
rush of glacial material and water, and in several instances extensive
surface subsidence resulted.
On June 10, 1914, at the Sugar Notch Mine, a breast in the Kidney
bed broke into the wash. The material entering the mine was largely
sand and clay in a semi-fluid state, and its volume was estimated at
20,000 cubic yards. This -filled several thousand feet of gangways and
tunnels, but no lives were lost. The accompanying illustrations show
the important data in connection with this accident. Fig. 4 shows the
mine workings, the contours of the top of the rock, the location of drill
holes, and the important surface features previous to the accident. The
cave occurred at the face of breast 15. Fig. 5 shows the conditions
*Bunting, D. "The Limits of Mining Under Heavy Wash." Amer. Inst. of Min.
Engineers, Bui. No. 97, p. 1, 1915.
ILLINOIS ENGINEERING EXPERIMENT STATION
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
33
ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 1.
ACCIDENTS IN WYOMING FIELD DUE TO INRUSHES OF SAND AND WATER.
Accident,
No.
Date
Mine
'
Location
Vein
Tapped
by
Result
1
July 4, 1872
Burroughs
P 1 ains-
Hillman
Breast
An inrush of sand and
ville
water. A pumpman,
the only man in the
mine at the time,
easily escaped.
2
June 30,1874
Wanamie
Wanamie
Red Ash
Breast
Gangway and workings in
No. 18
the vicinity were filled
for some distance from
the break.
g
Tan 1882
Maltby
Swoyers-
Rock
Gangways were filled;
ville
Plane
also the shaft for a
vertical height of 90 ft.
4
Apr. 23, 1884
Fuller
Swoyers-
ville
Six Foot
Slope
Slope filled to the top for
a distance of 900 ft.
g
1884
Ridge
Archbald
Archbald
g
May* 1885
Ridge
Archbald
Archbald
7
Dec.' 18, 1885
No. 1
Nanticoke
Ross
Breast
Gangways in the vicinity
Slope
were completely filled
in less than an hour.
g
Auir 1889
Fuller
Swoyers-
Rock
The planes and all work*
ville
Plane
ings tributary to it
were filled with sand
or water.
9
Mar. 1, 1897
Mt. Look-
Wyoming
Pittston
Breast
A large area of the
out
workings was filled; no
men at work at the
time.
10
Dec. 30, 1898
Wanamie
Wanamie
Copper
Breast
Gangway on lower level
No. 18
filled to a height of 2
ft. for a distance of 300
ft. Depression on the
surface 100 ft. east and
west and 75 ft. north
and south.
11
Feb. 2, 1899
Franklin
Wilkes-
Kidney
Breast
Filled gangway to a
Barre
height of 3 or 4 ft. for
a long distance.
12
Apr. 13, 1899
No. 2
Nanticoke
Hillman
Breast
Gangways were filled for
slope
several thousand feet.
Breasts had been
worked 26 years pre-
vious; no men at work
in the vicinity. Sur-
-
face depression was 70
to 80 ft. deep.
13
Apr. 25, 1899
Bliss
Hanover
Hillman
Breast
Gangways and tunnel in
the vicinity were filled
tight to roof. Conical
depression on surface
60 ft. in diameter and
40 ft. deep.
14
June 10, 1914
Sugar
Notch
Sugar
Notch
Kidney
Breast
Gangways and tunnels
were filled tight to the
No. 9
roof. Depression on
surface 150 ft. wide,
210 ft. long and 60 ft.
deep.
after the cave and indicates the points where additional drill-holes were
put down. Fig. 6 shows the conditions which existed in section C-C,
before the accident and indicates the supposed limit of the wash. Fig.
7 shows the conditions after the accident and shows the limits of the
wash as proven by the additional drill-holes. The face of breast 15 was
at an elevation of +590.0 when the break occurred. The elevation of
the surface directly above was +657.0 and it was thought that the hot-
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
35
torn of the wash was at +630.0. It was planned to carry the breast to
-f600.0. The bottom of the wash was actually at +600.0 instead of
+630.0.
One of the most serious of the accidents noted was the so-called
"Nanticoke disaster" of December 18, 1885, which resulted in the loss
of 26 men.* The mine workings tapped a pot-hole which was sub-
sequently found to be over 200 feet deep. The hole was 400 feet away
from the present stream and was covered by a culm-bank. The thick-
ness of the rock where the cave occurred has been estimated at from 22
FIG. 6. SUPPOSED CONDITIONS ALONG C-C BEFORE ACCIDENT.
to 48 feet. The subsidence produced a hole in the culm-bank 300 feet
across.
One of the most important occurrences of this nature in the an-
thracite district, as far as amount of material entering the workings
is concerned, was the cave at the Prospect colliery of the Lehigh Valley
Coal Co., December 12 and 26, 1915.
It was supposed that the rock over the upper bed of coal was 40 to
50 feet thick and that the surface soil was thin, these being the condi-
tions at points near the break. It was found, however, that the rock
where the break occurred was only about 10 feet thick and that the
*Williams, G. M. "Dangerous Outcrops," Mines and Minerals, Vol. 20, p. 410, 1900;
Ashburner, C. A. "The Geologic Relations of the Nanticoke Disaster." Trans. Amer. Inst.
Min. Engrs., Vol. 15, p. 629, 1886-87.
36
ILLINOIS ENGINEERING EXPERIMENT STATION
remainder of the cover was loose sand, clay and gravel, apparently
glacial material deposited in an old valley. Probably the break was due
to the collapse of the thin rock at the bottom of a pot-hole.
Two breaks occurred, both at times when a small stream flowing over
the loose material was flooded, and a large amount of this material was
washed into the mine. It was estimated that about 140,000 cubic
SCALE. OF FEET
DATUM 400.00
FIG. 1. ACTUAL CONDITIONS ALONG C-C AFTER ACCIDENT.
yards of earth and 350,000,000 gallons of water entered the mine. No
lives were lost, but the financial loss was very considerable, as large
expense was incurred in changing the channel of the stream, in addi-
tion to the cost of pumping out the water and to the loss due to inter-
ruption of the work of the colliery.*
Pennsylvania Bituminous Field. — In the bituminous fields of Penn-
sylvania some damage to the surface has resulted from mining operations,
but few references to such subsidence are found in the technical press.
Generally the deeds to the coal rights have not required the mining
companies to support the surface.
In the Connellsville region the surface is of little value as compared
with the coal, the topography is rugged and, although cracks extend
through from the mine workings to the surface, little attention is paid
to them unless they are near important structures. Mining 8 feet of
*Coal Age, Vol. 9, p. 373. 1916.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 37
coal at a depth of 600 feet produces cracks as much as 20 inches wide.
The recovery of coal varies from 84 to 90 per cent. When it is necessary
to protect buildings and railroads as much as 25 to 50 per cent of the
coal is left in pillars.* It has been found that at shallow depths, up to
approximately 150 feet, subsidence will amount to 50 per cent of the
thickness of the coal. At greater depths it will be less, approximating
25 per cent at 300 feet. The attempts to correlate data and to generalize
from the data available have not been satisfactory. In discussing the
observations made in southwestern Pennsylvania, J. P. K. Miller,
Chief Engineer of the H. C. Frick Coke Company, said: "The great
difference of strata overlying the coal no doubt contributed largely
to the great variation noticed throughout the district. In some part&
of this region, the stratum immediately above the coal, between it and
the sand formation, varies from a few inches to 16 and 20 feet of shale.
Where the sandstone is very close to the top of the coal, the subsidence
is considerably greater than it is where the shale thickens; then, too,
there is a very heavy percentage of limestone and sandstone in the
Leisenring district, while immediately southeast of this, or between
Uniontown and Fairchance, the sandstone measures rapidly thin out,
and this, too, contributes to the variation in subsidence, or, in a word,
where the coal has immediately over it a heavy percentage of sandstone
measures, the subsidence is greater than where a thick stratum of shales
appears immediately above the coal. Of course, this is only our opinion,
but it seems to be the only good reason we can give for the difference in
subsidence where the cover is approximately the same (thickness). As
an illustration, in the territory in the vicinity of Uniontown, where
heavy shales appear above the coal, we have observed 18 inches of sub-
sidence where the cover is 300 feet; in the Leisenring district where
heavy sandstone measures appear above the coal and there is a thin
layer of shale immediately above the coal, the subsidence is approximately
30 inches. There is another condition that, no doubt, contributes
largely in bringing about this difference in subsidences and that is the
heavy layer of fireclay immediately beneath the seam of coal appearing
in the Uniontown district; while very good bottom conditions — liard
bottom' — appear in the Leisenring district, and the writer believes it
may be concluded naturally that this difference in the condition of the
bottom section has more to do with the difference in subsidence than
the first two conditions above mentioned."
'Private correspondence.
38 ILLINOIS ENGINEERING EXPERIMENT STATION
The outcrop of the Pittsburgh coal bed extends for many miles
in western Pennsylvania, and above these shallow workings many sink-
holes have formed. These have attracted very little public attention, as
they are considered to be of only a temporary character and most of the
buildings above the mined areas are frame and the damage to them has
also been only temporary, for if tilted out of line, these buildings have
frequently resumed their normal condition after a few months.
Observations made by another company show that the surface sub-
sided 2 feet, 9 inches after practically all of an 8-foot seam had been
removed at a depth of 400 feet. The overlying rocks consisted of shales,
sandstone and limestone in alternating beds, the thickest limestone bed
being 200 feet from the surface and reaching a thickness of 50 feet. There
are six other beds of limestone varying from 20 to 30 feet, the total
thickness of the seven beds being about 170 feet. The remainder of the
column is about equally divided between fireclays, sandstones, and shales.
The subsidence took place about twelve months after the mining of the
pillars began.*
In the construction of the Greentree Tunnel of the Wabash Pitts-
burgh Terminal Eailway Company in the Pittsburgh district it was found
that early mining operations had removed coal from a bed immediately
beneath the projected line of the tunnel and that coal had been removed
from another bed overlying. W. F. Purdy, Chief Engineer, describes the
conditions as follows: "When the heading of the tunnel had pro-
ceeded about 500 feet from the west portal we encountered broken
ground. The material was fairly solid gray shale which was easy
to drill, but none of it could be removed without heavy blasting. At
first the only indication of disturbance was that the rock showed soft
pockets, and a little later the strata had separated so that large pockets
could be excavated without blasting. After having proceeded about
20 feet into the material which had become more or less loosened
without our having been able to account satisfactorily for the nature
of the ground, the bottom of the heading suddenly broke down about
30 feet back from the face of the heading, permitting partial collapse
of the timbering as the settlement was about 2 feet.
"It developed that the broken ground encountered in the heading
was at the apex of the mass affected by the subsidence in the mine and
the top of the heading was approximately 50 feet above the mine level.
Unknown to us at the time, we had been driving the heading for some
"Private correspondence.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
39
40 ILLINOIS ENGINEERING EXPERIMENT STATION
distance over the broken ground with a wedge of solid rock between
the bottom of the heading and the broken material beneath. When we
had reached the point where this continually thinning wedge would no
longer support the weight, the ledge broke, practically at right angles
to our tunnel, and allowed the timbering to drop as before stated.
"We moved back in the heading to the solid rock and drove a
shaft on a steep incline until we reached the floor of the mine about
35 feet below the bottom of our heading. There we found that a
considerable area of coal had been mined several years earlier and
because of a "swamp" and the apparently heavy expense for pumping
the mine was abandoned after having drawn nearly all of the ribs and
pillars.
"After reaching the mine level we drove two diverging drifts from
the foot of the shaft until we were under the two sides of the tunnel
and then carried the two drifts ahead under the prospective tunnel
walls. For about 70 feet the ground was entirely broken between the
mine and the grade of our tunnel and we built solid brick masonry
walls 18 feet in height to provide foundation for the regular tunnel
side-walls.
"After leaving the space of about 70 feet already mentioned the
ribs and pillars had not been withdrawn and the falling from mine roof
was not serious. At some points the roof slate had fallen in to a height
about 6 feet above the normal mine roof, and at other places there
had been no breakage whatever. We followed up the mine entries and
rooms for a distance of about 600 feet at which point on account of
the convergence of the tunnel grade toward the mine level the same
elevation was common to the floor of mine and the grade of the tunnel.
"The alinement of our tunnel makes an angle of approximately
thirty degrees with the rooms in the mine and the work was more com-
plicated on that account. We built solid brick masonry walls diagonally
across the mine entries and rooms under each of the two tunnel side-
walls. Where there was a space of several feet between the roof of the
mine and the normal foundation of tunnel walls, we built the brick
walls thick enough to prevent any danger of crushing the slate rock
between the brick foundation and the regular tunnel walls. When we
reached the point where only two or three feet of natural shale would
have been left between the roof of mine and bottom of tunnel wall
we cut it all out and carried the brick work up to the grade of the tunnel.
"The tunnel lining is of concrete and the tunnel has been in serv-
ice for ten years with no sign of settlement or cracking of the concrete.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 41
"We also experienced a good deal of trouble, expense and delay
on account of another coal mine above the eastern half of the same
tunnel. As the top of our tunnel heading approached the bottom of
the coal mine and as the intervening wedge of ground became thinner
it became very difficult to support the roof of tunnel and we had much
trouble on that account, and also because of the mine drainage which
poured through the thin ledge of shale between the roof of tunnel and
bottom of mine."
West Virginia.
Owing to the character of the topography and the low value of
the surface in the coal districts, very few reliable records are available
to show the extent of surface subsidence due to coal mining. Some sur-
face movement has been noted where from 7 to 8 feet of coal has
been mined and the pillars drawn at depths over 500 feet. When
the thickness of the covers is from 200 to 300 feet, the disturbance is
greater and "where the cover is light — from 50 to 150 feet — the cracks
are sometimes from 2 to 4 feet in width and show a vertical displace-
ment of from 1 to 2 feet."*
The problem of protecting a seam lying from 70 to 80 feet above
the seam now being worked has confronted some of the coal mining com-
panies. It is proposed to mine the upper seam before the pillars are
drawn in the lower seam, as the subsidence which follows the mining
of the pillars in the lower seam greatly disturbs the overlying seams
and makes it unprofitable to mine them.
NATURE OF DAMAGE DUE TO DISTURBANCE OF THE OVERLYING
MATERIAL.
The damage resulting from the excavation of minerals may be
(a) without the mine or (b) within the mine.
In this study the damage external to the mine is the subject of
investigation, the internal damage being noted only when it occurs
in connection with external damage.
(a) The damage external to the mine may be due to:
1. The vertical, or horizontal, or both vertical and horizontal
movement of surface material or surface structures, caused
by the subsidence of the strata overlying the excavation.
2. Surface cracks or fissures due to slips, faults, or shear,
or to the tension of the surficial beds.
"Private correspondence.
42 ILLINOIS ENGINEERING EXPERIMENT STATION
3. Pit-holes or caves, formed when, instead of gradual and
more or less uniform subsidence over a large area, the
movement is localized if the excavation is at a shallow
depth.
4. Damage by water on account of the lowering of land below
the former drainage channels or the high-water levels,
and by the derangement of artificial drainage systems,
such as sewers in cities or tiling on farms.
5. Interference with or destruction of natural or artificial
water-supply.
6. Miniature earthquakes occurring when large masses of
rock fall over great areas.
(b) Within the mine, damage may result from:
1. The inflow of water through cracks or breaks caused by
subsidence of the strata.
2. The inflow of sand through breaks extending to the sur-
ficial material.
3. Local or extensive falls of roof.
4. The failure of pillars, due to the excessive weight of the
superincumbent strata.
5. "Air-blasts" or "bumps" accompanying the sudden collapse
of pillars and the fall of large areas of roof.
6. Squeezes or creeps.
1. Nature of Earth Movement. — Damage to structures on the sur-
face may be the result of either vertical or horizontal movement, or both,
and engineering observations in Europe and in America show many
interesting facts regarding the extent, the rate, and the duration of
surface movements.
"Draw" or "pull" is the variation from the vertical of the line of
fracture of rocks that break when the supporting bed or stratum is
removed ; in other words, the variation from the vertical of the bound-
ary between the disturbed and undisturbed strata. In some cases this
is a well-defined plane; in others a zone of indefinite extent. In the
case of brittle rocks, the break will be sharp; while in the case of more
yielding deposits, such as shales and loose soil, it may be impossible
to determine exactly the limits of disturbance.
Several instances of the lifting of objects on the surface have been
reported, but no data are available at this time to prove definitely that
either a temporary or a permanent elevation of the surface has occurred.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
43
It is claimed that at Northwich, England, where subsidence has resulted
from the removal of salt, an elevation of certain streets has occurred.*
In Nottinghamshire, England, where a coal seam 3 feet 8 inches thick
was mined at a depth of 1,680 feet, it is claimed that there was locally
and temporarily an elevation amounting to 4 inches.f Also, it is re-
ported that an "earth tide" is evident in the diamond fields of South
Africa, there being noted a rise and fall amounting to 3 inches a day,
but this could have no connection with subsidence.^
The engineer's records at the Warrior Eun Colliery of the Lehigh
Valley Coal Company in Pennsylvania show that there was a lateral
I Ft. Vertical
E in. Horizontal
Final,
Position
\ final 'Pos/f/'on
\
Point A, onSection Lined*
Along Horth End V
of Property. \
Point B6 on5ec//on/Jne8'*~ .. ^
Center ofD/'sfurbecfdrea
South End
ofdffecfed/lrea
Point C/0 on Sect/on L
FIG. 10. LATERAL MOVEMENT OF MONUMENTS.
movement of surface monuments as well as vertical movement. (Fig.
10 shows the dates of observation and the amount of the movement.)
This resulted from a squeeze in workings extending from 500 to 1,000
feet in depth on a coal seam dipping approximately 30 degrees.fi
Sags of the surface, or depressions without important breaks or
cracks, occur when the movement is due to the bending rather than to
the breaking of the strata and when the surficial material, without sud-
*Trans. Inst. Min. Engrs., Vol. 19, 241, 1899.
fProc. Inst. of Civ. Engrs., Vol. 135. p. 114, 1898.
JJour. Chem. Met. and Min. 890. of S. A., October, 1911.
fEnzian, Charles "The Warrior Run Mine Disaster," Mines and Minerals, Vol. 27,
p. 439, 1907.
44
ILLINOIS ENGINEERING EXPERIMENT STATION
den movement, accommodates itself to the new inclination of the bed-
rock. Observations in the coal districts indicate that the extent and
the gradient of such sags are influenced by the rate of advance of the
working face, particularly in longwall mining; by the character and
:.. . -.-.-..-. |-*^-?-^Z^__ ^~*^^\ "•' ••*"• •" '••'
:/;:': : :. v TENSION /.;-
./.COMPR
ESS 10
•Tv
•'• *."." TENSION ."•* "."• *• " *•
TENSION
FIG. 11. TENSION AS A CAUSE OF SURFACE CRACKS.
amount of filling; and by the ratio between the depth and the lateral
extent of the mine workings; as well as by geological conditions in
general.
FIG. 12. SURFACE CRACKS IN WESTERN PENNSYLVANIA.
2. Surface Cracks. — The surface cracks and fissures that appear
commonly when mining is carried on at shallow depths may be due
to one of several causes. As the mine roof sags over an excavated area
the bending action produces compression in the upper part of the strata
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 45
near the center of the basin or sag, while around the rim of the basin
the upper strata affected are in tension which may be sufficient to cause
the surface to break or crack. (Fig. 11.) If the movement is an ex-
tensive one and if the height of the surface above the axis of bending
is great, the width of the fissure may be considerable. Fissures 2 feet
wide have been noted in Illinois and in West Virginia. Fig. 12 shows
such surface cracks in western Pennsylvania.
The formation of surface cracks by tension is well demonstrated
by an occurrence in Ashland in the anthracite district of Pennsylvania.
~J~i'de Level Scale I"=4-OO'
FIG. 13. SURFACE CRACKS AT ASHLAND, PA.
The crack (Fig. 13) extended for a distance of about a quarter of a
mile, and was from an inch to six inches wide, causing considerable
damage to property. The vertical distance to the first coal seam was
over 800 feet, and later development showed that the crack did not
extend to the coal. The coal along the outcrops on both the Holmes
and the Mammoth seams had been removed and it is pressumed that
the crack was due to tension resulting from the settling of the over-
lying beds into the worked-out portion.*
The importance of the effect of surface beds upon draw or pull
has been pointed out by A. Sopworth.f According to his observations
the following classification of overlying beds may well be made:
'Foster, R. T. Discussion of Paper, Proc. Coal Mining Inst. of America, p. 147, 1912.
tProc. Inst. C. E.. Vol. 135. p. 165, 1898.
46 ILLINOIS ENGINEERING EXPERIMENT STATION
(1). "Measures consisting of fairly equal proportions of rocky
and argillaceous beds, and containing thick beds of sandstone.
(2). "Measures including a small proportion of rocky beds, say
15 per cent, and only thin beds of sandstone.
(3). "Variations between these two/'
In the first case the edge of the subsidence will follow or lie over
the excavation and in the second case it will lie over the solid coal.
In the third case the draw will vary between (1) and (2).
Kay* has emphasized the serious effects which may result from
the "pull over" or draw. In his opinion this may cause much greater
damage than the actual downward movement. "The strata appear
to bend over the goaf in a curve of radius depending on the depth, and
thereby subject the strata overlying the recently- worked area to a strain
(rendered passive from the movement of the face), coincident with the
progress of the working face, and, owing to its great radius and slow
movement, doing very little damage to surface structures of ordinary
character, as a rule." If the advance of the face is stopped, buildings
over the line of the face may be seriously damaged.
R. E. Cooperf called attention to the absence of pull where the
overlying beds include strong layers of limestone, shale and sandstone.
Surface cracks may be due to shear. Cracks caused in this way
generally are parallel, but they may constitute more than one system.
If there are two systems of fissures, generally the openings due to one
system are larger and more regular than those due to the other system.
Cracks may be caused by sliding of surficial material particularly
where the topography is rough. The shifting of beds of clay may cause
subsidence and form a sag or basin, around the perimeter of which
tension cracks will appear.
3. Pit-holes or Caves. — When the mining is carried on at a
shallow depth where there is very little solid rock cover, or when the
roof fails under shear, the movement frequently causes a sharp break
in the surface, forming pit-holes or caves. (Fig. 14.) Such holes may
be caused by the surficial material running into the mine entries beyond
the point at which the break actually occurred.^ This type of disturb-
ance is the cause of much damage to the anthracite mines of Penn-
*Kay, S. R. "Effects of Subsidence Due to Coal Workings," Proc. I. C. E., Vol. 135,
p. 117, 1898.
fProc. I. C. E., Vol. 135, p. 133, 1898.
$Fig. 14 is from a photograph of pit-holes in Indiana. In this case, coal 6 to 7 feet
thick had been mined at a depth of about 100 feet. The overburden consisted of about 10
feet of shale and 90 feet of drift.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
47
sylvania.* In regions where the surface is valuable for agriculture
and for building sites, pit holes are frequently a serious problem because
the cost of filling may be great. Subsidence of filled material is likely
to continue for some time and the value of such filled ground for build-
ing sites is generally low.
Effect of Unwatering Surficial Beds. — Considerable discussion has
been aroused by the suggestion that the unwatering of water-bearing
beds of clay, marl, and sand may result in subsidence, when no mining
FIG. 14. CAVE IN SOFT SOIL. (Photo by H. I. Smith, U. S. Bureau of Mines.)
has been done. German engineers have had to contend with heavy beds
of marl overlying the coal, and have made a number of observations
upon the effect of unwatering the surficial beds. There is a difference
of opinion, but possibly the majority of the German engineers have
thought that unwatering will cause subsidence. It was held by
many that when the surficial beds are drained by boreholes or excava-
tion there is a reduction in volume of the beds and that sinking of the
*Bunting, D. "Limits of Mining Under Heavy Wash," Amer. Inst. Min. Eng., Bui.
No. 97, p. 1, 1915.
48 ILLINOIS ENGINEERING EXPERIMENT STATION
surface will result. The mining industry was held responsible for sur-
face damage, simply because it was acknowledged that unwatering had
taken place.
In studying the subsidences about Essen in 1866 and 1868, von
Dechen came to the conclusion that the subsidences and surface cracks
were not directly the result of the coal workings, but that they were
caused by the partial drying of the chalk marl and green sand overlying
the coal measures which was caused by unwatering through the mines,
boreholes and wells. He also pointed out that there was a shrinkage
in volume in the chalk marl, due to the dissolving of carbonate of
lime in the marl.
Later investigations led the German engineers to change their
views upon the effect of unwatering. Graff made tests and showed*
that drainage does not cause any changes in volume in gravel, sand,
and quicksand. He concluded that subsidence will not result from
unwatering if no solid material is carried away mechanically.
Tests made in the laboratories of the United States Bureau of
Mines at Pittsburgh have shown that materials flushed with water do
not compress nearly so much as the same material if dry. This would
seem to indicate that by unwatering the strata of a mineral deposit,
damage may be caused to the surface, even though no solid material is
carried away.
F. Bernardi holds that the drying of beds of sand does not cause
a decrease in volume or a reduced bearing power.f He reached this
conclusion because in "water-soaked sand strata, the grains of sand
rest upon grains of sand, and the weight of the surface is carried
by these grains of sand resting upon one another and not by the water."
If the drying of sand causes a decrease in volume, the wetting of sand
should cause an increase.
Of the Austrian engineers Rziha held that unwatering may cause
subsidence but the later writers, as Jicinsky and Goldreich,$ who have
had a better opportunity to make observations, hold that no movement
occurs if the water does not carry away any solids mechanically or in
solution. Data on the shrinkage of beds of loam and clay have been
assembled by R. Dawson Hall.fl "A clay slime, 200 feet thick, will
reduce to 50 feet and less, as a result of drainage, and though such a
*Graff "Verursacht der Bergbau Bodensenkungen durch die Entwasserung Wasserfuh-
render diluvialer Gebirgs schichter," Gliickauf, 1901.
tKolbe, E. "Translocation der Deckgebirge durch Kohlenabbau," p. 63.
JGoldreich, A. H. "Die Theorie der Bodensenkungen," p. 15, Berlin, 1913.
UHall, R. Dawson. "Data on Petro Dynamics," Mines and Minerals, Vol. 31, p. 605, 1910.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 49
result is rare, . . . , yet the figures suggest what an action
drainage has in shrinkage of roof coverings of mines and how even clays
of great age may lose bulk by mining operations and let down the
rock or surface with its buildings above them. German and English
investigations* have been made of the shrinkage in air of flint clays.
A flint clay drying in air will shrink in all directions 5 per cent, so
that it will measure linearly only 95 per cent as much as before shrink-
age. The loss in drying is 14.26 per cent, and this, if the clay were
plastic, so as to give laterally with freedom, would reduce the thick-
ness of the bed 14 feet 3 inches in every 100 feet of depth of measure."
4. Effect on Drainage. — In the prairie lands and the river-bottom
lands of the coal fields of the Middle West, the complete removal of
the coal from horizontal beds at comparatively shallow depths has been
attended with the problem of the drainage of the surface. Over large
areas of prairie land there may be almost no natural drainage, and
if the mining of several feet of coal permits the uniform subsidence
of the surface, large sheets of water may stand for a number of months
over the subsided land, thereby greatly reducing its value for farming
purposes. In many instances (as will be noted fully later) the value of
the land for farming purposes exceeds greatly the value of the coal in the
ground at the present leasing rates.
Satisfactory artificial drainage has been provided in such flat prairie
land by the laying of drain-tile at considerable expense. Subsidence
may seriously disturb this tiling and may make the entire drainage
system of little or no value. In a district such as the Mississippi
Valley, where the streams are bordered by extensive bottom lands that
are little if any above the high water line, it is claimed that surface
subsidence may materially increase the area flooded at a time of high
water and may even produce areas that are continually under water or
are too wet for farming purposes.
5. Effect on Water Supply. — Subsidence of strata generally re-
sults in the formation of cracks and fissures in the rock which may be
sufficient to permit the escape of water from a water-bearing bed which
may have been the source of the water supply of a community or of an
industry; thus the fissuring of the rock beneath gravel beds may permit
the drainage of the beds which have been the source of water.
Numerous wells and cisterns have been damaged permanently by
subsidence due to mining. Instances of only a temporary loss of water
*Reis, H. U. S. Geol. Survey, 19th Ah. Report, pp. 404-406, 1807-98.
50 ILLINOIS ENGINEERING EXPERIMENT STATION
in wells have been noted in Illinois, Oklahoma,, Maryland, and Penn-
sylvania, the wells furnishing the normal supply of water after sub-
sidence has ceased if below the wells there are beds of such texture that
the fissures will close tightly enough to hold water.
SUBAQUEOUS MINING.
The subaqueous mining of coal and other minerals may shatter
the overlying strata and permit an inrush of water which will destroy
life and property. A number of valuable mineral deposits have been
opened at the edge of the ocean, and from time to time the workings
first made on the shore portion have been extended seaward until the
mining of the under-sea portion by a safe method has become the
chief problem in the undertaking.
Much attention has been given to the study of pillars and of sub-
sidence owing to the vital necessity of mining in such a manner that
water may not enter the mine. Particulars regarding the working of
coal seams under the water of oceans, rivers and lakes are given in
table 2 :*
England, Scotland, and Wales.
Coal is being worked under the sea along the coasts of the counties of
Northumberland, Durham, Carmarthenshire and Flintshire in England
and Wales and also to some extent off the coast of Linlithgowshire in
Scotland. t The coal beds dipping under the Firth of Forth have been
mined extensively. Here there are a number of faults parallel to the
shore which drop the seams on the seaward side. The bed of the Firth
of Forth, although very deep at places, is covered first by a stratum
of very hard, stiff unstratified till or boulder clay, which covers the
solid rock, while above this is a deposit of reddish plastic clay, from
30 to 40 feet thick and in places finely laminated. This covering forms
a waterproof barrier and prevents the sea from reaching the underly-
ing strata. There are four important coal seams having a total thick-
ness of about 15 feet. The lowest one lies at a depth of 340 feet at
the shaft and dips rapidly seaward. "Operations of late years have
shown that seams can be worked on the longwall system under the
sea, with faces from 4 to 8 feet in height, at depths which are small
in comparison with those of the workings in most modern collieries.
The seams have been worked in three instances to their outcrop against
* Atkinson, A. A. Trans. Inst. Min. Engrs., Vol. 23. Appendix IV, p. 644, 1901.
tAtkinson, A. A. Trans. Inst. Min. Engrs., Vol. 23, p. 622, 1901.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
51
TABLE 2.
PARTICULARS OF COAL SEAMS WORKED UNDER THE WATERS OF OCEANS,
RIVERS, AND LAKES.
No.
Name of Colliery
Name of
Coal Seam
Being
Worked
Depth
Below the
Water
Feet
Thickness
of
Coal Seam
Feet
Water of
Oceans, Rivers,
and Lakes
1
New South Wales
Australian Agricultural
Company, Sea Pit or
145-190
15 to 16
Pacific Ocean (a)
2
Hetton
300
7 to 8
Pacific Ocean (b)
3
Helton
Borehole
165-300
7 to 15
River Hunter (c)
4
Newcastle Coal Mining
Company, A and B
Pits
Borehole
145-170
6 to 11
Pacific Ocean (d)
5
2 40-3 60
7 to 8
Pacific Ocean (e)
6
Wickham and Bullock
Island
120-260
6 to 16
River Hunter and
Throsby Creek
7
Cumberland
Harrington
126-168
§Vi
Irish Sea (g)
8
90
10
Irish Sea (h)
9
Northumberland
North Seaton and Cam-
360
4 to 6
German Ocean (i)
10
Durham
Ryhope**
Maudlin
1 830
7
German Ocean ( j )
11
Seaham**
Maudlin
1 830
5
German Ocean (k)
Hutton
I1/*
German Ocean (1)
12
Wearmouth**
51^
German Ocean (m)
Hutton
±y*
13
Whitburn**
(n)
*Dunn, M. "A Treatise on the Winning and Working of Collieries," p. 230, 1848.
**Information derived from Mr. Thomas Bell's "Notes on the Working of Coal Mines
Under the Sea, and Also Under the Permian Feeder of Water in the County of Durham."
Transactions of the Manchester Geological Society, Vol. 36, pp. 366 to 399 and 554 to 559,
1899.
(a) Workings extend about 600 feet beyond high-water mark. The pillars are 96 feet
by 36 feet, the bords are 18 feet wide and the cut-through or cross-holings 9 feet wide.
About 4 feet of top coal is left next to the roof.
(b) Workings extend about 500 feet beyond high-water mark.
(c) The pillars are made 90 feet by 24 feet; the bords are 18 feet wide, and the
cut-through or cross-holings 9 feet wide.
(d) The workings extend about 800 feet beyond high-water mark, including the win-
nings. About 3 feet of top coal is left next to the roof and a little bottom coal is also left.
(e) Workings extend about 2,500 feet beyond high-water mark. The pillars and bords
are of the same dimensions as those at the Hetton colliery.
(f) The pillars and bords are of the same dimensions as those at the Hetton colliery.
(g) About 2 feet top coal and slate is left on, next to roof, in narrow places. The
minimum thickness of cover has been fixed at 126 feet. The pillars are left 57 feet by 52
feet, the bords are 14 feet wide, and the walls or cross-holings are 9 feet wide. Thus, 32
per cent of coal is worked, and the pillars are not crushed. About 66 per cent of the over-
lying strata is compact sandstone. Feeders of water, occurring in workings where minimum
cover had been reached, have since become quite dry.
(h) The workings extend 4,500 feet under the sea. The bords were 15 feet wide and
the pillars 21 to 24 feet thick. The manager, in order to increase the output of coal, com-
menced to rob the pillars, this resulting in falls and feeders of salt water. Warnings were
given as to what would happen, but these were unheeded. On July 30, 1837, the sea
broke in and 36 men and boys and a number of horses were drowned, and the colliery
irrecoverably destroyed.
(i) At Cambois bord-and-pillar longwall is being worked under the sea and headings
are driven 300 feet in advance to ascertain the existence of any fault or break in the strata.
(j) The workings extend 5,500 feet from low-water mark under the ocean, and over
400 acres of goaf have been formed.
(k) The workings in the Maudlin seam extend 5,000 feet under the ocean and about
85 acres of goaf have been formed.
(1) Twelve pillars, each 120 feet by 90 feet, have been removed in this seam under
the goaf of the Maudlin seam, rising seawards from 2 to 2J4 inches per yard for the last
1,200 feet.
(m) Workings extend 4,000 feet under the ocean.
(n) Workings extend 4,000 feet under the ocean.
52 ILLINOIS ENGINEERING EXPERIMENT STATION
the boulder clay, at depths from 137 to 400 feet below high-water mark,
without any accident."* The thickness of the cover under which the
whole of the coal seam has been mined is less in this mine than in
any other submarine mine in Great Britain.
The workings extending farthest seaward are reported to be those
at Whitehaven, which at the William pit extend under the Irish Sea
a distance of 19,000 feet (1901) from high-water mark. The coal
seam is 10 feet thick and is worked by rooms 18 feet wide with pillars
75 feet square. There is also a higher seam about 7 feet thick which
has been worked in places. f North of the William pit is an old mine
which has been flooded.
The mining of under-sea coal will become a very important matter
in time in Scotland.^
Eestrictions have been imposed upon the working of Crown coal
in Great Britain. In the case of one colliery the working of coal under
the ocean, unless there is at least 126 feet of strata between the bed of
the sea and the top of the seam, and the removal of pillars or the adop-
tion of the longwall system, where there is less than 360 feet of interven-
ing strata are prohibited. Under specified conditions the entire removal
of the coal-seam is permitted where the minimum thickness of cover is
270 feet.fi
It has been advised that the workings of coal on the Northumber-
land coast be limited to areas where there is a minimum of 270 feet
of solid strata above the seam. The bed of the ocean generally con-
sists in this vicinity of a stiff clay.§
Australia.
In New South Wales coal mining has been carried on extensively
beneath the Eiver Hunter, the Pacific Ocean, and its tidal waters.**
Four seams have been worked in parts of this area, the total thickness
ranging from 19 to 43 feet. Operations in the vicinity of the outcrop
are dangerous because channels in the coal measures become eroded by
old streams, and later these channels become filled with alluvial de-
posits. In general, the coal measures dip slightly toward the ocean,
*Cadell, H. M. "Submarine Coal Mining at Bridgeness, N. B." Trans. Inst. Min.
Engrs., Vol. 14, p. 237, 1897.
tMoore, R. W. Trans. Inst. Min. Engrs., Vol. 23, p. 660, 1901.
JAtkinson, J. B. Trans. Inst. Min. Engrs., Vol. 14. p. 253, 1897.
flAtkinson, A. A. Trans. Inst. Min. Engrs., Vol. 23, p. 629, 1901.
§Robertson, J. R. M. Discussion. Trans. Inst. Min. Engrs., Vol. 28, p. 133, 1904.
**Atkinson, A. A. "Working Coal Under the River Hunter, the Pacific Ocean, and Its
Tidal Waters, Near Newcastle, in the State of New South Wales." Trans. Inst. Min.
Engrs., Vol. 23, p. 622, 1901.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 53
but there are many local dips and faults. The usual dip is given as
1 in 36. There are thick deposits of clay covering the outcrops in
places.
Owing to the weakness of the roof a number of inundations have
resulted at inshore mines from letting down the sand overburden. In
consequence of a fall of roof there was a rush of water into the Fern-
dale Colliery in 1886 and a miner lost his life.* A commission was
appointed to investigate this accident and the report submitted included
a review of conditions at all the collieries in the district. The title to
the coal beneath the Eiver Hunter and the tidal waters resides in the
Crown and the leases to these coal lands now include regulations con-
trolling the method of mining beneath bodies of water, with the view
of protecting life and also of preventing large volumes of water enter-
ing old workings, and thereby interfering with the mining of the coal
in the adjacent area.
The mines of the district use the pillar-and-room system. The
dimensions of pillars and rooms vary, but in general 50 per cent of
the coal is recovered. The practice in a number of the mines is to
drive 18-foot rooms, leave 24-foot pillars, and recover part of the pillar
coal. When the pillars were left only 18 feet wide on first mining a
number of crushes resulted. Owing to the presence of thick, impervious
beds of clay no water entered the mines where these crushes occurred,
although at equal depths on land the crushes caused surface subsidence
and some damage to buildings. In one of the mines the rooms are 18
feet and the pillars 36 feet.
The quantity of water being pumped from the mines varies from
50 to 600 gallons per minute and in most places this water is decidedly
salty. Vertical boreholes are put up to determine the thickness and
character of the overlying beds.
In determining the safe working limit under the ocean the follow-
ing conditions have been considered:
(1) The character of the overlying strata, with special reference
to loose deposits of alluvium or beds of clay between the bed of the
ocean and the coal seam.
(2) The presence of faults and dykes in the strata.
(3) The dimensions of pillars to be left and the width of open-
ings to be made.
(4) The utility of leaving coal next to the roof in some cases.
"New South Wales Royal Commission on Collieries. Report on the Accidents at Fern-
dale Colliery, p. 17, Sydney, 1886.
54 ILLINOIS ENGINEERING EXPERIMENT STATION
The special conditions of working under tidal waters prescribed
in the leases are notably as follows:
(1) The maximum width of rooms shall be 18 feet and the mini-
mum width of pillars 18 feet.
(2) The pillars 18 feet wide shall not be removed.
(3) All headings and rooms shall be driven on sights.
(4) All workings shall be surveyed accurately every three months.
All dates of working must be shown on the plan.
(5) The plan of the mine shall contain a faithful record of all
dykes, fissures, etc., and shall indicate all excavations as they actually
exist.
(6) In one road of every pair of leading headings, a borehole
shall be kept going 10 feet in advance, and all leading headings shall
be driven at least 150 feet in advance of the working rooms.
(7) When dykes or fissures are stuck in the boreholes, precau-
tions must be taken to protect against possible danger which may result
from weakness of roof or flow of water when the dykes or fissures are
penetrated by the heading.
(8) The coal under the ocean should not be attacked until after
a large goaf has been made by extensive workings under the mainland.
(9) The most accurate information available shall be obtained
as to thickness and character of the strata and estuarine deposits over-
lying the coal seam before commencing to work it.
Similar conditions are specified for working under the sea except
as follows:
(1) The minimum width of pillar shall be 24 feet.
(6) All leading headings shall be driven at least 300 feet in
advance of the working rooms.
(9) Boreholes penetrating the roof for a height of 30 feet above
the coal seam shall be driven on the leading headings 300 feet in ad- ,
vance of the work and 60 feet apart.
Newfoundland.
At Wabana there is a series of iron ore beds which lie in a synclinal
trough, one edge of which passes througli Belle Isle. The three upper-
most beds are mined in both the land and in the submarine areas. The
ore beds pass beneath Conception Bay and apparently outcrop in the
floor of the bay. The center of the basin is estimated to be about
three miles from shore. The lowest bed is from 15 to 30 feet thick.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 55
The method of mining is pillar and room, the rooms being 250 feet
long and turned on 35-foot centers with 20-foot pillars.
The development in the submarine territory is sufficient to allow
an annual output of 1,000,000 tons, and the total ore reserve has been
estimated at practically 400,000,000 tons after proper allowance was
made for pillars, faults, and poor zones. The principal ore bed outcrops
on Belle Isle and dips seaward so that at high water mark it has a
depth of 70 feet; at 3,000 feet from shore the bed is 268 feet deep
and has 180 feet of cover. The average grade of the slope is 16 per
cent.* According to a private communication from E. E. Ellis, Geologist,
Tennessee Coal, Iron & E. E. Co., Birmingham, Ala., 1913, the long-
est slope at the Wabana mines was 7,500 feet and the end was 6,000
feet under the water.
Cape Breton Island.
The coal measures of Cape Breton Island extend under the ocean,
and a number of the coal seams have been worked in these submarine
areas. The measures dip at a steep angle, while the sea floor dips at a
moderate angle so that the thickness of cover increases rapidly. Owing
to the rapid erosion of the outcrop by the sea, some of the seams have
been lost. The Mabou mine was flooded from the ocean, f because of a
break in the roof in 1909, and the Port Hood Colliery was lost by a
•flood resulting from the entrance of water through a feeder which
was opened when pillars were extracted at a point where 942 feet of
solid strata were supposed to lie between the coil seam and the floor of
the ocean.
The workings of some of the companies have already been extended
seaward a distance of 2% miles from high-water mark and it is prob-
able that in the future a large part of the coal output will be obtained
from these submarine fields. The government has prescribed regula-
tions to control the size of openings and methods of working under
shallow cover4 Where the cover is less than 180 feet the coal may not
be mined; mine openings may be driven where there is not less than
100 feet of cover. Where there is less than 500 feet of solid cover the
workings must be divided into sections not more than one-half mile
square and a coal barrier not less than 90 feet thick must be left
around each section. The barrier may be pierced by not more than
four openings, not more than 9 feet wide by 6 feet high. In 1904
*Cantley, F. "Wabana Iron Mines." Canadian Min. Inst., Vol. 14. p. 274, 1911.
f'Coal Mines Under the Sea," Coll. Enj?., Vol. 34, p. 17. 1913.
JCoal Mines' Regulation Act of 1912, Sec. 54, Nova Scotia.
56
ILLINOIS ENGINEERING EXPERIMENT STATION
the government mine inspectors and the management of the Dominion
Coal Company agreed upon the size of pillars to be left in the mining
of submarine coal.*
The dimensions of rooms and pillars, the percentage of coal left in
the form of pillars, and the thickness of cover are shown in Table 3.
TABLE 3.
DIMENSIONS OF ROOMS AND PILLARS, DOMINION COAL COMPANY.
Harbour Seam*
Hub and Phalen Seams**
Depth
of
cover
(feet)
Room width
(feet)
Size of pillar
(feet)
Room width
(feet)
Size of pillar
(feet)
Percentage of
coal left in
pillars
200
20
27x75
20
30x75
51
250
20
27x75
20
30x75
51
300
20
30x75
20
34x75
54
850
20
33x75
20
36x75
56
400
20
36x75
20
42x75
58
450
20
39x75
20
46x75
60
500
20
42x75
20
50x75
61
550
20
45x75
20
54x75
63
600
20
48x75
20
58x75
64
650
20
51x75
20
62x75
65
700
20
54x75
20
66x75
66
750
20
57x75
20
70x75
67
800
20
60x75
20
74x75
97
850
20
63x75
20
78x75
68
900
20
66x75
20
82x75
69
950
20
69x75
20
86x75
69
1,000
20
72x75
20
90x75
70
*Thickness mined from Harbour Seam, 6 feet.
**Thickness mined from Hub and Phalen Seams, 9 feet.
British Columbia.
A disasterf which may be compared with those occurring in suba-
queous mining resulted when the workings of the old Southfield Colliery
near Nanaimo, British Columbia, tapped the drowned workings of the
South Wellington Mine No. 1 of the Pacific Coast Coal Company on
February 9, 1915. The inrush of water resulted in the death of 20
men. It was believed that the new workings were 450 feet away from
the water and it was planned that a 100-foot pillar should be left be-
tween the water and the new workings. At the time of writing this
report no evidence is available showing whether or not the Coal Mines
*Dick, W. J. "Conservation of Coal in Canada," p. 85. Toronto. 1914.
f'Twenty Men Drowned in Mine Near Nanaimo, B. C." Coal Age, Vol. 7, p. 374.,
1916. Watson, R. L. "Coal Mining on Vancouver Island." Mines and Minerals, Vol. 21,
p. 849. 1001.
YOUNG-STOEK — SUBSIDENCE KESULTING FROM MINING 57
Regulation Act was being complied with; namely, that drill holes shall
be kept in advance of the workings.*
Japan.
A large proportion of coal is mined under the ocean in Japan.f
The most serious accident in the whole history of subaqueous min-
ing occurred in this country on April 12, 1915, when 237 men were
killed by the flooding of Higashimisome Colliery. The mine is situated
in Ube, Yamaguchi-ken and the chief production is from two beds lying
wholly under the sea. The output is about 500 tons per day. Four
shafts were sunk on the shore, each 119 feet deep, from which two beds
are worked to a distance of about 4,000 feet from the coast.
The cause of the accident was the entering of water into the un-
derground workings through a fault in a bed of sandstone 155.4 feet
thick, above which there is an alluvial deposit of clay and sand 82.6
feet thick.
A small flow of water occurred when the fault was first reached.
The final inrush followed the breaking of a hole about four feet square
in the floor of an entry of the upper bed, a few feet back from the
fault. Through this the water entered so rapidly that the mine was
completely flooded in two hours. The quantity entering was estimated
at 392,000 cubic yards. The sea bottom was lowered 60 feet over a
small area showing that a considerable amount of solid matter was
washed in.
The opening was apparently sealed by the solid material and it
was planned that the mine should be reopened by filling the depression
in the sea bottom with clay and sand, pumping out the water, and
building dams to protect the workings from any future break.J
INDUSTRIES AND INTERESTS AFFECTED BY SUBSIDENCE.
Surface subsidence involves more than the question of the present
value of the land; in many instances the fundamental problem involves
the relative present and future importance of various industries and
interests. Among the most important of these are agriculture, trans-
portation, and the various interests of municipalities.
