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PRACTICAL

TUNNELLING.

PRACTICAL

TUNNELLING.

PRACTICAL

TUNNELLING.

PRACTICAL

TUNNELLING.

PREFACE

It was originally my intention to have prepared a general history of Tun-
nelling operations, and to have given every particular that might be thought
interesting or instructive of all such works, from the earliest period. Such
a work would have necessarily been extensive, and have required more
time in its preparation than I could, at present, devote to it. Upon
explaining my plan, and shewing the memoranda that I had made, during
the progress of the works under my charge at Blechingley and Saltwood
Tunnels, I was advised that their publication, with a practical account of
Tunnelling operations as practised at the present time, would be accept-
able ; particularly to the junior members of the profession, and to many
contractors, whose experience has not hitherto been in the construction of
such works. I therefore undertook the preparation of this volume, which
has for the most part been written, and passed through the press, during
the time that I have been actively engaged in my professional pursuits;
and which must be my excuse for any trifling inaccuracies that may be
detected in it.

VIU. • PREFACE.

I do not profess to describe any new methods of carrying on the works
necessary for the construction of Tunnels, but to give in detail that which
I believe to be the most approved practice at the present time; and in
order to accomplish this, and supply data for correctly estimating the cost
of future works of the like kind, I have adopted, as my examples, the
two important works executed under my superintendence, with the
details and cost of which I am necessarily most familiar; and having
as is my custom, kept minutes of the amoimt of labour consumed in
the various parts of the work, I am thereby enabled to furnish the
particulars contained in the Tables embodied in the following pages.

The prices paid for Materials are likely to differ in every locality,
whilst the amount of labour required to execute any work will remain
the same ; for instance the article Bricks, which cost in the South-Eastem
parts of the country from thirty to fifty per cent, more than they can
be purchased for in the central parts of the kingdom; not but the
amount of labour consumed in their manufacture or the value of that
lnlK)ur, is the same in both districts, or nearly so, yet the difference
exists in the greater value of the fuel \\ith which they are burned. The
prices of Timber will also \wry; and subsequently to the time when the
works described in these pages were executed, a large portion of the duty
on foreign timber has boon taken off, which would make a considerable
reduction in tlie expenditure, if the same works had now to be con-

PREFACE. IX.

structed: the actual cost of the works described may, however, prove
useful information.

I am not aware that any part of the modus operandi has been omitted;
and if it be considered that I have gone more minutely into detail than
was necessary, it will, doubtless, at the same time be admitted that the
fault is on the right side, — as I do not expect that men experienced in
Tunnel works will read these pages in search of instruction; and for
those who have not had that experience, too much practical detail can-
not be given. There is no royal road to Knowledge, either theoretical
or practical ; and it is therefore the duty of those who profess to com-
municate it, to smooth the rugged uphill path thereto, in every possible
way. Such a course I have endeavoured to pursue in the preparation
of the following pages : — how far I have succeeded must be left for
others to judge.

F. W. S.

Hythe, Kent,
August 29th, 1844.

CONTENTS.

CHAP. I.

Geobgical features of the South-Eastem Railway—General account of
Blechingley and Saltwood Tunnels, their cost, &c. . . page 1

CHAP. II.

Description of the Observatory.— The Transit Instrument, and the method
of fixing and adjusting 19

CHAP. III.

Setting out the Shafts.— Ranging the line, both above and under grounds-
Taking the levels, and establishing bench marks, or points of
reference, &c. 29

CHAP. IV.

Shaft iiinking.— The Trial Shafts 41

CHAP. V.

Shaft sinking, continued. — Excavating and constructing the working

sliaftn, and supporting the brickwork by shaft sills and hanging rods 51

CHAP. VI.

Shaft sinking, concluded.— Excavating and square timbering the lower

portion of the shafts 59

CHAP. VII.

Driving the headings, and experiments upon horse power. 67

CONTENTS. XI.

CHAP. VIII.

Form and dimensions of Blechingley and Saltwood Tunnels.— Description
of the skips, &c.— And the horse-gins employed in the construction
of the works .73

CHAP. IX.