* "Where a place is likely to contain a dangerous accumulation of water, the working
approaching such place shall not exceed eight feet in width, or such greater width as may
be permitted by the Chief Inspector of Mines, and there shall be constantly kept at a
sufficient distance, not being less than five yards in advance, at least one borehole near the
center of the working, and sufficient blank boreholes on each side. (British Columbia Laws,
1911. Chap. 160, Part XT. Rule 14.)"
tTrans. Inst. Min. Engrs., Vol. 28, p. 133, 1904.
tCollicry Engineer, Vol. 86. p. 10. 1915.
58
ILLINOIS ENGINEERING EXPERIMENT STATION
1. Agriculture. — In the consideration of the agricultural inter-
ests involved, attention must be directed to the probabilities of subse-
quent use for agricultural purposes of land not tilled at present. Prob-
ably in no state where mining is important is the value of farm lands
in the mining districts higher than in Illinois. It will be shown in
another bulletin how the present value of these lands for mining pur-
poses (removing all the merchantable coal) and the present value for
farming purposes compare. It has been predicted that the value of
the fertile lands of the "corn belt" will increase greatly in fifty years.
FIG. 15. POND FORMED BY SUBSIDENCE.
An agricultural expert has expressed the belief that northern Illinois
land will sell for from $400 to $500 per acre, and the best land in
the southern counties for $200 by the year 1965.
In the longwall field of northern Illinois, where it is claimed that
mining has lowered the surface so that drainage is deranged, it is
estimated that large drainage projects have cost from $15 to $40 per
acre. Fig. 15 illustrates the formation of a pond in a nearly level
country by subsidence after mining. Coal of no greater thickness has
been mined and is being mined in adjacent states. Estimates of the
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 59
coal resources of Illinois show that only twenty per cent of the coal
occurs in beds more than four feet thick and of the total area (37,486
square miles) underlain by workable coal beds, 32,979 square miles do
not contain coal more than four feet thick. Over this great area it is
possible that sometime mining by the longwall system may produce
subsidence unless a filling system is used that is more effective than
any at present in use. This statement regarding the thin coal beds in
Illinois applies as well to large areas in Michigan, Ohio, Indiana, Ken-
tucky, Missouri, Iowa, Kansas and several other states, and it is evident
that the importance of the subject of subsidence will be even greater
in the future than at present.
2. Transportation. — Surface subsidence may interfere seriously
with transportation by injury to the beds of canals and railroads and
the caving of highways and streets. As previously noted, mining in
Great Britain and on the continent has necessitated the raising of
the banks and the filling of the bottom of many canals. In some in-
stances, canals have been maintained on grade, while the land which
they traverse has subsided as much as 20 feet. The necessity for pro-
tection of these interests has become so great that laws have been enacted
which require that thirty days5 notice be given of mining under rail-
ways, reservoirs, buildings, or pipes or within a prescribed distance.*
The practice regarding the protection of the right of way of rail-
roads has differed from time to time and has varied also in different
countries. The general policy in Europe seems to be to remove all
the coal if possible, and the tendency on the continent is to use filling
under railways in order to reduce the amount of subsidence.
In the United States many of the great railway systems do not
grant the right to mine coal beneath the right of way, if the com-
pany has ever owned the coal right. However, coal has been mined
under many branch lines and under some of the main lines of railroads
traversing the coal districts. Fig. 16 shows the effect of one sub-
sidence in southern Illinois. In the anthracite fields of Pennsylvania
many instances might be cited of subsidence of railway tracks. No
serious accidents have resulted, as the railway companies have guarded
carefully all points where movement is feared. There are no laws
regulating mining under railways in the United States. When a pit
hole or cave extends to the surface near or under a railway track,
the problem of restoration is principally a problem of filling. Good
*Cockburn, T. H. "Minerals Under Railways and Statutory Works." Trans. Inst of
Min. Engrs., Vol. 39, p. 104, 1909-10.
60
ILLINOIS ENGINEERING EXPERIMENT STATION
illustrations are found in some of the iron mines of the Lake Superior
district, where extensive filling has sometimes been necessary to preserve
the grade of tracks, amounting in one case to more than 50 feet.
When the movement is gradual and principally a horizontal one
due to tension or compression the problem is much different. In Ger-
FIG. 16. DISTURBANCE OF GRADE BY SUBSIDENCE.
many many observations have been made upon railway track subject
to tension or compression on account of subsidence over mines. In
one instance, because of the crowding of the ground toward the center
of the subsiding area, track 150 feet (50 meters) in length had to be
shortened from 1 to 2 inches (3 to 5 cm.). Rails were buckled up or
to the side, and the crowding forward of the rails and ties caused the
earth or ballast to be pushed forward or crowded up and an open space
appeared along one 'side of the tie. These spaces have been noted as
much as one-third of an inch wide. In one sag in which the maximum
subsidence was about 3 feet (1 meter) in five years it was necessary to
shorten the rails 2.66 meters (70 cm.) in a total distance of 658 feet
(200 m.). When the track was in tension the rails were stretched and
at times the ends were broken.* When the principal horizontal move-
ment is across the right of way, the trouble is easily seen on account
of the effect on alinement.
The effect of surface subsidence upon bridges has been noted by
*Nolden "Influence of Mining Upon Buildings and Railways." Elektrische Kraftbetriebe
and Bahnen, Oct. 4, 1913.
YOUNG-STOEK — SUBSIDENCE RESULTING PROM MINING 61
European engineers, including many British engineers.* English en-
gineers suggest steel construction, well-tied abutments and wings, and
plenty of height so that there will be sufficient clearance after the bridge
has been lowered by the removal of the coal. There has been a differ-
ence of opinion in regard to the adaptability of arched or girder bridges.
In the reference noted, an example is given of the mining of a seam,
7 feet 6 inches thick, at a depth of 216 feet beneath an arch of 20
feet on the main line of a railroad. The arch was not damaged by
subsidence. It was conceded that arches from 50 to 60 feet long
would not be advisable under similar conditions.
In 1868 several bridges were built in England on land that was
known to be subsiding on account of the mining of the coal, and spe-
cial precautions were taken to preserve these bridges. The rails were
carried on wrought iron girders and cross girders. The foundation
was carried deep enough to permit the construction of a concrete base
4 feet thick. On this base was laid two courses of elm planking, each
4 inches thick, on which four courses of brick footing were built, and
on these four courses was laid a hoop iron interlaced frame, 4%'-inch
mesh, extending over the whole of the abutments and wing walls. This
arrangement was repeated every four courses. Later, in some places,
the foundation sank as much as 4 feet, but the whole bridge was
lowered unbroken, and it was necessary only to lift the girders and the
track to grade.f
Experience has shown that the damage to a bridge will be least if
the workings (longwall) approach it broadside. The working face will
pass under the structure much more quickly with that plan of work-
ing and there will be probably less difference in elevation between the
ends of the structure at any stage of the subsidence.
In the construction of the Hull and Barnsley Railway across the
South Yorkshire coal field, which it traversed for twelve miles, the
problem of supporting bridges was of great importance. Owing to
the great value of the coal beds, the plan of reserving coal pillars was
given up. W. ShelfordJ advocated the separation of the bridge ma-
sonry into parts which could subside independently of each other, but
should have the materials in each part bonded together. Several bridges
were designed on this principle with abutments and wings separated
only by a straight joint of mortar, which was concealed by a pilaster.
*Kay, S. R. "Effect of Subsidence Due to Coal Workings Upon Bridges." Proc.
Inst. of Civ. Eng., Vol. 135, p. 114, 1898.
tLynder, J. H. Proc. Inst. of Civ. Eng., Vol. 135, p. 161.
JProc. Inst. Civ. Eng., Vol. 135, p. 164, 1898.
62 ILLINOIS ENGINEERING EXPERIMENT STATION
A large bridge built in 1884 after this plan subsided 3 feet in 1891.
The wing walls separated from the abutments, but the abutments them-
selves were uninjured and subsided bodily, so that they were only 3
or 4 inches out of plumb. When subsidence had ceased the wings
were repaired and the bridge was again placed in service.
The effect of subsidence upon railroad tunnels has been noted
previously, particularly in the construction of the Merthyr tunnel in
Wales, and the Greentree tunnel at Pittsburgh, Pa.
3. Municipalities. — As previously noted, many towns in Europe
FIG. 17. BREAK IN SIDEWALK DUE TO SUBSIDENCE.
and America have been damaged by subsidence caused by mining. The
damages to property in municipalities may include :
(a) Injury to Streets, Sidewalks, and Transportation Lines. —
When pit-holes or caves occur, it becomes necessary to fill until subsidence
has ceased and then reconstruct the street upon the most satisfactory
grade. When there is horizontal movement, due to tension or com-
pression, rather than caves, the streets, curbing, and sidewalks may be
crushed or heaved (Fig. 17), or there may be tension great enough
to cause serious cracks. This trouble has become so severe in certain
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING C3
German cities that in the sections where compression occurs the gutters
and curbs are laid so as to have elastic and waterproof joints. When
large gaps are left in construction between curbstones they are covered
with strips of sheet iron about 2 inches wide. In order to prevent the
overturning of curbing, due to compression occurring transversely, the
flagging is made narrower than the sidewalks and a strip of material
that will permit compression is laid between the flagging and the curb.
Coherent paving, such as asphalt, cement, and concrete, is not used
because it would be cracked or crushed.*
(b) Injury to Buildings, Toivers, and Chimneys. — This may be
due to caves, or to tension, compression, or twisting. Large high build-
ings suffer more than low buildings covering but little ground. Masonry
and concrete structures are damaged more than those of wood.
E. Kolbe has discussed at some length the nature of the damages
to buildings, •(• and has pointed out the various factors and conditions
with which one must deal in preserving buildings upon land which has
subsided as follows :
(1) A building may sink wholly or in part into a surface break.
(2) A building may stand upon the edge of a break and be sud-
denly and violently twisted or wrenched and shaken.
(3) A building may be located in the mining area and may be
subjected to the earth movement and be damaged by the jamming of
the adjoining houses.
(4) A building lying over the mined area may sink slowly in the
subsidence basin without undergoing greater damage than being placed
in an inclined position.
(5) A building may suffer on account of the shock resulting from
a fall of roof in the mine.
The types of cracks in brick buildings particularly around and
between (Fig. 18) windows have been noted by Kolbe, as shown in
the accompanying illustrations. As the illustrations show, the fracture
generally follows the joints of the mortar, as these offer the least resist-
ance. When cut stone window sills and lintels are used (Fig. 19), the
fracture naturally follows upward around the stone without cracking it.
In long brick or tile walls without openings, as for example walls (Fig.
20) surrounding estates, there may be three types of fractures in relation
to direction:
*Nolden "Influence of Mining Upon Buildings and Street Railways." Elektrische Kraft-
betriebe und Bahnen, Oct. 24, 1913.
fKolbe, E. "Translocation der Deckgebrige durch Koblenabbau." Essen, 1903.
64 ILLINOIS ENGINEERING EXPERIMENT STATION
FIG. 18. CRACKS IN BRICK BUILDINGS.
FIG. 19. EFFECT OF SUBSIDENCE ON STONE LINTELS AND SILLS.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 65
minium ini>Miiiiiiimniiiiiimiiniimiiiimiiiiiiinni(iiim
^w^
1
wss;?^//^y£^^^
FIG. SOb.
imiiimiiiiiiimiiiiiiiiiiiiiiiiiiimmiimmimmii minimi
FIG. 20c. CRACKS IN LONG WALLS.
66 ILLINOIS ENGINEERING EXPERIMENT STATION
(1) The fracture may go perpendicularly up the wall and break
the stone coping. (Fig. 20a.)
(2) It may extend diagonally away from the plane of the crack in
the ground following the joints in the brick work. (Fig. 20b.)
(3) It may extend along the joints of the brick work diagonally in
the same general direction as the plane of fracture in the ground.
(Fig. 20c.) The second type is of most frequent occurrence. The same
three types of fracturing are characteristic also of high enclosing walls,
partition walls, and fire walls and chimneys.
Buildings may be damaged by side movement in which structures
are crowded upon each other. When the mortar in masonry walls is
cracked, the arches over doors and windows fail and increased pressure
is thrown upon adjacent sections of the structure. When buildings are
located over the edge of a pillar or on the side of a trough caused by
subsidence, the cracks may extend in step fashion diagonally across a
masonry wall. Secondary stresses may cause additional cracks in other
directions. An example of this type of damage is shown in Fig. 21,
which is an elevation of a post office. The cracks extend in the same
general direction as the cracks in the ground.
In Germany, where subsidence has been anticipated, large build-
ings have been erected in sections from 60 to 120 feet long and these
sections have been reinforced in all directions by rods and plates so
that they will withstand both tension and compression. The joints
between the sections have been calked with suitable material or protected
with a covering. When buildings are not of great value European engi-
neers have removed the coal as rapidly as possible and completely if
possible, advancing the working face in a direction at right angles to
the axis of the most important structure. When such precautions were
used, the working of two 4-foot seams of coal at a depth of 600 to 780
feet in England caused practically no damage to two rows of 120 cot-
tages.*
When the structures are important and it is estimated that the
damage caused by subsidence will exceed the value of the coal, pillars
may be left or filling introduced to prevent or reduce the subsidence.f
The problem of protecting important public buildings has received
serious attention in Scranton, Pennsylvania. In several instances build-
ings have been erected on reinforced concrete piles constructed upon the
*Longden, J. A. "Effect of Coal Workings on the Surface." Colliery Engineer, Vol.
11, p. 5.
tSpencer, W. "The Support of Buildings." Tram. Inst. of Min. Eng., Vol. 6, p. 188,
1892-98.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
67
rock underlying shallow coal beds which had been worked by the pillar-
and-room method and of which the roof had fallen or seemed likely to
do so. Engineers Griffith and Conner made an inspection of the condi-
tions of mining beneath the city and school properties. The tabulated
results of their inspection indicate that some coal has been mined under
FIG. 21. CRACKS IN MASONRY WALL.
most of the buildings and that in a number of instances mining has been
carried on in several beds.* Several of the buildings have been dam-
aged by subsidence. The suggestions (op. cit., p. 60) by these engineers
of precautionary measures will be considered later.
'U. S. Bureau of Mines, Bui. No. 25, pp. 19-43, 1912.
68 ILLINOIS ENGINEERING EXPERIMENT STATION
The report of Enzian, Johnson, and Williams on the extent of
damage done, states the results of their examination as follows:
"In the consideration of a plan which might assist in the adjust-
ment of property damaged we considered it important to compile the
following information in connection with the properties of the thirteen
city blocks which have been more or less subjected to the influence of
subsidences that have occurred from time to time. The total assessed
valuation of these properties is $1,430,000. The assessed valuation of
the properties actually damaged is $411,000. The estimated damage
to properties actually affected is $68,700, or about 17 per cent of their
assessed valuation. The estimated damage to all the properties in the
thirteen city blocks amounts to approximately 4.7 per cent of their
assessed valuation. This estimate does not take into consideration any
damage that may have been done to public property."*
(c) Injury to water, gas, and steam lines. — This type of damage
is not unusual in communities in which mining has' been carried on ex-
tensively. The cracking of water mains has caused damage not only
through the direct injury to the main and the temporary failure of the
water supply, but also through the escaping water, which in a number of
instances has flooded buildings, washed out foundations, and destroyed
streets, roads, and earthen structures. Fires have resulted from the
escape of gas from broken gas mains. Necessity has brought about the
use of expansion and compression joints of various types for preventing
or reducing the damage to such lines. The need for frequent inspection
of such pipe lines has made it important that they be laid in tunnels or
large conduits.
(d) Injury to sewers and sewage plants. — Sewer lines as well as
steam, water, and gas mains may suffer from subsidence, but in the case
of sewer lines the difficulties are even greater, since these lines are gen-
erally constructed of materials which are less able to resist tension and
compression, and a change in elevation of part of the line may render
the entire system useless. An interesting experience regarding the sub-
sidence of sewage works is reported by an English engineer, Malcolm
Patterson.f
"At Eavensthorpe, in the Calder Valley, sewage works constructed
in 187'4 had remained intact for twenty-four years ; they lay on the verge
of a colliery leasehold. In August, 1897, the effluent outlet submerged
*Enzian, Johnson, and Williams "Report on Mining Conditions of the Oxford Colliery
Workings, Scranton, Pa., Dec. 12, 1913."
fProc. Inst. Civ. Engrs., Vol. 135, p. 162, 1898.
YOUNG- STOEK — SUBSIDENCE RESULTING FROM MINING 69
15 inches below the ordinary level of the stream into which it discharged.
At his (the author's) previous visit it was at its normal level, of about
6 inches above the stream. The settling tanks were cracked across the
center, and the tank sewer had settled considerably. These settlements
arose from getting a 20-inch seam of coal, besides the dirt, about 150
to 160 feet deep, and the boundary of the worked coal terminated in or
near the sewage workings. In the same year, a similar disturbance took
place at the Castleford sewage works in the same valley. Complete re-
levellings of the three roads intersecting the land were taken, and proved
an average settlement of 3.3 feet throughout nine-tenths of the 12.5
acres of sewage land, without the surface being broken. In this case the
getting of coal, 4 feet to 4% feet thick, at a depth of 603 feet, was the
cause. The contour was singularly constant, the new section being
almost parallel with the original section. The strata here were the
shales and sandstones of the coal measures, overlaid by the marls and
limestones of the Permian formation/'
CHAPTER II.
GEOLOGICAL CONDITIONS AFFECTING SUBSIDENCE.
The behavior of the measures overlying the mineral deposit which
is being worked depends to a large degree upon the physical character
and the structure of the measures themselves. In a recent paper* before
the International Geological Congress attention was called to the various
geological conditions which influence the effect of underground mining
upon the surface as follows:
(1) The general character of the overlying strata.
(2) The presence of faults, fissures, etc.
(3) The dip of the strata.
(4) The direction of the workings with regard to the jointing of
the strata.
(5) The compressive strength of the rocks of the various over-
lying beds.
(6) The bearing power of the underlying beds.
(7) The angles at which rocks break when stressed.
Geological conditions must be studied in each district, as no gener-
alizations can be made which will apply without reservation to all mining
fields. The measures overlying a flat seam may be made up of various
beds of sedimentary rocks and in places may include sheets or beds of
intrusives. The physical character as well as the thickness of each bed
may vary over different parts of the same mine, and there may be faults,
fissures, rolls, etc., which greatly influence the supporting power of the
bed, as well as the manner in which the weight of the bed itself is dis-
tributed upon the underlying supports. Unless the thickness and the
character of the beds have been proven, and unless it is known definitely
that the beds are fairly uniform throughout the field under consider-
ation, it will be impossible to formulate even approximate rules and
theories regarding subsidence which will be useful in the study of the
problem of surface support.
MINERAL DEPOSITS.
1. Physical Character. — Before considering the overlying and the
underlying beds, it will be well to note some of the conditions in the
deposit being worked which may greatly influence the problem of sur-
*Knox, George "Mining Subsidence." Proc. International Geological Congrew, Vol. 18,
p. 797, 1913.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 71
face support. The physical character of the material being mined and
of that part, if any, of the deposit which is left in the form of pillars
or of filling must be considered. The texture and the structure of the
rock left in pillars is of great importance in determining the burden the
pillars will carry and in affecting the stability of the pillar after it has
been subjected to the action of explosives in the adjacent portion of
the deposit and after it has been exposed to the action of the atmosphere
and water. In many coal mines, owing to the friability of the coal, it
has been necessary to reduce the charges of powder used along the rib
and in some instances to avoid the use of powder entirely because the
pillars are more or less shattered by the force of the explosives. Eock
and coal may be so weakened by jointing or cleats that the pillars offer
little support. Moreover, the action of the atmosphere and moisture,
particularly upon a deposit jointed as described, may greatly weaken
the pillar. Soluble minerals in the pillars may be dissolved by the mine
water or the moisture in the air and the pillar thus weakened. Pyrite
and other minerals may be oxidized and a deterioration of the pillar will
follow. It has been suggested by some that the loss of the included gas
in coal beds tends to reduce the strength of the coal. The hydration or
the dehydration of minerals may result in the weakening of pillars.
The terms "rashing," "slacking," and "slabbing" have been applied to
the process of weakening of pillars by the gradual dropping of material
from the ribs, due in part to the action of moisture, oxygen, or pressure,
or a combination of these agents. In mines operating in soluble minerals
the preservation of pillars may be difficult owing to the flow of water in
the mine or the moisture in the air. It may become necessary in mines
of all types when pillars deteriorate to protect important pillars by a
coating of cement or concrete.
Strength tests have been made upon coal and other minerals in
order to determine how serviceable they will prove when left in pillars
and in order to estimate, in advance of the opening of a mine in a new
field, the minimum size of pillar which may be left in safety for the pro-
tection of the mine openings themselves and of objects on the surface.
Numerous tests have been made upon rocks used for building pur-
poses, and the data thus secured are of service in determining the size
of the pillars to be left in such rock. But more commonly the pillars
left in mines are not composed of materials used for building purposes,
but rather of coal, ores of the various metals, and rock mineralized more
or less with substances which are not permitted in structural materials.
72
ILLINOIS ENGINEERING EXPERIMENT STATION
Moreover, the natural structural materials used are generally a selected
product. Underground the pillar is frequently made up of the weakest
portion of the deposit. Tests upon pillar materials are often of doubtful
service, for, as a rule, they indicate the maximum load which can be
borne by a unit of the mineral and one that is often a selected unit. A
coal bed, for instance, is composed of layers of varying hardness, and
frequently it contains streaks of mother coal that would not be included
in a sample tested for crushing strength.
TABLE 4.
COMPRESSION TESTS OF ILLINOIS COAL FEBRUARY 6, 1907.
Laboratory of Applied Mechanics, University of Illinois.
Laboratory
No.
Specimen from
>
Equivalent Section, Inches
Height,
Inches
Maximum Load
Top
Bottom
Pounds
Lb. per
Sq. In.
12401
12402
12403
12404
12405
12406
Penwell Coal Co.,
Pana, 111
Empire Coal Co.
W. W. Williams,
Litchfield, 111. .
Herdien Coal Co.,
Galva 111 ...
1134x12
15 1/5x17 3/5
13J4xl3J4
11^x1754
1324x12
11 #x 9J4
11^x12
15 x!5 1/3
14 x!4
16 x!3
13^4x12
11 xl!54
12^
11.3
14/2
12
15
13
316,000
540,000
186,000
208,000
224,000
140,000
2,090
2,170
1,000
1,020
1,360
1,280
T. H. Watson,
Litchfield, 111. .
C. N. & V. Coal
Co., Streator,
111
Tests were made in the Laboratory of Applied Mechanics of the
University of Illinois upon samples of Illinois coal furnished by the
Illinois Geological Survey.* The data regarding the samples and the
results of the tests are given in Table 4.
Dimensions in
Inches
Area in
Sq. In.
Crushing
Strength
per Sq. In.
Sample M —
Parallel with cleavage
2 01 by 2 02
4 060
3,170
Right angles to cleavage . .
1 75 by 1 70
2,975
2,970
Sample B—
Parallel with cleavage. ... ...
1 95 by 2 01
3,430
Right angles to cleavage
1.92 by 1.98
3,925
3,050
3,802
Tests were made by the H. C. Frick Coal Company upon samples
of coal from the Pittsburgh seam. These are particularly interesting
as they show the strength when compression is parallel to the cleavage
and also when it is at right angles to it.
*Talbot, A. N. "Compression Tests of Illinois Coal." 111. State Geol. Sur., Bui. No. 4,
p. 198, 1909.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING
A series of tests was made upon Pennsylvania anthracite during
1901 and 1902 by a committee from the Scranton Engineers' Club. In
all 416 samples were tested. The samples were uniformly 2 inches
square, but were of three different heights : namely, 1 inch, 2 inches, and
4 inches. The results are given in pounds avoirdupois per square inch
of horizontal area as presented in the following summary :
Grand Average
as Per Sq. In.
Samples
Height of
Sample
First
Crack
Maximum
Load
Number of
Tests
Northern Field
1
3022
6241
122
Eastern Middle Field. .
2
4
1
2025
1875
4996
4087
2854
7417
116
113
7
Western Middle Field
2
4
1
3343
3413
3001
3857
3821
8631
6
7
3
Southern Field
2
4
1
788
1440
1124
3499
2447
3814
3
3
12
2
4
1099
988
2377
1809
12
18
From the data obtained the following conclusions have been drawn :
"That the squeezing strength of a mine pillar of anthracite whose width
is twice its height is about 3,000 pounds to the square inch, and the
crushing strength about 6,000 pounds per square inch, or, approximately
twice as much. And in general, other things being equal, the crushing
strength of mine pillars would vary inversely as the square root of the
thickness of the bed.
"The same general rule apparently holds true also for the squeez-
ing strength in all cases in which the height of the pillar is less than
the width. In tall pillars, having a height greater than their width,
the squeezing strength apparently remains nearly constant while the
crushing strength continues to diminish with height according to the
foregoing rule."*
Subsequently additional tests were made at Lehigh University on
samples of anthracite and of bituminous coal.f Forty-five anthracite
specimens were tested. "There seems to have been no uniformity in the
amount of compression of the specimens taken as a whole or between
the specimens from the same seam." The results of the tests upon
twelve bituminous specimens were more uniform. The crushing strength
*Mines and Minerals, Vol. 23, p. 368, 1903. U. S. Bureau of Mines, Bui. No. 25,
Appendix, 1912.
tDaniel, J., and Moore, L. D. "The Ultimate Crushing Strength of Coal." Eng.
and Min. Jour., Vol. 84, p. 263, 1907.
74
ILLINOIS ENGINEEKING EXPERIMENT STATION
per square inch ranged from 584 to 1,583 pounds, but nine ranged from
1,000 to 1,538 pounds. All of the bituminous specimens were taken
from the Pittsburgh seam. Additional data on the crushing strength
of anthracite coal have been secured by Bunting* and Table 5 shows the
crushing strength and the relation between prism strength and cube
strength.
TABLE 5.
AVERAGE EESULTS OF TESTS ON ANTHRACITE SPECIMENS.
Name of Company
h
Ratio
b
Crushing Strength
Lb. per Sq. In.
Prism Strength
Cube Strength
P. & R. C. & I. Co.
1
2 393
1.00
2
2,296
0.96
L. V. C. Co.
1
1 982
1 00
2
1,591
0 80
3
1 405
0 71
L. & W-B. C. Co.
0 71
3 025
1 22
1.07
2,566
1.00
1 24
2,393
0.87
1 43
2 008
0 81
(20 specimens)
1 77
2,090
0.76
2 06
1 880
0 84
D. & H. C. et al.
0 50
5,113
1.63
1.00
3,131
1.00
2 00
2,234
0.71
b= Least lateral dimension.
h=Height of prism.
The crushing strength of some British coals has been measured and
reported by Henry Louis.f McNair in discussing the conditions of deep
mining in the Lake Superior District^ refers to the crushing strength
of the trap rock left in pillars as 1,200 tons per sq. ft. Eichardsonjf
gives a table of the compressive strength of quartzite cubes taken from
the depths of from 1,000 to 3,500 feet in Eand mines. The first frac-
tures appeared in the specimens under a pressure of 1,945 to 6,804
pounds per square inch. The crushing strengths of these specimens
were 8,054 and 9,029 pounds per square inch, respectively.
2. Extent and Dip of Deposit. — The problem of surface support is
naturally different in the case of a deposit which underlies an area of
great lateral extent from that of support when the lateral extent is
small. When the deposit underlies a small area the geological structure
•Bunting, D. "Chamber Pillars in Deep Anthracite Mines." Trans. Amer. Inst. Min.
Engrs., Vol. 42, p. 236, 1911.
tTrans. Inst. Min. Enjjrs.. Vol. 28, p. 319, 1904.
JEnj?. and Min. Jour., Vol. 23, p. 322, 1907.
fRichardson, A. "Subsidence in Underground Mines." Jour. Chem. Met. and Min.
Soc. of S. Africa, Mar., 1907. Eng. and Min. Jour., Vol. 84, p. 196, 1907.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 75
of that area may be worked out fairly accurately and precautions may
be taken to protect important structures on the surface.
The dip and the position of the deposit may greatly modify the
necessity for and the general policy of surface support.
3. Uniformity of Mineral Deposit. — If there is fair uniformity
in thickness,, structure, quality, and depth over a large area, a systematic
plan of support may be adopted, including, for example, pillars of
uniform size at regular intervals or a complete removal of the deposit
with or without filling. If there is not regularity as to these condi-
tions, it becomes more difficult to employ a system of support or of
working which will be economical and at the same time provide support
for the surface. Notable examples of such conditions may be found in
some of the coal fields of Illinois where rolls, horsebacks, and faults com-
plicate mining, and in some of the lead and zinc fields of the Mississippi
Valley, where pillars of barren rock are left in the mines and the rich
portion of the deposits is mined out as completely as possible under such
conditions. The pillars as a rule are neither uniform in size nor uni-
formly spaced. While such irregularities in the mineral deposit inter-
fere to a degree with systematic working, yet they at times assist
materially in preventing or checking extensive underground movements
or subsidence.
UNDERLYING EOCKS.
The physical character of the rocks immediately underlying the
mineral deposit is of great importance. Frequently coal beds are
underlaid with beds of clay of such consistency that it will not support
the pillars when the weight upon them is increased by the opening of
rooms. The pillars are slowly pushed into the clay while the clay is
forced into the rooms which have been mined. Similarly, when water
reaches clay beds underlying the coal, the clay may be softened and
forced into the rooms by the weight of the pillars, and a subsidence
results. The term "creep" is very commonly applied to such a move-
ment.
Very few tests have been made upon the bearing power of the clays
occurring in mines, but numerous tests have been made upon clays and
soils upon the surface. Owing to the importance of not placing upon
the clay floor of a mine a burden which shall exceed the bearing power
of clay, which is usually much less than the compressive strength of
coal, the following values are of interest :*
•Baker, I. O. "A Treatise on Masonry Construction," p. 842, 10th Ed., 19U.
76
ILLINOIS ENGINEERING EXPERIMENT STATION
Safe Bearing ]
per S
'ower in Tons
1. Ft.
Kind of Material
Minimum
Maximum
200.0
25.0
30
15.0
20
5.0
10
6.0
8
4 0
6
1.0
2
8.0
10
4.0
6
2.0
4
Ouirksand. alluvial soils, etc. . .
0.5
1
The data on clay given in the table are not for fireclay,, and no data
have been obtainable which are the results of observations upon the
supporting power of such clay of the character and occurring under
conditions similar to those found in coal mines.
OVERLYING ROCKS.
The study of subsidence due to mining operations involves par-
ticularly a consideration of the rocks overlying the mineral deposit.
Lack of uniformity in the overlying measures is the rule, not the ex-
ception, and this fact must be recognized in all attempts to formulate
theories and rules. The effect of different conditions of the overlying
beds is well illustrated by two examples in England. "At Sunderland,
where the measures contain 50 per cent of hard-rock beds, seams at a
depth of from 1,400 to 1,800 feet have been worked for seventy years
without reference to the surface. On the other hand, in the Midland and
South Yorkshire coal fields, where the cover is composed largely of soft
shales, the effect of workings at as much as 2,000 feet is appreciable on
the surface."*
Investigations of the thickness and physical character of each over-
lying bed are fundamentally necessary to the accurate study of sub-
sidence in any district. Much of the data as to the behavior of various
strata that can be secured will be at best only relative. However, the
more data that can be secured the fewer will be the variables with which
the investigator must deal.
Practically every theory of subsidence which has been advanced,
when analyzed, involves some fundamental principle of mechanics. The
beds may be subject to tension, compression, bending, or shear. Samples
*Eng. and Min. Jour., Vol. 84, p. 196, 1907.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING
77
of the various rocks may be tasted in the laboratory in order to secure
data to be used in the study of each problem. The great difficulty of
obtaining specimens which will be representative of the section under
investigation is largely responsible for the scarcity of data along certain
lines, notably those concerning the strength of rock in tension and in
bending.
Data on the strength of the rocks that are of importance in the
study of subsidence have been collected and published by Bunting.*
"Numerous tests of various stones have proved that sandstones take
permanent sets for the smallest loads, whereas granite and limestones
are nearly perfectly elastic. It has also been proved by tests on various
stones tliat the modulus of elasticity in compression is practically the
same as in cross bending, but no fixed relation has been determined of
the compressive, tensile, or shearing strength of the various kinds of
stone.
"The shearing strength of sandstones and slates per square inch is
generally slightly in excess of the modulus of rupture, and the com-
pressive strength of various stones is variable and of comparatively little
consequence here, as the compressive strength of even the lightest sand-
stone ranges from 4,000 to 6,000 Ibs. per sq. inch."
The moduli of rupture of various kinds of stone as given by a num-
ber of authorities are shown in Table 6.
"Safe unit stresses for various stones have been given by many
authorities. Below are given the stresses in pounds per square inch
recommended by W. J. Douglas as illustrative of possibly a fair aver-
age of such values :
SAFE UNIT STRESSES FOR STONE.
Compressive
Lb. per Sq. In.
Shear
Lb. per Sq. In.
Tension
Lb. per Sq. In.
1 500
200
1 020
200
150
Limestone
800
150
125
700
150
75
"It is to be observed, in the case of sandstone, that a safe tensile
strength of 75 Ibs. and a shearing strength of 150 pounds per square
inch are given. Now, in consideration of the fact that the modulus of
rupture is invariably in excess of the tensile strength, also that the re-
sistance to shear slightly exceeds the modulus of rupture, a value of 100
*Bunting, D. "The Limits of Mining Under Heavy Wash.'
Bui. No. 97, p. 1, 1914.
Amer. Inst. Min. Engrs.,
78
ILLINOIS ENGINEERING EXPERIMENT STATION
pounds per square inch for the modulus of rupture of standstone would
be consistent. . . .
"When sandstones and slates, which generally overlie the coal veins,
are considered as beams or slabs spanning mine openings for the support
of overlying strata or other superimposed load, their transverse strength
TABLE 6.
MODULI OF RUPTURE OP STONES.
Maximum
Minimum
Average
Authority
Blue stone flagging
4 611
360
2 700
Baker
Slate
9 000
1 800
6 400
Baker
Slate ..
11,230
7,425
Arsenal tests, 1902
Slate
8 480
Merriman
2,700
900
1,800
Baker
Granite
1 754
Merrill
Granite
2,610
Arsenal tests, 1907
Granite
1,667
Arsenal tests, 1905
Granite .
1 365
Bauschinger
1,194
Bauschinger
Glass
3,500
Church
Glass
4 132
Fairbairn
1,576
Technology Quarterly
1 200
Merriman
Sandstone
1,273
655
Arsenal tests, 1895
Sandstone
2,243
1,500
Arsenal tests, 1895
2 340
676
1 260
Baker
469
718
Bauschinger
1 109
341
Bauschinger
483
249
Bauschinger
135
156
597
Bauschinger
967
2,200
Kent
1,170
Kent
2,000
Merriman
654
Merriman
From the results of tests as given in Table 6, the average moduli
of rupture of the various stones are as follows:
Pounds per
Square Inch
Blue stone flagging.
Slate
Granite
Sandstone
2,700
7,736
1,681
806
is of first importance. The ability of such material to serve as a beam
depends upon its tensile strength, since that is always less than its com-
pressive strength." The action of the atmosphere and of water upon
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING
79
rocks which have previously been protected from these natural agents
occasionally reduces the strength of rocks.
TABLE 7.
SPECIFIC GRAVITY OF KOCKS.*
Rocks
Average Specific
Gravity
Lb. Wt. per
Cu. Ft.
No. of Cu. Ft. per
Ton 2,000 Lbs.
Quartz
2 6
162 1
12 3
2 9
181 0
11 1
Basalt
2 9
181 0
11 1
Diabase .
3 0
187 0
10 6
Diarite
3 0
187 0
10 6
Granite
2 7
168 0
11 9
2 7
168 0
11 9
Porphyry
2 7
170 0
11 8
Rhyolite
2 4
149 6
13 4
2 4
149.6
18 4
Schist
2 7
168 0
11 9
Shale
2.6
162.1
12.3
As previously noted, structural features are of great importance
and the application of theories and rules will serve only as an indication
of tendencies and possibilities. If the various rocks and strata were
uniformly homogeneous the problem would be greatly simplified.
Natural processes may give rise to conditions which result in sur-
face subsidence. Possibly the most comparable examples of subsidence
due to natural agencies are those of surface sinks which result from the
removal of portions of the supporting minerals by natural agencies.
Numerous examples of sink-holes and caves have been noted in the
salt districts of Europe and in areas underlaid by calcareous materials
which may be dissolved in part by underground waters.f In the United
States similar phenomena have been noted. The sink-holes of the
Ozark plateau have been studied in Missouri^ and the information avail-
able indicates that they have been caused either by the caving of the
roof over solution basins in limestone beds, or by the enlargement
through solution of joints leading from the surface to an underground
channel. It is probable that the larger sinks are the result of the
former cause. Usually these sinks vary in diameter from 100 to 300
feet, although single sinks are known to include as much as 150 acres.
In Illinois, near Millstadt, in the Waterloo Quadrangle numerous
sinks have resulted from solution cavities in limestone beds lying at
shallow depth.
Apparently the same forces which act during the subsidence of the
•Herzig, C. S. "Mine Sampling and Valuing," p. 139, San Francisco, 1914.
tWoodward, H. B. "Geology of Soils and Substrata." London, 1912. Quotes Darwin
on p. 64, reference to Cheshire salt district, p. 67.
JCrane, G. W. "Iron Ores of Missouri." Missouri Bureau of Geology and Mines.
Vol. 10, 2d sers., p. 84. Lee, Wallace, "Geology of the Rolla Quadrangle." Vol. 19, 2d
sers., ch. VIII.
80 ILLINOIS ENGINEERING EXPERIMENT STATION
surface over these cavities caused by nature also cause subsidence over
mine workings. It has been suggested that the fissure systems in volcanic
areas have resulted from vertical movement or settling due to the trans-
fer of material by volcanic action to the surface; the resulting cavity
having probably been closed, in part at least, by the subsequent settling
of the surface under the load of extrusive material.* The dropping of
a block of the earth's crust tends to produce normal faults, and it may be
appropriate to consult the authorities on structural geology regarding
the observations which have been made upon faults and fractures which
apparently have resulted from forces and processes somewhat similar
to those which characterize subsidence due to mining.
As will be noted later, the investigator of subsidence desires to learn
among other things how the strata bend and break when subjected to
various forces, and in what direction fracture will occur when various
forces act. He desires to learn how rapidly the deformation of rocks
occurs and to what depths mining openings may be carried with safety.
In the laboratory the angle of break of various rocks may be measured
and many other data may be obtained, but the investigator requires also
data based upon larger volumes of materials, greater and more slowly
acting forces, and conditions more nearly approximating those which
result from mining operations.
1. Cleavage. — "The planes of cleavage, incipient or pronounced,
existing in the overlying roof strata may strike in the same general
direction as the planes of cleavage existing in the coal below. The im-
portance of this principle and the necessity of its acceptance justify a
reference by way of proof to the natural philosophy of the case. Accord-
ing to geological theory, the cleavage in the coal and in the roof strata
was produced by the action of the same force. Assuming that in a
given case the planes of cleavage are vertical, the theory is that -some
force, acting laterally and at right angles to what are now planes of
cleavage, was the cause of such cleavage being created in the strata.
Such a lateral force is supplied by the shrinkage of the earth's crust.
This force, acting with immense energy on the particles of matter in the
strata and subjecting them to enormous lateral compression, obliged such
particles so to arrange themselves that their longer axes finally lay at
right angles to the line of action of the compressing force. The planes
of cleavage are thus defined as the planes in which the particles of mat-
ter now extend their longer axes."f
•Lindgren, W. "Mineral Deposits." P. 186.
tHalbaum, H. W. G. "The Action, Influence and Control of the Roof in Longwall
Workings." Trans. Inst. Min. Eng., Vol. 27, p. 214, 1903.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 81
2. Fractures. — The subject of fractures has been discussed in va-
rious works on geology, notably in the recent work of Leith.* "Under
tension fractures tend to develop in planes normal to the maximum
stress. Tension fractures may develop when a mass is deformed by
shearing. Under compressive stresses, fractures tend to develop above
the planes of maximum shear, which are inclined to the direction of
principal stresses ; but the degree of inclination and the direction of dip
of the planes away from the direction of maximum stress vary."f Joints
in rocks may be due to tension or to compression. Faults, which are
"fractures along which there has been some relative displacement of the
rock,":f may be regarded as the result of tension or of compression. A
"gravity" or "normal" fault is generally the result of tension while com-
pression causes "thrust" or "reverse" faults.
FIG. 22. ANGLE OF FRACTURE OF STONE.
The angle of fracture of rocks under stress has been noted and
measured in the field and in the laboratory. Daubree carried on extensive
experiments in 1879 to show the effect of tension and. compression.^
Experiments made upon wax and resin prisms showed that compression
causes rupture along a plane at an angle of 45 degrees to the line of
force. If there has been preliminary deformation, the angle will be
greater than 45 degrees.
Fayol tested pieces of sandstone and shale, as shown in Fig. 22, to
discover the angle of fracture when the test piece is held firmly by one
end and subjected to a steady and increasing pressure applied upon the
projecting portion.
Leith states that data given in United States Geological Survey
•Leith, C. K. "Structural Geology." 1913.
tin subsidence following the advance of longwall mining strata may first be subject to
tension and later to compression.
ILeith. P. 81.
jJDaubree, A. "fitudes Synthetiques de Geologic Experimentale." P. 179.
82 ILLINOIS ENGINEERING EXPERIMENT STATION
Folios show an average dip of 78 degrees for normal fault planes and
36 degrees for reverse fault planes. Faults noted in Illinois have dips
ranging from 35 degrees to 75 degrees, the majority, however, approxi-
mate 55 degrees.
Lindgren observes* that veins may dip at any angle but "veins
dipping 50 degrees to 80 degrees are most common."
Stevens has formulated a law of fissures.f "In a homogeneous mass
under pressure, slipping tends to take place only along those planes on
which the ratio of tangential stress to direct stress is equal to the co-
efficient of friction of the material sliding on itself. If the axis of
greatest principal stress is vertical, the displacement along the fissure
will be that of a normal fault, and the dip of the normal fault which
is most favorable to slipping will be 66 degrees. Similarly, when the
axis of greatest principal stress is horizontal, the displacement along the
fissures is that of a reverse fault, and the dip most favorable to slipping
is 24 degrees."
Spencer has studied in the field the veins of southeastern Alaska 4
There is a systematic arrangement of veinlets in two main sets standing
at right angles to each other and dipping in opposite directions.
Becker jf concluded that the fracture had been produced through com-
pressive shearing stresses which were caused by nearly tangential forces
acting in a direction normal to the strike of the two sets of fractures.
Spencer supports the theory that these fractures were caused by com-
pressive thrust but questions the statement that the thrust was the
result of tangential compression. He developed the theory that the
general fissuring was a result of "gravitative adjustment in the rock-
masses, tending to restore internal equilibrium disturbed during the
uplifts which are known to have taken place." A broad mountainous
zone rises about 5,000 feet above the interior plateau and 15,000 feet
above the plateau bordering the Pacific Ocean. "Standing so far above
the neighboring earth blocks, it seems that in this great orographic mass
there must even now exist a tendency to bulge toward the unrestrained
sides. If so, conditions are favorable for the opening of fractures at a
depth dependent upon the crushing strength of the rocks which compose
the great mountainous mass."
•Lindgren "Mineral Deposits." P. 151.
tStevens, B. "The Laws of Fissures." Trans. Amer. Inst. Min. Engrs., Vol. 40, p. 475,
1909.
JSpencer, A. C. "The Origin of Vein-Filled Openings in Southeastern Alaska." Trans.
Amer. Inst. Min. Engrs., Vol. 36, p. 581, 1906. "The Geology of the Treadwell Ore
Deposits." Trans. Amer. Inst. Min. Engrs., Vol. 35, p. 507, 1905.
UBecker, G. F. 18th Annual Report, U. S. Geol. Sur. Pt. Ill, pp. 7-86.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 83
The discussion and theory of Spencer is of great interest in this
connection as it develops the idea of the settling of a mass of rock under
its own weight and when movement is less restrained in one direction
than in another. It also emphasizes the question of angle of fracture
and systems of fractures which will be referred to later.
The theory of a "dome of equilibrium" developed by Fayol sug-
gests the question of the possibility of removing a layer or bed from the
earth without disturbing the surface, owing to the sphericity of the earth.
The question of the supporting power of the dome of the earth's crust
has been studied by a number of eminent geologists. Chamberlain and
Salisbury refer to each portion of the crust as "ideally" an arch or
dome. When large areas like the continents are considered, it is the
dome rather than the arch that is involved, and in this the thrust is
ideally towards all parts of the periphery. According to Hoskins, a
dome corresponding perfectly to the sphericity of the earth, formed of
firm crystalline rock of the high crushing strength of 25,000 pounds to
the square inch, and having a weight of 180 pounds to the cubic foot
would, if unsupported below, sustain only 1/525 of its own weight. This
result is essentially independent of the extent of the earth's radius.*
The idea that extensive areas can be left entirely unsupported if
the curvature of the arch corresponds to the sphericity of the earth is
entirely unwarranted, judging from the calculations made and from
the experience at many mines.
Various structural features must be noted in determining the cause,
effect, and probability of subsidence following mining operations.
Among the most important of these are the conformability of the over-
lying rocks, joints, cleavage, bedding planes, folds, faults, fissures, dikes,
and intrusives.
In many mining districts there are heavy beds of surficial material
which complicate the problem on account of the water they contain and
because they are more or less fluid and have little supporting power.
The lateral extent of subsidence is greater when the area is covered with
such beds. This is due largely to the smaller sliding angles upon which
beds of sand, earth, marl, and gravel will move.
EXPERIMENTS TO DETERMINE BOOK FRACTURE.
Many experiments have been carried on by eminent geologists in
order to discover by work in the laboratory fundamental data upon
•Chamberlain, T. C., and Salisbury, R. D. "Geology." Vol. 1, p. 681.
84 ILLINOIS ENGINEERING EXPERIMENT STATION
which theories may be based arid also to verify if possible, by artificial
processes, theories accounting for conditions which may have been the
results of complex forces and reactions.
As previously noted, numerous tests have been made to determine
the strength of rocks and minerals under various conditions and various
properties of rocks have been studied.* Among the most interesting
experiments in addition to the tests of materials are the following:
Payol conducted elaborate tests of materials such as those which com-
posed the beds overlying the Commentry Mine and by ingeniously con-
structed models attempted to measure the lateral and vertical extent
of subsidence.f The work of Daubree has been noted previously. Ex-
tensive experiments have been made also by Meade and by Paulcke. In
America among the experiments which have attracted most attention are
those described by Willis in "Mechanics of Appalachian Structure";
those by Adams and Coker on elastic constants, flowage, and the cubic
compressibility of rocks; those by Becker on schistocity and slaty cleav-
age; and those by Hobbs on mountain formation.
Most of these experiments consider tangenital pressures rather than
vertical pressure. Very few of them develop conditions which approxi-
mate those which occur when the support of rock is removed.
*Consult the Bibliography, p. 180, for records of these experiments.
tSee page 76.
CHAPTEE III.
THEOKIES OF SUBSIDENCE — GENERAL PRINCIPLES.