Construction of the Tunnels.— The side lengths, excavation, and timbering 81

CHAP. X.

Construction of the Tunnels, continued.— The side lengths, brickwork . 95

CHAP. XI.

Construction of the Tunnels, continued.— The shaft lengths, excavation,

and brickwork 109

CHAP. XII.

Construction of the Tunnels, concluded.— The leading and the junction

lengths, excavation and brickwork 117

CHAP. XIII.

Tunnel entrances.— 6haft towers, and culvert through the tunnel 137

CHAP. XIV.

The centres of ordinary construction :— and description of Frazer's patent
centres 147

CHAP. XV.

Miscellaneous.— Cast iron shaft curbs.— Cutting bricks.— Weight of
brickwork.— Brickmaking contract,— &c 16Z

APPENDIX.

Blechingley Tunnel sick fund.— The late Mr. Rennie's Report upon the
Highgate Archway Tunnel 169

ILLUSTRATIONS.

PLATES.

1. — ^Working sections of Blechingley and Saltwood Tunnels.

2. — Shaft sinking, and square timbering.

3. — Side lengths, excavating and constructing.

4. — Shaft lengths, excayating and timbering,

5. — Shaft lengths, brickwork.

6. — Leading lengths, timbering.

7. — Leading lengths, brickwork.

8.^ — Side lengths, with three sills.

9. — Blechingley Tunnel, centres and method of using them.

* > Frazer*s patent centres, and method of using them.

12. — Cast-iron shaft curbs.

WOOD ENGRAVINGS.

1. — ^The works at Blechingley Tunnel, frontispiece.
2.^Interior of a Tunnel, with the work pro-
gressing, .... page 1

3. — Section of the observatory, . . 20

4. — ^Transit instrument, • • . • 21
5.^Appearance of lines in the transit telescope, 31

6.— 'Ranging spike, . . • . 32

7. — Candle-holder for the headings, . 34

8. — Ranging the lines in the heading, . 35

9. — ^The levelling rods for the shafts, . 39

10. — Section of trial shafts at Saltwood, . 47

11. — Method of shaft sinking, • • 48

12.— ibid 49

13.— Shaft sills, 54

14. — ^Hanging rods, .... 57

15.— Water barrel, .... 63

16« — ^Rope cap and shackle, ... 64

17. — Square timbering of shafts, . . 65

18. > Transverse and longitudinal sections of

19. J heading, . , . . . 67
20. — ^Workmen constructing the heading, . 68

21.— Small skips, 75

22.— Skip hooks, 75

23.— Large skips on wheels, ... 76

24. > Horse gins, longitudinal and transverse

25. S views,

Top headings, getting in the crown bars,

83
84
85
88
97

26.

28. — Getting in the bars for the tops,

29. — Miner at work in the top,

30.— Brob, ....

31. — Miners at work in a length,

32. — Leading frame, skewback, .

33. — Diagram, method of setting the leading

frames, . . . . . 99

34. — Iron dogs, or holdfasts, ... 99

35. — Method of removing the bars, . . 103

36. — Keying-in laggins, ... - 103

37. — Miners drawing the crown bars forward, 119

38. — ^Timbering in chalk tunnels, . . 124
39. — Timbering face of tunnel, . . .131

40. — Bricklayer keying-in junction, . . 136

41. — Entrance to Blechingley tunnel, . 138

42. — Entrance to Saltwood tunnel, . . 139

43.— Section of ditto, .... 140

44.— Shaft towers, 141

45. — Culvert centre, 143

46. — Skip and tools, . . . tailpiece.

2 PRACTICAL TUNNELUNG.

The junction of the two fonnations at this place is described in an interesting
paper read before the Greological Society, April 17, 1844, by H. Warburton,
esquire, the President, containing some results of an examination of that
locality, in which I had the pleasure of assisting him ; and is represented in
the following section.

London Clav

ellow day, . . thickness not determined.

Blue or slate-coloared clay, thickness 10 to 15 feet.

Plastic Clay formation:

ft. in.

2. Rolled flint pebbles cur shingle, . thickness 1 10

3. Fine fawn-coloured sand, • . .03

4. Lignite, . . . . . . . Oi^

5. Fine fawn-coloured sand, . . . . .20

6. Ferruginous sand, with marine fossils, oyster shells, and cerithia 4

7. Loose grey sand, with fragments of cerithia, . .08

8. Strong black cky, . ^ . . . 10

9. Black clay and sand, with fragments of oysters and cerithia, . 9

10. Black dirty sand, . . . . . .04

11. Dark sand, containing fossils, oyster shells, &c. . .00

12. Calcareous stone, containing paludina, unio, kc (freshwater fossils) 6

13. Decomposed stone and sand, with oysters, kc. . .03

The shells belonging to the upper part of the Plastic Clay series in
this neighbourhood have been well described by Dr. Buckland in the
fourth volume of the first series of the Greological Society's Transactions,
but the occurrence of the paludina and unio in the stratum No. 12 of
the above section, which are fireshwater shells, thus included between
marine fossils, appears to have escaped obsen-ation, till now discovered
by Mr. Warburton; who describes the stone in which they are em-
bedded, as septaria of a texture considerably more earthy than the
septaria of the London Clay usually are.

The line of Railway continues upon the Plastic Clay as fiu: as Combe Lane,
Croydon ; where the Chalk crops out firom beneath the sands of the last named
formation, and is distinctly to be seen on the north-east slope of the cutting.
The Railway then crosses the great Chalk range that extends firom Dover to

EOLOGICAL FEATURES*

Hampshire, and rises towaids the Chalk escarpment at Meretham in Surrey,
where its greatest summit level between LoEclon and Dover is attained in the
tunnel near that place.

In the deep cutting at the south of the tunnel, a good section of the Upper
Green Sand stratum appears, cropping out from beneath the Chalk; this is
succeeded at the village of Mersthara by the Gault, through which the road to
Blechingley has been lowered that it might be passed under the Railway*

At a short distance further southward, the Lower Green Sand formation rises
to the surface, in beds of fawn-cx^loured sand, very sihcious, and good for
Engineering purposes. The middle beds of the Lower Green Sand, as indi-
cated by the presence of rushes and wet land, next appear; and these are
followed by the lower beds of the same formation, which contain the Kentisli
ragstone^ fiiller's earth, &c. — the fuller's earth pits of Nutfield being near this
locahty- The lower beds of this formation rise to a considerable height, and
form the range of sand hiUs that passes through the country, paiallcl to the
great chalk range before named.

The place where the railway crosses the sand range is called Redstone HUl,
and is the point where the Brighton radway diverges to the south, while the
Dover railway passes round the hUl with a curve of half-a-mile radius to the
eastward; and towaids the further end of this curve, near to a bridge at
Robert's Hole farm, the next inferior stratum, the Weald tlay, emerges from
beneatli the sand. This spot may be ftirther identified by the greater width of the
excavation, or flatness of the slopes, occasioned by the slipping of the earth at
the junction of the two fonnations, where much water was present. In making
this excavation, some stone was found, that was mucli jointed, and contained
iimumerable foBsUs, which, upon examination in April 1843, by Mr.Warburton,
Dr. Fitton, Mr. Austen, and myself, was found to include some of the most
characteristic of M. Leymerie's Neocomien species, with a few belonging also
to the quarrystone of Ilythe; as, area raidini, panopcca depressa, pholatlomya
acutisulcata (Leymerie), pecten obliquus (interstriatus), pinna sulcifcra, ger-
vUlia aviculoidi^s, pema mulleti, p. ala?fomiis, trigonia dccdalea, t. Fittoni,
gryph«ea sinuata, nautilus radiatus, &c. This stone appears to correspond
with the Atherfield rocks in the Isle of Wight ; which it resembles m its
mineralogical and geological character. [See paper, by Dr. Fit ton, read before
the Geological Society, May 24, 1843, entitled '' Observations on the Section of
the Lower Green Sand at Atherfield, on the coast of the Tsle of Wight"]

^ PRACTICAL TUNNELLING.