In this bulletin no attempt will be made to discuss theories of
mechanics or derive formulae applying to subsidence, but an effort will
be made to state briefly the conditions that exist and to point out the
fundamental and controlling factors in a study of the problem.
In order to study the reactions which may exist in the rocks over-
lying a mineral deposit, it will be necessary to make certain assumptions
in order to arrive at some definite conclusions. For example, it must
be assumed that the rock is uniformly of a known strength, that it is
free from structural weaknesses, and that it exists in masses or beds
whose extent, thickness, depth, and dip are known.
The principles of mechanics may be applied to various types of
mine openings, notably : ( 1 ) The long narrow excavation which may be
driven through massive or bedded rocks, or along the strike or the dip
of bedded rocks, as tunnels, drifts, crosscuts, and entries. (2) Excava-
tions of greater width, as rooms or stopes. (3) Excavations of great
lateral extent, as those of a longwall coal mine, or sections of a pillar-
and-room mine after the pillars have been drawn. In these various
types of openings the fact must be recognized that maximum pressure
may not always be due to a thrust acting vertically downward.
In order to simplify the problem it may be suggested that the rock
and mineral overlying and surrounding the excavation be considered as
forming one of the following:
(1) A beam of rock lying horizontally or inclined and extending
from pillar to pillar or column to column.
(2) A cantilever supported by a pier of rock or mineral.
(3) An arch or series of arches of equal or unequal spans.
(4) A column or pier, either vertical or inclined, supporting (1),
(2), or (3).
(5) A dome of the earth's crust.
It should be noted further that when the roof is considered as act-
ing as a beam it may be supported by piers of mineral, of noncoherent
filling, of timber, or of masonry, resting upon a more or less yielding
floor. With these explanatory statements, the various theories of sub-
sidence that have been formulated will be considered.
86 ILLINOIS ENGINEERING EXPERIMENT STATION
HISTORICAL EEVIEW OF THEORIES OF SUBSIDENCE.*
Belgian-French Theories.
Belgian engineers were among the first to make a scientific study of
earth movements due to mining operations. In 1825 a commission
investigating the cause of surface cracks about the city of Liege ex-
pressed the opinion that a distance of 300 feet between the mine workings
and the surface is more than sufficient to protect the surface. Further
disturbance of the surface raised the same questions in 1839. Another
commission of mining engineers concluded that there would be no danger
to buildings or wells from mining operations at a depth of 300 feet.f
Although credit for formulating the first theory of subsidence is
usually given to the Belgian engineer, J. Gonot, it is claimed by L. Thir-
n
FIG. 23. DIAGRAM ILLUSTRATING THE "LAW OF THE NORMAL/'
iart that the fundamental idea of the theory of the normal was first
presented by the French engineer, Toillez, in 1838. Gonot studied
surface subsidence in the vicinity of Liege in 1839 and formulated a
theory which was published in 1858. He claimed that following the
removal of coal the overlying strata would sink and the angle of fracture
would be perpendicular to the plane of the coal bed. (Fig. 23.) This
theory was later referred to as the "Law of the Normal." Mining oper-
ators in general and many engineers criticised this theory and, while
many later writers accepted the principle as it applied to horizontal
*Fayol, H. "Sur les Mouveraents de Terrain Provoques par 1'Exploitation des Mines."
Bui. Soc. Ind. Min., lie ser., Vol. 14, p. 862; Kolbe, E., "Tnanslocation der Deckgebirge
durch Kohlenabbau," pp. 2-51, Essen, 1908.
tVuillemin, E. and G. Bui. Soc. Ind. Min., lie ser.. Vol. 14, p. 858, 1885.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 87
/
and slightly dipping beds, various qualifications were suggested in
regard to the angle of fracture of steeply inclined beds. (Fig. 24.) Gonot
also held that the break extends through to the surface, irrespective o'f
the depth of mining. He based this theory on observations he had
made on subsidence at Liege. The Belgian engineer, Rucloux, who was
appointed with Wellekens to- investigate subsidence about Liege in 1858,
called attention to the fact that Gonof s theory undoubtedly could not
be applied to vertical and highly inclined beds. While many criticisms
were offered, no new theory was presented. The commission held that
the observed facts were sufficient to establish the principle that with
solid beds of an ordinary thickness and at moderate depths exploitation
by contiguous openings and successive fillings up to a considerable
extent may be made without affecting the surface. Where the depths
FIG. 24. THE "LAW OF THE NORMAL" NOT APPLICABLE TO STEEPLY DIPPING BEDS.
are slight, or when for one reason or another the beds lose their solidity,
subsidence may be prevented by preserving pillars. The subsidences
which are produced on account of the underground work generally fol-
low vertical lines, but may deviate from these lines according to the
direction of the beds, more often toward the lower side and often also
toward the upper side.
In 1868 four engineers were commissioned by the Prussian Govern-
ment to collect information on the question of the "influence that mine
workings may have on surface building" in the coal fields of various
countries. They found that at that time the majority of Belgian en-
gineers believed . that when the coal is entirely removed the most care-
ful packing gives no guarantee against damage to surface building; that
the packing only lessens the sinking; and that the surface may be pro-
tected by leaving pillars. In order to make this method effective only
half the area of the coal seams must be removed.
88 ILLINOIS ENGINEERING EXPERIMENT STATION
In 1871 the Belgian engineer, Gr. Dumont, who had been appointed
to make an investigation of conditions in and about Liege, made a
careful study of the problem and submitted a voluminous report of 331
pages, in which he supported the fundamental idea of the "Law of the
Normal" but limited its applicability to beds dipping not more than 68
degrees from the horizontal. This conclusion was based in part upon
upwards of a thousand levels at various parts of the town. He* called
attention to the direction and amount of the forces acting on the block
of rock overlying the excavation. The broken pieces must fall into the
excavation, and on highly inclined seams, according to Gonot's theory,
the masses of broken rock would have to move toward the excavation
on an angle less than the sliding angle. If a-b, in Fig. 25, represents the
weight of the rock A-B, and this force is resolved into the forces Ord and
FIG. 25. FORCES ACTING ON ROCK IN AN INCLINED BED.
a-c, it is evident that, as the bed becomes steeper, the force corresponding
to a-d will become less and the force corresponding to a-c greater. The
tendency, then, will be to create a cavity vertically above the excavation
rather than in a direction perpendicular to the plane of the bed.
Dumont held that the "inclination of the strata lessens the depth
of the subsidence, but increases the area damaged. Timbering hinders,
the beds forming the roof of a seam from breaking, and therefore pre-
vents the increase in their volume, which takes place when they break.
It thus increases rather than diminishes the subsidence at the surface."f
*Dumont, G. "Des Affaisements du Sol Produits par 1'Exploitation Houillere," Liege,
1871.
tColliery Ensrineer, Vol. 11. p. 25, 1890-91.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 89
The period during which, the movement of the surface may con-
tinue is uncertain. In Belgium it extends generally over ten to twelve
years but in certain instances has been known to continue twenty and
even fifty years. The draining of old workings or the flooding of a mine
may bring about fresh movements a long time after the original move-
ment has ceased.
J. Gallon, of the ficole des Mines, Paris, supported Gonot's theory
but with some reservations.* He believed that when the coal bed
is overlaid with unconformable beds, the angle of fracture will extend
through each bed perpendicular to its plane of bedding. (Fig. 26.) He
held that the amount of surface subsidence would depend on the com-
pressibility of the material which fell into the excavation. In hard rocks
a cavity narrowing upwards would be formed, while in soft rocks the
cavity would be funnel-shaped.
FIG. 26. FRACTURE NORMAL TO BEDDING PLANE.
The Colliery Owners' Association of Liege published a reply to
Dumont in 1875.f The validity of Gonot's theory for beds of low dip
was admitted, but his claim that the fracture would be normal to highly
inclined seams was disputed. They argued that the fracture over the
*"Cours d'Exploitation des Mines," Vol. 2, p. 334, 1874.
t"Des Affaisements du Sol. Attributes a 1'Exploitation Houillere,'
Liege, 1875.
90
ILLINOIS ENGINEERING EXPERIMENT STATION
workings would take place in a series of breaks approximately perpen-
dicular to the bedding plane of each stratum, but that the force of
gravity would cause the material to fall from the outcrop side of the
excavation, causing the line of fracture to lie between the vertical and
the perpendicular to the vein ; while on the lower side of the excavation,
each bed would tend to support the bed above and there would be an
overhanging of slabs of rock toward the excavation. Thus the line of
FIG. 27. LINE OF BREAK BETWEEN NORMAL AND VERTICAL.
fracture would be between the vertical and the normal to the bedding
planes. (Fig. 27.) They also called attention to Coulomb's measurement
of the angle of fracture by crushing. "The combination of this force pro-
ducing crushing with that tending to break the bed by bending induces
fracture along a line intermediate between the two directions, and such
line goes further from the normal as the inclination of the strata in-
creases."* On the whole the Colliery Owners' Association thought the
Dumont's theory was unsatisfactory and often of no practical use and
"Hughes, H. W. "Textbook of Coal Mining," London, 1904.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 91
that the only rule to follow was the examination of the special facts in
each particular case.
M. Haton de la Goupilliere (1884), Professor of Mining at the
ficole des Mines, Paris, held views similar to those of Gallon. He
pointed out the effect of the fallen material, which tends to check sub-
sidence and in fact may stop it at a certain level. With longwall mining
and filling he thought the movement would be almost independent of the
depth. He held that it would be impossible to have the "Law of the
Normal" completely verified in practice.*
The continued subsidence of the surface at Liege and the disagree-
ment among engineers as to the theories of subsidence induced H. Fayolf
to make observations of elevations at mines and to conduct laboratory
experiments. He first summarized the contradictory opinions of the
time as follows 4
(1) Upon the extension of the movement upwards.
(a) The movement is transmitted to the surface whatever may
be the depth of the workings.
(b) The surface is not affected when the workings exceed a cer-
tain depth.
(2) Upon the amplitude of the movements.
(a) Subsidence extends to the surface without sensible diminu-
tion.
(b) Movements become more and more feeble as they extend
upwards.
(3) Upon the relative positions of the surface subsidence and of
the mining excavation
(a) Subsidence always takes place vertically above the workings.
(b) Subsidence is limited to an area bounded by lines drawn
from the perimeter of the workings and perpendicular to the beds.
(c) Subsidence can not be referred to the excavation either by
vertical lines or lines normal to the beds, but only by lines drawn
at an angle of 45 degrees to the horizon, by the angle of repose of
the ground, or by some other similar angle.
(4) Upon the influence of gobbing.
(a) The use of packing protects the surface effectually.
(b) Packing simply reduces the effect of subsidence.
*"Cours d'Exploitation des Mines," 1883.
tDirector, Commentry and Montvicq Mines in France.
JBul. Soc. Ind. Min., lie ser., Vol. 14, p. 805, 1885.
92 ILLINOIS ENGINEERING EXPERIMENT STATION
(c) Subsidence is greater with stowing than without it.
Fayol conducted a long series of investigations and experiments*
and came to the conclusion that the movements of the ground are lim-
ited by a kind of dome which has for its base the area of the excavation
and that their amplitude diminishes by degrees as they extend further
away from the center of the area.
"FayoFs rule agrees with all the facts observed; absence of sub-
sidence, more or less important subsidences, movements limited to the
vertical above the perimeter of the excavations, those limited to the
normal or to other inclinations, and so on. It has the disadvantage of
being indefinite; but in a question which embraces so many elements,
many of which are unknown or not well known, such as the nature of the
rocks, the thickness of the beds, irregularities in geological structure, the
action of water, etc., we cannot hope to arrive at absolutely accurate
formula?; we shall have accomplished much when we get to know very
nearly the true form, the direction, and the relative amplitude of the
subsidences, and are in a position to combat false ideas successfully. "f
According to Fayol the disturbance of the strata is greatest over
the center of the area excavated and it diminishes in amount toward
the perimeter of the excavated area. As the vertical distance above the
excavation increases, the amount of the movement decreases, and, if
the workings are at great depth, there will be a depth beyond which the
movement will cease. When graphically represented the limits of the
movement are depicted by a dome ; outside of this dome there can be no
disturbance whatever. However, Fayol called attention to the possibility
of movement if there should be a series of these domes in close proximity
to each other, and to the effect of dip, rock structure, etc. upon the
practical application of this theory. As a result of his experiments and
observations, Fayol concluded:
(1) If excavations were stowed in a thoroughly tight and efficient
manner with incompressible materials there would be no subsidence,
but ordinary stowing is not done under these conditions, because the
materials employed are all more or less compressible and the excavations
are never perfectly filled up. When the roof settles the stowing resists
feebly at first, after which the resistance rapidly increases and finally
arrests the downward movement.
(2) The amplitude of the subsidence diminishes in proportion to
*See page 138.
tGalloway, W. "Subsidences Caused by the Workings in Mines," Proc. South Wales
Inst. of Engrs., Vol. 20, p. 811, 1897.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 93
the depth of the workings below the surface, the diminution being pro-
portional to the increase of depth.
Leon Thiriart in 1912 called attention* to the theory of Banneux,
which Thiriart called the "Law of the Tangent." Thiriart's theory is a
modification of Banneux's, and Banneux's theory resembles that of
Hausse.f The bending moment is considered for each bed successively,
beginning with the one immediately overlying the coal. By elaborate
calculation, based on observations of subsidence, formulae are derived by
which a table showing the angle of break for various dips has been com-
piled.
German Theories.
A. Schulz, one of the first German engineers to study surface sub-
sidence due to mining operations, in 1867 published his ideas on the
FIG. 28. VERTICAL FRACTURE OF DIPPING BEDS OF SHALE.
angle of fracture and the size of pillars necessary to protect objects on
the surface.^
FIG. 29. SCHULZ'S IDEA OF FRACTURE OF SANDSTONE BEDS.
He criticised Gonot's "Law of the Normal" and held that in dip-
ping beds of shale the fracture will occur along vertical planes (Fig. 28),
while in sandstone the fracture on the dip side will approach the nor-
*Thiriart Leon "Les Affaisements du Sol Produits par 1'Exploitation Houillere," Ann.
des Mines de Belgique, Vol. 17, p. 3, Bruxelles, 1912.
tSee page 97.
JSchulz, A. "Investigations on the Dimensions of the Safety Pillars for the Saarbuck
Coal Mining Industry and on the Angle of Fracture at Which the Strata Settle Into Worked-
Out Rooms." Zeit. fur B.-, IL-, u. S.-W., 1867.
94 ILLINOIS ENGINEERING EXPERIMENT STATION
mal, but on the outcrop side it will be vertical. He held in general
that the fracture would occur between the vertical and the normal to the
bed.
During the same year that Schulz published his paper on the angle
of fracture, Mining Assessor von Sparre published a criticism of Gonot's
theory.* He held ideas similar to those of Schulz; namely, that the
fracture will occur between the vertical and the normal. He suggested
the consideration of the separate beds and showed that for each bed
the fracture would occur between the vertical and the normal on both
sides of the excavation in a dipping coal seam. As shown in Fig. 30,
the bounding planes of the break will be not ab and Ih nor ac and Jim
but midway between.
FIG. 30. FRACTURE IN DIPPING BEDS ACCORDING TO VON SPARRE.
Von Dechen called attention in 1866 to the importance of studying
the part played in subsidence by the heavy marl beds overlying the coal
measures. Some engineers, in fact, held that subsidence was due en-
tirely to the unwatering and drying of these marl beds. Von Dechen
noted also that the "Law of the Normal" could not be applied to very
steeply inclined or vertical beds.f
In 1894 the project of constructing a canal between Herne and
Euhrart caused an investigation of the stability of the surface over
which it was proposed to build the canal. A survey of conditions in
the Dortmund district was made by the Board of Mines of Dortmund;
levels were run and maps were made, and a very complete report was
submitted in 189 7.f It was concluded from observation on the West-
*Von Sparre, J. "On the Angle of Fracture of Strata of the Coal Measures," Gluckauf,
1867.
tVon Dechen, H. "Opinion on the Surface Subsidence in and About the City of Essen,"
Manuscript, 1869.
t"On the Influence of Coal Mines Under Marl Capping Upon the Earth's Surface in
the Dortmund District." Zeitschrift fur B.-, H.-, u. S.-W., Vol. 46, pp. 372-392, 1897.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 95
phalian mines and for the conditions of that district that there would be
no "harmless depth." The lateral extent of subsidence was found to in-
crease greatly with thickness of the marl covering. It was noted that
careful filling pf the mine workings will greatly reduce the amount of
vertical subsidence but will not affect greatly the lateral extent, in fact,
in some instances it was found that with filling the lateral extent of sub-
sidence is greater than when no filling whatever is used.
From the data collected an effort was made to determine the angle
of fracture in rock and also the angle at which the limiting plane of
subsidence of the marl extends from bedrock to the surface. In rock
dipping not more than 15 degrees, the angle of fracture was found to
(rea M/'ne Out
FIG. 31. SUBSIDENCE BEYOND ANGLE OF BREAK ACCORDING TO WACHSMANN.
be about 75 degrees, measured from the horizontal (Fig. 31), while in
steep seams the angle approaches the natural slope, generally not less
than 55 degrees.
For dips up to 65 degrees the vertical amount of subsidence may be
found by the formula:
S = f. m. Cos a
in which 8 = vertical amount of subsidence,
m = thickness of coal worked,
a — angle of dip of coal seam.
/ is a coefficient whose maximum values are as follows, if filling is com-
plete:
0.40 for dips 0—10°,
0.30 for dips 10—35°,
0.25 for dips over 35°.
96
ILLINOIS ENGINEERING EXPERIMENT STATION
When no filling is used / may be as much as 0.80.
Wachsmann* held that when an underlying coal bed is mined, the
lowermost strata collapse, the next higher strata sink and crack if the
FIG. 32. ANGLES OF FRACTURE IN ROCK AND OF SUBSIDENCE IN MARL.
excavation is of sufficient extent, while the uppermost strata sink with-
out breaking or cracking. There is subsidence beyond the actual angle
of break, as shown in Fig. 32.
In 1885 Mining Engineer R. Hausse published some observations
*Uber die Einwirkung des Oberschlesischen Steinkohlenbergbaues auf die Oberflache.
Zeit. f. Obersches B.- u., Hiittenmannischen Verein, p. 313, 1900.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
97
on the angle of break.* Owing to the great interest in the problem of
subsidence, Hausse directed his entire time to the scientific investigation
of various phases of the problem in Germany, particularly in Saxony,
and published the results of his work in 1907-f In his preliminary
SURFACE.
FIG. 33. HAUSSE'S THEORY; ANGLE OF BREAK BETWEEN VERTICAL AND SLIDING
ANGLE.
chapter Hausse discusses the behavior of rocks over excavated areas and
distinguishes between the "first" or "main break" and the "afterbreak."
Over a horizontal bed he found that the main fracture is vertical and that
the after break extends upward over the unmined coal. He pointed out
that after the first falls occur, filling the cavity, the overlying strata
subside, compressing the fallen material as filling is compressed by the
roof in longwall mining. He stated that the plane of fracture lies be-
tween the vertical and the plane of sliding for the rock in question, and
generally the plane of fracture will bisect the angle between the two
limiting planes (Fig. 33). He discussed the relation between the di-
rections of the main break, the after break, and the angle of inclination
of the seam, as follows:
a
The angle of main fracture on the upper side = 90 — , in which
2
a= angle of dip. The angle of after break is assumed to be either con-
*Hausse, R. "Von der Niedergehen des Gebirges beim Kohlenbergbau und den damit
Zusammenhangenden Boden-und Gebaudesenkungen," Ziet fur das Berg-Hiitten und Salinen-
wesen, pp. 324-446, 1907.
tHausse, R. "Beitrag zur Bruch Theorie; Ehrfahrungen tiber Bodensenkungen und
Gebirgsdruckwirkungen," Jahrbuch fur das Berg-und Hiittenwesen in Sachsen, 1885.
98
ILLINOIS ENGINEERING EXPERIMENT STATION
stant or equal to 20°, or it is taken as decreasing from 20° to 10° in
proportion to the increase of the dip from 0° to 45°. In a series of
tables, Hausse presents the angle of fracture for various dips, making
certain assumptions. He determined coefficients of increase of volume
for mining with filling and without filling on the basis of observations
made in the Koyal Colliery at Plauen under the Dresden-Tharandt
Government Eailway. Where there was no filling, the coefficient was
found to be 0.01 and with filling the coefficient was found to be 0.002.
Starting from Kziha's assumption of sliding angles, Trompeter*
determined by the use of Hausse's observations the breaking zone with
A B
FIG. 34. "MAIN BREAK" AND "AFTER BREAK." (HAUSSE.)
regard to the expansive power or increase in volume of broken rock.
From his experience he found this for the Ehenish-Westphalian coal
district to be an increase of 12 meters for every 100 meters in depth.
Puschmann has described the subsequent working of overlying
seams in the coal district of Upper Silesia.f
According to many engineers, the unwatering of the surficial ma-
terial has been the immediate and sole cause of surface subsidence.
Those who hold this opinion claim that surface movement has resulted
from the sinking of shafts and the driving of boreholes alone and with-
out any actual removal of the mineral deposit. There is, however, a
wide difference of opinion on this matter. Von Dechen held that the
*Trompeter, W. H. "Die Expansivkraft im Gestein als Hauptursache der Bcwegung
des den Bergbau Umgehenden Gebirges," Oestreichishe Zeit., fur Berg.-und Hiittenwesen,
1899.
tPuschmann Uber den Nachtraglichen Abbau Hangender Floze beim Oberschleiischen
Steinkohlenbergbau," Zeit. fur d. B.-t H.-, u. S.-W., Vol. 68, p. 187, 1910.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 99
subsidences* near Essen in 1866 and 1868 were caused by the partial
drying of the marl and green sand overlying the coal measures. Grafff
demonstrated by tests that drainage does not cause any change of
volume of sand or quicksand and held that, when the water does not
carry away any solids, there can be no subsidence resulting simply from
unwatering.
The principal value of the work of the Germans has been in deter-
mining the angle of break, extent of surface subsidence relative to mine
workings, and the practical coefficients of increase in the volume of the
measures overlying the mined area, as these measures sink into the
worked out area. Data upon these phases of subsidence have been col-
lected in a systematic and accurate manner during a long period of
years by engineers in the coal mining districts of Germany.
Austrian Theories.
Subsidence of surface due to mining operations has attracted con-
siderable attention in the Ostrau-Karwin coal region in Austria. Minis-
terial regulations controlling the removal of coal under railways were
formulated and became effective January 2, 1859. In 1876 Mining
Director W. JicinskyJ published a treatise on subsidence.
The question of the applicability of the government regulations for
the protection of railroads to the railroads leading to the mines and serv-
ing the mines almost exclusively aroused discussion in the late 70's and
the early 80's. The Board of Mines of Olmutz framed a regulation to
modify the existing regulations so that they would not apply so strictly
to mining railroads. F. Eziha, Professor of Eailroad Construction at
the Technical School of Vienna, was engaged to advise on the proposed
regulation. He expressed his opinion on this question, formulated a
theory of subsidence, and presented regulations to govern the exploita-
tion of the coal under the mining railway.lj Eziha formulated a theory
covering (1) the direction of fracture and (2) the amount of the ver-
tical sinking of the earth, a brief statement of which follows:
(1) The Direction of Fracture. When rock is undercut, there is a
tendency for it to fall or sink in proportion as gravity exceeds cohesion.
The action may be falling or tearing, or both. He distinguished what he
*Goldreich Die Theorieder Bodensenkungen in Kohlengebieten, p. 20.
tGraff "Verursacht der Bergbau Bodensenkungen durch die Entwasserung Wasser-
fuhrender diluvialer Gebirgs-schichten," Gluckauf, 1901.
tjicinsky, W. "The Subsidences and Breaks of the Surface in Consequence of Coal
Mining." 1876. Published later as a monograph of the Ostrau-Karwin coal district, 1884,
"The Effects of Coal Mining on the Surface.'
flOest. Zeit. f. B.-, u. H.-W., Vol. 29, 1881, and Vol. 30, 1882.
100
ILLINOIS ENGINEERING EXPERIMENT STATION
called a "falling space" and surrounding it, more or less concentrically, a
"friability" or "tearing space." He found the falling space to approxi-
mate the shape of a paraboloid. First the rock becomes loosened and
afterwards falls when gravity exceeds cohesion. In time, limited by the
structure of the rock, a dome-shaped space abc is formed (Fig. 35),
FIG. 35. "ZONE OF FALLING" AND "ZONE OF TEARING."
working laterally and vertically from the center of disturbance. Outside
this space and more or less concentric is the dome of tearing, indicated
by the dotted line amc. If the tearing sphere extends to the surface, it
will cause surface disturbance within the area bounded by mn (Fig. 36),
and the overhanging wall will gradually change its slope, depending
upon the lateral extent and degree of the tearing and the relation be-
tween gravity and cohesion (see Fig. 37). Rziha thought that the
stratification of the beds did not have much effect upon the angle of
break. It may be noted that he did not make a detailed study of the
subsided area in the field. The Mining and Metallurgical Society of
M-Ostrau held that actual subsidence in the Ostrau-Karwin district did
not conform to Eziha's theory.
(2) Vertical Movement. Eziha treated this subject under two
headings: (a) The collapse into the underground excavation, and (b)
the unwatering of the roof, causing a decrease in volume. He held
YOUNG-STOEK — SUBSIDENCE RESULTING , FJIOM
: '' ,101
FIG. 36. "ZONE OF TEARING" EXTENDED TO SURFACE.
FIG. 37. SUBSIDENCE OUTSIDE UNDERMINED AREA.
102;>?* ILLINOIS ENGINEERING EXPERIMENT STATION
that when mining is carried on at a great depth there may be no dis-
turbance of the surface, and attempted to determine this depth by the
formula :
h==!L
a
in which h = harmless depth,
a = coefficient of increase of volume,
M = vertical seam thickness.
When pillars are left, he assumed that they will reduce subsidence, and
the formula used to determine the harmless depth is :
MB
h=s~T
in which B is a coefficient for pillars and the filling, varying from 0.50
to 0.60. Kziha presented coefficients for the increase in volume of six
kinds of rock. Goldreich* is of the opinion that an additional factor,
overlooked by Kziha, is height of excavation. The less the height, the
greater is the probability that the overlying rock will sink without com-
plete or extensive crushing. Moreover, the completeness of the compres-
sion of the packing under the roof weight depends somewhat upon the
height and extent of the excavation. These coefficients were not secured
by mine investigation.
Goldreich criticises Eziha's suggestion of leaving pillars, and states :
"If Eziha had been acquainted with the shape of the surface depressions,
he would never have recommended the working methods given in his
report." Objection is made also to the idea of a harmless depth as it
"logically implies there ought to be the possibility of creating cavities of
unlimited size beneath the harmless depth without giving rise to land
movements on the surface." The Mining and Metallurgical Society of
Ostrau (Moravia) to which organization Eziha's regulation was sub-
mitted, published its opinion in 1882.f Observations over a period of
thirty years in the Austrian coal fields lead Goldreich to support Jicinsky's
statement that no movement occurs if the water does not carry away
from the volume under observation any solids mechanically or in solution.
Goldreich states* that the efforts to study theoretically the causes
of subsidence in Austria date from the year, 1882. The Committee of
the Mining and Metallurgical Society of Ostrau, Moravia, consisting
of W. Jicinsky, J. Mayer, and von Wurzian, attacked Kziha's theory on
the basis of observations in the Ostrau-Karwin district. Eziha failed to
•Goldreich Op. cit., p. 53.
tOestrr. Zeit. fur B.-, u. H.-W., Vol. 30. 1882.
JGoldreich Op. cit., p. 45.
YOUNG-STOEK— SUBSIDENCE RESULTING FROM MINING 103
consider the probability of the overlying rock bending and sagging with-
out breaking to fill the worked-out space, as shown in Fig. 38. In the
event that sagging takes place, the increase in volume will be much
smaller than that figured by Eziha, who assumed a breaking up of rock.
(Fig. 39.)
The Committee preferred to use the term "undangerous depth" in
addition to Rziha's phrase '^harmless depth" for those depths at which
C,
FIG. 38. LARGE SUBSIDENCE IN CASE OF BENDING OF ROCK.
mining will produce a gradual subsidence of the surface without damage
to small objects or structures.
Jicinsky, a member of the committee, found the average increase in
the volume of the rock of the coal measures and calculated the harmless
depth from the maximum surface subsidence observed, according to the
formula :
s = t -\-m-a t
m — s
or a = 1 + —
t
in which
s = surface subsidence,
t = thickness of coal rock exclusive of the coal bed,
104
ILLINOIS ENGINEERING EXPERIMENT STATION
m = thickness of coal bed,
a = average coefficient of increase of volume of the coal rock
considered as a whole.
The term "coal rock" means the bed of rock overlying the coal which
is broken in the course of subsidence, with consequent increase of volume.
If s is made 0, the formula shows the thickness of overlying rock, ex-
clusive of the marl, necessary to prevent surface subsidence. The entire
mass of material above the coal rock is believed to settle without increase
in volume and is not taken into account in the formula.
The average coefficient of increase of volume of the coal rock is
found to be 0.01 (i. e., a = 1.01) for several cases of subsidence indicated
by Jicinsky. His conclusion is then, as expressed by the formula, that
the surface subsidence is equal to the thickness of the bed taken out
FIG. 39. SMALL SUBSIDENCE IN CASE OF BREAKING OF ROCK.
minus 0.01 of the thickness of the overlying rock which is shattered by
movement.
The Committee also noted the vertical amount of subsidence and
the duration of the movement, and special protective devices for shal-
low depths were considered. It was estimated that filling was com:
pressed to 0.6 of the thickness of the bed so that in determining the
harmless depth only 0.4 of thickness of the coal bed should be used
in the formula. The committee agreed that "the interests of national
economy demand that the leaving of coal pillars shall be prescribed in
the rarest cases" and "the cost of the surface objects to be protected
is to be compared with the coal losses." The Committee prepared
regulations for coal mining under the mining railways, and these
later became the basis of the regulations adopted.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 105
Jicinsky's* monograph on subsidence appeared in 1884 and con-
tained a complete statement of the principles accepted at that time by
the leading Austrian engineers, and in it he formulated the follow-
ing principles:
"The subsidence depends: (1) on the thickness of the seam,
(2) on the dip of the seam, (3) on the depth of the mine, and (4) on
the constitution of the roof rock of the seam. It may be regarded as
a rule: (a) That the depth of the land subsidence is directly pro-
portioned to the thickness of the seam, and the extension of subsidence
is in direct proportion to the mined area; (b) that the depth of the
surface subsidence increases with the dip of the seam, whereas its
extension decreases, and for this reason in vertical seams the land
subsidence is deep but manifests itself in the form of a kettle-shaped pit."
Jicinsky held further : "During every collapse of a solid rock there
takes place a piling up of the broken masses. It follows that such a
break causes an increase of volume and at a certain height in conse-
quence of this increase in volume the entire empty space is so filled
that no further after-break is possible; hence the effects of the break
upon the surface must decrease with increasing depth. Every rock,
even every single rock stratum, has its own hardness and toughness,
and for this reason not all the kinds of rock behave in the same way
during their collapse."
The subsidence formula of Jicinsky can be used to determine the
harmless depth. Jicinsky discussed this point at length. He also
made a study of the direction of fracture in the overlying rocks, and
held that along the strike fracture is always normal to the coal bed.
He objected to Gonot's and Schulz's theories for fracture on the dip
and held that the angle was midway between the normal and the
vertical. His views have been supported by 80 per cent of his ob-
servations.
He also considered in his monograph the amount of surface sub-
sidence resulting from the mining of several superimposed seams, the
various stages of rock movements, and safety pillars. In his opinion
arbitrary rules cannot be used for determining the size of pillars, but
each case must be studied separately and figured according to the
local conditions.
C. Balling made a study of the angle of fracture in the northwest
Bohemian brown coal basin and found that, for a depth of not more
'Jicinsky, 'W. "The Influences of Coal Mining Upon the Surface." Monogranfe^oTlitie
Ostrau-Karwin Coal District, 1884. .S? ; } »
106 ILLINOIS ENGINEERING EXPERIMENT STATION
than 300 feet and a dip of 8 degrees, the angle varied from 68 to 74
degrees.*
Chief Mine Inspector Anton Padonr also made a report upon sub-
sidence in the northwest Bohemian brown coal district.f He noted
the vertical amount of subsidence and found the following relation :
H = 4;§y~W
in which
H = vertical height of subsidence,
h = height of excavation.
He found that in the Bruch district, where the covering is firm marl,
the angle of fracture is as follows:
(1) Thickness of capping from 1,000 to 1,200 feet, angle of seam
from 0 to 8 degrees.
(a) towards the dip, angle varies from 72 to 69 degrees.
(b) towards the rise, angle varies from 72 to 74 degrees.
(2) Thickness of from 1,000 to 1,100 feet, angle of seam from
27 to 30 degrees.
(a) towards the dip, angle varies from 63 to 60 degrees.
(b) towards the rise, angle varies from 78 to 77' degrees.
In 1911 Goldreich delivered a lecture before the Austrian Society
of Engineers and Architects of Vienna on the "Theory of the Eailway
Subsidences in the Mining District, With Special Consideration of the
Ostrau-Karwin Coal District/' Since that date he has made several
important contributions to the literature of this subject.
In 1912 Franz Bartonic discussed the causes of subsidence, but made
no contribution to the theory.^
In 1913 Goldreich published his work on "The Theory of Land
Subsidence in Coal Eegions with special Eegard to the Railway Sub-
sidences of the Ostrau-Karwin Coal District," and followed this with
a volume entitled, "Land Movements in the Coal District and their
Influence on the Surface."^
Goldreich criticises Jicinsky's contribution and theory in a num-
ber of points. He takes no exception to the fundamental principles
but objects to the formula. Goldreich questions the assumption of a
coefficient of increase of volume that will be applicable to all cases.
"Bailing, C. "Die Schatzung von Bergbauen nebst einer Skizze fiber die Einwirkung des
Verbruches unter-irdischer, durch den Bergbau geschaffener Hohlraume, auf die Erdober-
flache," A. Becker, 1906.
t-Padour, Anton Chapter on "Damage to the Land and Buildings" in the "Guide
Through the Northwest Bohemian Brown Coal District," 1908.
JBartonic, Franz "Die Ursachen von Oberachenbewegungen im Ostrau-Karwiner Berg-
Revier. Montanist, Rundschau, Feb. 16, March 1 and March 16, 1912.
11 In press.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 107
He points out the fact that the so-called "after-slide" of surficial material
is not considered in the formula. He accepts Jicinsky's determination
of the fracture in the coal measures, but objects to the formulating of
general rules for determining the size of pillars. The principal por-
tion of Goldreich's work is given to a discussion of the phenomena of
subsidence in connection with railways. "From the profiles of sunken
railway sections of the Ostrau-Karwin coal district it can be seen that
these profiles have a parabolic form, that the maximum subsidences are
found in the middle of these depressions, and that the amounts of
subsidence decrease almost regularly towards the two ends of the curves
until they finally become equal to zero." This regularity of the depres-
sions caused Goldreich to undertake to formulate a theory of subsidence
applicable to conditions such as those which exist in the Ostrau-Kar-
win district, the most distinctive feature being the surficial bed of
plastic marl as much as 1,200 feet thick in places. Where the coal
measures outcrop, the regularity of the surface depressions disappears
and Goldreich takes refuge in the statement that we must depend merely
upon experience.
Goldreich's observations developed the fact that following the sub-
sidence of bed rock there is a vertical subsidence of the marl directly
overlying and a lateral after-sliding of the adjacent and outlying marl.
In discussing the subsidence of the roof strata he emphasizes the
effect of the elasticity of each stratum. "When the elasticity of the
subsiding roof strata is so great that the latter reach the floor of
the worked out room without any disturbance in the coherence of the
superimposed strata, then the volume of these subsiding strata remains
unchanged." The subsidence of roof strata without increase of volume
will occur in the case of the extraction of thin and flat seams. "The
increase of volume which takes place during the first stage of the sub-
sidence process is not enduring; for in consequence of the weight of
the following roof strata the broken rock is again compressed, so that
at the end of the rock movement there results a decrease of volume which
is certainly not identical with the initial increase of volume." Only by
observing the amount of surface subsidence caused by an underground
working can a basis for estimating the coefficient of increase of volume
under actual conditions be obtained. When the 9verlying beds are elastic
there will be little increase in volume as the movement proceeds upward ;
under such conditions the term "harmless depth" cannot properly be
used. "It cannot be pointed out strongly enough how absurd is the
establishment of a harmless depth which should be valid for all work-
108 ILLINOIS ENGINEERING EXPERIMENT STATION
ings; the harmless depth has rather a theoretical character because the
presuppositions required for the actual existence of the harmless depth
are very seldom true in practice."
British Theories.
As previously noted, subsidences resulting from the mining of salt
and coal in the British Isles were observed at an early date and were
the cause of investigation by British engineers, who in general have sup-
ported the important principles of Belgian-French theories, although
certain persons have taken exception to particlar points in these theories.
Numerous observations have been made upon subsiding areas and con-
siderable valuable information has been collected, the data have been
correlated and arranged, and empirical formulae have been constructed
so that adequate pillars may be left for the protection of surface struc-
tures and property of various kinds.
In 1868 a commission of Prussian engineers investigated subsi-
dence in the various coal mining districts of England, and found that
in England the opinion was approximately as follows:
(1) The working of coal at every known depth may affect the sur-
face, but at depths greater than 400 meters (1,300 feet) it can cause
damage only to certain buildings, such as cotton mills.
(2) In the case of complete extraction, filling may be a means of
effective protection against movements of the earth.
(3) The practice of leaving pillars constitutes an efficient protec-
tion against the effects of exploitation upon the surface. The extent
of these pillars of safety should be determined by the surface to be
protected, the depth being known and the angle of rupture being assumed.
Observations carried on by J. S. Dixon demonstrated that the
wave of maximum subsidence regularly followed the advancing face
and that a wave of disturbance was just as regularly projected in ad-
vance of it;* that is, the wave of disturbance preceded the working
face, but the maximum subsidence followed it. Joseph Dickinson
called attention to the similarity between earth movements due to
natural causes and those resulting from mining operations. He con-
sidered that "the direction of subsidence may be judged by analogy
from the slopes taken by faults and mineral veins. The slope of a
fault in horizontal strata averages about 1 in 3.07 from the perpendicular,
varying according to the hardness and cohesion of the strata from
*Dixon, J. S. "Some Notes on Subsidence and Draw." Trans. Min. Inst, Scotland,
Vol. 7, p. 224, 1885.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 109
about 1 iii 5 in hard rock to 1 in 3.75 in medium, and 1 in 2.5 in soft.
He considered that for horizontal seams not exceeding 6 feet in thickness,
and with strata of the average hardness of those in Lancashire, ordinary
subsidence may be taken as extending on all sides to one-tenth of the
depth, and that to obtain security a margin should be added. This mar-
gin is limited by some engineers to an additional one-tenth of the depth,
while others add an arbitrary amount. When the strata are softer the
extent of the subsidence is sometimes taken as one-sixth, or even one-
fourth of the depth of the working, while, on the other hand, for hard
siliceous rock, such as is found in South Wales, reductions are needed. He
also agrees with other writers, that in seams of moderate inclination
larger areas are required for support on the rise side than on the dip."*
T. A. O'Donahue in discussing subsidencef endorses the observations of
J. Dickinson in the following language: "Joseph Dickinson is prac-
tically the only writer who has succeeded in connecting the threads of
what was apparently a mass of contradictory evidence and in showing that
the majority of cases approximately agree with a more or less definite
rule/' In O'Donahue's opinion, which is the result of considerable experi-
ence in studying the effect of surface subsidence, including the taking of
levels, the breaking lines of strata may be estimated within narrow limits
with average conditions." He enumerates the important factors affect-
ing the position of the breaking lines and the ultimate extent of the
subsidence as (1) the relative hardness of the strata, (2) the inclina-
tion, and (3) the thickness of the coal seam. He also mentions the
influence of surface deposits. He considers the various angles of draw
that have been noted and points out that for safety the maximum
angle for given conditions must be taken as the limit for safety. For
coal beds 6 feet thick and overlying strata of moderate hardness, he has
found that the angle of draw is from 5 to 8 degrees beyond the vertical.
This means that if a pillar is to be left to protect objects on the surface, a
I margin of one-twentieth to one-tenth of the depth should be left in
i order to provide against the draw. With inclined strata the draw in-
creases roughly in proportion to the degree of inclination of the strata.
He accepts th normal theory as correct when applied to dips of 18
to 24 degrees, but only for dip workings. When the mine workings
I are on the rise the maximum draw is estimated at 8 degrees for strata
'Hughes, H. W. "A Textbook of Coal Mining," 5th Edition, p. 185, London, 1904.
Dickinson, J. "Subsidence Due to Colliery Workings," Proc. Man. Geol. Soc., Vol. 25,
p. 600, 1898, and Colliery Guardian, Oct. 28 and Nov. 11, 1898.
tO'Donahue, T. A. "Mining Formulae," p. 244, Wegan, 1907.
110 ILLINOIS ENGINEERING EXPERIMENT STATION
nearly horizontal and the draw is taken to cease with strata at an in-
clination of 24 degrees.
The ideas of O'Donahue are expressed in his formula for shaft
pillars as follows:
M = Margin of safety, say from 5 to 10 per cent of the depth,
D = depth of shaft,
X = distance at the seam, between two lines drawn from a point
at the surface, one line being vertical and the other at right angles
to the seam.
Shaft pillar in horizontal strata
Eadius of pillar = M -\ — - '
In inclined strata
Rise side = .M + ~ + ~X
For seams less than 6 feet thick the size of the pillar may be decreased,
while for thick seams it is suggested that the size of pillars determined
for a 6-foot seam be multiplied by the "square root of the thickness of
the seam in fathoms."
In discussing the effect of the thickness of the seam upon the
amount of subsidence, O'Donahue calls attention to the effect of the
material stowed in the goaf or gob. He makes the point that, other
conditions being the same, the mining of a 6 -foot seam would result
in more than twice the vertical subsidence caused by mining a 3-foot
seam, owing to the fact that little material is thrown into the gob in
mining the 6-foot seam, while in mining the 3-foot seam undoubtedly
much "brushing" would have to be done and, therefore, there would be
considerable material left in the goaf or gob. Therefore, the total sub-
sidence per foot of coal removed will be greater in the case of the
thicker seam.
He objects to the statement that mining at depths of 1,800 to 2,000
feet will not cause subsidence, because careful levellings will show that
the complete removal of the coal at even greater depths will cause
a sinking of the surface. "When the whole of the mine is taken out
subsidence of the surface follows at all workable depths. The writer's
observations show that the working of a seam, for instance 4 feet thick,
will cause the surface to subside about 3 feet if the seam be not greater
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 111
than 600 feet in depth, and will cause a subsidence of from 12 to 18
inches at a depth of 2,400 feet.
H. W. G. Halbaum has made a careful study of roof pressures
in longwall work and has made some notable contributions to the
theories of subsidence. In his study of the action of the roof in long-
wall mining* he called attention to the locking of the roof due to the
lateral thrust in great roof sections. "The great roof sections, by
successive slips, have descended a few inches. The motion has been
arrested for the time being by the lateral thrust, and the great body
of strata remains securely gripped in the powerful jaws of its natural
clamps." Subsequently Halbaum formulated the following propo-
sition: "Contained in the total force of the roof action, there is a
horizontal component, the action of which is contrary to the direction
of working, and the power of which is sufficient to deflect the roof
action from the vertical line."f
After discussing carefully the planes of strain, Halbaum con-
siders the cantilever idea. He likens the unsupported roof strata to a
huge cantilever whose load consists primarily of its own weight. "It is
evident that if the cantilever were homogeneous and if the neutral
surface were at half-depth, and if efficiencies of the compressive and
tensile stresses to propagate their respective strains were equal, we should,
under such conditions, obtain a mean line which would be vertical;
for the tensile and compressive components would be equal in length
and equal, though opposite in obliquity. The obliquity of one com-
ponent would thus exactly balance the opposite obliquity of the other,
and the mean line would be vertical." He then points out that such a
balancing of components is unlikely, for the resistance of ordinary coal-
measure strata to compression is usually greater than their resistance
to 'tension. The neutral surface of the cantilever must generally lie
below the half-depth, of the beam. Moreover, the beam is not homo-
geneous. "Viewed from the broader standpoint of internal nature and
external environment combined, there must be little or no exaggera-
tion in the statement that our cantilever is immeasurably stronger to
resist compression than to resist tension; and hence we are bound to
infer that its neutral surface is very low indeed and probably not many
feet above the roof-line itself." "It follows that by far the greater por-
tion of the absolute line of elementary strain is supplied by the tensile
'Halbaum, H. W. G. "The Action, Influence and Control of the Roof in Longwall
Workings." Trans. Inst. Min. Engrs.. Vol. 27, p. 211, 1903.
tHalbaum, H. W. G. "The Grfeat Planes of Strain in the Absolute Roof of Mines."
Trans. Inst. Min Ensrs., Vol. 30. p. 175, 1905.
112 ILLINOIS ENGINEERING EXPERIMENT STATION
component, that by far the greater portion is projected over and towards
the solid, and that the mean elementary line must, therefore, possess
a normal obliquity little less in magnitude than that of the tensile
component itself." Stated in brief the idea is this: "We start with
a thick unloaded cantilever and we end with a thinner but loaded
beam ; thinner, because from the standpoint of their efficiency, the upper
layers are gone; and loaded, because from the standpoint of their dead
weight, the upper layers remain only as a true load on the effective
beam beneath. This simultaneous thinning and loading of the effective
cantilever seems probable for several reasons: The principal one per-
haps is to be found in the fact that the original beam is a composite
beam formed by an aggregation of smaller beams (strata) in super-
position. The whole of the composite beam is an effective beam only so
long as its several layers firmly adhere at their conterminous horizontal
planes or boundaries. As soon as the uppermost layer (or series of
layers) separates from its subjacent layer, or tends to slide thereon,
it ceases at once to form any part of the effective cantilever, to which
cantilever it must thenceforward sustain the relation of a load only." He
calls attention to the fact that "when we examine the cases of natural
subsidences of the earth's crust, we find that the great planes of strain, in
the normal case, are always projected over and towards the solid (or un-
subsided) strata."
In a paper before the International Geological Congress, Professor
George Knox summarized the various points "which may be considered
sufficiently well established to form a basis for further investigations —
namely:
(a) That surface subsidence invariably extends over a greater
area than that excavated.
(b) The angle of pull is determined by the ratio between the
excavated and subsided areas.
(c) That this ratio is determined by a large number of factors,
among which may be included the following :
1. The amount of permanent support left in the unmined
area.
2. The thickness of the seam worked.
3. The depth of the workings from the surface.
4. The method of working adopted.
5. The direction of working in relation to the jointing of
the strata.
6. The rate at which the workings advance.
YOTJNG-STOEK — SUBSIDENCE RESULTING FROM MINING 113
7. The nature of the strata overlying the workings.
8. The presence of faults, fissures, etc., in the strata.
9. The permeability of the overlying rocks.
10. The dip of the strata.
11. The surface contour.
12. The potential compressive forces existing in the strata con-
taining the workings."*
He concludes that the ratio between subsidence and draw must be
the joint result of the forces liberated by the withdrawal of support
from underneath the strata in the mined area. The larger the propor-
tion of settlement resulting in subsidence the less can occur in the
form of draw, and vice versa "The number of factors that may influ-
ence the results produced by the settlement of undermined strata is so
great that only a wide and comprehensive inquiry by geologists and
mining engineers in those countries where mining is conducted on a
large scale can be hoped to provide sufficient evidence to establish a
definite theory or theories to assist in overcoming some of the more
common dangers due to subsidence."