From Redstone Hill the line passes eastward, along the Weald Clay, in suc-
cessive cuttings and embankments for many miles, except that near Bleching-
ley there is a timnel, bearing that name, formed through a spur of Tilburstow
Hill : the Weald Clay at this place is indurated into a shale, or blue bind, and
being full of joints and fiiults, caused much difficulty in the work, as will be
described in the following pages. The fossils found during the construction
of the tunnel, were, portions of the iguanodon, hylceosaurus, cypris, paludina,
clathraria (Lyelli), &c. &c. and a fine specimen of the lepidotus (Mantelli),
presented by me to the Geological Society, accompanied by a short paper
upon the subject of the strata at this place, which was read at the Society's
meeting on February 2l8t, 1844.

Near the town of Ashford the line leaves the Weald Clay, and again enters
upon the Lower Green Sand formation, which continues to be its base as far as
Folkestone, a distance of about fifteen miles : the summit is passed by means
of a Tunnel, at Saltwood, not far from the out-crop of the Sand from beneath
the Gault ; consequently the shafts were sunk through the upper beds, and
the tunnel is formed at the junction between that and the middle bed ; where
a large quantity of water was encountered, which greatly retarded the progress
of the works. Among numerous fossil remains found at Saltwood, chiefly in
ferruginous concretions, the following may be particularly enumerated : nauti-
lus radiatus, gervilia aviculoides, terebratula, tethys major, panopoea, trigonia
alceformis, venus, cardium, tornatella, pecten quinquecostatus, p. orbicularis,
&c. &c. with fossil coniferous wood pierced by gastrochaena ; together with a
remarkable product, a new and beautiful resin, which partakes of the properties
of amber and of retin-asphalt, and is principally marked by its clear red colour,
its infiisibility, and the difficulty with which it is acted upon by many chemical
solvents. I was indebted to Mr. Edward Solly, through the kindness of Dr.
Fitton, for a chemical examination of this substance, the results of which are
inserted at length in a paper read before the Geological Society, June 7th, 1843,
giving an account of an investigation of the strata from the summit of the Chalk
escarpment above Saltwood tunnel to the sea at Hythe ; or, at right angles
both to the range of hills and the direction of the line of Railway in that locality.
It may not be uninteresting to insert the result of such examination.

The Upper Green Sand stratum, which at the back of the Isle of Wight is
one hundred and four feet thick, is here altogether wanting, it having tliinned
out at this place.

GEOLOGICAL FEATURES.

Strata from beneath the Chalk to the Wealden, through Saltwood.

ft.

in.

Upper Green Sand,

(wanting,-

-but)

at Folkestone, five miles distant, it is in thickness

Gault

126

Lower Green Sand.

ft.

in.

Upper division.

•

Middle ditto

•
ft. in.

•

158

Sand above the quarries,

406

Quarry Rock,

(

178

6 1

Sand and Stone, previously concealed 14

f •

Clay beneath the sand and stone

. 49 6
he Wealden

•

Total thickness from the Chalk to t

547

Near Folkestone station the line leaves the Sand, and crosses the Gault
formation; where, at the junction of that stratum with the Upper Green
Sand, and then of the Chalk above, a tunnel is made through the hill to the
imdercliff called the Warren, and from thence to Dover, entirely in the Chalk,
through and along the hce of the cliflfs; — altogether one of the grandest
Engmeering Works in the kingdom ; — and where Mr. Cubitt, the Engineer-
in-Chief to the Railway Company, so successftdly introduced the use of gun-
powder in blasting rock upon a great scale, especially in removing that large
mass of chalk, " The Round Down," on January 26th, 1843: the particulars
of which are given by Lieutenant Hutchinson, R. E., in the sixth volume of
the Professional Papers of the Corps of Royal Engineers.

Such are the Geological Features of this line of Railway.