Alexander Richardson, in a paper before the Chemical, Metal-
lurgical, and Mining Society of South Africa, took up the question of
stresses in deep masses of rock unsupported for hundreds of feet hori-
zontally. "Where the strata are unfaulted, one would be justified in
considering the mass as a huge slab supported on two or more sides or
as a lever hinged at the bottom of the workings. Over extensive areas
the pressure on the roof of an excavation, assuming the bed to be
horizontal, will become in time equal to the weight of the superincum-
bent strata; under no circumstances is it immediately so, since the
overlying beds must have some carrying strength."f
Opinions of American Engineers.
While no new theories have been advanced by American engineers
it may be profitable to review their opinions as given to the public
through papers, investigations, or testimony.
As previously noted, a number of prominent engineers have made
investigations as to the nature, extent and cause of the damage to
property resulting from surface subsidence in Scranton, Pennsylvania.
The published and the special reports noted on page 28 include ex-
*Knox, George "Mining Subsidence." Proc. Int. Geol. C9ngress, Vol. 12, p. 798, 1918.
tRichardson, Alexander "Subsidence in Underground Mines," Jour. Chem. Met. and
Min. Soc. of S. Africa, Vol. 7, p. 279, March, 1907; Eng. and Min. Tour., Vol. 84, p. 196,
1907.
114 ILLINOIS ENGINEERING EXPERIMENT STATION
pressions of opinion, but little discussion of the principles and theories
of subsidence.
Douglas Bunting, who has made a study of the "Limits of
Mining under Heavy Wash" in the anthracite region of Pennsylvania,*
considered the various sedimentary rocks of the coal measures and
determined the minimum thickness of rock cover for various depths
below the surface and for rooms of various widths. He had previously
made a study of chamber pillars in deep anthracite mines, and had
calculated the width of rooms for various depths upon the basis of the
compressive strength of anthracite.f
In discussing subsidence in the longwall district of Illinois, G.
S. Rice said, "The roof settles most in the first few months, but it is
several years before it is entirely settled, by which time the gob has
been squeezed down to one-half or one-third its original thickness."
The roof is very free from slips and vertical cracks or joints until
the coal has been mined below it, but when the coal is brought down
in a long strip, it marks the roof just where the break of coal has
occurred, and along these marks the roof afterwards breaks. These
breaks seem to run up indefinitely, and oftentimes they can be followed
up to the black slate, 8 or 10 feet above. As a result of mining the
seam, which varies in thickness from 2 feet, 10 inches to 4 feet, or an
average of 3 to 3% feet, "the settling of the roof is appreciable at
the surface even when the seam is at a depth of 400 or 500 feet; but
so gradual is it and without vibration that the deep mines have caused
no trouble in going under railroad tracks, and even under brick build-
ings, as has been done at La Salle."$
Charles Connor believes "If we extract all the coal we, natu-
rally, will have a subsidence of the surface. That must inevitably fol-
low because, when the support is all removed, the rock settles down
on the floor of the mine." He cited observations made in the county
of Lanark, Scotland, where the mining of seven seams approximating
30 feet in thickness and lying at depths of from 900 to 2,700 feet neces-
sitated the raising of canal banks 18 feet. The sinking was gradual and
no water was lost out of the canal. j[
In discussing the action of beds overlying mine workings
*Amer. Inst. Min. Engrs., Bui. No. 97, p. 1, 1915.
fBunting, Douglas "Chamber Pillars in Deep Anthracite Mines." Trans. Amer. Inst.
Min. Engrs., vol. 42, p. 236, 1911.
$Rice, G. S. "System of Longwall Used in Northern Illinois Coal Mines," Columbia
Univ. School of Mines Quart., Vol. 16, p. 344, 1894.
flConnor, Charles "'Discussion of Paper." Proc. Coal Min. Inst. of America, p. 149,
1912.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 115
W. A. Silliman expressed the opinion that these beds do not act as a
monolith, but that the beds may have little adherence to each other.
Where the measures are weakest the strain will be greatest, as in the
fireclay bottom.*
S. A. Taylor has pointed out the fact that the tendency of one
measure to slip on another is "counteracted by the fact that the roof
is a continuous mass, so that as soon as any part tends to give, it has
to slide to get past adjacent surfaces and the surfaces are pressed to-
gether with no little weight. If any part is weak, it is nevertheless held
in place and the strain goes to the other measure." In his opinion the
roof rock acts as a monolith in most cases.* He also believes that
the occurrence or absence of subsidence depends on the height and
character of the overlying strata. "You cannot set any hard and fast
rule; the rule set down by the English authority cone to ten' (there
will be no breakage on the surface if the rock cover is ten times the
thickness of the coal worked) will not hold. It may be true in some
cases, but it will not serve as a universal rule, as its truth or falsity
in any instance depends on the character of the overlying strata.'^
E. D. Hall has suggested that when the roof sags down over
the edge of a pillar the curve of the roof tends to follow back over the
solid coal, criticising the general notion that the roof lies flat upon pillar
and then sags down over the edge of the pillar. j| He has also shown to
what extent in his opinion shear is the cause of the failure of mine roof.§
He concludes his discussion of shear, "In the case of mine roof, everyone
seems to be confident that we have a structure which invariably fails from
shear. The idea is contrary to all the evidence and should be dismissed.
The raggedness of roof fractures disproves it if other reasoning does
not."** In discussing the strength of mine roofs R. D. Hall has pre-
sented a series of sketches, showing conditions producing breakage of
roof .ff He suggests that the roof over rooms acts after the first fractures
not like a beam but like an arch, and that continuous beams or plates are
replaced by disconnected arches or vaults. He concludes by suggesting a
"progressive advance in demolition : First, a condition, as yet unnamed,
symbolized by the tunnel in solid rock in which roof and sides and floor
•Proc. Coal Mining Inst. of America, p. 84, 1911.
tOp. cit.. p. 85.
tTaylor, S. A. In discussion of R. D. Hall's paper, "Effect of Shear on Roof Action."
Proc. Coal Mining Inst. of America, p. 146, 1912.
flHall, R. D. "Action of the Roof." Proc. Coal Min. Inst. of America, p. 64, 1911.
§Hall, R. D. "Data of Petrodynamics." Mines and Minerals, Vol. 81. p. 210, 1910.
**Hall, R. D. "Effect of Shear on Roof Action." Proc. Coal Min. Inst. of America,
p. 144, 1912.
ffHall, R. D. "The Strength of Mine Roofs," Mines and Minerals, Vol. 80, p. 474, 1910.
116
ILLINOIS ENGINEERING EXPERIMENT STATION
all partake of the beam strain. Second, a horizontal shear which con-
verts the sides into mere supports and the roof into a true beam or plate ;
Third, a rupture of the roof which converts it into an arch, and finally, a
failure of the arch or vault by one of the many weaknesses to which
such structures are subject."*
The tendency of the roof to arch has long been noted, and the
mechanics of natural rock arches has been discussed by a number of
engineers. However, there has been little agreement among engineers
as to the portion of the burden of the overlying beds which is actually
borne by such natural arches. The strata acting as a uniformly loaded
?m
~i0
m
FIG. 40. STRESSES IN ARCH.
horizontal beam cannot support a great load, and as the strata sink
the upper measures tend to arch and eventually the entire mass may
be supported by the arch.
The theory of the arch as applied to this problem has been dis-
cussed by B. S. Eandolphf as follows: In the arch ABC, Fig. 40,
the two sides A B and B C are mutually supported at B where the
thrust is horizontal. Assuming the load to be evenly distributed over
the arch, it is found that the points B, G, K, J , L all lie in the line
of stress. This line of stress "when lying in solid material over an
excavated cavity will constitute, for all practical purposes, an arch
supporting all the material above it and allowing the removal of all
the material below it up to the point where this material becomes effective
. *Ha,n'AR- D; "The Last Stand of the Mine Roof." Coal Min. Inst. of Amer., 1914,
and Coal Age, Vol. 6, p. 982, 1914.
fRandolph, B. S. "Theory of the Arch Applied to Mining." Coll. Engineer, Vol. 35,
p. 427, 1915.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 117
in resisting the stress. There will, of course, exist along and on each
side this line of stress a zone of material under more or less pressure,
depending for its width on the total .stress and the elasticity of the
material. The position and character of the forces acting on the arch
will vitally affect the shape of this line of stress. In an arch under a
perfect fluid, where the pressures are all radial acting toward a common
center, the line of stress becomes the arc of a circle. With an excess
of load toward the center, it takes the shape of the parabola, the focal
distance shortening as the central load exceeds that on the side. With
the excess of pressure on the sides, say at an angle of 45 degrees, it
assumes the shape of an ellipse, the focal distance shortening as the
pressures at the side exceed those in the middle." In the arch formed
over rooms, as the load for all practical purposes is equally distributed,
"the curve will be a parabola with a longer or shorter focal distance
G H *• Fallen Material or Gob
FIG. 41. ARCH STRESSES IN MINE ROOF.
depending on the nature of the strata." "Let Fig. 41 represent the
section of a coal seam from which the coal has been removed between
A and B, the roof having fallen to the irregular line ACS. The
dotted line A' C' B' will indicate the line of stress. This, it will be
seen, impinges on the coal close to the edge at A. The stress at this
point represents half the weight of the strata overlying the span A B
which is assumed to be sufficient to crush the coal about the point A.
The integrity of the arch being destroyed, the line of stress must seek a
new position such as D E B. Naturally this movement will be no
greater than is absolutely necessary to gain a solid footing for the arch,
which will again be so near the edge of the coal already crushed that
it will fail again in a short while, necessitating a further adjustment
118 ILLINOIS ENGINEERING EXPERIMENT STATION
of the position of the arch. With this continuing failure and readjust-
ment we have the well-known phenomena of a crush or squeeze ad-
vancing slowly over the workings, destroying coal as it goes.
If now a considerable body of the seam, as A H Gr F, is quickly
removed a "fall" may result which will reach high above the seam, say
to the line F J B, which will cause the line of stress to move quickly
and reach the coal well back from the point F, where it is sufficiently solid
to give the needed support, and the working will be said to have "gotten
ahead of the crush," when in fact the crushing force has gone ahead of
the working. This explains the common experience of the relief at the
working end of the pillar caused by an extended break in the roof over
the exhausted area.
Under other conditions, especially when the arching line of stress
has a wide span, thus carrying a large amount of weight, the crushing
force may prove too much for even the solid coal well back from the
end of the pillar and cause the phenomena of crushed coal, broken tim-
Resistance Bed
Fallen fiafer/a/ or Gob
FIG. 42. SPACE SHORTENED BY FALLING OF ROOF.
bers, creeping floor, etc., well down the room or stall, while the ends of
the pillars will be free from any trouble, as they carry only the small
amount of material which is below the line of stress. This condition
will sometimes be cured automatically by the material falling from the
top of the cavity over the exhausted area in such a manner that the
space between the material already down and the undisturbed meas-
ures will be filled and the opposite limb of the arch (the right hand
in the figure) will find support on this already fallen material and
thus shorten the span of the arch and lessen the total weight, as illus-
trated in Fig. 42.
When the break has reached the surface, this filling takes place
more rapidly owing to the fracture of the overhanging beds along the
edge of the break and, since the arch has a new point of support for
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 119
its inner or right hand limb, the conditions are ripe for further working
undisturbed under the smaller arch.
While the general shape of the line of stress in the cases under
consideration is the parabola, for all practical purposes the ratio be-
tween the span and the rise or height of the arch will vary much as
the material varies in which it exists. After the fall of the first mass
the cavity grows through the crushing and falling of the material along
the top of the arch, due to the pressure along the line of stress, and
by the splitting off along the joint planes of the material on the sides
due to the same cause. Since the pressure along the upper portion
of the line of stress is manifestly less in a high sharp arch than in a
low flat one, the shape of the arch in this respect may be expected to
vary with the capacity of the material to withstand this stress. Hence,
there will be a high arch in a soft material with numerous joints and
a flat arch in tough material with fewer joints. This may be verified
practically by the examination of old drifts or tunnel* where the over-
lying material has had an opportunity to fall and take the shape due to
such conditions without regard to other influences.
If, then, the cavity in its upward progress encounters a bed of
tough resistant shale or sandstone, it may fall so slowly that a large
area may be opened by continuous mining during the delay, result-
ing in a heavy weight along the line of stress due to the wide span and
crushing the coal either at the working end of the pillar or at such
point along the course of the room as the line of stress may meet the
coal as shown in Fig. 42. Such a crush is not likely to find relief
until the overlying measures are sufficiently broken down to fill the
space 8 S, and allow the development of a new smaller arch of stress
ABC, which, having less span and consequently less load, will trans-
mit less load to the point A.
Dr. F. W. McNair has reviewed the question of pressures and sup-
port in the deep copper mines of the Lake Superior region. In a lode
dipping 38 degrees and with pillars 50 feet wide, having on either side
an open space of 150 feet, the pressure on the pillar at a depth of 5,000
feet would be 1,239 tons per square foot, allowing for neither rigidity
nor arching and supposing the weight on the pillar evenly distributed.
The pillar would fail under this pressure if it were mainly trap rock.
"As a matter of fact, in such a case, the rigidity of the mass distributes
a large part of the load out over the rock beyond the walls of the open-
ing. That this rigidity may be considerable is illustrated in several
cases in which areas of hanging wall as wide as 200 feet or more have
120 ILLINOIS ENGINEERING EXPERIMENT STATION
no support between walls and yet have stood up for several years. As
the rock between pillars and walls bends downward the tendency is
to concentrate the load at the edge or face of the pillar or walls. The
outer parts of the pillar may thus become overloaded and fail by the
splitting off of pieces of rock, that break from the base as well as the
top, and like any hard rock under a crushing load, the pillar usually
fails suddenly. The hanging rock mass moves, of course, when the
pillar crushes, and the vibration due to the sudden though slight disr
placement is often conveyed to the surface. The result is a miniature
but perfectly genuine earthquake that may be felt over a distance
several times that of the pillar from the surface. With the crushing
of the pillar and the movement of the hanging wall, a readjustment
of the weight takes place, and the process begins over again. Eventu-
ally, at great depths, the hanging and foot walls must come together.
"The readjustments that take place when a pillar fails sometimes
put an enormous longitudinal thrust on the foot wall, and in places its
surface portion has buckled under such stress. Experience seems to
show that at the great depths recently reached it is useless to expect
to hold up the hanging rock mass for a long time by any scheme of
pillars unless far too much of the lode is left in place, and that the
only feasible method is to cut away the entire lode and permit the
hanging to cave as rapidly as it will to the point where the broken rock
fills again the whole space and redistributes the weight over the foot
wall."*
C. T. Rice objects to the general statement that stopes will cave
until filled, except in the case of running ground. In the few caved
stopes which he has inspected he has "always found an open space between
the arched roof and the pile of caved rock. In general, such a large
stope opening is necessary before caving commences; the self-supporting
dome is assumed before the stope fills itself. The caving action is pro-
gressive, and as the slabs accumulate in the stope they so support the
sides that caving ceases. Finally, owing to the weakening of other
stopes, the faulting stage is reached; not until then does the opening
become completely filled.
"In supporting the roof of a stope, only that portion of the roof
that is below the line of the dome of equilibrium requires support; the
rock above this dome sustains itself. If, therefore, the shape of this
dome of equilibrium in each kind of rock were known, it would be easy
*McNair, F. W. "Deep Mining in the Lake Superior Region," Min. and Sci. Press,
Vol. 94, p. 275, 1907, and Eng. and Min. Jour., Vol. 84, p. 322, 1907.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 121
to calculate the weight of rock hanging below the dome, and so timber
the stope as to hold up this weight." C. T. Eice is under the impression
that the shape of this dome is fairly constant in each kind of rock;
especially in the same rock in the same district. "Of course, slips and
joints, sudden changes in chemical composition, the dip of the strata in
sediments, and many other facts, would affect the shape of the dome,
but as long as these were small their effect would also be small. If in-
vestigation of the shape of this dome should suggest any formula to
determine the strength of timber necessary to support the ground below
the dome, the effect of these joints, etc., could easily be included by the
factor of safety used/'*
*Rice, Claude T. "The Dome of Equilibrium and the Caving System of Mining." Mining
and Sci. Press, Vol. 95, p. 85, 1907.
CHAPTER IV.
ENGINEERING DATA AND OBSERVATIONS.
In America very few data have been collected on subsidence due to
mining operations, at least the data, if collected, have not been made
available for scientific purposes.
In order that observations may be of value the following correlated
data are desirable:
(1) The elevations of a number of points on the surface for a
period of years both prior to, during, and following the mining directly
beneath.
(2) The position of these points with regard to permanent sta-
tions located outside of the mining field or upon ground which has not
been or will not be subject to the influence of the mining operations.
(3) The position of the working face in the mine on the various
dates of survey.
(4) An accurate location and description of the character of the
portions of the mineral deposit left unmined.
(5) An accurate location and a description of the supporting
materials placed in the excavated area.
(6) The thickness and dip of the material mined.
(7) The thickness and character of the bed immediately under-
lying.
(8) The thickness, dip, and character of the overlying rocks and
all available information in regard to structure.
(9) The thickness and character of the surficial material.
(10) The quantity of water removed from the mine.
(11) The location, extent, and data of underground movements of
rocks overlying the mineral deposit.
In Europe records have been kept for many years in various dis-
tricts in order to determine the vertical amount, lateral extent, rate, and
duration of subsidence.
Among the first surveys made to determine the movement of the
surface were those of Fayol.* At Commentry Mine from 1879 to 1885,
as shown in Figs. 43 and 44, surveys were made to correlate surface
movement and the advance of the working face. The seam which was
almost 48 feet thick was worked in horizontal slices of about 8 feet in
*Fayol, H. Bui. Soc. Ind. Min., II ser., Vol. 14, p. 818, 1886. Coll. Eng., Vol. 11, p.
2fl, 18&0-91.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
123
ascending order. The thickness of rock cover was 321 feet. Some filling
of shale and sandstone quarried on the surface was used. It was ob-
served that:
(1) During the removal of the first slice, the lowering of the sur-
face gradually grew greater, and was further increased considerably by
the working of the second.
(2) The area of subsidence was about four times larger than the
area worked.
(3) The maximum sinking was 3 feet 5 inches or one-fifth of the
height of the two slices:
C\ 5ecfion through M-N
FIG. 43. SUBSIDENCE AT COMMENTRY MINE.
(4) The movements of the ground appeared at first at a certain
horizontal distance in advance of the working faces and this distance
remained nearly constant.
(5) The subsidences increased during a certain time while the
Corking proceeded.
(6) The second lift caused a total subsidence almost equal to that
)f the first lift. This subsidence was 2 feet 1 inch for the first and 1
)t 11 inches for the second, in all 4 feet.
124
ILLINOIS ENGINEERING EXPERIMENT STATION
(7) The area of subsidence cannot be determined, either by nor-
mals or verticals from the bed worked.
The surveyor's records showing surface movement in connection
with the Warrior Run Mine disaster have been noted previously.* The
ratio between the volume of subsidence as noted on the surface and the
volume of excavation has been noted for the caving system of mining
on the Gogebic range.t "When a slope caves, and the dome above it
runs up into sand or loose rock, the depression formed is usually in the
shape of an inverted cone ; but where the ore body is wide, or deep below
the surface, the subsidence usually takes the form of terraces. Some-
times comparatively large areas will break through cleanly and the
whole surface will drop suddenly and as a unit, but this is exceptional.
Section through CD
FIG. 44. SUBSIDENCE AT COMMENTRY MINE.
After the back has once started to cave, the surface usually sinks in
terraces." In the area under observation the deposit consisted of a lense
of soft hematite about 40 feet in average width and 150 feet high, with
a length of nearly 1,600 feet on the incline, lying in a trough between
a dike of diorite and a thick band of slate. The trough pitched 11.
degrees, the hanging wall was hard jasper, and the ore was mined
first by square-set rooms and pillars, about 60 per cent of the ore being
secured on first mining, but later the pillars were robbed. The hanging
wall has dropped from 15 to ?'5 feet and subsidence has extended to
*See page 43.
tEaton, L. "Surface Effects of the Caving System," Min. and Sci. Press, Vol. 97,
p. 428, 1908.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 125
the surface. The proportion between the volume of surface subsidence
and the volume of excavation is shown by the following figures:
-
Cubic Feet
Original volume of ore body
7,680,000
2,360,000
Present volume of ore body, including
5,320,000
2,300,000
Volume of material removed under c
Volume of material removed under si
ave . . . .
3,020,000
790,000
1,430,000
Volume of subsidence on surface
Volume of cave on surface
i
Volume of ore taken from under it
Volume of subsidence on surface
2.91
1
_ 2.11
Volume of ore taken from under it
J. S. Dixon made observations at Bent Colliery* A line was selected
at right angles to the advancing workings and as nearly as possible on
the level course of the coal. Stations were put in every 100 feet and
afterwards every 50 feet. .The excavation was 5 feet 6 inches high and
the overlying strata were allowed to fall and fill it. The surface was
principally boulder clay. The original level of the surface before the
pillars were drawn is shown in Table 8.
The pillars were removed for a distance of 240 feet back from the
solid coal on Jan. 21, 1882, and no subsidence of the surface had ensued.
On May 27, 1882, the levels showed the maximum subsidence to have
been 1.80 feet at station 1650, which was 145 feet back from the face, and
the draw extended to 60 feet in advance of the working face. On Novem-
ber 14, 1882, the face was 610 feet from the solid, and the subsidence
was as is shown in the table. On April 15, 1883, the face was 750 feet
from the solid; on November 27, 1863, it was 1,060 feet distant; and on
October 23, 1884, the removal of the pillars had been completed for some
months, and the face was 1,230 feet from the solid. On June 17, 1885,
the workings had been in the same position for about a year. On Decem-
ber 4, 1885, it was found that subsidence had practically ceased and the
draw had not altered.
The conclusion arrived at is that subsidence from the removal of
coal in this case attains its maximum towards the center of the excavated
space, and gradually decreases in each direction. The maximum sub-
sidence, 4 feet, was 73 per cent of the thickness of the coal, and the
average, 3.76 feet, was 68 per cent. The wave of maximum subsidence
regularly followed the working face at an average distance back of 186
*Trans. Mining Inst., Vol. 7, p. 224, Scotland, 1886. Cit. in Brough, B. H., "A Treatise
on Mine Surveying," pp. 241-245.
126
ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 8.
OBSERVATIONS AT BENT COLLIERY.
Peg.
Original
Level of
Surface
Subsidence From Original Level at
1881
Nov. 14,
1882
April 5,
1883
Nov. 27,
1883
Oct. 23,
1884
June 17,
1885
Dec. 4,
1885
600
650
700
750
800
850
900
950
1000
1050
1100
1150
1200
1250
1300
1350
1400
1450
1500
1550
1600
1750
1850
1950
2000
640.6
648.9
657.2
664.6
667.5
673.1
675.6
676.0
677.1
677.3
678.8
679.7
680.6
680.9
679.2
677.9
677.5
680.8
680.1
677.1
675.5
672.8
663.4
648.6
649.7
0.25
0.35
0.77
1.18
1.37
1.50
2.57
2.97
3.27
3.32
3.52
3.57
3.52
3.45
3.42
3.27
3.17
3.42
3.05
8.20
3.00
2.80
1.70
0.60
0.04
0.35
0.60
0.94
1.27
1.75
2.24
2.74
3.14
3.49
3.64
3.80
3.81
3.52
3.45
3.42
3.27
3.17
3.42
3.05
3.20
3.00
2.80
1.70
0.60
0.04
0.45
0.60
0.94
1.40
2.00
2.34
2.82
3.22
8.60
3.75
4.00
3.92
3.52
8.45
3.42
8.27
3.17
3.42
3.05
3.20
3.00
2.80
1.70
0.60
0.04
0.23
0.63
1.13
1.61
2.10
2.43
2.80
2.93
0.50
0.70
1.20
1.60
2.00
2.25
2.45
2.90
3.05
3.20
3.00
2.&0
1.70
0.60
0.04
" 0.60 '
0.40
1.60
1.60
2.30
3.08
3.03
3.00
3.83
3.42
3.05
3.20
3.00
2.80
1.70
0.60
0.04
2.90
3.00
2.80
1.70
0.60
0.04
feet, or 1 foot horizontal for each 3% feet perpendicular. The permanent
lengths of the draw may be taken as 100 feet on one side and 83 feet
on the other. At these points the depth of the coal was 650 and 646
feet, representing a draw of 1 horizontal for each 7.14 feet perpendicular
on the average. The coal dips at 1 in 20.
Surveys were made at the South Kirby Colliery in order to determine
the extent and amount of surface movement due to the removal of a shaft
pillar.* No observations were made until two years after the mining
of the pillar was commenced. The seam in which the pillar was removed
lies at a depth of 2,108 feet, is 3 feet 9 inches thick, and dips 1 in 18.
Above the coal is one foot of clod. Some movement of the surface was
noted before the surveys were made. At depths of 1,600 and 1,800
feet occur the Beamshaw seam of 3 feet and the Barnsley seam of 9
feet which had been worked previously. The data of the surveys are
given in Table 9. The unusually large ratio of subsidence (3.47 feet)
to the total thickness excavated in removing the pillar (4.75 feet) is
attributed to the failure of the shaft pillar in the overlying Barnsley
seam.
*Snow, Charles
Vol. 46, p. 8, 1913.
'Removal of a Shaft Pillar at South Kirby Colliery." Trans. I. M. E.,
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
127
f TABLE 9.
DATES OF LEVELING AND PARTICULARS OF SUBSIDENCE AT SOUTH
KIRBY COLLIERY.
Dates of Levelings
Subsidence Since
Previous Leveling
Total Subsidence
November, 1903
Feet
Nil
Feet
Nil
July, 1904
Nil
Nil
March, 1905
Nil
Nil
October, 1905 -
0 74
0 74
April, 1906
0 17
0 91
October 1906
0 22
1 13
June, 1907
0 77
1 90
April, 1908 ;
0.17
2 07
December, 1908 ...
Nil
2 07
May 1909
Nil
2 07
May, 1910
0 82
2 89
May, 1911
0 18
3 07
June 1912
0 40
3 47
June 1913
Nil
3 47
Levelings made by Chas. Snow at the Hickleton Main Colliery (de-
tails not given) showed that subsidence was evident 433 feet in advance
of a rapidly advancing longwall face, and that total subsidence occurred
> FEET
Scale. USO feet to 1 1nch
FIG. 45. ANGLE OF FRACTURE AT SHIREBROOK COLLIERY.
666 feet back from the face, the amount of subsidence being 4.5 feet.
At the edge of the shaft pillar, 500 feet back from where the greatest
subsidence occurred, the subsidence was 1.28 feet. Subsidence extended
for a distance of approximately 600 feet over the shaft pillar.*
*Trans. I. M. E., Vol. 46, p. 21, 1913.
128
ILLINOIS ENGINEERING EXPERIMENT STATION
For a period of 16 years surveys were made at the Teversal and
Pleasley Collieries by J. Piggford,* but details of the surveys have not
been published. The angle of draw or fracture was estimated to be
approximately 16 degrees from the vertical and toward the un worked
coal. The depth of the coal seam was approximately 600 feet and the
coal was from 5 to 6 feet thick.
Scale, /eo feef to / Inch
FIG. 46. FRACTURES AND SURVEY STATIONS, SHIREBROOK COLLIERY.
Kecords were kept at Shirebrook Colliery and reported by W.
Hay.f The coal lies at a depth of from 1,500 to 1,700 feet, dips 1 in
24, and is 5 feet thick. When the longwall face was 240 feet from
Stuffynwood Hall cracks were noted in the surface, the direction of
fracture varying as much as 15 degrees from the direction of the coal
*Trans. I. M. E., Vol. 38 p. 128, 1909.
tHay, W. "Damage to Surface Buildings Caused by Underground Workings." Trans.
I. M. E., Vol. 36, p. 427, 1908.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
129
face. Fig. 45 shows the angle of fracture in section. When the work-
ing face was almost vertically beneath, the cracks had attained their
maximum width and thereafter commenced to close. When the face
had advanced 300 feet farther, the walls of the buildings had assumed
practically their normal position.
Levels taken at regular intervals are given in Table 10. The survey
stations are indicated on Fig. 46.
TABLE 10.
i SUBSIDENCE AT STUFFYNWOOD HALL.
Time in
Ttn*..
Months
Station
Station
Station
Station
Station
Station
JJatc
From First
No. la
No. 1
No. 2
No. 3
No. 4
No. 5
Levels
March 7, 1906
0
0.00
0.00
0.00
0.00
0.00
0.00
May 18, 1906.
2
0.00
0.00
0.00
0.00
0.00
0.00
June 11, 1906.
8
0.00
0.00
0.00
0.00
0.00
0.00
une 20, 1906 .
3
0.00
0.00
0.00
0.00
0.00
0.00
uly 10, 1906.
4
0.02
0.00
0.01
0.02
0.02
0.03
Aug. 27, 1906.
5#
0.11
0.09
0.16
0.18
0.18
0.20
Oct. 25, 1906.
ix
0.19
0.17
0.17
0.19
0.18
0.20
Dec. 10, 1906.
9
0.20
0.18
0.17
0.19
0.17
0.21
Feb. 6, 1907..
11
0.22
0.18
0.17
0.19
0.23
0.29
Mar. 9, 1907.
12
0.26
0.26
0.17
0.25
0.31
0.37
Mar. 29, 1907.
12^
0.28
0.26
0.26
0.25
0.31
0.37
June 20, 1907.
15^
0.67
0.43
0.44
0.44
0.52
0.63
Aug. 21, 1907.
17 J*
0.86
0.67
0.67
0.68
0.80
0.91
Nov. 12, 1907.
20
1.09
O.S4
0.83
0.84
0.99
1.10
Tan. 30, 1908.
23
1.2S
0.96
0.91
0.97
1.15
1.26
July 9, 1908..
28
1.56
1.23
1.21
1.34
1.41
1.51
Nov. 12, 1908.
32
1.74
1.34
1.35
1.37
1.54 -
1.63
The maximum subsidence was 1.74 feet and the minimum 1.34
feet, the average being practically 30 per cent of the total height of
excavation.
Levels extending over a period of five years were taken by S. E. Kay
on the surface of a portion of two collieries mining at depths of 360
feet and 990 feet.* Where the levels were run, the surface was fairly
level, the strata were nearly horizontal and were free from faults of
any magnitude. The strata consisted of alternating beds of shale, sand-
stone and limestone, none being massive. Figs. 47 and 48 show the
data secured. The working of the 5-foot seam at a depth of 360 feet
resulted in subsidence amounting to practically 70 per cent of the
thickness excavated. Similar effects resulted from mining the 3-foot,
6-inch bed. At the greater depth subsidence began about six months
after the coal had been mined and continued for years.
*Kay, S. R. "Effect of Subsidence Due to Coal Workings." Proc. I. C. E., Vol. 135,
p. 115, 1898.
130
ILLINOIS ENGINEERING EXPERIMENT STATION
A report by C. Menzel* showed that since 1885 observations of
the rate of settlement had been made at eight-two points in the vicinity
of the collieries of Zwickau, Saxony. The depth of the coal beds varies
from 600 to 2,400 feet. A maximum subsidence of ?'.! feet was noted
twelve years after three seams had been mined out at a depth of from
JAN.
MM
DATE: OF WORKING
FIG. 47. DATA OBTAINED BY S. R. KAY.
600 to 900 feet. At a depth of 1,500 feet the subsidence was only 0.6
feet. By the use of filling subsidence was greatly reduced, it being noted
that on an average the filling was compressed to one-half of its volume
when stowed. The ratio of subsidence to thickness of seam excavated
was found to vary from 1:1 to 1 :7, the average being 1 :2. Frenzel sug-
gested this latter ratio for shallow seams.
Numerous observations have been made in Germany during the
last thirty years. E. Hausse has reported upon the angle of break,
angle of draw, and the coefficient of increase of volume. Jicinsky, Gold-
Ortginal Ground Level reduced -to plane surface
— f^=
I
Juno
1890
z
NOV.
1830
3
4
Hay
Dec
1892
1094
FIG. 48.
DATE OF WORKING
DATA OBTAINED BY S. R. KAY.
reich, and others have reported upon subsidence in Austria-Hungary
but in general these data have been secured in districts where the
coal measures are covered with heavy beds of marl. From the foregoing
statements of observations the following may be presented as representa-
tive in so far as general statements can be made to apply to mining
operations each of which is conducted under different geological con-
ditions.
ANGLE OF BREAK AND DRAW.
Dr. Mesz has made many observations upon subsidence, particularly
on the angle of fracture in various kinds of rock and on the com-
*Menzel, C. "On the Relation of Surface Subsidence to the Thickness of Worked-Out
Coal Seams at Zwickau." Abs. Proc. I. C. E., Vol. 140, p. 331. Jahrbuch fur B.-, u. Hiitten-
wesen im K. Sachsen, p. 147, 1899.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MIXING 131
pressibility of filling. He states that "the angle of fracture of lime-
stones, conglomerates, etc., is found to be from 45 to 48 degrees —
nearly the angle of repose. In quicksand the angle is greater, while
in clay, slate, and marl it may be 60 degrees, and in stone under favor-
able conditions even 75 degrees. Sandstones with silicious binding ma-
terial are ranked as nonplastic strata. Initial subsidences in these are
followed by others, but at longer intervals than in plastic strata. The
angle of fracture is generally not less than 82 degrees."*
Dr. J. S. Dixon reported, "In a level seam about 6 feet thick, by
careful leveling on the surface prior to and after working, it was found
that the draw or angle of subsidence of the strata was about 76 degrees
. from the horizontal plane."f
H. F. Bulman says that in a seam dipping 1 in 10, the lines
of break extended over the solid coal forming an angle of 45 degrees
with the horizontal on rise workings, 50 degrees in level workings, and
56 degrees on dip workings. In a wide goaf area the average inclina-
tion of the planes of fracture was 68 degrees from the horizontal plane ;
and at the rise side of a shaft pillar, the inclination was roughly 58
degrees from the horizontal plane over the solid coal. J
S. R. Kayfl has presented the following formula for determining
the radius of support :
3 y"g x $~t
0.8
r = radius of support in feet,
d — depth in feet,
t = thickness excavated in feet.
This allows for the angle of break or draw.
Joseph Dickinson says, "the direction of subsidence may be
judged of from the slopes of faults and mineral veins." He gives these
slopes as 1 in 5 for hard rock, 1 in 3.75 for medium rock, and 1 in
2.5 for soft rock.§
O'Donahue says that the angle of break will be from 5 to 8 degrees
beyond the vertical for horizontal beds, and that the maximum draw
on dip workings will be 24 degrees; he finds the same angle to be the
limit for workings to the rise.**
*Zeit. fur Berg.-, Hiitt.-, u. Salinenwesen, Vol. 58, p. 418, 1910.
fTrans. Inst. Min. Eng.. Vol. 34. p. 41fi, 1907.
JTrans. Inst. Min. Eng., Vol. 34, p. 417, 1907.
fiProc. Inst. Civ. En*., Vol. 135, p. 149, 1898.
STrans. Manchester Geol. Soc., Vol. 25, p. 600, 1885.
**O'Donahue, T. A. "Mining Formula," p. 248.
132 ILLINOIS ENGINEERING EXPERIMENT STATION
O'Donahue* offers two formulae to determine the angle of draw:
d'= 8 — % D, in which
D = inclination of seam in degrees,
d = angle of draw toward dip workings,
$ = angle of draw toward rise workings.
E. H. Eoberton gives a rule for shaft pillars (used in Northumber-
land and Durham) which allows for the angle of break and draw:
Eadius of shaft pillar in feet = — + %VDt,
D
D = depth of shaft in feet,
t = thickness of seam in feet.
'Level
Vertical Section on A-A
Plan
FIG. 49. LOCATION OF SHAFT PILLAR IN DIPPPING BED. (O'DONAHUE.)
*O'Donahue, T. A. "Mining Formula," p. 248.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 133
Hausse estimated that in general the line of fracture will be be-
tween the vertical and the normal to the seam. In addition to the
line of main fracture, Hausse refers to the secondary break or draw.
He says that in case of horizontal beds this line of secondary break is
situated along the bisector of sliding materials of the supplementary
angle of the natural slope.
The effect of the dip of the strata has been considered by many
authors in their discussion of the simplest cases, in fact, most of the
formulae for angle of break consider the dip of the strata.
Gonof s law of the normal and Schulz's rule, the earliest of the
theories, considered the angle of dip. As previously noted, Hausse,
following Jicinsky, supports the theory that the angle of break will
fall midway between the normal to the seam and the vertical. From
a careful study of the subsidence occurring in the Saxon coal field R.
Hausse determined the direction of the plane of fracture by the follow-
ing formula :*
a Bangle of fracture,
d = dip of strata,
l + cos2d .
tan a= — — 3 =-, m which,
sin d cos d
if d = 0°, tan a = oo and a = 90°
and if d = 90°, tan a = oo and a = 90°.
S. E. Kay suggests that for inclined strata the angle of frac-
ture will be midway between the perpendicular to the seam and the
vertical. If the angle between the perpendicular to the seam and the
vertical is a, then the pillar necessary to protect a given object on the
surface must be shifted, on account of the dip, from a position directly
beneath the object by an amount equal to d tan y2 a cos a, in which d
equals the depth.
Goldreich gives Table 11 showing the angle of break according to the
most important theories.f
•Results actually obtained in practice confirm this theory. Thus, for supporting the
glass works at Doehlen, in Saxony, a 76.8-foot pillar was left; nevertheless the surface sank
considerably. The coal seam dipped 12° and was 540 feet deep. Calculated from the depth
and size of the pillar, the angle of fracture was found to be 82°, or 2° 20 less than the
result obtained from the theoretical formula. In another case in the same district the value
of a was found to be 82° 80', or 1° 50' less than that found theoretically. (Brough, B. H.
Proc. Inst. Civ Engrs., vol. 135, p. 150, 1898.)
tGoldreich, A. H. "Die Theorie der Bodensenkungen in Kohlengebieten," p. 42.
134
ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 11.
ANGLE OF BREAK.
Rule of Hausse
German Rule
Dip
First
Hypothesis
Second
Hypothesis
Rule of
Thiriart
First
Hypothesis
Second
Hypothesis
Rule cf
Jicinsky
English
Rule
*
Toward the Dip
0
70
70
70
75
70
90
81 J4
10
65
67
67#
75
70
85
7324
20
60 1A
64}4
65^4
70
70
80
6624
30
56
62
63
60
60
75
64
40
5224
6024
6154
55
55
70
64
50
50^4
6024
eo y*
55
55
70
64
60
51
61
60^
55
55
75
64
70
54
61
62
55
55
80
64
80
61^
65^
65^4
55
55
85
64
90
70
70
70
55
55
90
64
Toward the Rise
0
70
70
70
75
70
90
8ll/4
10
75
77
72^
75
70
85
8324
20
7924
8324
7424
75
70
80
88 l/2
30
84
90
77
75
70
75
90
40
871/4
95 1A
7824
75
70
70
90
50
89y4
99^4
7924
75
70
70
90
60
89
99
79^
75
70
75
90
70
86
93
78
75
70
80
90
80
78X
82 Y4
7424
75
70
85
90
90
70
70
70
75
70
90
90
AMOUNT OF SUBSIDENCE.
Various writers have attempted to express the amount of subsidence
as a percentage of the thickness of the seam worked. In Table 12 data
from various districts are assembled, showing the depth of the work-
ings, the thickness of the coal mined, and the vertical amount of sub-
sidence expressed as a percentage of the thickness of the material removed.
TABLE 12.
AMOUNT OF SUBSIDENCE EXPRESSED IN PERCENTAGE.
Depth in
Feet
Percentage
Subsidence
Thickness
of Coal
Required
Feet
Filling
Locality
Authorities
360
70.0
5.0
England
S. R. Kay
990
64.0
3.5
England
S. -R. Kay
46.0
29.36
Stowing
Bully -Green ay.
432
44.4
30.0
France, England
600
75.0
4.0
O'Donahue
2400
25.0
4.0
O'Donahue
650
68.0
5.5
England
Dixon
748
19.0
7.5
Stowing
France
Fayol
2600
00.0
13.0
Harmless depth
1040
00.0
13.0
without stowing
Harmless depth
France
Fayol
with stowing
France
Fayol
390
40.0
7.0
33% of seam put
in gob
England
Gresley
325
87.0
30.0
England
Grazebrook
1500
30
5.0
Stowing
England
Hay
600-2400
50
Germany
Menzel
YOUNG-STOEK - SUBSIDENCE RESULTING FROM MINING 135
Attempts have been made to formulate rules by which the amount
of subsidence may be predicted in advance. Some of the formulae
are based upon the thickness of coal and depth of workings. Most of
them include factors for character of rock and filling, but few introduce
factors for inclination of the beds.
The discussion of the relation between the depth of workings and
the vertical amount of subsidence has brought to the foreground the
question as to whether or not subsidence will result irrespective of
depth. According to the formulae of Jicinsky and Menzel there is for
each thickness of coal -bed a depth beyond which mining will not affect
the surface. In 1884 Jicinsky suggested the following:
in which 8 = vertical subsidence,
m = vertical thickness of coal,
t — thickness of overlying beds.
Menzel suggests the formula
£ + 350
350 ?ft
in which 8 = subsidence in yards,
t = depth in yards,
m = thickness of seam in yards.
The factor 350 must be increased to 400 for depths greater than 350
yards. This principle that there is a harmless depth has been sup-
ported by Fayol, Banneux, Thiriart, Rziha, Jicinsky, and Menzel.
Fayol formulated two rules as follows :
(1) The height of the zone of subsidence where sandstone pre-
dominates and the beds have an inclination less than 40 degrees, and
where the area is infinite, does not exceed 200 times the height of the
excavation.
(2) When the area is limited, the height of the dome is about
twice the breadth excavated for excavations less than 6 feet and up to
four times the breadth excavated for seams more than 6 feet.
In general the Germans say that the "dead point" or '^harmless
depth" has not been reached in Westphalia and question whether or not
the term should be used. Gallon said that there is no harmless depth,
and the majority of the British engineers hold that the removal of all
the coal over extensive areas will produce subsidence.*
*The efficiency of filling in reducing subsidence will be considered in Ch. V, see p. 138.
136 ILLINOIS ENGINEERING EXPERIMENT STATION
TIME FACTOR IN SUBSIDENCE.
In a study of subsidence it is frequently important to know (1)
how soon after the movement shows in the mine workings it will mani-
fest itself upon the surface; (2) the period during which the move-
ment is most severe, and (3) the duration of subsidence.
Upon all of these points there seems to be a great difference of
opinion, which is due undoubtedly to the great variety of conditions
under which the observations have been made. Fayol wrote, "The
period during which movement of the surface may continue is very
uncertain. It is allowed to be ten or twelve years in Belgium and at
Saarbruck. In other places it has been as long as twenty and even
fifty years."*
The committee of the Mining and Metallurgical Society of Ostrau,
Moravia, reported in 1881, "The land subsidence manifests itself within
one to three months after the collapse observed in the mine. It mani-
fests itself most intensely during the first half year, and then becomes
less noticeable. According to our experience it may be assumed that
after two years, or more safely, after three years, there do not occur
any measureable land subsidences in consequence of a collapsed work-
ing."f
S. R. Kay reported that, in working a 5-foot seam at 360 feet,
subsidence began about six months after the coal was removed and
continued four years.J
Elevations taken at the Bent Colliery by J. S. Dixon showed
that the greater part of the subsidence took place within the first year
and that the maximum subsidence came within three years. The depth
to the seam was approximately 650 feet.fl
In observations made by W. Hay at Shirebrook Colliery, in which
mining was being conducted at 1,700 feet, the maximum subsidence
appeared in two years.§
G. E. J. McMurtree reported that the mining of 8 feet of coal
at a maximum depth of 800 feet caused subsidence continuing fifteen
years.**
In discussing the timbering of roadways in longwall mines in
Illinois, S. 0. Andros says, "Permanent timbering can be extended
•. .. •• , m
*Colliery Engineer, 1890, Vol. 11, p. 25, 1890.
tGoldreich, p. 63.
tProc. Inst. Civ. Eng., Vol. 185, p. 115, 1898.
ITrans. Min. Inst. of Scotland, Vol. 7, p. 224, 1886.
STrans. Inst. Min. Eng., Vol. 36, p. 427, 1908.
**Proc. Smith Wales Inst. of Engrs., Vol. 20, p. 367, 1897.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 137
only to that point where the first rapid and violent subsidence has
ceased, and it is not usual to extend permanent timbering to any point
until the face has been advanced beyond it for at least two years."*
George Knox says:
''When workings advance rapidly the tendency will be for tho
strata to bend without fracturing; whereas if the opposite is the case,
the force of the motive zone has time to break through, as is fre-
quently shown on the working face after a prolonged stoppage."f
'Illinois Coal Mining Investigations, Bui. No. 5, p. 32, 1914.
tKnox, George "Mining Subsidence," Int. Geol. Congress, Vol. 12, p. 804, 1913.
CHAPTER V.
LABORATORY EXPERIMENTS AND DATA.
TESTS AND EXPERIMENTS FOR SECURING DATA.
In the laboratory various experiments and tests can be made to
secure data which will be of assistance in the study of subsidence.
Among these may be noted the following:
General tests of the materials entering into the problem.
Effect on superimposed material of the removal of part or all of
the supports.
Probably the most extensive experiments along this line which have
been described in scientific publications have been those made by H.
Fayol.*
His experiments to demonstrate subsidence included a variety of
materials, as iron, fibre, canvas, rubber, sand, clay, and plaster. He
placed iron bars 1.9 inches by 0.19 inch (50 millimeters wide by 5 milli-
meters thick) one above the other horizontally, the whole being sup-
FIG. 50. SAGGING OF IRON BARS.
ported by blocks of wood, A, B, C, D, E, F, Fig. 50. These blocks
rested upon an iron table G. A strong iron rule H was placed upon
the upper bar of iron, and by means of stays I, and bolts, the rule and
bars were fastened together and to the table. The wooden blocks B,
C, D, E, were removed over a length of about 4 feet, and the sagging
of the iron bars was noted.
It was found that the deflection of the lower bar was 5 millimeters
(0.19 inch), of the tenth bar from the bottom 3.25 millimeters, of
the twentieth 1.75 millimeters, and that after the thirtieth bar there
*Fayol, H. "Sur les Mouvements de Terrain Provoques par 1'Exploitation des Mines."
Bui. de la Societe de 1'Industrie Minerale. 11° ser., Vol. 14, p. 818, 1885. Translation
Coll. Eng., Vol. 11, p. 25, and Vol. 23, p. 548.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 139
was no more bending. The limit of the deflections is the curve MN
shown in Fig. 49.