The Engineer-in-Chief charged with the construction of the line was
William Cubitt, esquire, F. R. S. &c. &c. That gentleman divided the whole
line into thi-ee districts ; over each of which he appointed a resident Engineer.
To that nearest London he appointed the author; the district through the
Weald of Kent was assigned to Mr. Barlow ; and the third, or Dover district,
was given to Mr. Wright. In the district first named the Blechingley Tunnel
is situated: and, upon its completion, the author was ftirther appointed to
superintend the construction of the Tunnel at Saltwood : — ^the particulars of
which two works form the subject of the following pages. And to my col-

b PRACTICAL TUNNELLING.

leagues, and myself^ it is gratifyiiig to know that our Engineer-in-Chief has
expressed himself, both in public and private, satisfied with the maimer in
which we, severally, have carried his views and intentions into execution.

A general description of the Blechingley and Saltwood Tunnels, explaining
their cost, and the circumstances under which they were constructed, is an-
nexed, previously to entering upon the details of the same.

BLECHINGLEY TUNNEL.

So named from the Parish where it is situated, is in the coxmty of Surrey,
and about twenty-five mUes from London. The Tunnel is twenty-four feet
A>ddc in the clear, and twenty-one feet from the upper surface of the rails to the
crown of the arch ; its figure is elliptical above the skewback, or springing of
the invert : the versed sine of the invert is three feet, and the level of the
rails is one foot above the skewback. The Tunnel is inclined from west to
east, at the rate of three feet per mile. The dimensions of the brickwork
varied, and were regulated according to the appearances of the ground, from
time to time, as the lengths, which were twelve feet long, were excavated :
these particulars are given in figure 3, plate i. the left half of which shews
half the cross-section of the Tunnel at Blechingley ; and the right half, that at
Saltwood. Figure 1, plate i., is a longitudinal section of Blechingley tunnel,
and figure 2 that of Saltwood ; she^^ing the positions of the working shafts,
and of the Obser\'atory, &c. — all of which subjects will be described m fiirther
details in the course of the work in each tunnel.

The ridge through which the Tunnel i)asses is the main axis of elevation of
this part of the country ; and, from the dip of the strata in both directions from
its summit, forms a north and south anticlinal axis ; its direction being that of
the meridian, nearly ; which, so far as I can judge, extends from the chalk range
between Godstone and Merstham in Siurey, to about Ditchling in Sussex:
the waters which fSall on the surface along the said line of direction, form
sources or feeders to the rivers Medway and Ouse, on the cast, and to the
Mole and Adur on the west. Besides the inclination of the beds both ways
from the axis, they dip to the north at an angle of about thirteen degrees ;
but westward, from the summit of the ridge, there is no regularity in this
respect, the strata lying as it were in heaps, at almost every angle, from five

BLECHINGLEY TUNNEL.

to sixty degrees, and dipping in all directions^ from west-by-north to east ;
besides which a detached mass of sand-rock lay across my path, near the top
of the Tunnel, and from whence a great body of water was discharged into
the workings, causing no small trouble and difficulty.

The Blue Clay of the Weald in which I w^as working was at first greasy to
the touch ; and when drj% and in situ, formed a hard shale, requiring an ex-
tensive use of gunpowder in its excavation, but upon exposure to damp and
atmospheric action, it swelled considerably and then slaked : this obliged me
to close-pole the face of the work in all directions as far dawn as the lower sUl,
and frequently to the bottom* The expansion, or swelling, was occasionally so
great as to thi^eaten the hurling in of the lengths after they were completely
timbered, and would probably have done so but for constant watchfulness, and
strong timbers properly applied. The pressure upon the work was sometimes
so great that sound oak bai*s, fourteen or fifteen inches in diameter, were
cracked and broken as if they had been mere sticks*

The pressure we had to contend with was variable, and uncertain in the
highest degree ; sometimes a length could be got out, and the arch turned,
without any apparent movement of the earth around and above us ; at other
times, the ground when partly excavated would begin to move, and press upon
the bars on one side of the aich ; at others, it would act upon the crown bars ;
the former action was principally confined to those parts of tiie Tunnel that
were deepest below the surface, whilst the greatest pressure (which mostly
acted upon the crown) took place towaida the ends of the Tunnel, where the
surface was so much nearer to the arch. It sometimes occurred that after a
length had been excavated satisfactorily, and by the time the bricklayers had
built up the side walls, the weight on the top was so great as to press the bais
down to an extent nearly equal to their own thickness, wliich was seldom less
than fifteen inches ; consequently, when the centres were set, there was not
sufficient space between them and the bars to insert the brickwork of the arch :
the remedy for this was, to remove the poling, and excavate more earth from
above the bars^ and to prop them again at a higher level ; which occasioned
considerable loss of time, and consequently increased the expense.