The same experiment was tried with flat aloe ropes and with straps
of canvas and India rubber in place of the iron bars. With straps of
canvas and India rubber the curve of the limits of deflection, that is
to say, the limit of the zone of subsidence, had a height nearly equal
to the distance between the points of support. This height was about
one-third of the same distance for the ropes and one-sixth for the iron
bars. Wood and rocks also bend in a manner similar to the materials
mentioned.
In order to study the movement in beds of loose materials and
in strata that might have been crushed by subsidence, Fayol used
artificial beds of earth, sand, clay, plaster, or other materials, and
constructed boxes of various dimensions having one side of glass.
The box usually employed was 2 feet 7 inches (.80 meter) long, 1
foot (.30 meter) broad, and 1 foot 7 inches (.50 meter) deep. On
the bottom of the box were placed, side by side, small pieces of wood
of equal thickness, a few centimeters in width, and as long as the breadth
of the box. Experiments were made both with one row of these little
pieces of wood, and with several placed one above the other. Upon
them were laid successive layers of artificial strata, varying from 1
millimeter to several centimeters in thickness. To note the movements,
small pieces of paper about % inch (2 centimeters) in length and %
inch (1 centimeter) in width, were put into the planes of stratifica-
tion, and, on the glass, lines were marked in ink, covering exactly the
lines formed by the paper. These lines enabled the least movement
to be followed.
By withdrawing the little pieces of wood, excavations were formed
and movement produced in the artificial strata.
Fig. 51 represents the movements by taking away, in the order
indicated by the numbers, the upper row of wooden pieces, where there
were three rows each 0.3937 inch (1 centimeter) in thickness.
The first bed (dry sand), which rests directly on the pieces of
wood, falls in as each pillar is withdrawn. The second bed commences
to sink only when a certain number of pillars have been taken away.
The sinking is shown at first by a slight curve, which has its greatest
deflection toward the center of the excavation. Then the third bed
follows the second. The movement gradually extends in depth, and
reaches the upper bed after the removal of the twelfth pillar. After
140
ILLINOIS ENGINEERING EXPERIMENT STATION
the removal of the seventeenth, the beds have become bent, as shown in
the sketch, the limits of the deflection being the curves Z^ and Z^.
(The index figure of the curves is the number of the last pillar taken
away; namely, the curves ZBZ± indicate the extent of the movements
after the removal of pillars 4 and 8.)
It is apparent that the zone of sinking is a sort of expanding dome,
which grows in proportion as the excavation extends.
The bending of the first bed, hardly observable at first, is con-
siderably increased. The second bed sinks rather less than the first, the
third less than the second, and the sinking of each diminishes regularly
FIG. 51. SUBSIDENCE OF ARTIFICIAL BEDS.
in proportion as it is higher above the excavation. This sinking takes
the form of a basin, the center of which is on the vertical axis of the
excavation.
The lines
A A A
A13, A
are lines followed by the
greatest deflections of the sunken beds after the removal of the pillars
4, 7, 8, 9, 11, 18, 17. These lines nearly coincide with the axes of the
domes, which show the limits of the movement.
Throughout the experiments it was evident after the removal of a
certain number of the pillars that the pressure of the superincumbent
mass was strong at the center and weak at the circumference of the
excavation.
The second row of wooden pillars was taken away and thus the
depth of the excavation was doubled. The sinking of the lower beds
YOUNG-STOEK — SUBSIDENCE RESULTING tfROM MINING 141
increased; some of them fell in; and the broken ground occupied much
more space. The disturbance was greater below, but not at the surface.
The line of maximum deflection did not remain vertical, and some of
the limiting domes were inclined.
Bemoval of the third row increased the disturbance caused by the
removal of the two former; the fractures of the beds and the spaces
between the strata were multiplied; some opened more, others closed.
As before, the movement started at the lower beds and reached the upper
as the excavation extended. The removal of each row of supports re-
sults in a new state of stability, which continues if no more pillars
are taken away.
Similar experiments were made with beds at various inclinations,
and it was found that the line of greatest deflection was between the
vertical and the normal, and that it departed further from the normal
(that is, the perpendicular to the inclination of the beds) in propor-
tion as the beds became more inclined. Whatever the inclination, the
subsidence of each bed had always the form of a basin.
When horizontal beds were covered over by beds dipping at various
inclinations; that is, resting unconformably on them, the zone of set-
tlement took the direction of the inclination of the beds and its axis
tended to become perpendicular to the beds affected. The lines drawn
through the maximum bend of each bed were no longer continuous, but
in passing from one set of beds to another were broken and shifted
in the direction of the dip of the new set. In all cases the sinking
of each bed and of the surface was in the form of a basin.
An experiment was made with horizontal beds, which showed that
a block of coal left between two worked-out places may be of no use
to protect the surface above it, because the zones of subsidence due to
the excavation on either side, which, as already seen, take the form
of domes, may overlap each other between the coal and the surface.
As the area of subsidence increases in proportion as the excavation
is extended, it may be asked whether there is any limit in depth to the
propagation of the movement when the excavation extends indefinitely.
To answer this, a mass of horizontal beds was isolated round about by
a space being left between them and the vertical sides of the box, and
then the wooden pillars (in this case .03937 inch thick) were taken
away from under the whole area of the mass. Being entirely free at
the sides it might be considered to represent a mass of strata lying
over the middle of a working of large extent.
142 ILLINOIS ENGINEERING EXPERIMENT STATION
On taking away the pillars, the zone of sinking was seen to in-
crease little by little, and to stop at a certain depth; the movement did
not reach the surface. The expansion of the lower beds filled the
space excavated and the upper beds rested on the fallen rock. The pres-
sure exerted by the upper strata was very much greater in the middle
than at the circumference, and in this case, too, the sinking of the
strata was in the form of a basin.
The effect of faults was tested by inserting in a mass of horizontal
beds a thin plate of metal, placed at an inclination, and extending the
whole width of the beds. This broke the continuity of the beds and
represented a fault without throw. Its tendency was to stop the move-
ment from extending above it, though the sinking occurred as usual on
its low side, leaving an opening in the plane of the cut, which ex-
tended to the surface.
Fayol also made experiments upon the angle of fracture of rocks,
the increase in volume of crushed rock, and the compressibility of
crushed rock of various sizes.
Effect of Lateral Compression Upon Stratified Materials.
Elaborate experiments were made by Willis* in order to study the
deformation of strata by compression. The substance used was bees-
wax with plaster of Paris to harden it and Venice turpentine to soften
it so that by using different proportions of these materials, beds of a
wide range of consistency could be constructed. A load of shot was
applied upon the beds when constructed, in order to approximate the
conditions under which strata at depth are deformed. The machine used
for compressing the piles of strata endwise was a massive box of oak
provided with a piston which could be advanced by a screw. The pres-
sure chamber was 3 feet .3% inches long by 6 inches wide. The depth
of the box was 1 foot.
T. M. Meadef made a number of experiments, and considered in
detail the types of surface which may be developed. He used various
kinds and combinations of bars and applied pressure in various ways.
An elaborate set of experiments was made to demonstrate circumfer-
ential compression. He used for this purpose discs of clay placed
within a circumferential band which could be shortened.
*Willis, B. "The Mechanics of Appalachian Structure." 13th An. Rep. U. S. Geol.
Sur., Part II, pp. 211-281, 1891.
tMeade, T. M. "Evolution of Earth Structure," p. 146, London, 1903. "The Griffin of
Mountains," p. 331, London, 1886. Cadell. Trans. Royal Soc. of Edin., Vol. 35, part 7, 1888.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING
143
Effect of Vertical Compression Upon Beds of Stratified Materials.
Various tests upon bedded materials used for filling in mines
have been made by the United States Bureau of Mines. Incidentally
these tests have demonstrated the movement or flow of material in beds
FIG. 52. BENDING OF SHALE UNDER PRESSURE.
(Photo by H. I. Smith, U. S. Bureau of Mines.)
under pressure. Fig. 52 illustrates the bending of shale under pres-
sure in a mine. In this case, however, the bending is accompanied by
fracture because of the large movement allowed by the absence of re-
straint on the under side.
Effect of Lateral Tension Upon Stratified Material.
Not very much work has been done to determine the tensile strength
144 ILLINOIS ENGINEERING EXPERIMENT STATION
of rocks and practically nothing has been done upon beds of stratified
material.
General Experiments.
General experiments to illustrate geological phenomena and to dis-
cover the properties of rocks under conditions of pressure and tem-
perature which may exist at great depths, have been conducted by
Daubree, Adams, and Coker, and various other scientists working at
times privately and at other times under the auspices of scientific
bureaus of governments and of societies.
The Behavior of Various Types of Artificial Supports.
Extensive tests have been made by the United States Bureau of
Mines in various government laboratories and by various mining com-
panies in order to determine the actual and the relative strength of
different types of supports.*
SUGGESTED EXPERIMENTS AND TESTS.
(1) In order to study surface subsidence resulting from the re-
moval of supports, it is suggested that a model be constructed, say on a
1/lOOth scale, both horizontal and vertical, approximating relatively
the geological sequence of beds in a given district. The beds should
have the same strength relatively in proportion to their weight, or the
weight applied, as exists in the geological section which the model
represents. The model should be of sufficient extent laterally to rep-
resent several panels of a pillar-and-room mine laid out on the panel
system. Provision should be made for removing supports so that con-
ditions such as would exist when pillars are drawn may be created.
Observations should be made upon the height of surface from
time to time and, after surface movement has ceased, the model should
be dissected so that the effects of subsidence below the surface may be
noted. Similar models should be constructed to demonstrate working
beds of various thicknesses, depths, and dips, and under other systems
of mining.
(2) Strength tests of roof materials should be made. The tensile
strength and the angle of fracture in bending tests should be determined.
(3) The bending power of the various materials which constitute
the mine floor should be measured.
*See Bibliography on Prevention of Subsidence.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 145
(4) In typical mines and under normal working conditions, the
pressure or weight of roof should be measured and recorded over as
long a period as possible at each point selected.
(5) A study should be made of the composition and physical
properties of the rock strata between the beds mined and the surface and
also immediately below the beds mined.
CHAPTER VI.
PROTECTION OF OBJECTS ON THE SURFACE.
The surface may be protected by the use of natural or artificial
supports. Probably the most general method of preventing subsidence
and of protecting objects on the surface is by leaving unmined a por-
tion of the mineral deposit,, with the idea that the pillar thus left will
have sufficient strength to support the overlying rocks.
In considering the service which a pillar may render and in de-
termining the size of the pillar or other support for protecting specific,
mine openings or objects on the surface, it will be necessary to consider
some of the following factors, and in some cases all of them :
(1) The unit strength of the material forming the pillar.*
(2) The height of the mine opening.
(3) The dip of the mineral deposit.
(4) The angle of break of the overlying rock.f
(5) The angle of draw or drag or pull over the pillars, as observed
in the district or under similar conditions.
(6) The strength of the overlying rocks.J
(7) The nature and amount of filling in the mined-out area ad-
jacent.
(8) The depth at which mining may be carried on without affect-
ing the surface.
(9) The bearing-power of the bottom or floor.
(10) The weight of overlying materials which must be supported.
To determine the size of pillar necessary to protect mine open-
ings of a given width, it is customary in some textbooks to assume a
span of roof and overlying rock to be supported, to estimate the total
weight of such a block for the depth of workings, and then, with the
known or assumed unit crushing strength of the material to be left
in the pillar, the cross-section may be calculated. Such calculations
are seldom used in practice and they are open to the objection that they
assume a pillar to be uniform throughout, while, as a matter of fact, all
bedded deposits are composed of a large number of layers that may vary
widely in hardness. For instance, some beds of very hard coal contain
*See p. 70-76.
tSee p. 130.
ISee. p. 76.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 147
thin layers of mother coal which reduce the strength of the bed, thus
vitiating any calculated results for strength of pillar based on tested
specimens taken from the solid part of the bed.
SHAFT PILLARS.
Numerous rules have been formulated for the calculation of shaft
pillars in flat seams. Among the best known are the following:*
VD
"50
in which S equals length of side of pillar in yards and D
equals depth of shaft in fathoms.
Andre. Up to 150 yards deep, a pillar 35 yards square. Up to 175
yards deep, a pillar 40 yards square. Up to 200 yards deep, a
pillar 45 yards square, and so on, increasing 5 yards for every
25 yards of depth.
Dron. Draw a line enclosing all the surface buildings, such as engine
houses, fans, etc. Make the shaft pillar of such a size that
solid coal will be left in around this line for a distance equal
to one-third the depth of the shaft.
Wardle. The shaft pillars should not be less than 120 feet square, and
the deeper the shaft the larger the pillars. Supposing the
minimum to be 120 feet for a depth of 360 feet, 30 feet
should be added for every 120 feet in depth.
Hughes. Leave one foot in breadth for every foot in depth; that is,
a shaft 600 feet in depth should have a pillar 300 feet in
radius.
Pamely. For any depth to 300 feet, it may be sufficient to have a
pillar 120 feet square. Adopting this size as a minimum,
we may fix any size of pillars for greater depths by increas-
ing the pillar one foot for every four feet in depth.
Foster, R. J. To include the factor of thickness of seam, when con-
ditions are normal, the following formula is suggested:
Radius of pillar = 3^/Dt, in which
D = depth of shaft,
t = thickness of seam.
Mining Engineering (London). For shallow shafts a minimum of 60
feet radius should be adopted,f and for deeper shafts this
should be increased by one-tenth of the depth multiplied by
the square root of one-third the thickness of the seam in feet.
"Colliery Engineer, Vol. 17, p. 538, 1897. Coal and Metal Miners' Pocket Book.
tColliery Engineer. Vol. 18. p. 117. 1897.
148
ILLINOIS ENGINEERING EXPERIMENT STATION
Roberton, E. H. In Northumberland and Durham the practice is
shown by the following formula:
O
R = radius of the shaft pillar in feet,
D = depth of shaft,
t = thickness of seam.
Scotch engineers, in order to protect buildings have pillars from 1/3 to
1/5 larger than the floor plan of the building. This diversity
of opinion among engineers is well shown by Fig. 53.*
•Scale
9OO
FIG. 53. SIZES OF SHAFT PILLARS ACCORDING TO DIFFERENT FORMULAS.
The Central Coal Basin Rule, presumably founded upon the ex-
perience of mining men in Illinois and surrounding states, is : "Leave
100 square feet of coal for each foot that the shaft is deep. If the
bottom is soft, the result given by this rule is increased by half. For
5 or 6-foot coal beds, the Central Basin Rule may be used unless it
*Knox, G. Proc. Int. Geol. Cong., Vol. 12, p. 798, 1913.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 149
has been shown by other operating mines in the district that a larger
pillar is needed. With thicker coal a larger pillar should be left."*
The practice of some coal companies in the Connellsville region of
Pennsylvania is to leave pillars under buildings so that there is a mar-
gin of from 25 to 30 feet of coal around the building. If the tract is
large, from 50 to 60 per cent of the coal is removed, the remainder being
left in pillars proportioned so that they will serve in the most advan-
tageous way to -protect the building. This is the practice for depths from
150 to 300 feet.
In determining the size of the pillar necessary to protect objects
upon the surface, as has previously been noted, the ability of the pillar
to carry the load is not the only- question to be considered. Among the
most important of the other problems is that of draw or pull over the
pillar previously noted, and the ability of the underlying bed to sustain
the load concentrated upon it by the pillar. Quite frequently the un-
derlying bed is less stable and has less crushing strength than the pillar.
It seems logical then to proceed as follows in determining the size of
pillar necessary to protect an object upon the surface:
(1) Determine the lateral extent of pillar necessary in order to
prevent damage by draw.
(2) Determine whether the pillar thus outlined is sufficiently
large to support, without crushing, the burden of the overlying beds.
(3) Determine whether the load upon the pillar will cause the
pillar to be forced down into the underlying beds, or cause a flow of
the underlying material.
ROOM PILLARS.
In his discussion of methods of protecting the surface, M. Fayol
referred to the use of pillars between the working places. "The meshes
of the network consisting of pillars with working places between them
should be made smaller as the workings are shallower. As the depth
becomes greater the size of the meshes can be enlarged and dimensions
of the areas worked can be increased relatively to the sizes of the pillars
that are abandoned, regard being had to the height and width of the
zones of subsidence so that the various zones may be kept distinct from
each other. This general rule is susceptible of many combinations
according to the thickness, the inclination, the number and depth of
the seams worked. If the excavation is of small dimensions the sub-
sidences which take place above them are restricted in size and become
'Illinois Miners' and Mechanics' Institutes, Instruction Pamphlet No. 1, p. 49.
150 ILLINOIS ENGINEERING EXPERIMENT STATION
enlarged both in width and height as the excavation increases in area.
If each of the pillars, 1, 3, 5, and 7 (Fig. 54) be taken out singly,
zones of subsidence similar to Z1? Z3, Z^ and Z7, would be produced;
but when pillar 2 is taken out the line of roof subsides on to the floor,
and the zone of subsidence rises to Z2. The same thing happens when
No. 6 pillar is taken out, and if No. 4 pillar is taken out, the space
comprised between the zones Z2 and ZQ is set in motion and determines
the formation of zones Z4."*
It follows from this statement of Fayol that if the room pillars
are properly proportioned and properly spaced, the disturbance of the
strata may be limited to the volume within the zones. The material
:r.-_>a^ z.
Hf
12 3 4- S & 7 8 3 to II /f /J /* JS
FIG. 54. EFFECT OF EXTENT OF EXCAVATION ON AMOUNT OF MOVEMENT.
outside these zones throws no weight upon the material within the
zones. Necessarily, then, any vertical pressure must fall upon unmined
material forming the pillars and the pillars must be large enough to
withstand the pressure.
In a paper before the Pennsylvania State Anthracite Mine Cave
Commission, 1913, Douglas Bunting said: "The application of a
formula for determining the 'safe size of coal pillars for various thick-
nesses of veins and depths can be considered practical for depths greater
than 500 feet, but it is doubtful if the same formula would be of any
practical value for application to veins at less depth and certainly of
diminishing practical value with reduction in depth and thickness of
veins for the reasons that the variable conditions of vein, top, bottom,
etc., are of more consequence with small pillars than with large pillars." t
D. Bunting^ made a careful study of chamber pillars in deep an-
thracite mines on light dips. He considered the crushing strength of
coal which for anthracite was found to average 2,500 pounds per square
*Proc. South Wales Inst. Eng., Vol. 20, p. 340, 1897. It should be noted that these
zones outline the dome through which the movement extends, and not the limit of the falling
zone, as described by Rziha.
tBunting, D. "Pillar and Artificial Support in Coal Mining, With Particular Reference
to Adequate Surface Protection." Pa. Legislative Journal, Appendix, Vol. 5, p. 5988, 1913.
tBunting, D. "Chamber Fillers in Deep Anthracite Mines," Trans, A. I. M. E., Vol.
42, p. 236, 1911.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 151
inch for cubes. The ratio between the strength of prisms and cubes
was taken as follows:
° = 0-70 + 0.3<'
Strength 01 cube
in which
&± = width of pillar,
h = thickness of vein.
The weight of overlying strata was taken at 144 pounds per cubic foot.
144 11 z bi
(1) Load per square foot on a pillar = - ^ — — , in which
PI
y = depth below the surface,
b^= width of pillar,
z = distance between chamber centers.
With 1,000 pounds per square inch as the safe load for a cube we
obtain by substituting in equation (1) :
144 yg6i
= 144,000 (0.70 + 0.30)
h/
or y s = l,000 (0.70 + O.SO-1) 6X
ft
By making proper allowance for the crushing strength of the pillar
material and the weight of overburden, this formula may be used gen-
erally for flat beds.
The relative widths of rooms and pillars are determined largely by
practice. For bituminous coal of medium hardness and good roof and
floor, the following rule is sometimes used : "Make the thickness of room
pillars equal to one per cent of the depth of cover for each foot of thick-
ness of the seam, according to the expression :
w p = loo ' in which
Wp = pillar width,
t = thickness of seam,
D = depth of cover,
and then make the width of room or opening equal to the depth of cover
divided by the width of pillar thus found, according to the expression :
w— 2-
°~~~W
PTp
in which W0 is the width of room.
"Frail coal and coal that disintegrates readily when exposed to the
air, and a soft bottom, may increase the width of pillar required as much
as 50 per cent of the amount found above ; also, a hard roof may increase
152
ILLINOIS ENGINEERING EXPERIMENT STATION
the same as much as 25 per cent; while, on the other hand, a frail roof or
a hard coal or floor may reduce the width of pillar required 25 per cent."*
"As to the thickness of pillars in the Pittsburgh seam with strata
100 to 500 feet thick, the following rule should be a safe one to follow,
in which the pitch is from 1 to 5 per cent :
Thickness
of Surface
Feet
Thickness of
Pillars
George's Creek
Feet
Thickness of
Pillars
Fairmont
Feet
100
25
18
150
32
20
200
40
25
250
50
30
300
60
35
350
70
40
400
80
45
450
90
50
500
100
55
These figures are based on experience in this seam, where the floor
or bottom is hard and not affected by water. For a fireclay bottom some-
what thicker pillars would be necessary to withstand any extraordinary
weight. Eooms should be not more than 14 feet in width in the Georges
Creek region and 20 feet in the Fairmont region."f
Th'e average dimensions of pillars and rooms in ordinary pillar-and-
room mining in Illinois are shown in Table 134
TABLE 13.
DIMENSIONS OF PILLARS AND ROOMS IN PILLAR-AND-ROOM
MINING IN ILLINOIS.
District
Average
Depth in
Room
Width in
Pillar
Width in
Average
.Thickness of Coal
Feet
Feet
Feet
in Feet
II
140
26
19
f top bench 2 ft.
1 bottom bench, 3 ft. 9 in.
III
90
22
18
4ft.
IV
201
25
9
4 ft. 8 in.
V
243
26
16
4 ft. 8 in.
VI
270
22
18
9 ft. 5 in.
VII
227
31
30
7ft.
VIII
174
27
8
(Seam No. 6—6 ft.
1 Seam No. 7 — 5 ft.
Average of 48
Representative mines
208
26
19
The question of the thickness of cover is an important one in con-
nection with the size of the room pillars and particularly when the draw-
*Coal and Metal Miners' Pocket Book. 9th Ed., p. 286, 1907.
fReppert, A. E. "Pillar Falls and the Economical Recovery of Coal From Pillars."
W. Va. Coal Min. Inst., p. 116, 1911.
till. Coal Min. Investigation, Bui. No. 13, p. 76, 1915.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING
153
ing of pillars is considered. This has been emphasized by P. W.
Cunningham as follows : "The topography of the surface relative to hills
and vales should be considered when starting to draw pillars and relative
to this subject a question may be asked, which is an important one, viz.,
How many coal properties have contour maps of the surface ? Suppose,
for example, the rocks at the surface rise abruptly on each side of a nar-
row valley to say 200 or 300 feet. Would it be proper to commence pil-
lar drawing under this valley?"*
STRENGTH OF ROOF.
In determining the limits of mining under heavy wash, D. Bunt-
ing considered the strength of slabs of roof rock supported by pillars. "In
deriving a formula for computing the breaking load of a slab of stone
from the formula — — = lfm, let W represent the distributed loading
6
plus the weight of the beam itself in pounds, b, d, L represent the breadth,
depth, and span, respectively, in inches, and R equal the modulus of rup-
ture in pounds per square inch.
Bunting suggests that "the modulus of rupture does not express
the actual stress in the extreme fiber of the beam of rock, but is a quan-
tity useful only as a basis of comparison." He gives the following safe
unit stresses for stone, recommended by W. J. Douglas as illustrative of
possibly a fair average of safe stresses:
Compression
Lbs. per sq. in.
Shear
Lbs. per sq. in.
Tension
Lbs. per sq. in.
Granite
1200
200
160
Limestone
800
150
125
700
150
75
The maximum bending moment for a constrained or prismatic beam
is equal to — • By substituting in the formula for flexure ( — - — = Mm)
1/w 6
we obtain the formula W =—f — R. Likewise, the maximum moment at
L
WL
the center of such beam being equal to , the formula becomes
It is evident that failure of flexure would theoretically take place at
the points of support and not at the center of the span.
*Cunningham, F. W. "Methods of Removing Coal Pillars." Proc. Coal Min. Inst. of
America, p. 35, 1911.
154 ILLINOIS ENGINEERING EXPERIMENT STATION
In applying the formula W = -j — R to the case of a slab spanning
a breast or other mine opening, the weight of the overlying material will
be taken at 108 pounds per cubic foot, and the depth of the opening below
the surface will be designated by df in feet.
Then, W = — ^ — , which would be the loading of the slab with a
2 bd2
breadth of 1 foot. Substituting this value of W in the equation W = — =—
R and simplifying, the equation d2R = % L2 $ is obtained. If, how-
ever, the weight of the overlying material per cubic foot be represented by
w, the expression becomes d2R = _
/coo
In the use of the formula derived for determining the minimum
safe thickness of rock over mine openings for various depths below the
surface, consideration must be given to a number of conditions, the more
important of which are :
1. Nature of the top immediately above the coal seam and its com-
parative strength and liability to disintegration upon exposure to the
atmosphere.
2. Nature and thickness of the bed, the ability of the pillars to re-
sist squeezing, and the liability of disturbance of the overlying strata,
due to covering or squeezing in underlying beds.
3. Probable errors in relative vertical location of top of rock and
mine workings.
4. Possibility of the existence of deep gorges and pot holes.*
In order to arrive at a brief solution in calculating pillars of quartz-
ite for Rand mines, Richardsonf made us? of the following formulae:
Bending
1. fb = l06-^
Kt
L =
W = 106 Kt2 — Ptw
Shearing
__ 34.2 die
s~ Pw
~~dk
2. L = 5.i
*Bunting, D. "Limits of Mining Under Heavy Wash." Amer. Int. Min. Engrs. No.
97, p. 18, 1915.
fRichardson, A. "Subsidence in Underground Mines." Eng. and Min. Jour. Vol. 84,
p. 196, 1907.
YOUXG-STOEK SUBSIDENCE RESULTING FROM MINING 155
3. TF= (34.2 dk — l*w) t
in which Fb = factor of safety for bending,
Fs = factor of safety in shearing,
I — length of side of slab or distance from center to center of
pillars,
L = length of side of a slab which will only support its own
weight,
W = total distributed load which the slab will carry in addition
to its own weight,
K — compressive strength of pillar material pounds per square
inch,
t = thickness of slab in feet,
w = weight of a cubic foot in pounds,
d — diameter of pillars in feet.
He presumes that "where the slope areas are not extensive the weight
of the upper masses will be supported by their own strength," and calcu-
lates the size of pillar which will support continuous slabs of rock, homo-
geneous and uniformly loaded. By use of the formula he prepared a
table of sizes of pillars for various spaces and concluded that slabs usually
break up by shearing and that the strength to resist this depends on the
size and distance apart of supports.
FILLING METHODS.
Various materials and methods are employed to protect the surface
if it is deemed advisable to remove all the material deposit, or if the
material left in the forms of pillars is found inadequate to support the
surface.
Waste material resulting from the regular mining operations or
broken for this particular purpose may be stowed or packed into the
excavation. If sufficient or suitable material is not available under
ground it may be lowered or dropped from the surface and stowed where
needed. Crushed materials may be introduced from the surface and
transported through pipes and stowed by water or compressed air. Tim-
ber, steel, or various forms of masonry may be employed to support areas
upon which important structures may be erected.
This entire subject has been studied by the engineers engaged upon
investigations of subsidence and surface support in the Pennsylvania
Anthracite field, who say:
"Most coal beds consist of interstratified layers of coal, fireclay, slate,
and bony coal, the latter three composing the principal refuse material
of the mine. In these beds, in which it is necessary to remove some of
the roof rocks or take up some of the floor of the mine in order to obtain
156 ILLINOIS ENGINEERING EXPERIMENT STATION
height sufficient for the mules and the men to travel along the roads,
much mine refuse is produced, which is stored in the chambers. In beds
less than four feet thick many chambers are filled with mine refuse or
gob from floor to roof. In places this gob is merely thrown in carelessly
or is shoveled in; in other localities it is packed as tightly as possible by
hand. When there is much interstratified fireclay or bone in the coal
beds there will be larger quantities of the gob, and the thinner the bed
the greater will be the quantity of mine rock raised or taken down for
roads. The supporting value of stored gob depends upon the com-
pressibility of the material of which it is composed."*
Griffith's Method of Filling. — It has been suggested by William
Griffith that worked-out portions of mines be filled by blasting up the
bottom and shooting down the roof. The suggestion was made in con-
nection with a report to the Scranton Mine Cave Commission and Mr.
Griffith has secured patent (U. S. Patent 1,004,418) covering this
method. W. Griffith and E. J. Conner say: "It is a well known fact
that loose rock occupies from 1% to twice the volume of the same weight
of rock in place. Your engineers have conceived the idea of taking
advantage of this fact, well known to engineers, for the purpose of cheaply
producing an adequate support of the rock and surface above certain
classes of coal beds under the city of Scranton. So far as we know, this
method, in its entirety, has never been used before in any coal mining
district, and the suggestion is here made for the first time.
"The process is applicable to beds less than 6 feet in thickness and
consists simply in blowing up the floor and shooting down the roof of the
mine, each to a depth equal to the thickness of the coal bed. This pro-
duces a total thickness of loose rock equal to three times the thickness of
the coal. The rock would be well packed together and have great sup-
porting power, and, moreover, the desired ends would be attained in a
comparatively inexpensive manner.f
The method of blasting stowing material from the hanging or foot
walls is commonly used in metalliferous mines.
GOB STOWAGE IN LONGWALL MINING.
In longwall mining "the rock obtained from brushing the roof, that
which remains after building the pack walls, and the clay obtained from
undermining the coal are thrown behind the pack walls lining the roads.
•Griffith, Wm., and Conner, Eli T. "Mining Conditions Under the City of Scranton,
1 U. S. Bureau of Mines, Bui. No. 25, p. 52, 1912.
fGriffith, William, and Conner, Eli J. "Mining Coi
Pa." U. S. Bureau of Mines, Bui. No. 25, p. 57, 1912.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 157
The gob area is usually filled with rock and clay to within 2 to 5 feet of
the coal face. This loose rock and clay helps to support the roof and
control the roof weight on the coal face. The waste should fill the gob
sufficiently to allow the roof to come down gradually without breaking off
short at the face of the pack walls, but should not fill the gob so com-
pletely that it carries too much of the roof and does not throw enough
weight on the face of the coal. The width of the pack wall, called 'build-
ing/ necessary to prevent the walls from squeezing out and filling the
roadway when the roof weight comes on them depends upon local con-
ditions. The Third Vein District Agreement between the Illinois Coal
Operators' Association and the United Mine Workers of America pro-
vides : 'The miner shall build 4 yards of wall at each side of his road,
and if he has more rock than is required therefor he shall not load any
of it until he has filled his place therewith.' Eoom centers at the long-
wall face (in Illinois) are usually 42 feet apart."*
GOB PIERS.
In some cases, especially when the prevention of any movement of
the surface is especially desirable, gob piers are used. These are pillars
of waste rock, either laid up by hand throughout, or having the outer
wall carefully laid while the interior is rilled with refuse shoveled in.
The resistance of such supports to compression depends upon the material
used and the care with which they are built.
CONCRETE AND MASONRY PIERS.
These forms of support are more expensive than those previously
mentioned and are likewise more substantial. Masonry has frequently
been used to support the roof below important structures and occasionally
to support the walls of inclined beds and the overburden.
One of the earliest and also one of the most notable examples of the
extensive use of masonry in metal mines was the construction at the Tilly
Foster Iron Mines. f The total masonry constructed amounted to 20,189
cubic yards.
Whenever possible the concrete used is introduced from the surface
through boreholes. An interesting example of such use of concrete is
reported by Mr. Temple Chapman of Webb City, Missouri. In a zinc
mine six concrete piers were constructed, 35 feet high by 16 feet wide and
*Andros, S. O. "Mining Practice in District I." Illinois Coal Mining Investigations.
Bui. No. 5, p. 20, 1914.
tEngel, L. G. "Masonry Supports for Hanging Walls at the Tilly Foster Iron Mines."
Columbia School of Mines Quarterly, Vol. 6, p. 289, 1885.
158 ILLINOIS ENGINEERING EXPERIMENT STATION
20 feet long. The measures were horizontal and the distance from the
surface to the roof was 150 feet. First a 6-inch hole was drilled from
the surface to the roof with a churn drill at a cost of $0.90 per foot. A
large pile of tailings was close at hand, consisting of crushed rock passed
through a half -inch hole and containing some finer material and sand.
The mixture was six parts of tailings to one part of cement, which is
about equal to four parts of gravel, two of sand, and one of cement. This
was mixed mechanically and discharged direct from the mixer into the
drill hole. Underground two men were kept busy building up the form,
which was made of 1 by 12 inch board laid on edge and 2 by 6 inches set
vertically at 2-foot intervals and wired together across through the form.
Worn perforated trommel screen jackets cut in strips 10 feet long by 4
inches wide were used to reinforce the concrete. These were laid east
and west a foot apart and the concrete was poured. A foot higher similar
strips were placed at right angles to the first, and so on. A few 60-pound
rails were put into the tops of the piers, projecting from pier to pier
where possible. These piers were placed between ore pillars, the plan
being to remove these ore pillars. The piers were built at a cost of $3 per -
cubic yard at a time when the ore in the pillars was worth $12 per cubic
yard.*
A novel method of using concrete in connection with packing or
stowing was employed in France and reported by J. H. Piffaut.f
The coal bed, quite thick and highly inclined, was worked in 8-foot
slices in descending order. Upon the floor of a slice was spread a layer
of coal dust from 1 to 1% inches thick; then a layer of concrete from
8 to 10 inches thick ; and upon this was placed the ordinary packing. As
the working place had previously been timbered, the concrete surrounds
the base of the posts. When the next slice is removed the concrete floor
of the upper slice acts as a roof for the lower slice, which is timbered in
the regular manner in order to support the concrete loaded with packing.
It is claimed that this has proved satisfactory in the mining of thick beds.
COGS.
Cogs are cribs of timber filled with waste rock. They may be
erected quickly and they have great strength. They find some use in the
ordinary course of mining, but they are especially useful in preventing
an impending squeeze, or in stopping one that has already started by
Correspondence.
tPiffaut, J. H. "The Use of Cement-Concrete in the Working of Thick Coal Seams. '
Trans. Inst. Min. Eng., Vol. 29, p. 274, 1904.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 159
supplying such support that the overlying strata break through to the
surface. Their strength is, of course, lost when the timber decays.
SPECIAL TYPES OF COGS AND PIERS.
William Griffith has recently developed a cog which it is expected
will be many times as strong as the ordinary timber cog and both stronger
and more durable than the common concrete pier. The objection to con-
crete cogs or piers is that when the compressive strength is exceeded the
mass of concrete will go to pieces and will give no support whatever.
With rock and timber piers, even though the percentage of compression
may be large, the piers do not go to pieces but have some supporting
power. The concrete pier will collapse suddenly while the other types
of piers will be gradually deformed. Mr. Griffith says that what is needed
is something that will bear up under the heaviest weight, that will "give"
to a certain extent and will then withstand the continuing burden. In
his new pier, concrete is the basic material with timber to reinforce it.
The piers are constructed so that it is impossible for the timber to pull
away and for the concrete to be crushed. "The timber should be creosoted
and after the pier is constructed it should be coated on the outside with
cement by the use of the cement gun."
Tests show that a cog or pier, forty days old, will sustain for each
square foot of horizontal area :
7 tons with a compression of 1 per cent.
130 tons with a compression of 3 per cent.
140 tons with a compression of 14 per cent.
IRON SUPPORTS.
From time to time various types of metal supports have been tried
in the working places of mines. Where iron props or posts have been
installed in the Scranton district no subsidence occurred and it is the
opinion of the local engineers that the effectiveness of such props has
not been demonstrated. Rolled steel shapes are being quite extensively
used as legs and collars and as beams for the support of wide openings,
such as shaft bottoms. Iron supports have also been tried in metalliferous
mines, but, except for the support of the shafts, stations, and passage-
ways, they have never found extensive application. Iron props have
been used in foreign mines.
HYDRAULIC FILLING.
One of the most important methods of protecting the surface above
160 ILLINOIS ENGINEERING EXPERIMENT STATION
mine workings is by filling the workings with fine material carried by
water through pipes. In his report upon this method as used in the
Pennsylvania Anthracite fields, Charles Enzian says: "Heretofore
the process has been termed and even at present is known in the Penn-
sylvania Anthracite region as 'slushing/ 'flushing/ and 'silting.' As a
result of various suggestions from men of long experience in this work,
the name 'hydraulic mine filling' was adopted for the use of the report."*
The process has been used in (a) extinguishing mine fires, (b) arresting
mine squeezes, (c) supporting the surface, (d) reclaiming pillars and in-
creasing the yield of coal, (e) disposing of spoil banks, and (f ) in lessen-
ing stream pollution.
According to the Colliery Engineer, Vol. 33, p. 537, flushing was
first used August, 1884, by John Veith, General Inside Superintendent
of the Philadelphia & Eeading Coal and Iron Company, who employed
it to extinguish a fire in the Buck Eidge slope near Shamokin, Pennsyl-
vania.
The second use of flushing and its first use to support or control
overlying strata is credited in the same reference to Frank Pardee of
Hazleton, Pennsylvania. In 1886 F. Pardee used the system to stop a
squeeze which threatened the slope and breaker of the Laurel Hill colliery
at Hazleton. He accomplished this by flushing adjacent breasts with
culm. The breasts were steeply pitched. The squeeze was stopped by
means of natural pillars, each 10 yards wide, and two breasts filled with
culm, each 10 yards wide, and the subsiding rock broke off.
The most extensive early use of flushing was at the Kohinoor colliery
at Shenandoah, Pennsylvania. When this colliery was taken over by the
Philadelphia & Eeading Coal and Iron Company, January 1, 1884, it
was found that because of workings in the thick Mammoth seam a large
part of the town of Shenandoah was likely to be affected by a subsidence
of the surface. The Mammoth seam was from 40 to 60 feet thick, thus
making timbering impossible. The coal was about 400 feet from the
surface. After various methods had been suggested, the officials of the
company decided to flush culm into the workings, none of those engaged
in the enterprise knowing of the previous use of culm for roof support by
F. Pardee.
A very detailed description of the method used in flushing the culm
into the workings can be found in the above reference in the Colliery
Engineer and in Bulletin No. 60 of the U. S. Bureau of Mines.
The materials that have been used or may be available for hydraulic
•Enzian, Charles "Hydraulic Mine Filling." U. S. Bureau of Mines, Bui. No. 60, 1918.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 161
mine filling include culm, ashes, crushed refuse from coal washing plants,
sand, gravel, clay, loam, granulated slag, and crushed rock.
The methods employed and results accomplished have been described
by Davies, Griffith, and Enzian.*
The process consists of conveying culm, sand, ashes, etc., to the de-
sired place by means of water, the method used depending upon condi-
tions. If the pipe line can be laid on a steep grade from end to end, the
material will flow easily and little water will be required. On the other
hand, if the grade is light or if it must be reversed over part of the line
a larger quantity of water is required and, of course, a larger pipe. There
must always be sufficient velocity to prevent settling of the solids and this
can be obtained only by having sufficient head. Naturally the whole
operation is easiest when the grade is steep, the pipe short, and the curves
and connections few.
To avoid blockage of the pipe, clear water should be allowed to flow
for a few minutes before filling is added, in order to establish a current
throughout the pipe and when the flushing is to be interrupted, the addi-
tion of filling should be stopped some time before the water is shut off,
so that the solid matter may be washed out of the pipe.
The proportion of water required depends upon the velocity of the
current and the nature of the filling material. In general practice about
90 per cent of the material carried by the line is water. f
Good practice requires absolute control of the filling until it is
deposited at the desired place. This necessitates carrying the pipe line
to the place of deposit, no allowance being made for flow in chambers.
As the filling should be interrupted after 200 to 400 cubic yards
have been deposited and the material be allowed to settle for fifteen
to eighteen hours, it is desirable that branch lines be laid to different
points, so that the process, as a whole, need not be interrupted. During
the period of settling, water seeps out and the material shrinks from
1 to 10 per cent in volume. It is necessary that the drainage be so con-
trolled that the least possible solid matter will be carried away. The
finest part of the filling has an important part in the cementation of the
mass.
The process requires careful and continuous attention, though the
number of men employed need not be large. Generally, there should
*Davies, J. B. "Flushing Culm." Mines and Minerals, Vol. 18, pp. 342, 389. 1898.
Griffith, William. "Flushing Culm." Mines and Minerals, Vol. 20, p. 388, 1900. Enzian,
Charles "Hydraulic Mine Filling." U. S. Bureau of Mines, Bui. No. 60, pp. 58-60.
fWilson, H. M. "Irrigation Engineering." Pp. 61-69, 838, 344, Revised edition, 1910.
162 ILLINOIS ENGINEERING EXPERIMENT STATION •
be one man for the surface, one to patrol each 1,000 feet of pipe line,
and one to inspect the filling.
The results obtained have been very satisfactory and a large amount
of material formerly deposited on the surface is now washed back into
the mines.
In discussing wastes in Illinois coal mining, G. S. Rice com-
mented upon the feasibility of employing hydraulic fillings. He noted
the use of culm for filling in Pennsylvania and stated that "In Illinois,
the substitute would have to be surface sands and gravel. That this
would be impracticable in the great majority of cases throughout the
State is self-evident, particularly if water, the usual vehicle for trans-
portation, is employed, inasmuch as the majority of the thick seams in
Illinois have clay under them which water would soften, and thus tend
to cause a 'squeeze.' Aside from this, much farm land would be de-
stroyed in getting the filling material."*
In longwall mining the application of hydraulic filling under pres-
ent practice does not seem to be generally feasible. Hydraulic filling in
flat seams worked on the longwall plan was inaugurated near Liege,
Belgium, in 1913, but has not been employed on a sufficiently large scale
to justify a statement that it is practicable for flat seams. f
' Over a hundred collieries in Upper Silesia have employed hydraulic
filling^ in seams varying from 4 to 40 feet in thickness. Subsidence
has been reduced from 30 to 70 per cent to 0.3 to 7.8 per cent of the
height of the seam. In 1914 twenty-seven collieries, employing forty
equipments, used hydraulic filling. The sand commonly used in Silesia
for filling is mined with steam shovels and then transported by railroad,
sometimes for considerable distance, to the mine, where it is dumped on
a grizzly to remove the boulders and then mixed with a suitable amount
of water to flush it into the mine. At one mine, at least, the boulders
are crushed and mixed with sand filling. A detailed description of the
methods used in Upper Silesia will be found in the reports of the
Upper Silesia Mining Association. In the Saarbriicken district there
are on state-owned lands more than twenty independent hydraulic-filling
installations, costing $350,000. This method is employed for iron and
potash mines as well as in the coal mines.
"The only fairly extensive installations at work in Britain is that
*Rice, G. S. "Mining Wastes and Mining Costs in Illinois." 111. State Geol. Sur., Bui.
No. 14, p. 220, 1909.
tSee Trans. Inst. Min. Eng., Vol. 46, p. 439, 1913-1914.
$Trans. Inst. Min. Eng. Vol. 46, p. 534, 1912. Report of British Consul-General,
Westphalia, p. 25, 1911.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 163
of the Wishaw Coal Mining Company, Motherwell. There are other
installations in a small form,, or under consideration,, but nothing yet
has been adopted on an extensive scale. A small trial outfit has been
installed at one of the Fife pits, and there is a proposition to use
hydraulic stowing where the seams run under the sea. There is a small
installation at the Crowgarth iron-ore mine."*
"In France it has been used, especially at the collieries in the De-
partment of the Pas-de-Calais,, and also in the coal fields of St. Etienne.
In Belgium it is used at several collieries. In Spain the Penarroza
Colliery is erecting a plant, and several collieries in Austria, as well as
Poland and Kussia, are employing the system. It is used also at lignite
mines in Manchuria and in the gold mines of Australia and the Trans-
vaal.'^
Gullachsen reports that in order to avoid the great expense of
pumping to the surface the water used in hydraulic filling the Cin-
derella Deep mine introduced a system by which sand is sent into the
mine in a dry condition. A wooden box-launder was constructed
measuring 12 by 11 inches in inside cross-section. This launder was
carried down the vertical shaft to a depth of 3,900 feet to the level at
which the filling material was required. The sand, which should not
contain more than 7 per cent of moisture, is stored in a surface bin,
from which it is taken on a conveyor belt to the top of the shaft and
there discharged into the launder. On reaching the bottom of the
launder, it falls on a steeply inclined iron plate, at which point jets of
water are turned into the sand, which is then carried away as a pulp.
The great objection to this system is the difficulty of securing a constant
supply of dry sand. As soon as the sand contains more than 7 per cent
of moisture, it is inclined to adhere gradually to the sides of the launder,
which in time becomes choked. The launder was connected to a Eoots
blower and jets of compressed air introduced, the idea being to assist
the drying of the sand and to increase the velocity of the falling stream,
but this device was found to result in only a very slight improvement."
PNEUMATIC FILLING.
The stowing of crushed rock by means of compressed air has been
successfully employed in the Lake Superior copper district at several
*Paton, J. D. "Modern Developments in Hydraulic Stowing." Trans. Inst. Min. Engrs.,
Vol. 47, p. 468, 1914. See also Trans. Inst. Min. Engrs., Vol. 48, p. 134, 1914, and Iron
and Coal Trades Review, Vol. 89, p. 454, 1914.
fGullachsen, B. C. "Hydraulic Stowing in the Gold Mines of the Witwatersrand."
Trans. Inst. Min. Eng., Vol. 48, p. 122, 1914. See also Trans. Inst. Min. Eng., Vol. 41,
p. 586, 1910, and Trans. Inst. Min. Eng., Vol. 43, p. 632, 1911.
164
ILLINOIS ENGINEERING EXPERIMENT STATION
mines, having been developed at the Champion mine of the Copper
Range Company by F. W. Denton. Stamp sands or tailings from
the concentration plant are hauled in railroad cars a distance of eighteen
miles and discharged through pipes into the worked-out stopes. It is
claimed that by the use of this material a saving is made over the method
of support formerly used. In order to provide sufficient material for
filling the stopes, waste rock secured from sorting in the stopes was sup-
plemented by rock blasted out of the walls. At present the sand is used
in addition to the waste material discarded in the stopes.*
SUPPORTING POWER OF FILLING.
The problem of support of surface by filling suggests two important
points, in addition to the controlling factor of the cost of filling. When
the worked-out portions of the mine are filled by the natural process of
caving, the factor of increase of volume of material should be known.
Moreover, as the overlying beds sink upon this filling the factor of com-
pressibility of the filling must be considered. Fayol made extensive and
careful investigations along these lines, and his determinations of the
increase of volume are shown in Table 14.
TABLE 14.
INCREASE IN VOLUME OF MATERIALS IN FILLING.
Relative Volumes
Nature of
Rock
Unbroken
Crushed to
Powder
Grains
.078 to .118
inch
(2-3 mm.)
Grains
.393 to .59
inch
(10-15 mm.)
Grains
.59 to .787
inch
(15-20 mm.)
Mixtures,
Grains and
Fine Dust
Clay .
100
196
209
226
225
216
Shale
100
213
210
221
224
229
Sandstone . . .
Coal
100
100
219
207
214
224
211
199
810
223
214
202
The mixture of large and small pieces of sandstone and shale com-
monly used for stowing increases in volume about 60 per cent. The
greater the increases in volume, the more easily is the crushed material
compressed. Fayol's results of tests of compression upon crushed ma-
terial are given in Table 15.
The pressures noted in Columns I, II, III, and IV correspond to
depths of strata of 1,638, 3,2?'6, 8,190, and 16,380 feet, respectively.
*"Sand Filling at Champion Copper Co., Painesdale, Michigan."
Vol. 41. p. 1194. 1914.
Min. and Eng. World,
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING
165
TABLE 15.
EESULTS OF TESTS OF COMPRESSION UPON CRUSHED MATERIAL.
Nature
of
Rock
Space
Occupied
Before Being
Broken
Rocks Having Been Previously Crushed or Broken, the
Space Occupied under Pressure of
I.
1422 Ib. per
sq. in.
100 kgm. per
sq. cm.
II.
2844 Ib. per
sq. in.
200 kgm. per
sq. cm.
III.
7110 Ib. per
sq. in.
500 kgm. per
sq. cm.
IV.
14,220 Ib. per
sq. in.
1000 kgm. per
sq. cm.
Clay
100 .
100
100
100
100
128
136
130
90
116
125
125
75
110
120
118
70
97
105
109
Shale
Coal
Fayol concluded that the material which ordinarily fills the goaves of
mines always occupies a larger space than it did originally, and after an
expansion of about 60 per cent it appears to undergo in workings of from
300 to 900 feet in depth a compression of about 30 per cent, which leaves
a volume about 12 per cent larger than the volume of the unbroken rock.*
The supporting strength of dry filling as studied in connection with
the problem of surface support at Scranton, Pennsylvania, is shown in
Table 16.f
Anton Frieser reports that in coal mining in Bohemia hydraulic
filling has been carried on extensively and that, with such filling at depths
of from 60 to 200 feet, the roof pressure compresses one volume of ordi-
nary stone-and-sand packing to 0.6, clay packing compresses to 0.5,
and puddled sand and ashes to 0.8 or 0.9.$
In the Euhr coal district of Germany, filling has been used exten-
sively and the amount of compression has been noted carefully. jf This
has been possible as new openings were driven through workings which
had been filled from two to eight years previously.
Dr. Niesz has found that gobbing, under pressure, may lose four-
tenths of its height, small-grained pit-heap material 25 per cent, and
pure loose sand 8 per cent.§
The commission reporting upon the slide at Turtle Mt., Frank,
Alberta, Canada, commented upon the efficiency of various kinds of
filling in mine workings. The general statement was made that under
'Colliery Engineer, Vol. 33, p. 548, 1913.
tU. S. Bureau of Mines. Bui. No. 25, p. 59. 1912.
tOesttr. Zeit fur Berg.-und Huttenwesen, Vol. 43, p. 253, 1895.
HOberhausen, J. "Compression of Slope Fillings," Gliickauf, p. 1146, Nov. 22, 1902.
Translation in Columbia School Mines Quarterly, Vol. 26, p. 271, 1904.
§Zeit fur Berg.-, Hutt.-, u.-Salinew., Vol. 58, p. 418, 1910.
166
ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 16.
SUPPORTING STRENGTH OF VARIOUS FORMS OF DRY FILLING.
Kind of Material Comprising the
Artificial Supports
Approximate Depth, in Feet, of Column of Coal Measure
Rock, 1 hoot Square, Necessary to Compress
Artificial Roof Support
Per Cent, of Compression
1
3
5
10
20
30
1. Rectangular gob piers, ordinary
Feet
Feet
10
46
8
Feet
12
75
6S
20
21
<;o
45
74
77
25
70
801
190
(e)
Feet
36
146
182
53
53
121
117
177
325
70
442
2,310
472
Feet
125
292
270
124
186
351
434
619
6,000
143
1,715
Feet
*306
*512
*419
*298
*465
*492
a615
1,310
bS.SfiO
332
6,640
c8,860
5,905
2. Circular piers of mine rock,
3. Timber cogs filled with gob,
4. Loose pile of broken sand-
stone through ly* -inch ring,
5. Pile broken sandstone, 40 per
cent, voids, voids filled with
6. Loose pile large size broken
sand rock, 45 per cent, voids.
7. Mine room filled with large
broken sand rock, 50 per
48
27
44
46
13
40
522
118
1,092
12
8. Mine room filled with broken
sandstone, 40 per cent, voids
9. Mine room filled with broken
sandstone, 40 per cent, voids
filled with sand
10. Mine chamber filled with dry
coal ashes, 64 per cent, voids
11. Mine room filled with dry river
12
111
32
117
12. Mine room filled with river
sand flushed in with water. .
13. Mine chamber filled with coal
culm flushed in with water..
14. Concrete pier, 1 part cement,
7 parts sand and gravel; 5
months old
1,852
Resistance of flushed culm
1.0
3.5
3.6
1.0
4.4
9.0
1.0
4.7
(d)
1
5
(d)
1
4
(d)
t
f
Resistance of flushed sand
Concrete pier
tfd)
a 27 per cent, settlement,
b 23 per cent, settlement,
c 20 J4 per cent, settlement.
d Worthless,
e Gradually cracked to pieces under continuous load equal to 600 feet of rock.
*Free to expand laterally.
•{•Comparative.
average conditions the settlement would be 5 per cent of the thickness
of the bed if ordinary sand were used ; an inappreciable amount if granu-
lated slag were used; 10 to 15 per cent with loam, sandy clay, and
ashes; and 40 to 60 per cent with dry packing. Under the conditions
at Frank the coal pillars left merely serve "to delay the process (of
movement) for under the great pressures due to depth, shales, such as
here constitute the hanging wall, will 'flow' and seal all openings."*
*Daly, R. A., Miller, W. G., and Rice. G. S. "Report of Commission Appointed to
Investigate Turtle Mt., Frank, Alberta, 1911." Can. Dept. Mines, Geol. Survey Branch,
Memoir No. 27, p. 30.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING
TABLE 17.
EXTENT OF FILLING IN EUHR COAL DISTRICT, GERMANY.
167
Per Cent, of
Compression
Referred to
r Original
Thickness
Area
Worked Out
Square Metre
Average
Depth from
Surface
Age of
Workings
at Time of
Reopening
Composition
of
Filling
29
14,400
370
8
Waste rock, slates,
„
and sandstones
from surface.
23
20,800
450
2
Granulated slag
and waste rock
(clay and slate).
37
104,000
360
5
Waste from seam
and from roof
and footwall.
39
26,400
300
4
Waste from seam
and from roof
and footwall.
60
36,000
270
5
Waste rock from
bottom of gang-
21
21,000
380
2
ways.
Waste rock from
surface, granu-
lated slag and
clay slate.
2S
25,000
440
2
Same as preced-
ing.
CONSTRUCTION OVER MINED-OUT AREAS.
When a building is threatened by subsidence resulting from mining
operations, or when it is planned to erect a structure upon land which
has been undermined and which does not offer sufficiently stable material
for a foundation, various steps may be taken to prevent damage to the
structure erected or proposed.
Owing to the danger of surface subsidence, the Central Eailroad of
New Jersey introduced sand into the old mine workings beneath the site
of a proposed depot in Scranton in 1911. The Diamond and the Rock
seams had been worked and after investigation of the workings it was
decided that it would not be necessary to fill the entire area of the
workings, but only to reinforce sufficiently the smaller pillars in both
seams and fill the wider areas in the Diamond seam so as to prevent any
further caving of the roof. In an 8-inch borehole, drilled for this
special purpose, a 6-inch pipe was placed. The depth to the lower seam
was 80 feet. Sand was brought in railroad cars and flushed into the
workings, a total of 9,400 cubic yards being placed at a cost for labor of
29 cents per cubic yard of sand filling.*
*Bunting, D. "Pillar and Artificial Support in Coal Mining."
Appendix V, p. 5989. 1913.
Penn. Legis. Jour.,
168 ILLINOIS ENGINEERING EXPERIMENT STATION
The problem of constructing a six-story building, 60 feet wide by
157 feet 7 inches long, on Wyoming Avenue, in Scranton, Pa., was solved
by constructing a series of concrete columns. The Big, or 14-foot, bed
was close to the surface and had been mined beneath the property, but
no maps were available to show the exact location and size of the pillars,
and the old workings were inaccessible. Beneath the 14-foot bed other
thinner beds had been worked. Five lines of holes were drilled to the
rock under the 14-foot bed, the average depth being 40 feet. They were
spaced 14 feet 10 inches in one direction and 16 feet 4 inches in the
other. Twelve-inch steel pipes were driven into the holes and filled
with concrete and, on the top of these, reinforced concrete beams were
built.*
The Scranton Electric Company flushed ashes into the old work-
ings under its new power house on Washington avenue. At the present
time it is sinking a shaft to be used for dumping ashes into these work-
ings, thus avoiding the expense of hauling them away.
In Pittsburgh, Pennsylvania, the residence section of the city ex-
tends over areas from which coal has been mined and it has been thought
advisable to construct special foundations under buildings which might
be endangered by surface subsidence. Exploratory holes at Beacon
Street and Shady Avenue showed that the mine workings were 35 to 55
feet below the surface. Some of the roof had fallen, but some pillars
had been left and it was anticipated that subsidence might not be
uniform. A pillar of coal extended under one corner of the site for a
house. Holes 10 and 14 inches in diameter were drilled to the rock
below the coal and six concrete columns were constructed in order to
provide support for that part of the house which would be unaffected
by caving over the rooms in the mine. No column was constructed under
the corner of the house where the coal pillar was located. The concrete
columns were 8 inches and 12 inches in diameter inside the galvanized-
iron lining which was placed in each hole. The lining was slightly smaller
than the hole so that the rock might sink without disturbing the columns.
Each column was reinforced and upon these columns were erected re-
inforced concrete girders which served as a foundation for the house.f
When it is proposed to remove all the mineral in a horizontal bed
beneath a structure, it is advisable to mine out the coal in advance in
a direction at right angles to the longer axis of the structure and to
*Stevenson, G. E. "Founding a Building Over Coal Mine Workings." Eng. News,
Vol. 71, p. 791, 1914.
t"Concrete Column Foundation for a Building Over Coal Mine Workings." Eng. News,
Vol. 117, p. 632, 1912.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 169
advance the face at a uniform rate as rapidly as possible so that the
structure may be subjected to stress for as short a period as possible.
Reference has previously been made to the special types of con-
struction employed in buildings* and bridgesf when surface movement
is anticipated. Foundations may be reinforced, long buildings may be
divided into units, joints permitting expansion and contraction may be
provided, expansion pieces may be placed in railroad tracks, pipe line,
cables, etc. In cities in German coal mining districts gutters and
curbing are laid with elastic and waterproof joints. Asphalt, cement,
and concrete pavements are not used because they are not easily repaired.
RESTORING DAMAGED LANDS.
When subsidence causes breaks and pit holes in agricultural lands,
the surface may be rendered temporarily almost valueless for certain
kinds of tilling. When the land is of great value for farming, these
holes may be filled with waste rock from the mine, cinders, and other
refuse, to within four feet of the surface. The remainder of filling
necessary to restore a regular surface slope should consist of good soil.
At a number of mines in Illinois where such surface damage has resulted
from mining operations, the mining companies cooperate with the farmers
in filling the pit holes with mine rock.
When subsidence does not break the surface but simply causes shal-
low basins below the general drainage levels, large ponds form during
the spring and may result in the permanent flooding of valuable land.
In Northern Illinois, in the longwall field, the topography is such that
tile drains have been laid to permit the use of the land. Longwall
mining frequently causes a surface movement sufficient to destroy the
usefulness of such artificial drainage systems. Referring to the problem
in Northern Illinois, G. S. Rice said: "It may be solved to a
certain extent through draining the sunken lands by pumping, but even
with such a method, aside from the expense, there is a serious difficulty
from storm water. When the subsidence is from 2 to 4 feet it will
render previously level lands of little use for raising crops until the
particular area has come to full settlement and has been retiled. If it
were possible to systematize mining so that the land nearest the water
courses was first undermined and then in succession the land further
away, the damage done to farming would be minimized.''^
*P. 68~
tP. 60.
JRice, G. S. "Mining Wastes and Costs in Illinois." Geol. Survey, Bui. No. 14, p. 48.
CHAPTER VII.
LEGAL CONSIDERATIONS.
RIGHT OF SUPPORT.
The title to the minerals, and the right to work them may be
held separately from the surface. Under the common law the owner
of the surface is entitled to surface support, even though the owner of
the minerals finds it impossible to remove them without disturbing the
surface. Moreover the owner of the surface is entitled not only to
vertical support, but also to lateral support from his neighbors even
to the extent that minerals upon adjoining lands cannot be removed in
such a manner or to such an extent that the surface of adjoining prop-
erties is disturbed.
Leases of coal rights often state distinctly that the lessee shall
not be liable for damage to the surface, and where surface rights only
are sold, the deed often states that the title to the surface does not
include the right to surface support if the owner of the mineral rights
mines out the mineral. In spite of such clauses in deeds and in leases
suits are of common occurrence when surface and mineral rights are
owned by different parties.
MINING UNDER MUNICIPALITIES.
The problem of the claims of municipalities in the coal districts
has aroused considerable discussion. In many instances coal mines
have been opened upon lands remote from towns and upon which no
buildings other than the mine structures were erected at the time.
Later mining villages have grown up near the mines and residences
and other buildings have been constructed upon the land which had
previously been undermined. In many instances, owing to the im-
portance of locating near an abundant fuel supply, industrial plants
have been erected in these mining villages or in other towns in the
coal district. Eventually large cities have grown up on the lands on
which coal mining was the pioneer industry. Similarly mines have
been opened outside the limits of important cities and mining opera-
tions have been confined to the area which was outside the limits of
the city when the mine was opened, but in the course of years the
city has extended its limits to include the mine and the area undermined.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 171
The claims of the municipality upon the mining interests, which
may have a right by contract and under the law to mine all the coal
and to be exempt from liability for damages to the surface, were
forcibly presented by Mayor B. Dimmick of Scran ton before the Penn-
sylvania Anthracite Mine Cave Commission, as follows:
"I am of the opinion that there is no constitutional barrier against
the inclusion in the general police power of a state or a community of
the specific power to declare as null and void and as against sound
public morals any and all contracts that waive the right to a reasonable
support of the surface which is to be occupied and used for community
purposes. I would recommend submitting to the Legislature an act
that would declare null and void and as being contrary to public policy
any and all contracts that waive the right to, or release from responsi-
bility for, reasonable support of the surface wherever such surface is
actually devoted to community life.
"Fortunately this problem has been attacked at a period in which
public opinion is slowly but surely crystallizing in favor of acceptance
of two general principles, the first being in the direction of such quali-
fications to the ownership and use of property as are exacted through
the increasing interdependence of modern life, such qualifications being
in no sense a redistribution of property, in no sense a taking away from
one and giving to another, but simply such restrictions and regulations
as are demanded, not only in the carrying out of the ancient rule, 'So
use your own as not to injure another,' but also for the general welfare
of the community. The second principle is that Society must accom-
modate itself to such costs as are incident not only to fair return to
both capital and labor, but also to all the accidents and burdens that
result from any activities that Society desires or is compelled to enjoy,
and this principle is being regarded as so clearly equitable that its
enforcement is being demanded, all private contracts to the contrary
notwithstanding. If this principle can and should be enforced when the
health of the community or individual is at stake, surely it can and
should be enforced when, as in the case of support of the surface, the
very lives of men, women, and children are jeopardized.
"The maintenance of the surface, upon which are located the
communities that extract the coal, should be regarded as a necessary
factor in the cost of mining and should be paid for by the consumer.
Such inclusion of the cost of the support of the surface in the general
cost of production will be fairer than any fixed tax to be imposed by
172 ILLINOIS ENGINEERING EXPERIMENT STATION
the State and then paid out, say to municipalities, to be expended in
securing such support.
"It is possible that even under the existing welfare clauses of the
acts governing municipalities of Pennsylvania, the proposed exercise of
police power might be upheld, but certainly the hands of these munici-
palities in the anthracite region would be greatly strengthened by
such proposed legislation.
"In contemplating this exercise of police power, I realize that
there is possibly no exact precedent therefor, yet such exercises would
clearly fall within not only the modern but even the ancient definition
of the power. So eminent a judge and publicist as Jeremiah S. Black
once said that "the police power of the State, of which she cannot dis-
arm herself if she would, enables her to regulate the use even of private
property in such manner that neither the general public nor particular
individuals can be made to suffer by it unjustly/ ''
With these claims of Mayor Dimmick many eminent lawyers have
taken issue.*
Opinions upon a number of the points under discussion are given
in the following citations:
"In the natural state of land one part of it receives support from
another, upper from lower strata, and soil from adjacent soil." (Per
Lord Selborne in Dalton v. Angus, 6 A. C. 791.)
"Where the surface belongs to one and the minerals to another,
no evidence of title appearing to regulate or qualify their rights of
enjoyment, the owner of the minerals cannot remove them without
leaving sufficient support to maintain the surface in its natural state."
(Wilms v. Jess, 94 111. 464, 1880.)
The same principles hold between the owners of different minerals
lying in separate beds. If one bed lies above another the owner of
the lower bed must give support to the upper bed. (MacSwinney p. 301.)
A coal mine operating beneath a clay mine is liable for injuries to
the upper mine caused by failure to leave sufficient pillars in the coal
mine. (Yandes v. Wright, 66 Ind. 319, 1879.)
The right of support is not affected by the nature of the strata
nor by the difficulty of propping up the surface. (MacSwinney p. 292.)
The right of support is wholly independent of the comparative
*For a complete statement of American cases on the various points of discussion between
surface and mining rights, see Lindley on mines, Title IX, Ch. II and III, 3d Ed., 1914.
For British cases, see MacSwinney, K. F. "The Law of Mines, Quarries and Minerals."
Ch. XIV, 4th Ed., 1912.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 173
values of the substance receiving and the substance giving support.
(Op. Cit., p. 292.)
The right of lateral support is an absolute one. The obligation to
respect it is in no way affected by the question of negligence. (50 Mo.
App. 525.)
"Every owner of land in its natural state has a prima facie right
to support, lateral as well as vertical; and the adjacent or subjacent
owner has no right, prima facie, in order to win his minerals, to with-
draw such support. The burden, both in pleading and in proof, is
upon him who asserts that the position is different from that existing
as of common right." (Op. Qit., p. 299.)
EXEMPTION FROM LIABILITY FOR DAMAGE TO SURFACE.
A conveyance of the right to mine all the underlying minerals
implies that in so mining such minerals the surface land shall be
sufficiently supported and that so much of such minerals may be mined
as can be obtained without injury to the surface. A waiver of the
obligation to support the surface must be made by the owner of the
surface land by language clear and unequivocal. Such a waiver does
not follow a conveyance of all such minerals, nor from the use of language
in such a conveyance to the effect that the mining operations shall
be "conducted with as little damage to the surface as conveniently
may." (Seitz v. Coal Valley Mining Co., 149 111. App. 85, 1909.)
Where a land owner sells the surface, reserving to himself the
minerals with power to get them, he must, if he intends to have power
to get them in a way which will destroy the surface, frame the reserva-
tion in such a way as to show clearly that he is intended to have that
power. (Wilms v. Jess, 94 111. 464, 1880.)
When an instrument excludes the right of the surface owner to
support, the mine owner may be liable, if he works negligently, or con-
trary to the custom of the country. (MacSwinney p. 311.)
The right of support by land in its natural state may also be
excluded, wholly or in fact, by statute. Examples of this may be found
in various English Acts. (See MacSwinney p. 312.)
In an investigation of the surface damage in a section of Scranton,
Pennsylvania, it was found that 48 per cent of the titles contained a
clause completely waiving surface support, in the following language:
"All the coal in, under and upon said lot, together with the sole right
and privilege to mine and remove all the coal under said lots without
174 ILLINOIS ENGINEERING EXPERIMENT STATION
incurring in any event whatever any liability for injury or damage
done to the surface of said lots or improvements thereon or that may
thereafter be put thereon caused by mining or removal of said coal."
Fourteen per cent of the titles contained waivers which are more
or less conditional in their nature: "All the anthracite coal lying
underneath, also half the width of streets adjoining. It being under-
stood and agreed that at least one-fourth thereof, properly distributed,
shall be left for surface support and the coal shall be mined in a work-
man-like and skillful manner, it being understood that all the coal is
to be mined and paid for except so much left thereof as may be neces-
sary to be left for pillars to support the surface thereof, and it being
possible that there may be a difference of opinion relating to the ful-
fillment of this provision it is agreed that the matter shall be submitted
to a board of competent and skillful engineers, each party to select one
and, in case of failure to agree, said engineers are empowered to call
in a third mining engineer and the decision of the majority shall be
final."
Ten per cent of the titles contained the following clause : "All the
coal and minerals under said lot, together with the right to mine and
remove all of said coal and minerals, provided also that in removing
the coal the second party shall leave one-fourth thereof in place for
the protection of the surface."
The remainder of the titles examined by the investigators contained
the following clause: "All right, title, etc., to all coal in and under
said lots, also the coal under the surface in front of said lots to the
center of the street."
In the report of the Pennsylvania State Anthracite Mine Cave
Commission excerpts of 42 deeds are given showing the various forms
in which reservations have been made when the title to the surface
has been severed from the mining right.*
In the bituminous fields a customary form of exemption clause
in deed for coal, separate from the surface, is as follows : "All the
coal underlying and within the described lands together with the right
to take the entire quantity, or a less quantity of said coal, without
leaving any support for the overlying strata, and without liability for
any injury or damage which may result from the breaking of said
strata." Another type of exemption clause employed in Illinois is
as follows: "Releasing and surrendering any and all claims for dam-
*Pa. Legislative Journal, Appendix, Vol. 5, p. 5953, 1913.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 175
ages and all liability by reason of damages either to person or prop-
erty which may in any way be caused or occasioned at any time hereafter,
directly or indirectly, by the mining or removing of coal or other
minerals."
PROTECTION OF SURFACE BY GRANTS AND BY LEGISLATION.
The right of support for land in its non-natural state may be
acquired by express or implied grant.* Where land is severed from
adjoining land for a particular purpose, and such purpose is known at
the time the mineral right is severed from the surface, there is, prima
facie, an implied grant of a reasonable degree of support for carrying
out the particular purpose under consideration.
In order to protect railways, canals, waterworks, sewers, etc., the
British Parliament has enacted legislation which guarantees that such
structures shall not be undermined, if liable to be damaged, without
notice. In accordance with these acts, the mining company may be
required to leave a pillar, but the mining company is compensated for,
the coal left in the ground and for any damage that may be
sustained by the interruption with the system of mining. In the case
of the Railway Act, it is specified that "the (railway) company shall
from time to time pay to the owner, lessee, or occupier of any such
mines, extending so as to lie on both sides of the railway, all such
additional expenses and losses as shall be incurred by such owner,
lessee, or occupier by reason of the severance of the lands lying over
such mines by the railway, or of the continuous working of such mines
being interrupted, or by reason of the same being worked in such a
manner and under such restrictions as not to prejudice or injure
the railway, and for any minerals not purchased by the company which
cannot be obtained by reason of making and maintaining the railway;
and if any dispute or question shall arise between the company and
such owner, lessee, or occupier as aforesaid, touching the amount of
such losses or expenses, the same shall be settled by arbitration.t
Similar sections are included in the Wat. Cl. Const. Act, 1847 ; the
Pub. Health Act, 1875 (Support of Sewers); Amendment Act, 1883;
the Local Government Act, 1894; the Small Holdings and Allotments
Act, 1908 ; and the Housing and Town Planning Act, 1909.$
Under these acts, as noted, the intention of a mining company to
*MacSwinney Pp. 315, 316.
tRailwav Clauses Consolidation Act, 1845. Sec. 81. 8 and 9 Viet., c. 20.
JMacSwinney P. 370.
176 ILLINOIS ENGINEERING EXPERIMENT STATION
remove the mineral beneath any of the legally specified structure must
be announced through a regular "notice of intention to work." This
notice is given in most cases thirty days in advance of the intended
working. If, after notice has been given, the owner of the structure
does not agree to negotiate with the mining company, it is lawful for
the mining company to proceed in the regular manner of working. If
damage results, it shall be repaired by the mining company.*
Gas works and gas mains are not within the British mining code
excepting in so far as they are vested in local authority. Private gas
companies are not entitled to support if the mineral right has been
severed, but the colliery company would be liable for damages to gas
pipes and leakage of gas. In the absence of special provisions, owners,
lessees, and occupiers of mines are not liable for damage caused to
tramways by working mines or minerals in the usual and ordinary
course.f This mining code of Great Britain is not applicable to burial
grounds, school sites, public highways, bridges, nor canals.
In several states of the United States there are statutes in regard to
support, particularly in western states in which the lode mining law
permits extralateral mining. The statutes of Colorado, for example,
prescribe that "when the right to mine is in any case separate from
the ownership or right of occupancy to the surface, the owner or rightful
occupant of the surface may demand satisfactory security from the
miner, and if it be refused, may enjoin such miner from working until
such security is given." No person shall have the right to mine under
any building or other improvement unless he shall first secure the
parties owning the same against all damages, except by priority of
right."$
Other states, such as Idaho, North Dakota, South Dakota, and
Wyoming, have similar laws. In commenting on this type of legislation,
Lindley says, "We are not aware that this class of legislation has been
the subject of judicial investigation. It seems to us that such legisla-
tion is not altogether free from constitutional objections/'^
Arkansas has a law, approved Feb. 28, 1907, forbidding the min-
ing of coal or any other mineral substance from beneath a cemetery
or burial place. No openings whatever may be driven under or through
*Cockburn, J. H. "Minerals Under Railways and Statutory Works." Trans. Inst.
Min. Engrs., Vol. 39, p. 104, 1909.
tOp. cit. P. 128.
JRev. Stat., Colorado, p. 4213, 1908.
flLindley "American Law Relating to Mines and Mineral Lands." Vol. 8, p. 2016.
3d Ed.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 177
the mineral directly beneath the cemetery under penalty of a fine of
$5,000 or imprisonment of from one to five years.*
In Pennsylvania the Davis Mine Cave Act, approved July 26, 1913,
provides regulations governing the mining of coal and other minerals
and the "support underlying and beneath the surface of the several
streets, avenues, thoroughfares, courts, alleys, places, and public high-
ways within the limits of the several municipal corporations, and author-
izing the creation of a Bureau of Mine Inspection and Surface Support,"
by any municipal corporation within the anthracite coal fields. Mem-
bers of the Bureau of Mine Inspection and Surface Support have the
right and power to enter, examine, and survey any mine within the
limits of the municipality. Mining companies are required to furnish
accurate and complete maps of the workings and to keep the same up
to date.
The mining companies are required to "maintain, uphold, and pre-
serve the stability of the surface" of the various streets, etc. The officers
of mining companies are made responsible for the violation of the
provisions of the act and for violation are subject to a fine of $1,000
or imprisonment for ninety days, or both.f
An ordinance was enacted by the Borough of Plymouth, Luzerne
County, Pennsylvania, forbidding mining within 200 feet of the street
lines and as the borough is platted in 400-foot squares, this prohibited
any mining whatever. The county courts in Borough of Plymouth
v. Plymouth Coal Co. restrained the coal company from mining under
the streets.
REMEDIES.
In the event that the owner of the surface is entitled to surface
support and is sustaining damages by the mining operations beneath
or adjacent to his land he may recover damages or if the damage is
irreparable or immeasurable he may apply for an injunction to restrain
mining operations. If the mining operations are being conducted by
parties whose financial resources are not adequate to insure the pay-
ment of damages in case such are assessed, an injunction may be issued.
The right of support is not infringed by excavation, but by sub-
sidence and damages do not exist until subsidence has actually occurred.
(Catlin Coal Co., v. Henry Lloyd, 109 111. App. Eep. 122, 1902.)
The Pennsylvania court now holds, however, that the cause of action
'Arkansas Acts of 1907, Sec. 566 d-f.
tPa. Acts of General Assembly, 1918. No. 857.
178 ILLINOIS ENGINEERING EXPERIMENT STATION
accrues when the support is removed and is barred after the lapse of
six years from such removal. It is said by the Pennsylvania court that
the adoption of any more onerous rule "would encourage the purchase
of surface over coal mines for speculation in future law suits." (Noonan
v. Pardee, 200 Pa. 474, 86 Am. St. Eep. 722, 55 L. R. A. 410.)
"The owner of the subsidence estate is not liable to the surface
proprietor for a subsidence caused by excavations made by his pred-
ecessor in title, although damage does not occur until after such
owner came into possession. This results from the fact that, while
the subsidence gives the cause of action, the responsibility therefor
attaches to him whose acts and ommissions have brought about the
mischief."*
If the owner of real estate which has been injuriously affected or
damaged by a permanent structure has not brought an action to recover
damages and conveys the land to another, the cause of action does not
pass with the title nor inure to the benefit of the depreciation in value
in the price paid. (La Salle County Carbon Coal Co. v. Sanitary Dis-
trict of Chicago, 260 111. 423, 1913.)
Depreciation in the value of the surface caused by the mere appre-
hension of future damage gives no cause of action. f Only damage
which has actually occurred may be considered by a court, but each
fresh subsidence constitutes a basis for a new claim for damages.
(Catlin Coal Co. v. Henry Lloyd, 124 111. App. 394, 1906.)
"The right of support is not infringed unless the subsidence is
substantial. There must be some real sensible interference with the
land. The right of support in ordinary cases is infringed where the
subsidence is substantial, but the damage is inappreciable; and it is
now settled that an injunction may be obtained where the subsidence
is substantial, although the damage is inappreciable. The right of
support is analogous to a right of property, and is a right to have the
surface kept securely at its ancient and natural level.":]:
A mine owner cannot avoid liability by showing that his workings
have been proper and in the customary manner. "The act of removing
all support from the superimcumbent soil is, prima facie, the cause of
its subsequently subsiding." (Wilms v. Jess, 94 111. 464, 1880.)
Where land has been artificially burdened by a building and no
contract or prescription is available to regulate its right to support,
no right to support, lateral or vertical, exists for the building. In an
•Lindley P. 2021.
tMacSwinney P. 294.
JMacSwinney P. 297.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 179
action for removing support from land artificially burdened, the plain-
tiff has always been obliged, as a matter of pleading, to show that he is
entitled to have the weight supported.*
Where the injury to the surface would have resulted from min-
ing operations if no buildings existed upon the surface, the act creat-
ing the subsidence is wrongful and renders the owners of the mine
liable for all damages that result from mining to the buildings as
well as to the land itself. (Wilms v. Jess, 94 111. 464, 1880.)
As a general rule, the measure of damages in actions for injuries
to real property is the difference in market value before and after the
injury to the premises. But to this rule there are exceptions, and it
has been held that the cost of repair or of restoring the premises to
their original condition is the true and better rule to apply. The
valuation should be adopted which will be most beneficial to the injured
party, for he is entitled to the benefit of the premises intact. (Donk
Bros. Coal and Coke Co. v. Slata, 133 111. App. 280; 135 111. App. 633.)
A bill in equity to restrain the mining of coal was dismissed as
there is a remedy at law in case damage is done to surface by sub-
sidence. (Henry Lloyd v. Catlin Coal Co., 109 111. App. 37, 1902.)
What amount of coal may be safely mined and what amount must
be left for necessary support of the soil are largely engineering ques-
tions, and it is only in rare cases, where the remedy at law is so inade-
quate as to render such course necessary, that a court of equity will
direct the work by injunction. (Henry Lloyd v. Catlin Coal Co., 210
111. 460, 1904.)
As previously noted •(• considerable damage has resulted in England
from the pumping of brine. Under the Brine Pumping Act of 1891
(54 and 55 Viet. c. 40), upon application, compensation districts may
be formed within the pumping fields. For every compensation district,
under the act, there is established a compensation board. This board
is incorporated and consists of representatives of the various interests
concerned; one-third shall be persons not interested in the brine busi-
ness and appointed by the county council; one-third elected by the
brine pumpers; and one-third (not interested in brine pumping) ap-
pointed by the local sanitary authority. A compensation fund is main-
tained in each district; upon each pumper is levied a tax not exceeding
3 pence per 1,000 gallons pumped for a twelve-month period. Out of
this fund damages allowed by the compensation board are paid.
•MacSwinney P. 304.
tCh. I.
BIBLIOGRAPHY
EFFECTS OF SUBSIDENCE
AIR-BLASTS
ADAMSON, T. "Goaf-Blasts in Mines in the Giridih Coal-Field." Trans. Inst.
Min. Engrs., Vol. 29, p. 425, Bengal, India, 1904.
AIR-BLASTS. "Air-Blasts at the Green Hill Cleveland Mine." 16th Annual
Report, Idaho State Inspector of Mines, p. 14, 1914.
See miscellaneous articles listed by Crane, Min. Index, Vol. 1, p. 338.
ANON. "Air-Blasts at the Quincy Mine." Eng. and Min. Jour., Vol. 99, p. 914,
1915, and Min. and Sci. Press, Vol. 90, p. 690, 1915.
"So-Called Air-Blasts on the Witwatersrand." Min. and Eng. World,
Vol. 37, p. 236, 1912.
HOARD, H., and SIZER, F. L. "Air-Blasts or Earth Movements in the Coeur
d'Alenes." Mines and Minerals, Vol. 23, p. 87, 1912.
JOHNSON, TOM. "So-Called Air-Blasts and Roof Pressure." Jour. Chem.,
Met. and Min. Soc. of S. Africa, Oct., 1911, p. 37, Aug., 1912.
KOTZE, R. N. "Air-Blasts and Subsidences on the Rand." Eng. and Min. Jour.,
Vol. 94, p. 556, 1912, and S. Africa Min. Jour., p. 623, Jan. 22, 1912.
STEFAN, H. "Stress in the Country Rock as the Cause of Air-Blasts in the
Mines at Pribram, Bohemia." Sch. Mines Quart, Vol. 27, p. 423, 1905-1906 ;
also published under the title "Causes of Air-Blasts in the Mines at Prib-
ram, Bohemia." Min. and Sci. Press, Vol. 93, p. 789, 1906.
BUILDINGS AND MUNICIPAL IMPROVEMENTS
CONNER, ELI T. "Mine-Caves under the City of Scranton, Pa." Trans. Amer.
Inst. Min. Engrs., Vol. 42, p. 246, 1911.
GUSHING, G. H. "Near-Doomed Cities." Tech. World Mag., Vol. 19, p. 660,
July, 1913. Edit, comment in Coll. Eng., Vol. 34, p. 1, 1913.
EDIT. "Anthracite Mine Cave Problem." Coll. Eng., Vol. 34, p. 264, 1913-14.
"Scranton Mine Cave Inquiry." Mines and Minerals, Vol. 31, p. 620,
1910-11.
FOSTER, R. J. "Mine-Caves under the City of Scranton, Pa." Trans. Amer.
Inst. Min. Engrs., Vol. 42, p. 921, 1911.
HAY, W. "Damage to Surface Buildings Caused by Underground (Longwall)
Workings." Trans. Inst. Min. Engrs., Vol. 36, pp. 427, 432, 1908-09, and
Vol. 37, pp. 354, 647i, 1909-10.
MAGER, F. W. "Coal Mining Subsidences in Relation to Sewage Works." Trans.
Inst. Min. Engrs., Vol. 22, p. 616, 1901-02.
NOLDEN. "Influence of Mining upon Buildings and Street Railways, and Meas-
ures for Decreasing the Damages." Elekt. Kraftbetriebe und Bahnen, Oct.
4, 1913, and Oct. 24, 1913.
SPENCER, W. "The Support of Buildings." Trans. Inst. Min. Engrs., Vol. 5,
pp. 188, 197 ; Vol. 7, p. 382, 1892-93 ; Vol. 9, p. 102.
VON BRUNN, BERGRECHT. "Mittheilungen uber die Bodensenkungen bei Essen."
Zeit. f. 1874.
VON DECHEN, H. "Gutachten uber die Bodensenkungen in und bei der Stadt
Essen." Als. Manuscript gedruckt, 1869.
UNSIGNED. "Report on Surface Caving at Scranton." Eng. and Min. Jour.,
Vol. 91, pp. 609, 774, 1911.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 181
GENERAL
CREMER, L. "Erdbeben und Bergbau." Gliickauf, 1895.
DICKINSON, J. "Subsidence Due to Colliery Workings." Coll. Guardian, Oct.
28, and Nov. 11, 1898.
DILL. "Rock-Thrusts in Westphalian Collieries." Abs. Trans. Inst. Min. Engrs.,
Vol. 27, p. 720, 1903-04. Zeit. fur B.-, H.-, u. S.-W., Bd. 51, ss. 439-466.
DRON, R. W. "Effect of Coal Workings on the Surface." Jour. Brit. Soc.
Min. Stud., Vol. 11, p. 122, 1889.
DRASSDO. "Uber die in den Jahren 1856 und 1857 an einer langs des Quai de
Fraynee zu Liittech belegenen Reihe von Hausern vorgekommenen Beschad-
igungen." Zeit. fur B.-, H.-, u. S.-W., 1869.
"Uber die im Konigreiche Belgien giiltigen gesezlichen Bestimmungen
uber den Schutz der Stadte, Dorfer u. s. w. gegen die beschadigenden Ein-
wirkungen des Bergbaubetriebes." Gliickauf, 1869.
ELWITZ. "Uber die Durchbildung von Bauten zur Verhiitung von Bergschaden."
Gliickauf, Bd. 49, s. 278, 1913.
FAIRLEY. Colliery Managers' Pocket Book, p. 16, 1888.
FAYOL, M. "The Effect of Coal Mining on the Surface." (Translation of Bui-
man) Coll. Engr., Vol. 11, p. 25, 1890-91, or Vol. 33, p. 548, 1912-13.
FROM ME. "Earth Settlements in Mining Districts." Gluckauf, Oct. 8, 1910.
GRIFFITH, W. "No Likelihood of Municipal Fires Following Surface Caving."
Black Diamond, p. 22, Sept. 21, 1912.
HILL, H. A. "Subsidence Due to Coal-Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 155, 1898.
KOLBE, E. "Translocation der Deckgebirge durch Kohlenabbau." Essen, 1903.
LONGDEN, J. A. "Effect of Coal Workings on the Surface." Coll. Eng., Vol. 2,
p. 5, 1890-91. Note from Jour, of Brit. Soc. of Min. Students.
MAC.DONALD, D. F. "Some Engineering Problems of the Panama Canal in Their
Relation to Geology and Topography." U. S. Bureau of Mines, Bui. 86.
PARKER and CAMPBELL. Report on Surface Caving at Scranton. Eng. and
Min. Jour., Vol. 91, 1914.
PATERSON, MALCOLM. "Subsidence Due to Coal Workings." Proc. Inst. Civ.
Engrs., Vol. 135, p. 162, 1898.
PENNSYLVANIA STATE ANTHRACITE MINE CAVE COMMISSION. Report to the
Governor of Pennsylvania, Mar. 1, 1913. Journal Pa. Legis. 1913, Appen-
dix, Vol. 5, p. 5947.
SANER, J. A. "Effects of Subsidence Due to Brine-Pumping in the District of
Northwich." Proc. Inst. Civ. Engrs., Vol. 135, p. 124, 1898.
SOPWORTH, A. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 165, 1898.
WARD, T. "The Subsidences in and Around the Town of Northwich in
Cheshire." Trans. Inst. Min. Engrs., Vol. 19, p. 241, 1899-1900.
OVERLYING MINES AND BEDS
ELLIOTT, G. "Effect Produced upon Beds of Coal by Working Away the Over-
lying or Underlying Seams." Min. Mag., Vol. 9, p. 333, 1913.
RAILWAYS, TUNNELS, BRIDGES
BAKER, BENJAMIN. "Subsidence Due to Coal Workings." Proc. Inst. Civ.
Engrs., Vol. 135, p. 145, 1898.
COCKBURN, J. H. "Minerals under Railways and Statutory Works." (England.)
Trans. Inst. Min. Engrs., Vol. 39, p. 104, 1909-10. Notice of Intention to
Work, p. Ill; Support Required, p. 115; Claims, Compensation, pp. 115-116.
GOETZ, FR. "Studies in Street Railway Construction with Special Reference to
Subsidences in the Rhine-Westphalian Coal Mining Region." Darmstadt
Techn. Hochschule Thesis, 1911.
182 ILLINOIS ENGINEERING EXPERIMENT STATION
INGLES, J. E. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs., Vol.
135, p. 130, 1898.
KORTEN. "Influence of Pit- Workings upon Tramway Rails." (In Rhenish
Westphalia.) Abs. Trans. Inst. Min. Engrs., Vol. 38, p. 730, 1909-10.
Gliickauf, Vol. 45, pp. 865-874, 1909.
MACDONALD, J. A. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 128, 1898. Notes on Effect on Bridges in England.
READ, R. I. G. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 143, 1898.
SIMEON and Wussow. "Railway Damage in Consequence of the Subsidence of
the Ground Caused by Mining." Zeit. fur Kleinbahnen, p. 503, 1905.
STRETTON, C. E. "Subsidence of Coal Workings under a Railway." Coll.
Guard, Mar. 10, 1905.
UNSIGNED. "The Support of Railways." Coll. Guard, Vol. 107, p. 523, 1914. ^
THIRIART, L. "Les Affaisements de Sol Produits par 1'Exploitation Houillere."
Annal. des Mines de Belgique, Vol. 17, pp. 1-62, 1912.
WORTHINGTON, W. B. "Subsidence Due to Coal Workings." Proc. Inst. Civ.
Engrs., Vol. 35, p. 138, 1898.
WATER SUPPLY
HILL, H. A. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs., Vol.
135, p. 155, 1898.
KELLER, M. "Supporting the Underground Quarries Beneath the Montrouge
Reservoirs." Eng. and Min. Jour., Vol. 25, p. 204, 1898.
THORNTON, N. M. "Longwall Methods in the Eastwood District, Nottingham-
shire." Trans. Inst. Min. Engrs., Vol. 19, p. 129, 1899-1900.
SOPWORTH, A. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 165, 1898.
TRAINER. "Die mit dem Steinkohlenbergbau in ursachlichem Zusammenhang
stehenden Vorfluthstorungen im Emscher-Gebiete und die zur Beseitigung
getroffenen Masznahmen." Zeit. fur Bergrecht, Bd. 38, 1897, s. 190, ff.
EXPERIMENTS, TESTS AND DATA
DATA ON STRENGTH OF MATERIALS
ADAMS, F. D., and COKER, E. G. "An Investigation into the Elastic Constants
of Rocks, More Especially with Reference to Cubic Compressibility." Car-
negie Inst. of Wash., No. 46, 1906.
COAL TEST COMMITTEE, SCRANTON ENGINEERS' CLUB. "Compressive Strength of
Anthracite." U. S. Bureau of Mines, Appendix Bui. No. 2-5, 1912.
DANIELS, J., and MOORE, L. D. "The Ultimate Crushing Strength of Coal, An-
thracite and Bituminous." Eng. and Min. Jour., Vol. 84, p. 263, 1907.
KING, L. V. "On the Limiting Strength of Rocks under the Conditions of Stress
Existing in the Earth's Interior." Jour of Geol., Vol. 20, p. 119, 1912.
Louis, HENRY. "Crushing Strength of British Coal." Trans. Inst. Min. Engrs.,
Vol. 28, p. 319, 1904-05.
SCRANTON ENGINEERS' CLUB. "Compressive Strength of Anthracite." Mines
and Minerals, Vol. 23, p. 368, 1903. See also Coal Test Committee.
TALBOT, A. N. "Compressive Tests of Illinois Coal." 111. State Geol. Survey,
Bull. No. 4, p. 198, 1906.
EXPERIMENTS AND TESTS
i ADAMS, FRANK D. "An Experimental Investigation into the Action of Differ-
ential Pressure on Certain Minerals and Rocks, Employing the Process Sug-
gested by Professor Kick." Jour, of Geol., Vol. 18, p. 489.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 183
"An Experimental Contribution to the Question of the Depth of the
Zone of Flow in the Earth's Crust." Jour, of Gepl., Vol. 20, p. 97, 1912.
ADAMS, F. D., and COKER, £. G. "An Investigation into the Elastic Constants
of Rocks, More Especially with Reference to Cubic Compressibility." Car-
negie Inst. of Wash., No. 46, 1906.
BAKER, BENJAMIN. "Subsidence Due to Coal Workings." Proc. Inst. Civ.
Engrs., Vol. 135, p. 145, 1898.
BECKER, G. F. "Experiments on Schistosity and Slaty Cleavage." U. S. Geol.
Survey, Bui. No. 241, 1904.
DAUBREE, A. "fitudes Synthetiques de Geologic Experimental, 1879. (Cited
by Becker, G. S. A., Bui. No. 4, pp. 74-75.)
FAYOL, M. "The Effect of Coal Mining on the Surface." (Translation by Bui-
man.) Colliery Engineer, Vol. 11, p. 25, 1890-91, or Vol. 33, p. 548.
GRAVES, H. G. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 154, 189S.
HOBBS, W. H. "Mechanics of Formation of Arcuate Mountains." Jour, of
Geol., Vol. 22, pp. 71, 166, 193.
MEADE, T. M. "The Evolution of Earth Structure." Experimental Geology,
Book II, London, 1903.
MEEM, J. C. "Notes and Experiments in Earth Pressures." Proc. Engrs.' Club
of Phila., Apr. 1912.
PAULCKE, W. "{Jber tektonische Experimente." Int. Geol. Cong., Vol. 12, p.
835, 1913.
"Das Experiment in der Geologic." Berlin, 1912.
SCRANTON MINE CAVE COMMISSION. "Mine Support Tests in the Anthracite
Fields of Pennsylvania." Mines and Minerals, Vol. 31, p. 749, 1911.
UNSIGNED. "Testing the Bearing Capacity of Earth in Excavations." Eng. Rec-
ord, p. 584, May 25, 1912.
WILLIS, BAILEY. "Mechanics of Appalachian Structure." 13th An. Rep. U. S.
Geol. Sur., Part II, pp. 211-281, 1893.
FORMULAE AND CALCULATIONS
BROUGH, B. H. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 150, 1898.
"A Treatise on Mine Surveying." pp. 241-245.
BUNTING, DOUGLAS. "Mining under Heavy Wash." Colliery Engineer, Vol. 34,
p. 701, 1913-14. A. I. M. E. Bui. No. 97, p. 1, 1914 (data on strength of
rocks, pillar formulae, etc.).
FOSTER, H. T. "Roof-Weights in Mines." Trans. Inst. Min. Engrs., Vol. 34,
p. 405, 1907.
FRITZ, W. "Computation of Rock Pressure on Mine Chambers." Berg.-, und
Hiittenm. Rundschau, s. 1, Oct. 5, 1912.
GILLOTT, THOMAS. "Subsidence Due to Coal Workings." Proc. Inst. Civ.
Engrs., Vol. 135, p. 152, 1898.
GOLDREICH, A. H. "Die Theorie der Bodensenkungen in Kohlengebieten." Ber-
lin, 1913.
HUGHES, H. W. "A Text-Book of Coal Mining." 5th Ed., p. 186, London, 1904.
KOMMERRELL, O. "Statistics and Formulae for Stresses, Strains, and Loads
upon Tunnels and Tunnel Walls." Berlin, 1912.
LUPTON, ARNOLD. "Mining." London, 1907. Notes on shaft pillars and angle
of break, pp. 150-151.
"A Practical Treatise on Mine Surveying." p. 342, London, 1902.
LYNDE, F. "A Safe Working Rock Cover Limit; Method of Calculation." Eng.
and Min. Jour., Vol. 89, p. 1188, 1910.
NELSON, A. "Shaft Depth and Seam Inclination as Affecting Size of Shaft
Pillars." Sci. and Art of Mining, p. 547, June 22, 1912.
O'DoNAHUE, T. A. "Empirischer Regeln fur die Bestimmung der Richtung
der Bruchlinien." Revue Universelle des Mines, Bd. 18, s. 212, 1907.
184 ILLINOIS ENGINEERING EXPERIMENT STATION
PRELINI, C. "Tunneling." p. 74.
REDMAYNE, R. A. S. "Modern Practice in Mining." Vol. 3, pp. 7-10, and p. 170,
London, 1914.
UNSIGNED.
nungen
520, 1911.
SURVEYORS' RECORDS
.U11, J.J7J.1.
x "Zur Frage der Proportionality Zwischen Dehnungen und Span-
en bei Sandstein. Zeit. d.. Ver. d. Eng., p. 1169, 1900, Hiitte, Bd. I, s.
BROUGH, B. H. "A Treatise on Mine Surveying." pp. 241-245.
DIXON, J. L. "Experiments on the Amount of Sinking of Surface Due to
Coal Mining." Jour. Brit. Soc. of Min. Students, Vol. 12, No. 2.
DIXON, J. S. "Some Notes on Subsidence and Draw at Bent Colliery." Trans.
Min. Inst Scot., Vol. 7, p. 224, 1886.
ENZIAN, CHARLES. "The Warrior Run Mine Disaster." Mines and Minerals,
Vol. 27, p. 439, 1906-07.
KAY, S. R. "Subsidence Due to Coal Workings." Mines and Minerals, Vol.
19, p. 484, 1898-99. Coll. Guardian, Dec. 2, 1898, and Aug. 4, 1899.
KNOX, GEO. "Relation of Subsidence to Packing." Coll. Eng., Vol. 34, p. 87,
Sept., 1913. Trans. Inst. Min. Engrs., Vol. 45, p. 527, 1912-13.
LUPTON, ARNOLD. "A Practical Treatise on Mine Surveying." London, 1902.
(Leveling to ascertain subsidence of surface due to underground work-
ings, p. 342.)
MENZEL, C. "Subsidence at Zwickau." Proc. Inst. of Civ. Engrs., Vol. 140,
p. 331. (Cited in Hughes, p. 186.)
PATERSON, MALCOLM. "Subsidence Due to Coal Workings." Proc. Inst. Civ.
Engrs., Vol. 135, p. 162, 1898.
PIGGFORD, J. "Notes on Subsidences Caused by Coal Working at Teversal and
Pleasley Collieries." Trans. Inst. Min. Engrs., Vol. 38, p. 129, 1909-10, and
Vol. 39, p. 137.
SANER, J. A. "Effects of Subsidence Due to Brine-Pumping in the District of
Northwich." Proc. Inst. Civ. Engrs., Vol. 135, p. 124, 1898.
SNOW, CHAS. "Removal of a Shaft-Pillar at South Kirby Colliery." Trans.
Inst. Min. Engrs., Vol. 46, p. 8, 1913.
GENERAL WORKS AND REFERENCES
BARTONEC, FR. "The Cause of Surface Subsidence and Movement in the
Ostrau-Karwin Coal Basin, Austria." Montan. Rundschau, p. 145, Feb. 16,
1912, p. 211, Mar. 1, 1912, p. 247, Mar. 16, 1912.
\!BRADSHAW, H. "Suggestions on the Development of New Colliery Districts,
with Special Reference to the Support of the Surface." Trans. Inst. Min.
Engrs., Vol. 45, pp. 171, 371, 1912-13.
BRINSMADE, R. B. "Mining Without Timber." New York, 1911.
CAIN, WM. "Earth Pressures."
DIANCOURT. "Tiefkaltverfahren zum Schachtabteufen." Berg.- und Hiittenm.
Rundschau, s. 277 ff., 1912.
V/EATON, L. "Surface Effects of the Caving System." Min. and Sci. Press, Vol.
97, p. 428, 1908.
ELLIOTT, G. "Effect Produced upon Beds of Coal by Working Away the Over-
or Underlying Seams." Min. Mag., Vol. 9, p. 333, 1913.
FAYOL, M. "Effect of Coal Mining on the Surface." Coll. Eng., Vol. 33, p. 548,
1913. Bui. de la Societe de 1'Industries Minerale, IP serie, Vol. 14, p. 818,
1885.
GILLETTE, H. P. "Earthwork and Its Cost." Ch. 18, p. 184.
GOLDREICH, A. H. "Die Theorie der Bodensenkungen in Kohlengebieten." Ber-
lin, 1913. '
HALBAUM, H. W. G. "The Great Planes of Strain in the Absolute Roof of
Mines." Trans. Inst. Min. Engrs., Vol. 30, p. 175, 1908.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 185
HAUSSE, R. "Von dem Niedergehen des Gebirges beim Kohlenbergbaue und
den damit zusammengehangenden Boden-und Gebaudesenkungen." Zeit. f.
das. B.-, u S.-W., Bd. 55, ss. 324-446, 1907.
KNOX, GEORGE. "Mining Subsidence." Proc. Int. Geol. Congress, Vol. 12, p.
797, 1914.
NIESZ. "Gebirgsdruck und Grubenbetrieb under besonderer Beriicksichtigung
des Steinkohlenbergbaues." Zeit. f. d. Berg.-, Hutten.-, u. Salinenwesen, Bd.
43, s. 418, ff., 1910. Trans. Inst. Min. Engrs., Vol. 41, p. 588, 1910.
PENNSYLVANIA STATE ANTHRACITE MINE CAVE COMMISSION. Report to the Gov-
ernor of Pennsylvania, Mar. 1, 1913. Journal of Pa. Legis., Appendix, pp.
5947-6006, 1913.
PUSCHMANN. "Uber den nachtraglichen Abbau hangender Flosze beim ober-
schlesischen Steinkohlenbergbau." Zeit. f. d. Berg.-, Hutten.-, u. Salinen-
wesen, s. 387, ff., 1910.
RICHARDSON, ALEX. "Mine Subsidence." Jour. Chem. Met. and Min. Soc. of
S. A., Vol. 7, pp. 279, 325, 362, and Vol. 8, pp. 16, 46. Eng. and Min. Jour.,
Vol. 84, p. 196, 1907.
S
GEOLOGICAL CONSIDERATIONS
ASHBURNER, C. A. "The Geologic Relations of the Nanticoke Disaster." Trans.
Amer. Inst. Min. Engrs., Vol. 15, p. 629, 1886-87.
BANCROFT, GEORGE J. "Depth of Zone of Fissures." Trans. Amer. Inst. Min.
Engrs., Vol. 38, pp. 260-261, 1907.
BARRELL, Jos. "Strength of the Earth's Crust." Jour, of Geol., Vol. 22, pp. 28,
145, 209, 289, 537.
BARUS, C. "The Viscosity of Solids." U. S. Geol. Sur., Bui. No. 73, 1891.
"The Mechanism of Solid Viscosity." U. S. Geol. Sur., Bui. No. 94,
1892.
BECKER, G. F. "The Torsional Theory of Joints." Trans. Amer. Inst. Min.
Engrs., Vol. 24, p. 131, 1894.
"Experiments on Schistosity and Slaty Cleavage." U. S. Geol. Sur.,
Bui. No. 241, 1904.
"Finite Homogeneous Strain, Flow, and Rupture of Rocks." Geol. Soc.
of America, Bui. No. 4, p. 13, 1893.
BOOTH, W. H. "Clay Shrinkage." Mines and Minerals, Vol. 31, p. 615, 1910-11.
BREWER, W. M. "The Rock-Slide at Frank, Alberta Territory, Canada." Trans.
Inst. Min. Engrs., Vol. 26, pp. 34, 157, 1903-04.
BROCK, R. W., and MCCONNELL, R. G. "The Great Landslide at Frank, Alberta,
Can." Geol. Sur., An. Rept, Part 8, 1903.
CAPPS, S. R., JR. "Rock Glaciers in Alaska." Jour, of Geol., Vol. 18, p. 359.
CHAMBERLIN, T. C., and SALISBURY, R. D. "Discussion of Strength of Domes."
Geology, Vol. 1, p. 58, New York, 1906.
"Structural Features Arising from Disturbance." Geology, Vol. 1, pp.
500, 511, New York, 1906.
CHANCE, H. M. "Rock Pressure and Metamorphism." Min. and Sci. Press,
Vol. 97, p. 299, 1908.
COM STOCK, C. W. "The Great Tunnels of the World." Proc. Colo. Sci. Soc.,
Vol. 8, p. 363, 1907.
CRANE, G. W. "Iron Ores of Missouri." Mo. Bur. of Geol. and Mines, Vol. 10,
2d ser.
"Surface Subsidence or 'Sink Holes' Due to Natural Causes." Ibid., p. 34.
CREMER. "Erdbeben und Bergbau." Gliickauf, Jahrgang 31, nr. 22.
DALY, R. A., MILLER, W. G., and RICE, G. S. "Report of Commission Appointed
to Investigate Turtle Mountain, Frank, Alberta, 1911." Can. Dept. of
Mines, Geol. Sur. Branch, Memoir No. 27.
DAUBREE, A. "fitudes Synthetiques de Geologic Experimentale." Cited by
Becker, Geol. Soc. America, Bui. No. 4, pp. 74-75.
186 ILLINOIS ENGINEERING EXPERIMENT STATION
DOWLEN, W. E. "The Turtle Mountain Landslide." Eng. and Min. Jour., Vol.
76, p. 10, 1908.
ELLS, R. W. "Landslide at Notre-Dame de la Saltette, Lievre River, Quebec."
Can. Dept. of Mines, Geol. Sur. Branch, 1908.
FISHER, O. "Physics of the Earth's Crust." 2d ed., p. 216, London, 1889.
GILLETTE, H. P. "Earthwork and Its Cost." 3d ed., Ch. 18, p. 184, New York,
1912.
HAYFORD, JOHN F. "The Figure of the Earth and Isostasy from Measurements
in the United States." Coast and Geodetic Sur., pp. 65, 166, 169, Wash-
ington, 1909.
HEIM, ALBERT, "tjber Bergstiirze." Zurich, 1882. Cited U. S. Geol. Sur. Prof.
Paper 67, p. 41.
HOBBS, W. H. "Earthquakes." New York, 1907.
HOLLAND, T. H. "The Earth's Crust." Science, new ser. 40, p. 533. Geol. Sec.
of Brit. Ass. for Ad. of Science, Australia, 1914.
HOSKINS, L. M. "Flow and Fracture in Rocks as Related to Structure." U. S.
Geol. Sur. 16th An. Rep., Part 1, p. 845, 1895.
HOVEY, E. O. "Notes on Landslides." Proc. Int. Geol. Congress, Vol. 12, p. 793,
1913.
HOWE, ERNEST. "Landslides and the Sinking of Ground Above Mines." Proc.
Int. Geol. Congress, Vol. 12, p. 775, 1913.
"Landslides in the San Juan Mountains, Colorado, Including a Consid-
eration of Their Causes and Their Classification." U. S. Geol. Sur. Prof.
Paper 67, p. 567, 1909.
KING, L. V. "On the Limiting Strength of Rocks under the Conditions of Stress
Existing in the Earth's Interior." Jour, of Geol., Vol. 20, p. 119, 1912.
KREY, H. "Rock Pressures, Rock Resistances, and Load Capacity of Earth and
Bedrocks at Greater Depths." Berlin, 1912.
LEE, WALLACE. "Geology of the Rolla Quadrangle." Mo. Bur. of Geol. and
Mines Bui., Vol. 12, 2d ser., Ch. 8.
LEITH, C. K. "Rock Cleavage." U. S. Geol. Sur., Bui. No. 239, 1905.
"Structural Geology." Henry Holt, New York, 1913.
LINDGREN, WALDEMAR. "Mineral Deposits." Ch. 9, pp. 109-130; Ch. 10, pp.
131-139, and Ch. 11, pp. 140-165. New York, 1913.
LOVE, A. E. H. "Some Problems of Geodynamics." Cambridge, 1911.
MACDONALD, D. F. "Excavation Deformations." Proc. Int. Geol. Congress,
Vol. 12, pp. 779, 783, 1913.
"The Landslides of Culebra Cut." Ann. Rep. of Isthmian Canal Com-
mission, pp. 205-214, 1912, and pp. 580-581, 1913.
McNAiR, F. W. "Rock Pressure." Min. and Sci. Press, Vol. 94, p. 275, 1907.
MILNE and GRAY. "Modulus of Rigidity of Granite." Quart. Jour. Geol. Soc.,
Vol. 39, p. 140, 1883.
PAULCKE, W. "tJber tekonishe experimente." Proc. Int. Geol. Congress,
Vol. 12, p. 835, 1913.
"Das Experiment in der Geologic." Berlin, 1912.
PENCK, A. "Morphologic der Erdoberflache." Stuttgart, 1894. Cited in U. S.
Geol. Sur. Prof. Paper 67, p. 43.
RANSOME, F. L. "Economic Geology of the Silverton Quadrangle, Colorado."
U. S. Geol. Sur., Bui. No. 182, p. 66, 1901.
REBHANN, G. "Theorie des Erddruckes und der Futtermauern." Wien, 1871.
RICE, G. S. "Notes -on Landslides and Slides from Mining Excavations." Jour.
West. Soc. Engrs., Vol. 18, p. 626, 1913.
"A Suggested Method of Preventing Rock Slides" (Culebra Cut).
Jour. West. Soc. of Engrs., Vol. 18, p. 585, Sept., 1913.
RICHARD, T. A. "Flowage of Rocks." Trans. Inst. Min. and Met., Vol. 21.
p. 527, 1912.
SHELDON, PEARL. "Some Observations and Experiments on Joint Planes." Jour.
of Geology, Vol. 20, pp. 53, 164, 1912.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 187
SOPWORTH, A. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 165, 1898.
SPENCER, A. C. "Origin of Vein-Filled Openings in Southwestern Alaska."
Trans. Amer. Inst. Min. Engrs., Vol. 36, pp. 581-586, 1906.
1 STEFAN, H. "Stresses in the Country Rock as the Cause of Air-Blasts in the
Mines at Pribram, Bohemia." Sch. Mines Quart., Vol. 27, p. 423, 1905-06.
(Translated from Oestr. Zeit., p. 256, 1906, also in Min. and Sci. Press,
p. 789, 1906.)
STEVENS, BLAMEY. "The Laws of Fissures." Trans. Amer. Inst. Min. Engrs.,
Vol. 40, p. 475, 1909.
STRAHAN. "Explosive Slickensides." Geol. Mag., Nov., 1887.
UNSIGNED. "Earth Tremors on the Rand." Eng. and Min. Jour. p. 833, 1915.
"Effect of Pressures of Overlying Strata on Coal Seam in South Stafford-
shire Coal Fields." Trans. Amer. Inst. Min. Engrs., Vol. 8, p. 410, 1894-95.
"Movement of Large Masses of Earth, Miles in Extent." Min. and Sci.
Press, Vol. 60. p. 347.
"Pressure of Superincumbent Strata in the Transvaal Mines." Min. and
Sci. Press, Vol. 101, p. 333, 1910.
"Side of Mountain Sliding Due to Mining Operation at the Comstock
Lode." Min. and Sci. Press, Vol. 53, p. 214.
"Subterranean Pressures." Engineering, London, Vol. 73, pp. 25, 225,
311, 419.
VAN HISE, C. R. "Earth Movements." Wis. Academy of Sciences, Vol. 11,
p. 465, 1896.
"A Treatise on Metamorphism." U. S. Geol. Sur., Monograph 47, 1904.
VAN HISE, C. R., and LEITH, C. K. "Pre-Cambrian Geology of North America."
U. S. Geol. Sur., Bui. No. 360, 1909.
VON WILLMANN, E. "Some Rock Pressure Phenomena in Their Bearing on Tun-
neling." Darmstadt Techn. Hochschule, Dissert., 1911.
WILLIS, BAILEY. "Mechanics of Appalachian Structure." 13 Ann. Rep. U. S.
Geol. Sur., Part 2, pp. 211-281, 1893.
WOOD, H. E. "Earth Tremors on the Rand." Min. and Sci. Press, Vol. 109,
p. 149, July 25, 1914.
WOODWARD, H. E. "The Geology of Soils and Substrata." London, 1912. Note
on subsidence due to solution of salt by salt wells. Cheshire, England, p. 67.
WOODWARD, R. S. "Mathematical Theories of the Earth." Proc. Am. Assn. for
Adv. Sci., p. 49, 1889.
ZINN, A. S. "The Truth About the Culebra Cut Slides." (Criticism of Rice's
plan.) Eng. News, Vol. 70, p. 406, 1913.
MINING CONDITIONS *
BRADSHAW. "Suggestion on the Development of New Colliery Districts, with
Special Reference to the Support of the Surface." Trans. Inst. Min. Engrs.,
Vol. 45, pp. 171-371, 1912-13.
BRINSMADE, R. B. "Mining Without Timber." New York, 1911.
BROWN, E. F. "The Caving System of Mining." Min. and Sci. Press, Dec. 9,
1899.
HESSE, A. W. "Maximum Coal Recovery." Coll. Eng., Vol. 35, p. 13, 1914.
Also, Coal Age, Vol. 5, p. 1051, 1914, and W. Va. Min. Inst., June 3, 1914.
MORIN. "Some Effects of Rock Pressure in Coal Mining." Soc. de rind. Minrl.
St. Etienne Bui., pp. 241-279, Sept., 1912, and p. 604, Oct., 1911.
RICE, C. T. "Dome of Equilibrium and the Caving System of Mining." Min.
and Sci. Press, Vol. 95, p. 85, 1907.
STEWART, W. "Laying Out Pit-Bottoms." Proc. South Wales Inst. Engrs.,
Vol. 20, p. 128, 1896.
UNSIGNED. "How Deep Can We Mine?" Min. and Sci. Press, Vol. 25, p. 396.
"Limits of Deep Mining." Proc. Chem. Met. and Min. Soc. S. A.,
Vol. 10, p. 414.
"Limits and Possibilities of Deep Mining." Eng. Mag., Vol. 25, p. 546.
188 ILLINOIS ENGINEERING EXPERIMENT STATION
"Location of Roof Pressure." Mines and Minerals, Vol. 19, p. 319,
1898-99.
"Mining in Transvaal 12,000 Feet Deep." Eng. and Min. Jour., Vol. 71,
p. 615, 1901.
WILLIAMS, G. F. "Mud Rushes in De Beers Mines in 'Diamond Mines of South
Africa/ " pp. 400-404, London, 1902.
WILLING, H. "Falls, Creep, and Underground Pressure Breaks, Dortmund I
District, and Precautionary Measures." Techn. Blatter, July 13, 1912, and
June 20, 1912.
CLEAT
ANDRE, G. G. "On Cleavage Planes, and Their Influence on the Economical
Working of Coal." N. Staff. Inst., Vol. 2, p. 132.
UNSIGNED. "Influence of Cleat in Longwall Mining." Eng. and Min. Jour.,
Vol. 85, p. 213, 1908.
"Cleats and Bedding Planes in Coal Seams." Mines and Minerals, Vol.
21, p. 122, 1900.
LONGWALL
BEARD, J. T. "The Action, Influence, and Control of Roof in Longwall Work-
ings." Trans. Inst. Min. Engrs., Vol. 28, p. 341, and Vol. 30, p. 550, 1904-05.
HALBAUM, H. W. G. "The Action, Influence, and Control of the Roof in Long-
wall Workings." Trans. Inst. Min. Engrs., Vol. 27, p. 205, 1903-04, and Vol.
28, p. 316, 1904.
HAY, W. "Damage to the Surface Buildings Caused by Underground Work-
ings." Trans. Inst. Min. Engrs., Vol. 36, p. 427, 1908-09.
JOHNSON, JASPER. "The Wilmington, Illinois, Coal Field." Trans. Amer. Inst.
Min. Engrs., Vol. 3, p. 188, 1874-75.
PELTIER, W. F. "Longwall Mines in Illinois." Eng. and Min. Jour., Vol. 89,
p. 380, 1910.
RICE, G. S. "System of Longwall Used in Northern Illinois Coal Mines."
Columbia School of Mines Quart., Vol. 16, p 344, 1894-95.
ROBERTON, E. W. "Action, Influence, and Control of the Roof in Longwall
Working." Trans. Inst. Min. Engrs., Vol. 28, p. 341, 1904-05.
THORNTON, N. M. "Longwall Methods in the Eastwood District, Nottingham-
shire." Trans. Inst. Min. Engrs., Vol. 19, p. 129, 1899-1900.
UNSIGNED. "Control of Roof Pressure in Longwall Mining." Mines and Min-
erals, Vol. 19, p. 350, 1898-99.
"Location of Roof Pressure in Longwall Working." Mines and Min-
erals, Vol. 19, p. 319, 1898-99.
"Roof Action in Longwall Workings." Coal Age, Vol. 1, p. 779, 1912.
ORE MINES
^ BROWN, E. F. "The Caving System of Mining." Min. and Sci. Press, Dec. 8,
1899.
EATON, L. "Surface Effects of the Caving System." Min. and Sci. Press, Vol.
97, p. 428, 1908.
"Settlement of the Surface in Mining Ore Bodies at Butte, Montana."
Min. and Eng. World, Vol. 39, pp. 147-240, 1913.
ENZIAN, C. "Studies of Subsidence in New Mexico." Science N. S., Vol. 40,
p. 518, Oct. 9, 1914.
^ UNSIGNED. "Cave-in at Miami Mine, Apr. 17, 1913." Eng. and Min. Jour., Vol.
95, p. 872, 1913.
"Mine Subsidences on the Rand." (From official report.) S. Afr. Min.
Jour., p. 143, Oct. 5, 1912.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 189
PILLAR AND ROOM
v GRIFFITH, W., and CONNER, E. T. "Mining Conditions under the City of Scran-
ton, Pa." U. S. Bur. of Mines, Bui. No. 25, 1912.
HESSE, A. W. "Maximum Coal Recovery." Coll. Eng., Vol. 35 p 13 1914
Coal Age, Vol. 5, p. 1051, 1914.
REPPERT, A. E. "Pillar Falls and the Economical Recovery of Coal from Pil-
lars." Proc. West Va. Coal Min. Inst, p. 110, 1911.
EDIT. "The Anthracite Cave Problem." Coll. Eng., Vol. 34, p. 264, 1913.
PILLARS
ACHENBACH. "Sichcrheitspfciler in England." Zeit. fur Bergrecht, s. 70 ff., 1870.
ANDRE, G. G. "A Practical Treatise on Coal Mining." Vol. 1, p. 278, London,
1876.
BUNTING, DOUGLAS. "Chamber-Pillars in Deep Anthracite Mines." Trans.
Amer. Inst. Min. Engrs., Vol. 42, p. 236, 1912.
CUNNINGHAM, F. W. "The Best Methods of Removing Coal Pillars." Proc.
Coal Min. Inst. of America, p. 275, 1910. Mines and Minerals, Vol. 31,
p. 495, 1910-11.
DADDOW, S. H. "Strength of Pillars." Trans. Amer. Inst. Min. Engrs., Vol. 1,
p. 172, 1871.
Vol. 94, p. 275, 1907. Proc. Amer. Ass. Adv. Sci., 1906.
PAMELY, CALEB. "The Colliery Managers' Handbook." London, 1891. (Size
of shaft pillar, p. 158.)
-PICKERING, W. H., and PICKERING, B. H. "Why Leave Shaft Pillars?" Trans.
Inst. Min. Engrs., Vol. 43, pp. 428, 451, 1912.
ROBERTON, E. H. "Shaft Pillars." Practical Coal Mining, Vol. 2, p. 299, Lon-
don, 1908.
ROWLEY, W. W. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 139, 1898.
SCHULZ, A. Untersuchungen uber die Dimensionen der Sicherheitspfeiler fur
den Saarbriicke Steinkohlenbergbau und iiber den Bruchwinkel, unter
welchem die Gebirgschichten in die abgebauten Raume niedergehen. Zeit.
fur B.-, H.-, u. S.-W., 1867.
STEWART, W. "Laying Out Pit-Bottoms." Proc. Wales Inst. Engrs., Vol. 20,
p. 128, 1896-98.
UNSIGNED. "Failure of Pillars." Proc. Chem. Met. and Min. Soc. S. A., Vol.
8, p. 49, and Vol. 10, p. 279.
"Method of Determining the Size of Shaft Pillars in the Primal Devel-
opment of a Coal Field." Mines and Minerals, Vol. 18, p. 117, 1897-98.
"Size of Pillars." (Tabulated.) Mines and Minerals, Vol. 17, p. 189,
1896-97, and Vol. 29, p. 375. Eng. and Min. Jour., Vol. 90, p. 871, 1910.
"Width of Rooms and Pillars." Mines and Minerals, Vol. 26, pp. 25, 107.
QUICKSAND
ASHBURNER, C. A. "The Geologic Relations of the Nanticoke Disaster." Trans.
Amer. Inst. Min. Engrs., Vol. 15, p. 629, 1886-87.
BUNTING. DOUGLAS. "The Limits of Mining under Heavy Wash." Amer. Inst.
Min. Engrs., Bui. No. 97, p. 1, 1915. Coll. Engrs., Vol. 34, p. 701, 1915.
WILLIAMS, G. M. "Dangerous Outcrops, Nanticoke Disaster, Dec. 18, 1885."
Mines and Minerals, Vol. 20, p. 410, 1899-1900.
UNSIGNED. "Accident Causing Loss of Seven Lives. Run of Sand and Water
on First Level of Balkan Mine, near Alpha, Crystal Falls Region." Eng.
and Min. Jour., Vol. 98, p. 184, 1914.
190 ILLINOIS ENGINEERING EXPERIMENT STATION
ROOF
(See also "Longwall")
S. T. A. "Seismic Unrest and Falls of Roof." Coal Age, Vol. 1, p. 751, Mar. 16,
i 1912.
FOSTER, H. T. "Roof-Weights in Mines." Trans. Inst. Min. Engrs., Vol. 34,
p. 405, 1907.
HALBAUM, H. W. G. "Great Planes of Strain in the Absolute Roof of Mines."
Trans. Inst. Min. Engrs., Vol. 30, p. 175, 1905.
HALL, R. D. "Action of the Roof." Proc. Coal Min. Inst. of America, p. 63,
1911.
"The Strength of Mine Roofs." Mines and Minerals, Vol. 30, p. 474,
1909-10.
HEPPLEWHITE, W. H. "The Action and Control of Differently Constituted Coal-
bed Roofs." Trans. Inst. Min. Engrs., Vol. 42, p. 356, 1911-12. Iron and
Coal Trades Review, p. 970, Dec. 15, 1911, and p. 372, Mar. 8, 1912. Coll.
Guard., p. 1247, Dec. 22, 1911, and p. 481, Mar. 8, 1912. Coal Age, p. 779,
Mar. 23, 1912.
UNSIGNED. "Control of Roof Pressure." Mines and Minerals, Vol. 19, p. 350,
1898-99. "Rock Falls at Night." Min. and Sci. Press, Vol. 43, p. 172, 1906.
SQUEEZES
BROWN, G. M. "A Sudden Squeeze in an Oklahoma Mine, Adamson, Okla."
Coal Age, Vol. 6, p. 532, 1914.
-HALL, R. D. "Squeezes in Mines and Their Causes." Mines and Minerals,
Vol. 30, p. 286, 1909.
- JONES, ED. "The Control of Creeps." Mines and Minerals, Vol. 18, p. Ill,
1897-98.
• UNSIGNED. "Treatment of Squeezes and Creeps." Mines and Minerals, Vol. 29,
p. 460, 1908-09.
SUBAQUEOUS MINING
ATKINSON, A. A. "Working Coal under the River Hunter, the Pacific Ocean
and Its Tidal Waters, near Newcastle in the State of New South Wales."
Trans. Inst. Min. Engrs., Vol. 23, p. 622, 1901-02; Vol. 26, p. 254, and
Vol. 28, p. 130.
BROWN, R. H. "Submarine Coal Mining." J. M. Soc. N. S., Vol. 9, p. 43.
BUKER, H. W. "Mining Iron under the Sea at Bell Island, Newfoundland."
Mines and Minerals, Vol. 31, p. 569, 1911.
CADELL, H. M. "Submarine Coal Mining at Bridgeness, N. B., England." Trans.
Fed. Inst. Min. Engrs., Vol. 14, p. 237, 1897-98.
CANTLEY, THOS. "Wabana Iron Mines of the Nova Scotia Steel and Coal Com-
pany, Limited." Jour. Can. Min. Inst., Vol. 14, p. 274, 1911.
DICK, W. J. "Conservation of Coal in Canada." Pub. by Commission of Con-
servation, Ottawa, Can., 1914. (Submarine coal mining, p. 34.)
GRAY, F. W. "Coal Fields and the Coal Industry of Eastern Canada." Trans.
Inst. Min. Engrs., Vol. 46, p. 43, 1913.
NOVA SCOTIA. "Report of Inspector of Mines on the Flooding of Port Hood
Mine and of Mabou Mine." Halifax, 1913.
"Submarine Coal Mining." Coal Mines Act, Sec. 54, 1912.
"Twenty Men Drowned in Mine Near Nanaimo, B. C." Coal Age,
Vol. 7, p. 374, 1915.
ROBERTON, E. H. "Coal Mines under the Sea, Cape Breton Island." Coll.
Eng., Vol. 34, p. 17, 1913-14.
"Under-Sea Working." Boulton's Practical Mining, Vol. 2, p. 333.
SELWYN-BROWN, A. "Submarine Coal Mining." Eng. and Min. Jour., Vol. 80,
p. 913, 1905.
YOUtfG-STOEK — SUBSIDENCE RESULTING FROM MINING 191
UNSIGNED. "Coal Mining under Sydney Harbor, N. S. W" Mines and Min-
erals, Vol. 21, p. 557, 1901.
"Drowning of Higashimisome Colliery." Coll. Eng., Vol. 36, p. 19.
"Submarine Coal Mining, New South Wales." Mines and Minerals,
Vol. 26, p. 471, 1906.
J "Summary of Recommendations Made by the Royal Commission Ap-
pointed to Report on the Condition of the Collieries Adjacent to Ferndale."
Sydney, N. S. W., p. 67, 1886. Abs. Trans. Inst. Min. Engrs., Vol. 23, p. 636,
1901-02.
PHENOMENA OF SUBSIDENCE
• ROBERTON, E. H. "The Action, Influence and Control of the Roof in Longwall
Workings." Trans. Inst. Min. Engrs., Vol. 29, p. 5, 1904-05.
AIR-BLASTS
/
MEACHEM, F. G. "Notes on an Earth Explosion or 'Bump' at Hamstead Col-
liery." Trans. Inst. Min. Engrs., Vol. 5, p. 381, 1892-93.
ANGLE OF BREAK AND OF PULL
•
•/FAYOL, M. "The Effect of Coal Mining on the Surface." Coll. Eng., Vol. 33,
p. 548, 1912-13.
LINDGREN, W. "Mineral Deposits." pp. 137-138, 151, New York, 1914.
LUPTON, ARNOLD. "Mining." pp. 150-151, London, 1907.
SPENCER, A. C. "Origin of Vein-Filled Openings in Southeastern Alaska."
Trans. Amer. Inst. Min. Engrs., Vol. 36, pp. 581-586, 1906.
' STEVENS, BLAMELY. "The Laws of Fissures." Trans. Amer. Inst. Min. Engrs.,
Vol. 40, p. 475, 1909.
WAIN, ED. B. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 169, 1898. Trans. Fed. Inst. Min. Engrs., Vol. 4, p. 33, 1892-93.
BREAKS
BANCROFT, GEORGE J. "Depth of Zone of Fissures." Trans. Amer. Inst. Min.
Engrs., Vol. 37, p. 260, 1907.
^DAHLBLOM, T. "The Angle of Shear." Proc. Int. Geol. Cong., Vol. 12, p. 773,
1913.
DAUBREE, A. "Geologic Experimentale." p. 300, Paris, 1879.
COMPRESSION
HALL, R. DAWSON. "Squeezes in Mines and Their Causes." Mines and Min-
erals, Vol. 30, p. 286, 1909.
LINDGREN, W. "Mineral Deposits." p. 137.
DRAW OR PULL
'COOPER, R. E. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 132, 1898.
DURATION OF SUBSIDENCE
HILL, H. A. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 155, 1898.
RATE OF SUBSIDENCE
DIXON, J. S. "Some Notes on Subsidence and Draw." Trans. Min. Inst., Scot-
land, Vol. 7, p. 224, 1885.
192 ILLINOIS ENGINEERING EXPERIMENT STATION
GOLDREICH, A. H. "Die Theorie der Bodensenkungen in Kohlengebieten." Ber-
lin, 1913.
WRIGHT, T. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 126, 1898.
SHEAR
DAHLBLOM, T. "The Angle of Shear." Proc. Int. Geol. Congress, Vol. 12,
p. 773, 1913.
4 HALL, R. D. "Effect of Shear on Roof-Action." Proc. Coal Min. Inst. of
America, p. 135. 1912.
SLIDES
-BAUMGARTEN, KARL. "Thunder Mountain Landslide." Min. and Sci. Press,
Vol. 101, p. 698, 1910.
* CANADA, DEPARTMENT OF INTERIOR. "Report on the Great Landslide at Frank,
Alberta, 1903." Extract from Part 8, Annual Report, 1903.
^ CANADA, DEPARTMENT OF MINES, GEOL. SUR. BRANCH. "Report of the Commis-
sion Appointed to Investigate Turtle Mountain, Frank, Alberta, 1911." p. 34.
.' CLARKE, D. D. "A Phenomenal Landslide." Trans. Amer. Soc. Civ. Engrs.,
Vol. 53, pp. 322-412, 1904.
-.CORNISH, VAUGHAN. "The Panama Canal and the Philosophy of Landslides."
Edinburgh Review, Vol. 271, p. 21, 1913.
ELLS, R. W. "Report on the Landslide at Notre Dame de la Saltette, Lievre
River, Quebec." Canada Dept. of Mines, Geol. Sur. Branch, Publications,
No. 1030, 1908.
FORD, F. L. "The Settlement of Lorraine Street, Hartford, Conn." Eng. Rec-
ord, Vol. 45, p. 172, 1902.
GAILLARD, D. D. "Culebra Cut and the 'Problem of the Slides." Sci. American,
Vol. 107, p. 388, 1912.
j HOWE, ERNEST. "Landslides in the San Juan Mountains, Colorado, Including
a Consideration of Their Causes and Their Classification." U. S. Geol.
Sur., Prof. Paper N9. 67, 1909.
1 MACDONALD, D. F. "Slides in the Culebra Cut at Panama." Eng. Record,
Vol. 46, p. 228, 1912.
UNSIGNED. "Landslides of Culebra Cut." Ann. Rep. Isthmian Canal Com-
mission, pp. 205-214, 1912.
-"Sliding Ground in Culebra Cut." Eng. News, Vol. 70, p. 408, 1913.
MERRICK, A. W. "Clay Slide at Boone Viaduct, Boone, Iowa." Jour. W. Soc.
Engrs., Vol. 11, p. 332, 1906.
MITCHELL, G. E. "Landslides and Rock Avalanches." Nat. Geog. Mag., Vol.
21, p. 277, 1910.
MOLITOR, DAVID. "Landslides." Jour. Assn. Eng. Soc., Vol. 13, p. 12, 1894.
RICE, G. S. "Method of Preventing Rock Slides." Jour. West. Soc. Engrs.,
Vol. 18, p. 585, 1913.
4 ROWHER, H. "Discussion on Earth Slides." Amer. Ry. Eng. and Maint of
Way Assn., Bui. No. 90, p. 4, 1907.
"Earth Slides," Eng. Record, Vol. 56, p. 374, 1907.
'RussEL, I. C. "Landslides." U. S. Geol. Sur., Ann. Report, Part 2, pp. 193-
204, 1898-99.
VAN HORN, F. R. "Landslide Accompanied by Buckling." Geol. Soc. Amer.,
Bui. No. 20, p. 625, 1910.
ZINN, A. S. "The Truth About the Culebra Cut Slides." Eng. News, Vol. 70,
p. 406, 1913.
UDERGROUND EFFECTS
HALL, R. D. "Squeezes in Mines and Their Causes." Mines and Minerals,
Vol. 30, p. 286, 1909.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 193
WILLING, H. "Falls, Creep, and Underground Pressure Breaks in the Newfloz
Coal Seam, Dartmund I District, and Precautionary Measures." Tech
Blatter, p. 217, July 13, 1912.
PREVENTION OF SUBSIDENCE
FILLING WITH MINE ROCK
BACON, D. A. "The System of Filling at the Mines of the Minnesota Iron Co.,
Soudan, Minnesota." Trans. Amer. Inst. Min. Engrs., Vol. 21, p. 299, 1892.
FRIESER, ANTON. "Packing of Coal Seams in Bohemia." Trans. Inst. Min.
Engrs., Vol. 10, p. 597. Oest. Zeit. fur B.-, u. H.-W., Bd. 43, s. 253, 1895.
GALL, W. C. "Convej'or Belts for Distributing Filling." Eng. and Min. Jour.,
Vol. 97, p. 759, 1914. Abs. from Proc. Aust. Inst. Min. Engrs.
GRIFFITH, WM. "Method of Supporting Mine Roofs by Blasting Down Roof
and Blasting Floor Up." U. S. Pat. No. 1,004,419. Mines and Minerals,
Vol. 32, pp. 279, 402, 1911. Coal Age, Vol. 1, p. 481, Jan. 20, 1912.
HALL, A. E. "Building Drywalls in the Sudbury District, Ontario." Eng. and
Min. Jour., Vol. 97, p. 949, May 9, 1914.
HALL, E. K. "Stope Filling, and Caving for Mullock." Min. and Eng. Rev.,
p. 325, May, 1912.
HALL, R. D. "Permanent Roof Sustention." Coal Age, Vol. 1, p. 48, Jan. 20,
1912. Discusses Griffith's patent.
UNSIGNED. "Stope Filling on Rand." Min. Mag., Vol. 10, p. 376.
GENERAL
ANDREE, TH. "Protection of the Surface from Subsidence." Oest. Zeit. fur B.-,
u. H.-W., Bd. 47, s. 525, 1899. Abs. Trans. Inst. Min. Engrs., Vol. 23, p. 728,
1901-02.
DALY, R. A.. MILLER, W. G., and RICE, G. S. "Report of Commission Appointed
to Investigate Turtle Mountain, Frank, Alberta, 1911." Can. Dept. Mines,
Geol. Sur. Branch, Memoir No. 27, p. 30.
HASSE. "Fire in the Shaft Safety Pillars of the Oberhausen Colliery and Its
Control by Packing." Kohle und Erz, p. 79, Jan. 22, 1912.
HESSE, A. W. "What Shall We Use for Roof Support in Coal Mines?" Coal
Age, Vol. 5, p. 344, Feb. 28, 1914.
JONES, ED. "The Control of Creeps." Mines and Minerals, Vol. 18, p. Ill,
1897-98.
LYNDE, F. "A Safe Working Rock Cover Limit." Eng. and Min. Jour., Vol.
89, p. 1188, 1910.
OBERHAUSEN, J. "Compression of Stope Fillings." Columbia Sch. Mines
Quart., Vol. 26, p. 271, 1904-05. (Translated from Gliickauf, p. 1146, Nov.
22, 1902.)
READ, T. T. "Sandfilling Difficulties in Lake Superior Copper Mining." Min.
and Sci. Press, Vol. 60, p. 215, 1915.
RICE, G. S. "A Suggested Method of Preventing Rock Slides." (Culebra Cut.)
Jour. W. Soc. of Engrs., Vol. 18, p. 585, 1913.
ROBERTS, JOHN. "New Method of Making Large Arches in Mines." S. Wales
Inst. of Engrs. Ir. and Coal Tr. Review, p. 127, Jan. 23, 1914. Coll. Guard.,
p. 243, Jan. 30, 1914.
ROSSENBECK. "Tests Made with a New Kind of Mine Filling." Gluckauf, Bd.
46, s. 565, 1910.
UNSIGNED. '''Note on Use of Stamp-Sands for Filling (Using Compressed Air
for Distribution) by Copper Range Mines." Min. and Sci. Press, Vol. 109,
p. 763, 1914.
See also "Filling Systems in Metal Mines." Crane's Index of Mining
Engineering Literature, Vol. 2, p, 379.
ZINN, A. S. "The Truth About the Culebra Cut Slides/' (Criticism of Rice's
plan.) Eng. News, Vol. 70, p. 406, Aug. 28, 1913.
194 ILLINOIS ENGINEERING EXPERIMENT STATION
HYDRAULIC FILLING
ACKERMANN. "Wirkungen des Abbaues mit Spiilversatz auf das Deckgebirge im
Felde der Konigen Luise-Grube." Gliickauf, No. 34, 1910.
ANNETT, H. C. "Hydraulic Stowing of Gob at Shamrock I and II Colliery,
Herne, Westphalia, Germany." Trans. Inst. Min. Engrs., Vol. 37, p. 257,
1908-09.
ARBENZ, H. "Die Einfuhrung des Sandspiilversatzes auf dem staatlichen Stein-
kohlbergwerk Konigen Louise bei Zabosa, O. S." Gliickauf, Bd. 42, ss.
606-632, 1906.
BAIJOT and DEMURE. "Notes on Hydraulic Filling Collected in a Few Mines
of the Rhenish-Westphalian Region in the North and in Pas-de-Calais."
Rev. Univ. Mines, Vol. 26, p. 225, and Vol. 30, June, 1909.
BERGMANN, W. "Method of Filling with Sand in a Bituminous Limestone Mine
Near Hanover, Germany." Gliickauf, Nov. 5, 1904.
BROWN, E. O. F. "Packing Excavations in Coal Seams by Means of Water."
Trans. Inst. Min. Engrs., Vol. 28, p. 325, 1904-05.
BUCHERER, L. "Hydraulic Filling in European Mines." Mines and Minerals,
Vol. 32, p. 715, 1912. Trans. Mex. Inst. M. and Met, Vol. 2, p. 231, 1912.
BUNTZEL. "tJber die in Obeischliesen beim Abbau mit Spiilversatz beobachteten
Erdsenkungen." Zeit. f. d. Berg.-, Hutten.-, u. Salinenwesen, Bd. 59, s. 293,
ff., 1911.
CALDECOTT, W. A., and POWELL, O. P. "Sand-Filling of Mines on the Rand."
Jour. Chem. Met. and Min. Soc. of S. Air., p. 119, Sept., 1913.
CIZEK, K. "Packing Goaf with Sand and Granulated Slag by the Flushing
Process." Coll. Guard., Vol. 85, p. 1274, 1903.
"Versatz mittels Wasserspiilung vom Tage aus am dreifaltigweits-
schachte in Polnish-Ostrau." Oestr. Zeit. Hiittenwesen, Bd. 51, s. 293, 1903.
CORYELL, MARTIN. "The Conflagration Now Existing in the Coal at Kidder
Slope." Trans. Amer. Soc. Civ. Engrs., Vol. 3, p. 147, 1874.
DARTON, N. H. "Sand- Available for Filling Mine Workings in the Northern
Appalachian Basin of Pennsylvania." U. S. Bureau of Mines, Bui. No. 45,
1913.
"Notes on Sand for Mine Flushing in the Scranton Region." U. S.
Bureau of Mines, Bui. No. 25, p. 72.
DAVIS, J. B. "Flushing Culm at Black Diamond Colliery, Pennsylvania." Coll.
Eng., Vol. 14, p. 11, 1893.
DEMETER. "Improvements in Hydraulic Filling Method." Berg.-, u. Huttmann,
Rdsch., Vol. 6, p. 209, 1910.
DOBBLESTEIN. "Combined Hydraulic Sand Filling and Gob Hand Filling at the
Katharina Mine of the Essen Coal Mine Works," "Gluckauf, Bd. 44, s. 145,
1908.
ENZIAN, CHARLES. "Hydraulic Mine Filling." U. S. Bureau of Mines, Bui.
No. 60, 1913.
"Mine Caving Prevented by Hydraulic Filling." Coal Age, p. 555,
Apr. 4, 1914.
"Physical and Geological Difficulties of Anthracite Mining with Special
Reference to Surface Support in the Northern and Wyoming Basin."
Thesis, Lehigh Univ., 1913.
EDIT. "Origin of Sand Filling." Min. and Sci. Press, Vol. 109, p. 790, 1914.
FIEDLER. "The Hydraulic Filling Method in Mining and Hydraulic Engineer-
ing." Oestr. W. Schr. off. Bandienst, Vol. 24, p. 368, 1909.
FORD, L. D. "Hydraulic Packing of the Goaf of the St. Nicholas Pit, Near
Liege, Belgium." Trans. Inst. Min. Engrs., Vol. 46, p. 439, 1913.
FRIESER, ANTON. "Packing of Coal Seams in Bohemia." Trans. Inst. Min.
Engrs., Vol. 10, p. 597, 1895-96. Oest. Zeit. fur B.-, u. H.-W., Bd. 43, s. 253,
1895.
GAMZON, L. "Hydraulic Stowing at French Collieries." Coll. Engr., Vol. 34,
p. 289, 1913-14.
YOUNG:STOEK SUBSIDENCE RESULTING FROM MINING 195
GILBERT, G. K., and MURPHY, E. C. "Transportation of Debris by Running
Water." U. S. Geol. Sur., Prof. Paper No. 86, 1914.
GRESLEY, W. S. "Culm Filling." Coll. Eng., Vol. 14, p. 32, 1893.
GRIFFITH, W. "Flushing of Culm in Anthracite Mines." Jour. Frank. Inst.,
Vol. 119, p. 271, 1900.
GULLACHSEN, B, C. "Hydraulic Stowing in the Gold Mines of the Witwaters-
rand." Coll. Guard., Vol. 108, p. 817, 1914. Min. and Sci. Press, Vol. 109,
p. 801, 1914. Trans. Inst. Min. Engrs., Vol. 48, p. 122, 1915.
HASSE. "Fire in the Shaft Safety Pillars of the Oberhausen Colliery and Its
Control by Packing." Kohle und Erz, p. 79, Jan. 22, 1912.
HILL, L. R., and BURR, M. "Hydraulic Filling of a Coal Seam at Lens, Pas-de-
Calais, France." Eng. and Min. Jour., Vol. 82, p. 543, 1906. Trans. Inst.
of Min. and Met., Vol. 15, p. 371, 1905-06.
JOHNSON, H. B. "Protection of the Surface Above Anthracite Mines." Eng.
and Min. Jour., Vol 89, p. 167, 1910.
JULIN, J. "Water-Packing at the 185-Meter Level, St. Nicholas Colliery, Bel-
gium." Annales d. Mines, No. 1, p. 177 (Belgian), 1912.
KEGEL. ''Proposals for Applying Hydraulic Filling in the Brown Coal Mining
Industry." Braunkohle, Vol. 7, p. 653, 1908.
KELLEY, ED. J. "Slushing of Openings in Collieries." Penn. State. Min. Quart,
p. 31, Jan., 1914.
KNOX, GEORGE. "Hydraulic Filling as Roof Support." Coll. Engr., Vol. 34, p.
225, 1913. Min. Engr., p. 7, Feb. 1913.
"The Hydraulic Stowing of Goaves." Trans. Inst. Min. Engrs., Vol. 45,
p. 13, 1912. Coll. Engr., Vol. 34, p. 225, 1912.
"Relation Between Subsidence and Packing with Special Reference
to the Hydraulic Stowing of Goaves." Trans. Inst. Min. Engrs., Vol. 44,
p. 527, 1912-13.
LEE, RICHARD. "Recovery of Anthracite from Culm Banks." Eng. and Min.
Jour., Vol. 85, p. 720, 1908.
LEVY, ERNEST. "Rock Filling at Rio Tinto." Eng. and Min. Jour., Vol. 89,
p. 363, 1910. Trans. Amer. Inst. Min. Engrs., Vol. 40, p. 893, 1909.
LUECK. "The Various Flush Pipes in the Filling Works." Zeit. Oberschles,
Berg., Bd. 49, s. 185, 1910.
MARTIN, A. H. "Sand Filling as Support of Mine Workings." Mines and Min-
erals, Vol. 33, p. 223, 1913.
MAYER, L. W. "Back-Filling by Flushing in the Silesia Coal Mines." Eng. and
Min. Jour., Vol. 86, p. 889, 1908.
"Sand Filling in the Iron Mines of Peine, Germany." Trans. Amer.
Inst. Min. Engrs., Vol. 39, p. 355, 1908.
MAYER, L. W. "The Advantage of Flushing in Coal Mining." Eng. and Min.
Jour., Vol. 86, p. 1, 1908.
"Subsidence with Hydraulic Filling Hardly Noticeable at Carmaux,
France." Mining Methods in Europe, p. 154, New York, 1909.
MEYER, KURT. "The Flushing Plant and the Classification of Flushing Water
at the Hoisting Shaft of Consolidated Fiirstenstein Mine, Germany."
Gliickauf, p. 1391, Aug. 30, 1913.
"Mine Tailings for Filling". Used by Frisco R. R. Mining Details,
p. 22.
MULLER, K., and MUSSMAAN. "Water-Packing of Seams." Trans. Inst. Min.
Engrs., Vol. 27, p. 722, 1909.
PAM, EDGAR. "Water-Borne Packing for Stope Filling." Min. Mag., Vol. 5,
p. 295, 1911.
PATTON, J. D. "Hydraulic Stowing." Trans. Inst. Min. Engrs., Vol. 47, Part 4,
p. 468, 1914. Coll. Guard., p. 1121, May 22, 1914.
PAUR E "Sand-Filling on the Witwatersrand." Proc. Chem. Met. and Min.
Soc. of S. A., Vol. 10, p. 429.
PAYNE, H. M. "European Practice of Filling Abandoned Workings with Sand.
Eng. and Min. Jour., Vol. 89, p. 522, 1910.
196 ILLINOIS ENGINEERING EXPERIMENT STATION
PENNSYLVANIA STATE ANTHRACITE MINE CAVE COMMISSION REPORT. Journal
Pa. Legislature, Appendix, pp. 5947-6006, 1913.
Puxz, O. "The Present Status of the Hydraulic Filling Method in Germany."
Zeit. Oberschles. Berg.-, Hutt. Ver., Bd. 49, s. 3421, 1910.
"Das Spiilversatzverfahren." Berlin, 1907.
"Advantages of Oval over Circular Pipes for Hydraulic Gob Stowing."
Iron and Coal Trade Rev., p. 720, London, Nov. 7, 1913.
RICE, G. S. "Filling System." 111. Geol. Sur., Bui. No. 14, p. 220, 1908.
RODATZ, G. "The question of Hydraulic Filling for Potash Mines." Kali., p. 1,
Jan. 1, 1914, to p. 136, Mar. 15, 1914.
ROSENBERGEN, A. "Studies on the Theoretic Requirements for the Movement
of Sand in Pipes in Stowing." Zentral Verbd. Bergbau Betriebsl Oestr.
Zts., p. 574, Sept. 15, 1912.
SAINTE-CLAIRE-DEVILLE. "A Simple Method of Water Stowage Employed at
No. 5 Pit of the Escarpelle Mines." Trans. Inst. Min. Engrs., Vol. 35,
p. 79, 1907-08.
SAWYER, R. E. "Sand Filling at Cinderella Consolidated, South Africa." S. A.
Min. Jour., p. 271, Nov. 2, 1912. Eng. and Min. Jour., Vol. 94, p. 1213, 1912.
Trans. Inst. Min. and Met, Vol. 22, p. 58, 1912-13.
SCHAEFER. "The Hydraulic Filling Features of the Consolidation Mines."
Gluckauf, Vol. 46, p. 1440, 1910.
SCHNEIDER, H. "Methods Employed for Filling Underground Mine Workings
with Material Flushed from the Surface." Revue Univ. d. Mines, Dec.,
1904.
SCHMERBER, H. "Le remblayage par 1'eau." Genie Civil, Vol. 49, p. 57, 1906.
SEDIL, K. "Das Spiilversatzverfahren in Oberschlesian." Zeit. f. Oberschles.
B.-, u. H. Ver., Jan., Feb., Mar., 1911.
STEEN, THEODOR. "The Removal of Slimes in Hydraulic Stowing." Kohle and
Erz., p. 918, Sept. 1, 1913.
STORMS, W. H. "Filling Mine Stopes with Sand." Eng. and Min. Jour., Vol.
92, p. 585, 1911.
"Filling Stopes with Mill Tailings." Min. and Eng. World, Vol. 38,
p. 113, Jan. 18, 1913.
UNSIGNED. "Flushing Anthracite Workings." Coll. Engr., Vol. 33, p. 537, 1913.
"Flushing Culm in Germany." Coll. Guard., June 12, 1903.
"Flushing Culm into Anthracite Mines, Cost and Method of." Pa.
State Mine Insp. Rep., Vol. 35, 1897.
"Flushing or Silting of Mine Workings." Mines and Minerals, Vol.
32, pp. 321, 385, 1912. Coll. Eng., Vol. 34, p. 537, 1914.
"Hydraulic Filling at the Descazeville Mines." Revue Industrielle, p. 9,
No. 16, 1912.
"Hydraulic Packing in German State Mines." Coll. Guardian, p. 903,
Nov. 1, 1912.
"Innovation and Improvements in Mining Practice in Prussia in 1911."
Zts. f. d. Berg.-, H.-, u. Salinenwesen, Bd. 60, s. 92, 1912.
"Lining the Flush Pipe." Coal Age, Vol. 4, p. 82, July 19, 1913.
"Origin of the Stowing System." Zentrl. Verbd. Bergbau, Betriebsl
Oestr. Zts., p. 198, Apr. 1, 1912.
"Surface Protection over Coal Mines." Mines and Minerals, Vol. 30,
p. 568, 1910.
"Stowing Practice in Upper Silesia." Kattowitz, 1911.
"Transporting and Handling Materials in Sand-Filling Plants for
Mines." Kohle und Erz., p. 1070, Oct. 14, 1912.
VIAUNAY, V., and BAUER, J. "On the Wear of Delivery Pipes in Hydraulic
Stowing." Kohleninteressent, s. 163, July 1, 1913, and s. 177, July 15.
VOLMER. "Der Spiilversatz auf den Staatlichen Steinkohlenbergwerken bei
Saarbriicken." Zeit, f. d. B.-, H.-, u. S.-W., Bd., 49, s. 366.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 197
WALKER, W. "Hydraulic Stowage at Dalzell and Broomside Colliery." Ir.
and Coal Tr. Rev., p. 51, July 12, 1912. Coll. Guard., p. 122, July 19, 1912.
WILLIAMS, E. H. "Utilization of Anthracite Culm." Eng. Mag., Vol. 11, p. 644,
1896.
PILLARS
ACHENBACH. "Sicherheitspfeiler in England." Zeit. fur Bergrecht, s. 70 ff., 1870.
BUNTING, D. "Chamber-Pillars in Deep Anthracite Mines." Trans. Amer. Inst.
Min. Engrs., Vol. 42, pp. 236-245, 1911.
HARDY, W. "Removing Pillars in Coal Mines." Min. World, Vol. 26, p. 334,
1907.
KELLER, M. "Supporting of the Underground Quarries Beneath the Montrouge
Reservoirs." Eng. and Min. Jour., Vol. 25, p. 204, 1898.
OTTEN, H. "Pillar Construction with Concrete Headers and Caps." Gluckauf,
Sept. 5, 1914.
TIMBER, MASONRY, AND METAL SUPPORTS
CABOLET. "Iron Props of the Winze System." Gliickauf, Bd. 46, s. 1780, 1910.
CAMP, C. L. "Filling Mine Workings Under Railway Bridges with Concrete
at Scranton." Eng. News., p. 60, Jan. 11, 1912.
CHAPMAN, TEMPLE. "Concrete Bulkheads for Pillar Extraction." Eng. and
Min. Jour., Vol. 97, p. 1145, 1914.
CRANE, W. R. "The Use of Concrete for Mine Support." Trans. Inst. Min.
Engrs., Vol. 37, p. 560, 1909. Min. Sci. Press, Vol. 38, p. 320.
ELWITZ. "t)ber die Durchbindung von Bauten zur Verhiitung von Bergschaden."
Gliickauf, s. 278, Feb. 22, 1913.
ENGEL, L, G. "Masonry Supports for Hanging Walls at the Tilly Foster Iron
Mines." Sch. Mines Quart., Vol. 6, p. 289, 1884-85.
GEHRING. "A Cap for Props." Bergbau, Vol. 23, p. 466, 1910.
HECKER. "Innovations in Mine Lagging and Supports." Gluckauf, Vol. 44,
p. 553, 1908.
HEPPLEWHITE, W. H. "Substitutes for Wooden Supports of the Roof in Long-
wall Working." Trans. Inst. Min. Eng., Vol. 48, pp. 67, 387, 1915.
"The Action and Control of Differently Constituted Coal-Roofs."
Trans. Inst. Min. Eng., Bd. 42, s. 370, 1911.
HOMANN, LABES, and OTHERS. Manual of Reinforced Concrete Engineering,
Ch. 7 ("Railroads, Tunnels and Mining," Ch. 7, by B. Nast, 2d Ed., Berlin,
1912.)
KUPFER. "Lining of a Gallery with Reinforced Concrete Plates." Zeit. Ober.
Berg.-Hiitten., Verein., Vol. 49, p. 249, 1910.
MEUSKENS, C. "Use of Reinforced Concrete in Shafts Subjected to Heavy
Pressure." Braunkohle, p. 725, Feb. 16, 1912; p. 741, Feb. 23, 1912; p. 773,
Mar. 8, 1912. Abs. in Tech. Blatter, p. 148, May 11, 1912.
PENKERT. "Concrete Lining as a Self-Supporting Mine Lagging." Kohle und
Erz, s. 269, 1908.
PRELINI, C. "Formula for Determining Thickness of Masonry Lining of Tun-
nels." Tunneling, p. 74. ffl
REINHARD. "Portable Mine Linings." Bergbau, Vol. 23, p. 297, and Vol. 34,
1910.
RYBA. "Iron Mine Props Made of Seamless Mennesmann Pipes." Kohle und
Erz, s. 1, 1908.
SARGENT, E. C. "Use of Concrete in Mine Operation." Amer. Min. Congress,
Vol. 16, p. 256, 1913.
STARK. "Lining of Galleries by Means of Reinforced Concrete." Gluckauf,
Vol. 44, p. 668, 1908.
STENS. "On the Properties of Impregnated Mine Timber, Particularly on
Their Strength." Gluckauf, Bd. 45, s. 317, 1909.
198 ILLINOIS ENGINEERING EXPERIMENT STATION
UNSIGNED. "Method of Packing the Space Between the Shaft Lining and the
Surrounding Rock by Rising Moss." Tiefbohrwesen, Vol. 8, p. 1, 1910.
"Rigid and Yielding Iron Mine Props." Kohle und Erz, p. 639, 908.
"Use of Iron Face Props in Driving of Galleries." Gliickauf, Vol. 44,
p. 978, 1908.
"Yielding Iron Mine Props." Gliickauf, Bd. 46, s. 139, 1910.
RECORDS OF SUBSIDENCE
AMERICAN
BROWN, G. M. "A Sudden Squeeze in an Oklahoma Mine (Adamson, Okla.)."
Coal Age, Vol. 6, p. 532, 1914.
CONNER, E. T. "Mine-Caves under the City of Scranton." Trans. Amer. Inst.
Min. Engrs., Vol. 42, p. 246, 1911.
GUSHING, G. H. "Near-Doomed Cities." Tech. World Mag., Vol. 19, p. 660,
1913.
ENZIAN, CHARLES. "The Warrior Run Mine Disaster." Mines and Minerals,
Vol. 27, p. 439, 1907.
FOSTER, R. J. "Mine Caves under Scranton and Shenandoah." Trans. Amer.
Inst Min. Engrs., Vol. 42, p. 921, 1911.
GRESLEY, W. "Subsidence Due to Coal Working." Coll. Eng., Vol. 21, p. 29,
1891.
GRIFFITH, W., and CONNER, E. T. "Mining Conditions under the City of Scran-
ton, Pa." U. S. Bureau of Mines, Bui. No. 25, 1912.
REPPERT, A. E. "Subsidence in the Georges Creek Region, Maryland." Proc.
W. Va. Coal Min. Inst, p. 110, 1911.
RICE, G. S. "Slides Resulting from Mining." Noted in paper on "Method of
Preventing Rock Slides." (Lake Superior Iron mines.) Jour. West Soc.
Engrs., Vol. 18, p. 626, 1913.
"Surface Subsidence Due to Mining." Illinois Geol. Sur., Bui. No.
14, pp. 218, 220, 1908.
"System of Longwall Used in Northern Illinois Coal Mines." Columbia
School of Mines Quart., Vol. 16, p. 344, 1894-95.
FOREIGN
ATKINSON, A. A. "Subsidence Due to Mining of Coal under the River Hunter."
Trans. Inst Min. Engrs., Vol. 28, p. 130, 1904-05.
BAILLY, L. "Subsidences Due to Salt- Workings in French Lorraine." Annales
des Mines, Sers. 10, Vol. 5, pp. 403-494, 1904. (Ch. 4, Legislation on Sub-
sidence.) Abs. Trans. Inst Min. Engrs., Vol. 27, p. 724, 1903-04.
BALLING, C. "Subsidence Due to Mining Operations." Oster. Zeit. fur d. B.-, u.
H.-W., nr. 36, u. 37, 1902.
"Uber die Schatzung von Bergbauen." Prag, 1898.
"The Evaluation of Mines Together with a Sketch of the Influence
upon the Earth's Surface of the Collapse of Underground .Openings Caused
by Mining." 1906. (Cited by Goldreich, p. 34.)
BARTLING, R. "Unwatering of Strata and Subsidences in the Rhenish-West-
phalian Coal Field." Abs. Trans. Inst. Min. Engrs., Vol. 37, p. 691, 1908-09.
Zeit. fur prakt. Geologic, Bd. 15, s. 148, 1907.
BARTONEC, FR. "The Cause of Surface Subsidence and Movement in the Ostrau-
Karwin Coal Basin, Austria." Montanist Rundschau, p. 145, Feb. 16; p. 211,
Mar. 1, and p. 247, Mar. 16, 1912.
BECKER, H. "Schneidenmiihl Springs, Germany." Trans. Inst. Min. Engrs.,
Vol. 10, p. 593, 1895-96.
BOOTH, W. H. "Clay and Shrinkage." Mines and Minerals, Vol. 31, p. 615,
1910-11.
COOPER, R. E. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 132, 1898.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 199
CREMER. "Erdeben und Bergbau." Gliickauf, Jahrgang 31, Nr. 22.
DICKINSON, J. "Subsidence Due to Colliery Workings." Coll. Guard., Oct. 28,
1898, and Nov. 11, 1898. Proc. Manchester Geol. Soc., Vol. 25, p. 600.
DILL. "Rock Thrusts in Westphalian Collieries." Abs. Trans. Inst. Min. Engrs.,
Vol. 27, p. 720, 1903-04. Zeit. B.-, H.-, u. S.-W., Bd. 51, ss. 439-466, 1903.
DIXON, J. S. "Some Notes on Subsidence and Draw." Trans. Min. Inst., Scot-
land, Vol. 7, p. 224, 1885.
DRASSDO. "{jber die in den Jahren 1856 und 1857 an einer langs des Quai de
Fragnee zu Liittich belegenen Reihe von Hausern vorgekommenen Beschad-
igungen." Zeit. fiir B.-, H.-, u. S.-W., 1869.
"tiber die im Konigreiche Belgien giiltigen gesetzlichen Bestimmungen
liber den Schutz der Stadte, Dorfer u. s. w. gegen die beschadigenden Ein-
wirkungen des Bergbaubetriebes." Gliickauf, 1869.
"Uber die Aeuszerung der Bodenbewegungen in Folge des Steinkohlen-
bergbaues im Oberbergamtsbezirk Dortmund 1 ; Vortrag der Berghauptmanns
Prinz. zu Schonaich." Berggeist, s. 35, 1873.
DRON, R. W. "Effect of Coal Working on the Surface." Brit. Soc. Min. Stud.,
Vol. 11, p. 122.
DUMONT, GUSTAV. "Des affaisements du sol attribues a 1'exploitation
houillere. Response de 1'union des charbonnages, etc., au memoire de M.
Dumont, Liittich, 1875.
"Des affaisements du sol produits par 1'exploitation houillere." Liittich,
1871.
ELWITZ. "Uber die Durchbildung von Bauten zur Verhiitung von Bergschaden."
Gluckauf, s. 278, Feb. 22, 1913.
FAYOL, M. "Sur les mouvements de terrain provoques par 1'exploitation des
mines." Bui. de la societe de 1'industrie minerale, II e serie, Vol. 14, p. 818,
1885.
FROM ME. "Earth Settlements in Mining Districts." Gluckauf, Oct. 8, 1910.
GOLDREICH, A. H. "Die Theorie der Bodensenkungen in Kohlengebieten."
Berlin, 1913.
"Die Bodenverschiebungen im Kohlenrevier und ihr Einfluss auf die
Tagesoberflache." Berlin, 1914.
DE LA GOUPILLIERE, HATTON. "Cours d'exploitation des mines." Paris, 1896.
GRIMSHAW, W. J. "On Sinking of Surface Owing to the Working of Coal
Mines." Manchester Geol. Soc., Vol. 14, p. 455.
HABETS, A. "Des affaisements de sol observes dans la ville et les environs
d'Essen par H. V. Dechen, Liege." Imprimerie de. J. Desver, Libraire, 1871.
HALBAUM, H. W. G. "Great Planes of Strain in the Absolute Roof of Mines."
Trans. Inst. Min. Engrs., Vol. 30, p. 176, 1906.
HAUSSE, R. "Von dem Niedergehen des Gebirges beim Kohlenbergbaue und
den damit zusammengehangenden Boden- und Gebaudesenkungen." Zeit. f.
d. B.-, H.-, u. S.-W., Bd. 55, ss. 324-446, 1907.
HEISING. J. "Uber das Nachbrechen der Schichten des Steinkohlengebirges."
Berggeist. S. 355, 1868.
HELMHACKER, R. "Land Subsidence at Brux, Bohemia." Trans. Inst. Mm.
Engrs., Vol. 10, p. 583, 1895-96. Gluckauf, Vol. 31, pp. 1215-1217, 1895.
HOFER, H. "Taschenbuch fur Bergmanner." Bd. I, Bodensenkungen, p. 297,
Loeben, 1911.
JICINSKY. "Bodensenkungen infolge Bergbaubetriebes mit besonderer Beruck-
sichtigung des Mahisch- Ostrauer Kohlenreviers." Oest. Zeit. fiir B.-, u.
H.-W., 1882.
"Uber Senkungen und Briiche der Tagesoberflache infolge des Abbaues
von Kohlenflotzen." Oestr. Zeit. f. B.-, u. H.-W., 1876.
"Die Einwirkungen des Kohlenabbaues auf die Tagesoberflache Monog-
raphic des Ostrau-Karwiner Steinkohlenreviers, 1884."
"Senkungsfrage im Ostrau-Karwiner Reviere." Bergmannische Notizen,
1898.
200 ILLINOIS ENGINEERING EXPERIMENT STATION
KAY, S. R. "Subsidence Due to Coal Workings." Mines and Minerals, Vol.
19, p. 484, 1899.
KEGEL. "Ein Beitrag zur Frage der Bergschaden durch Wasserentziehung."
Gliickauf, s. 246, Feb. 15, 1913.
KIRKUP, J. F. "Discussion of Paper by H. W. G. Halbaum." Trans. Inst. Min.
Engrs., Vol. 28, p. 320, 1904.
KOLBE, E. "Die Translokation der Deckgebirge durch Kohlenabbau." Essen,
1903.
KONDGEN, H. "Seitliche Verschiebungen infolge von Bergbau im Stadtgebiet."
Essen. Zeitschrift fur Vermessungswesen, Stuttgart, 1903. (Oster. Zeit.
fur Berg.- u. Hiittenwesen, 1903.)
KOTZE, R. N. "Mine Subsidences on the Rand." S. Afr. Min. Jour., June 22,
1912. Eng. and Min. Jour., Vol. 94, p. 656, 1912.
LANG, OTTO. "Subsidences at Eisleben in the Mansfeld Mining District." Bui.
de la Societe Beige de Geologic, 11, pp. 190-220, 1898. Abs. Trans. Inst.
Min. Engrs., Vol. 15, p. 603, 1898.
LEWIS, W. T. "Note on Subsidence in Wales, Mining at 1,800 to 2,400 Feet."
Trans. Inst. Min. Engrs., Vol. 22, p. 290, 1901-02.
LOTTNER. "Grundsatze beim Abbau der Steinkohlenflotze in Westfalen." Zeit.
f. B.-, H.-, u. S.-W., Band 7, p. 292, 1859.
LUTHCEN. "Westfalische Abbaumethoden." Zeit. fii B.-, H.-, u. S.-W., Bd.
40, s. 296, 1892.
MAYER, L. W. "Surface Subsidence in Cumberland, England." "Long-wall
Methods." "Surface Subsidence." "Surface Subsidence in Northumber-
land, England." Mining Methods in Europe, Ch. 6, pp. 6, 23, 33, 46.
MEACHEM, F. G. "Notes on an Earth Explosion or 'Bump' at Hamstead Col-
liery." Trans. Inst. Min. Eiigrs., Vol. 5, p. 381, 1892-93.
MENZEL, C. "Subsidence at Zwickau." Proc. Inst. Civ. Engrs., Vol. 140, p. 321.
NASSE. "Der technische Betrieb der Koniglichen Steinkohlengruben bei Saar-
briicken." Zeit. fur B.-, H.-, u. S.-W., s. 57, 1885.
O'DONAHUE, T. A. "Subsidence Caused by Workings." Mining Formulae, p. 253.
PADOUR, ANTON. "Flur- und Gebaudeschaden." 1908.
PIGGFORD, J. "Notes on Subsidence Caused by Coal Working at Teversal and
Pleasley Collieries." Trans. Min. Inst. Engrs., Vol. 38, p. 129, and Vol. 39,
p. 137, 1909-10.
POLLACK, V. "Beitrage zur Kenntniss der Bodenbewegungen." Jahrbuch der
K. K. Geologischen Reichsanstalt, Wien, 1882.
PUSCHMANN. "tiber den pachtraglichen Abbau hangender Flosze beim ober-
schlesischen Steinkohlenbergbau." Zeit. f. d. B.-, H.-, u. S.-W., Bd. 58, s.
387, 1910.
READ, R. J. G. "Subsidence due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 143, 1898.
REDMAYNE, R. A. S. "Modern Practice in Mining." Vol. 3, pp. 7-10, and p. 170,
London, 1914.
RICHARDSON, ALEX. "Mine Subsidence." Jour. Chem. Met. and Min. Soc. S. A.,
Vol. 7, pp. 279, 325, 362, and Vol. 8, pp. 16, 46. Eng. and Min. Jour., Vol. 84,
p. 196, 1907.
ROBERTON, E. H. "Subsidence in English Coal Districts." Practical Coal Min-
ing, Vol. 2, p. 299. (Edited by W. S. Boulton.)
RUMBERG. "Der Gebirgsschlag auf der Schachtanlage." Ill, u. IV der Zeche
Consolidation am 10 June, 1910. Zeit. f. d. Berg.-, H.-, u. S.-W., s. 68 ff.,
1911.
RUNGE, W. "Influence of the Westfalian Mining Methods Upon the Surface of
the Earth." Das Ruhrsteinkohlenbecken, ss. 215, 216, 322, Berlin, 1892>.
RZIHA, F. "Subsidence Due to Mining Operations." Zeit. B.-, u. H.-W., Oest,
Vol. 30, 1882. (See also 1881.)
SNOW, CHARLES. "Removal of a Shaft-Pillar at South Kirby Colliery." Trans.
Inst. Min. Engrs., Vol. 46, p. 8, 1913-14.
YOUNG-STOEK SUBSIDENCE RESULTING FROM MINING 201
SPENCER, W. "The Support of Buildings." Trans. Inst. Min. Engrs., Vol. 5. pp.
188, 197 ; Vol. 7, p. 382, and Vol. 9, p. 102, 1892-93.
STONIER, G. A. "Amount of Subsidence in the Bengal Coal Fields." Trans.
Inst Min. Engrs., Vol. 28, pp. 544, 545, 547, 554, 1904-05.
TRAINER. "Die mit dem Steinkohlenbergbau in unsachlichem Zusammenhang
stehenden Vorfluthstorungen im Emscher-Gebiet und die zur Beseitigung
getroffenen Masznehmen." Zeit. fur Bergrecht, Bd. 38, s. 190 ff., 1897.
TROMPETER, W. H. "Die Expansikraft in Gestein als. Hauptursache der Bewe-
gung des den Bergbau umgebenden Gebirges." 1899.
DE VAUSE, A. "L'amchement de terraine affaisses par suite de 1'exploitation
souterraine en Westphalie (Analyse du projet de M. I'ingenieur Michailis)."
Rev. Universelle des Mines, etc., 2e Serie, Tome 17, p. 124, 1885.
VON BRUNN. "Mitteilungen iiber die Bodensenkungen bei Essen." Zeit. f.
Bergrecht, 1874.
VON BOLESTA-MALEWSKI. "Abbau mit hohem Stosz unter Verwendung von
Abbaufordereinrichtungen." Gliickauf, Bd. 48, ss. 1749, 1789, 1912.
VON SPARRE, J. "Uber das Nachbrechen der Schichten des Steinkohlengebirges."
Gliickauf, 1867.
WACHSMANN. "tiber die Einwirkung des oberschlesischen Steinkohlenberg-
baues auf die Oberflache." Zeit. f. Oberschles B.-, u. H.-Ver., p. 313, 1900.
WARD, T. "The Subsidences in and Around the Town of Northwich in Cheshire."
Trans. Inst. Min. Engrs., Vol. 19, pp. 241, 263, and Vol. 21, p. 440, 1899-1900.
WRIGHT, TYLDEN. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 126, 1898.
YATES. "Mining Subsidence." Mines and Minerals, Vol. 28, p. 27, 1907. Jour.
Chem. Met. and Min. Soc. S. Afr., Apr., 1907.
UNSIGNED, "liber die Einwirkung des unter Mergeluberdeckung gefiihrten
Steinkohlenbaues auf die Erdoberflache in Oberbergamtsbezirke Dort-
mund." Zeit. f. d. B.-, H.-, u. S.-W., s. 372, 1897.
"Unwatering of Strata and Subsidences in the Rhenish-Westphalian
Coal Field." Abs. Trans. Inst. Min. Engrs., Vol. 37, p. 691, 1908-09.
"Earthquake at Dortmund Due to Mining Operations." Gliickauf, B'd.
31, No. 22, Mar. 16, 1895.
"Mining Subsidence at Raibi, Bohemia." Oestr. Zeit. f. B.- u. H., Bd.
58, s. 31, 1910. Abs. Trans. Inst. Min. Engrs., Vol. 40, p. 621, 1910-11.
NOVA SCOTIA. "Report of Inspector of Mines on the Flooding of Port Hood
Mine and of Mabou Mine." Halifax, 1913.
RIGHTS, LAWS, AND DECISIONS
DECISIONS AND CASES
MORRISON, R. S., and DESoro, E. D. Mining Reports. Chicago, 1883-1906.
STATE LAWS COVER PAYMENT FOR SURFACE CAVES. Black Diamond, p. 20, Mar. 8,
1913.
GENERAL WORKS ON MINING LAW
BARRINGER, D. M., and ADAMS, T. S. "The Law of Mines and Mining in the
U. S." Vol. 1, Ch. 21, pp. 675-688, St. Paul, 1900; Vol. 2, Ch. 21, pp. 624-
644, St. Paul, 1911.
COCKBURN, J. H. "Minerals under Railways and Statutory Works (England)."
Trans. Inst. Min. Engrs., Vol. 39, p. 104, 1909.
COCKBURN. J. H. "The Law of Coal, Coal Mining, and the Coal Trade." Lon-
don, 1902.
"Colliery Owners and the Law of Support." Coll. Guard., Vol. 107,
p. 1400, 1914.
COSTIGAN, GEO, P., JR. "Handbook on American Mining Law." St. Paul, 1908.
(Right to lateral and subjacent support, pp. 502-508.)
202 ILLINOIS ENGINEERING EXPERIMENT STATION
LINDLEY, CURTIS H. "A Treatise on the American Law Relating to Mines and
Mineral Lands." 3d Ed., San Francisco, 1914. (Vertical and lateral sup-
port, Vol. 3, pp. 2010-2037.)
MAC&WINNEY, R. F. "Law of Mines, Quarries, and Minerals." 4th Ed., Lon-
don, 1912. (Support, Ch. 14, pp. 286-450.)
MORINE, A. B. "The Mining Law of Canada." Toronto, 1909. (Support, pp.
264-271.)
"Right of Support (Howley Park Appeal)." Coll. Guard., Vol. 104, p.
951, 1912.
SHAMEL, CHARLES H. "Mining, Mineral and Geological Law." New York,
1907. (Lateral and subadjacent support, pp. 309-313.)
SNYDER, W. I. "Mines and Mining Rights." Sec. 964, pp. 1016-1043, Chicago,
1902.
WHITE, E. J. "Law of Mines and Mining Injuries." Sees. 212, 215, 490, St.
Louis, 1903.
LAWS
ANDREE, TH. "Protection of the Surface from Subsidence." Oest. Zeit. fur
B.-, u. H.-W., Vol. 47, p. 525, 1899. Abs. Trans. Inst. Min. Engrs., Vol. 23,
p. 728, 1901-02.
ARKANSAS ACTS OF 1907, Sec. 566.
BAILLY, L. "Subsidence Due to Salt- Workings in French Lorraine." Annales
des Mines, Vol. 5, Sec. 10, pp. 403-494, 1904. (Ch. 4, on legislation.)
BELGIUM LAWS OF 1911. "Reparation of Surface Damage in Belgium." Ann.
des Mines de Belgique 1911, Vol. 14, p. 751. Noted in Trans. Inst. Min.
Engrs., Vol. 43, p. 603.
CALIFORNIA CIVIL CODE OF 1909, Sees. 801, 832. (See also 10th Census, Vol.
14, p. 57.)
COLORADO REVISED STATUTES OF 1908, Sees. 4213-4217, and 5134.
DE MARMOL, J. Zur Reform der belgischen Gesetzgebung inbetreff der Boden-
senkungen bei dem Steinkohlenbergbau. Zeit. fur Bergrecht, 1875.
IDAHO CIVIL CODE OF 1901, Sec. 2571. Rev. Code of 1907, Sec. 3214.
NORTH DAKOTA REVISED CODE OF 1899, Sec. 1436 ; 1905, Sec. 1810.
OHIO GENERAL CODE OF 1910. Right to quarry under road, Sec. 7493.
PENNSYLVANIA LAWS OF 1913, Act. 857.
SOUTH DAKOTA REVISED POLITICAL CODE OF 1913, Sec. 2542, p. 636.
VIRGINIA CODE OF 1904, Sec. 2570.
VON BRUNN, J. "Die Beschadigungen der Oberflache durch den Bergbau nach
franzosischem Bergrecht." Zeit. fur Bergrecht, 1875.
WYOMING REVISED STATUTES OF 1910, p. 3458.
LITIGATION AND ARBITRATION
BULMAN, H. F., and REDMAYNE, R. A. S. "Colliery Working and Manage-
ment." London, 1906.
MAAS. "Vergleichsverhandlung iiber Bodensenkungen." Zeit. f. Bergrecht, p. 19
ff., 1878.
RIGHT TO SUPPORT
MAAS. "Rechtsverhaltnisz zwischen Grundbesitzer und Bergwerksbetrieber."
Zeit. fur Bergrecht, s. 369 ff., 455 ff., 1876.
THEORIES OF SUBSIDENCE
BARTLING, R. "Zur Frage der Entwasserung lockerer Gebirgschichten als
Ursache von Bodensenkungen besonders im rheinisch-Westfalischen Stein-
kohlenbezirk." Zeit. fur Prakt. Geo., Bd. 15, s. 148. Trans. Inst. Min.
Engrs., Vol. 37, p. 691, 1908-09.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 203
•BROUGH, BENNETT H. "A Treatise on Mine-Surveying." 3d Ed., London, 1891.
(Subsidence and draw, pp. 241-245; Hausse's theory, pp. 243-244, and Gal-
lon's theory, pp. 244-245.)
"Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs., Vol. 135,
p. 150, 1898.
*BULMAN, H. F. "Translation of Paper, by M. Fayol." Trans. Soc. de 1'Ind.
Mineral, 1885. British Society of Mining Students. Coll. Eng., Vol. 33,
p. 548, or Vol. 11, p. 25.
•BULMAN, H. F., and REDMAYNE, R. A. S. "Colliery Working and Manage-
ment." ' London, 1906. (Historical notes, first damage suit in England on
record, p. 9. Angle of break, illustrated, p. 136; footnote on "draw," p. 212.)
• CALLON, M. J. "Cours d'exploitation des mines." Paris, 1874. (Subsidence,
Vol. 2, p. 327.)
•DAHLBLOM, T. "The Angle of Shear." Proc. Int. Geol. Cong., Vol. 12, p. 773,
1913.
ECKARDT, A. "Die mechanische Einwirkung des Abbaues auf das Verhalten des
Gebires." Gluckauf, Bd. 49, ss. 353, 397, 1913.
* FAYOL, M. "Sur les Mouvements de terrain provoques par 1'exploitation des
mines." Bui. de la Societe de 1'industrie minerale, IP serie, Tome 14 p.
818, 1885. Translation by Bulman, H. F. Coll. Engr., Vol. 11, p. 25, or
Vol. 33, p. 548.
i FOSTER, C. LE NEVE. "Ore and Stone Mining." 4th Ed., London, 1901. (Shaft
pillars and subsidence, pp. 349-351.)
GALLOWAY, W. "Translation of Fayol's Report on the Effect of Coal Work-
ing on the Surface." So. Wales Inst. of Engrs., Vol. 20, pp. 304-342, 1897.
GILLOTT, THOS. "Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs.,
Vol. 135, p. 152, 1898.
GOLDREICH, A. H. "Theorie der Bahnsenkungen im Bergbaugebieten mit
besonderen berucksichtigung des Ostrau-Karwiner Kohlenreviers." Oest
Zeit. f. B.-, u. H.-W., 1912.
"Die Theorie der Bodensenkungen in Kohlengebieten." Berlin, 1913.
"Die Bodenverschiebungen im Kohlenrevier und ihr Einfluss auf die
Tagesoberflache." (To be pub. by J. Springer, Berlin.)
DE LA GOUPILLIERE, HATTON. "Cours d'exploitation des mines." Paris, 1896.
GRAFF. "Verursacht der Bergbau Bodensenkungen durch die Entwasserung
wasserfuhrender diluvialer Gebirgsschichten." Gluckauf, 1901.
HALBAUM, H. W. G. "The Great Planes of Strain in the Absolute Roof of
Mines." Trans. Inst. Min. Engrs., Vol. 30, p. 175, 1906.
HALL, R. D. -"Action of the Roof." Proc. Coal Min. Inst. of America, p. 63,
1911.
» ""Data on Petrodynamics." Mines and Minerals, Vol. 31, pp. 210, 505,
1911.
"Effect of Shear on Roof Action." Proc. Coal Min. Inst. of America,
p. 135, 1912.
v"The Last Stand of the Mine Roof." Coal Age, Vol. 6, p. 982, 1914.
/The Strength of Mine Roofs." Mines and Minerals, Vol. 30, p. 474,
1910.
"Squeezes in Mines, and Their Causes." Mines and Minerals, Vol. 30,
p. 286, 1910.
HAUSSE, R. "Beitrag zur Bruchttheorie Erfahrungen iiber Bodensenkungen und
Gebergsdruckwirkungen." Jahrbuch fur das B.- und H.-W., im Konigreich
Sachsen, 1885. Also, Brough, Mine Surveying, p. 243.
"Von dem Niedergehen des Gebirges beim Kohlenbergbaue und den
damit zusammengehangenden Boden- und Gebaudesenkungen." Zeit. f. das
B.-, H.-, u. S.-W., Bd. 55, ss. 324-446, 1907. Abs. Trans. Inst. Min. Engrs.,
Vol. 37, p. 691, 1908.
HIISING, J. "tiber das Nachbrechen der Schichten des Steinkohlengebirges."
Berggeist, s. 355, 1868.
204 ILLINOIS ENGINEERING EXPERIMENT STATION
HOFER, H. "Taschenbuch fur Bergmanner." Loeben, 1911. Band I, Boden-
senkungen, s. 297.
HOLLAND, L. "Problems of Thick Coal Workings in Deep Mines." Coll.
Guardian, Jan. 27, 1906.
HUGHES, HERBERT W. "A Text-Book of Coal Mining." 5th Ed., London, 1904.
(Shaft pillars and subsidence, pp. 178-188.)
"Subsidence Due to Coal Workings." Proc. Inst. Civ. Engrs., Vol.
135, p. 157, 1898.
JICINSKY, W., MAYER, and WURZIAN, J. "Report of Committee on Rhiza's
Theory of Subsidence." Oest. Zeit. f. B.-, u. H.-W., Bd. 30f 1882.
"Bodensenkungen infolge Bergbaubetriebes mit besonderer Beruck-
sichtigung des Mahrisch-Ostrauer Kohlenreviers." Ost. Zeit. fur B.-, u.
H.-W., 1882.
"Senkungsfrage im Ostrau-Karwiner Reviere." Bergmannische Noti-
zen, 1898.
"tiber Senkungen und Briiche der Tagesoberflache infolge des Abbaues
von Kohlenflotzen." Osterreichische Zeit. f. B.-, u. H.-W., s. 457, 1876.
"Die Einwirkungen des Kohlenabbaues auf die Tagesoberflache."
Monographic des Ostrau-Karwiner Steinkohlenreviers, 1884.
KAY, S. D. "The Effect of Subsidence Due to Coal Workings upon Bridges
and Other Structures." Proc. Inst. of Civ. Engrs., Vol. 135, p. 114, 1898.
Abs. Mines and Minerals, Vol. 19, p. 484.
KEGEL. "Ein Bertrag zur Frage der Bergschaden duch Waserentziehung."
Gliickauf, s. 246, Feb. 15, 1913.
•KNOX, GEORGE. "Mining Subsidence." Proc. Int. Geol. Cong., Vol. 12, p. 797,
1913.
"Mining Subsidence." Iron and Coal Trades Rev., Nov. 13, 1914.
KOHLER. "Bergbaukunde, Clausthal." Osterr. Zeit. fur Berg.- u. Hiittenwesen,
1900.
KOLBE, E. "Translocation der Deckgebirge durch Kohlenabbau." Essen, 1903.
KORTEN. "Subsidence." Gliickauf, Nos. 25 and 40, 1909.
• KREY, H. "Rock Pressure, Rock Resistances, and Load Capacity of Earth and
Bedrock at Great Depths." Berlin, 1912.
LOVE, R. G. "Estimating the Strength of Pillars." Coal Age, Vol. 2, p. 676,
1912.
• LUPTON, ARNOLD. "Mining." London, 1907. (Notes on shaft pillars and angle
of break, pp. 150-151.)
• MCDONALD, D. F. "Excavation Deformations." Proc. Int. Geol. Cong., Vol. 12,
p. 779, 1913.
McNAiR, F. W. "Pillars in the Deep Mines of the Lake Superior Copper Dis-
trict." Eng. and Min. Jour., Vol. 83, p. 322, 1907. Min. and Sci. Press,
Vol. 94, p. 275, 1907. Proc. Amer. Assn. Adv. of Science, 1906.
' NELSON, A. "Shaft Depth and Seam Inclination as Affecting Size of Shaft
Pillars." Sci. and Art of Mining, p. 547, June 22, 1912.
NIESZ. "Gebirgsdruck und Grutenbetrieb." Zeit. f. B.-, H.-, u. S.-W., Bd. 58,
ss. 418-440. Abs. in Trans. Inst. Min. Engrs., Vol. 41, p. 588, 1910.
• O'DONAHUE, T. A. "Mining Formulae." Wigan, Ch. 14. 1907.
PADOUR, ANTON. "Flur- und Gebaudeschaden, 1908.
• PICKERING, W. H., and PICKERING, B. H. "Why Leave Shaft Pillars?" Trans.
Inst. Min. Engrs., Vol. 43, p. 428, 1912.
POLLACK, V. "Beitrage zur Kenntnis der Bodenbewegungen." Jahrbuch der
K. K. Geologischen Reichsanstalt, Wien, 1882.
PRINZ zu SCHONAICH UND KUPFER. "Ehrfahrungen iiber Bodenbewegungen
infolge des Steinkohlenbergbaues in Oberbergamtsbezirk Dortmund. Vor-
trag gehalten auf der Versammlung technischer Bergbeamte." Berggeist,
1873.
PUSCHMANN. "Uber den N'achtraglichen Abbau Hangender Floze beim ober-
schlesischen Steinkohlenbergbau." Zeit. f. d. Berg., Hiitten.- u.- Salinen-
wesen, Bd. 58, s. 387 ff., 1910.
YOUNG-STOEK — SUBSIDENCE RESULTING FROM MINING 205
REBHANN, G. "Theorie des Erddruckes und der Futtermauern." Wien, 1871.
REDMAYNE, R. A. S. "Modern Practice in Mining." London, 1914. (Sub-
sidence in Vol. 3, pp. 7-19, 170.)
' RICE, C. T. "Dome of Equilibrium and the Caving System of Mining." Min.
and Sci. Press, Vol. 95, p. 85, 1907.
ROWLEY, W. W. "Subsidence Due to Coal Workings." Proc. Inst Civ. Engrs.,
Vol. 135, p. 139, 1898.
RZIHA, F. "Subsidence Due to Mining Operations." Zeit. f. B.-, u. H.-W., Oest.,
Vol. 30, 1882.
SAINT-CLAIRE-DEVILLE. "fitude sur les affaisements dus aux exploitations
houilleres." Bui. Soc. Ind. Min., 4 Ser., Vol. 6, p. 411, 1907.
SARNETZKI. "Effect of Mining with Regard to Horizontal Displacements."
Deutsche Strassen- und Kleinbahn-Zeitung, No. 46 and 47.
SCHULZ, A. "Untersuchungen iiber die Dimensionen der Sicherheitspfeiler fiir
den Saarbriicker Steinkohlenbergbau und iiber den Bruchwinkel, unter
Welchem, die Gebirgschichten in die abgebauten Raume niedergehen." Zeit.
fur B.-, H.-, u. S.-W., 1867.
* SCHWEIZ, E. WIESMANN. "Rock Pressure." Bau, Aug. 17, 1912.
THIRIART, L. "Les affaisements de sol produits par 1'exploitation houillere."
Ann. des Mines de Belgique, Vol. 17, p. 3, 1912.
TRIPPE, F. "Effect upon the Surface of Unwatering Surficial Beds." Gliickauf,
May, 1906.
TROMPETER, W. H. "Die Expansivkraft im Gestein als Hauptursache der
Bewegung des den Bergbau umgebenden Gebirges." Essen-Ruhr, 1899.
DE VAUSE, A. "L'affichement de terrains affaisses par suite de 1'exploitation
souterraine en Westphalie." Rev. universelle des mines, etc. 2e Serie,
Tome 17, p. 124, 1885.
VAN HISE, C. R. "Earth Movements." Wis. Academy of Sciences, Vol. 11,
p. 465, 1896.
* VILLOT. "Lateral Effects of Falls in Mines." Trans. Inst. Min. Engrs., Vol. 1,
p. 422, 1890.
VON BOLESTA-MALEWSKI. "Abbau mit hohem Stosz unter Verwendung von
Abbauforderunrichtungen." Gliickauf, Bd. 48, s. 1749, 1789, Oct. 26, 1912.
VON BRUNN. "Die Beschadigungen der Oberflache durch den Bergbau nach
franzosischem Bergrecht." Zeit. fiir Bergrecht, 1875.
VON DECHEN, H. "Gutachten uber die Bodensenkungen in und bei der Stadt
Essen." Als Manuscript gedruckt, Bonn, 1869.
VON SPARRE, J. "Uber das Nachbrechen der Schichten des Steinkohlengebirges."
Gliickauf, 1867.
• VON WILLMANN. "Some Rock Pressure Phenomena in Their Bearing on Tun-
neling." Darmstadt Techn. Hochschule Dissert., 1911.
WACHSMANN. ""Uber die Einwirkung des oberschlesischen Steinkohlenbergbaues
auf die Oberflache." Zeit. f. Oberschles Berg, und Huttenmannischen
Verein, s. 313. 1900.
• YATES. "Mining Subsidences." Jour. Chem. Met. and Min. Soc. of S. Afr.,
Apr., 1907. Mines and Minerals, Vol. 28, p. 127, 1907.
UNSIGNED. "Uber die Einwirkung des unter Mergel- iiberdeckung gefiihrten
Steinkohlenbergbaues auf die Erdoberflache im Oberbergamtsbezirke Dort-
mund." Zeit. f. d. B.-, Hiitt.-, u. S.-W., Bd. 55, s. 384, 1897.
RETURN CIRCULATION DEPARTMENT
TO-— ^ 202 Main Library
LOAN PERIOD 1
HOME USE
2
3
4
5
6
ALL BOOKS MAY BE RECALLED AFTER 7 DAYS
Renewals and Recharges may be made 4 days prior to the due date.
Books may be Renewed by calling 642-3405
DUE AS STAMPED BELOW
"MAR"
FORM NO. DD6
UNIVERSITY OF CALIFORNIA, BERKELEY
BERKELEY, CA 94720
U.C.BERKELEY LIBRARIES
UNIVERSITY OF CAUFORNIA UBRARY
Live Music Archive
Librivox Free Audio
Metropolitan Museum
Cleveland Museum of Art
Internet Arcade
Console Living Room
Books to Borrow
Open Library
TV News
Understanding 9/11