In one of the pits, — No. 11, at the east end, — ^this weighting of the crown
occurred constantly after getting in three lengths west of the shaft, and there-
fore we elevated the extremity of the bars suflSciently high, upon their first inser*
tion, to allow for the expected subsidence: in the other pits its occuiTcnce was

O PRACTICAL TUNNELLING.

uncertain ; consequently it was impossible to provide for it, without running
the risk of having a great opening above the arch, to be filled solid with brick
work, or with earth, which is often imperfectly done, and would be liable to
bring a greater weight upon the work when the earth again takes its bearing,
after the mass has been in motion. It is the general movement of the mass in
adjusting itself to equilibriimi, after the disturbance occasioned by the excava-
tion, that causes the weight, and whose searching influence finds out the weak
points in the work.

The greater pressure upon the work in shallow ground over that where the
tunnel is very deep below the surface, I can explain only upon the supposition
that, in the former case, the whole superincumbent mass is acting perpendicu-
larly downwards ; whilst, in the latter case, a small portion only gets into
motion, the upper part acting as a key, (if I may so express myself,) by which
the mass supports itself This action was clearly shewn in pit No. 11, above
referred to ; where the working below could be distinctly traced upon the sur-
fece of the ground, by its sinking in the form of a basin as our work proceeded,
and at the same time cracking into large fissures.

The sinking of the shafts was commenced in the beginning of August, 1840.
These were down to the depth necessary for the shaft^sills by the middle of
September ; which, together with the ftirther sinking, including the square
timbering to the bottom of the Tunnel, was completed by the end of October.
The driving of the heading at the level of the top of the invert was then com-
menced, and was finished by Christmas. From this time till February 12th,
1841, preparations were made for commencing the excavation of the Tunnel:
these consisted in making a gin for each shaft, and the ground-moulds, leading-
frames, and centres. On the above date the miners broke ground in No. 3
pit, being the first commencement of the tunnelling ; but it was not until early
in April that the whole of the shaft;s were got to work ; and as soon as each
was started, the work was pushed on with the utmost vigour, night and day.

On September 3d, the first junction was effected; and on November 1st,
the last junction was keyed in ; the Tunnel, as originally intended, was there-
fore complete ; but it was resolved to extend it at each end in consequence
of the backwardness of the open cuttings that were let to two diffierent con-
tractors. My instructions were, to extend the tunnel until I should meet the
open cuttings, and thus enable the Directors to open the Bailway to the public
at the time proposed, which otherwise could not have been done. The exten-

BLECHINGLEY TUNNEL,

ston of the Tunnel, and the erection of the entrances, were not completed until
early in the following May; and the Railway was opened to the public on
May 26th. The Tunnel, as completed, is 1324 yards in length.

Although it would appear, from what has above been stated, that the sink-
ing of the shafts did not commence until the month of August, — yet this must
be understood as in reference to the working-shafts only ; because^ in the pre-
ceding February, two trial-shafts were sunk, to ascertain the character of the
ground in which the Tunnel was ultimately to be constructed. The particulars
of this work wiQ be given in chapter iv. After two trial shafts had been sunk,
it still appeared desirable to examine the ground at two intermei^ate points ;
accordingly two other shafts were commenced early in the spring, and, to save
expense^ they were made the full size of working-shafts in the first instance,
with the intention of employing them as such in the course of the work. The
working-shafts were nine feet diameter in the clear, while the trial-shafts were
but six feet. These large shafts had, however, not been far proceeded with,
when an unpleasant diiference arose between the Company and the Occupiers
of the land, who demanded an exorbitant amount of compensation, forbidding
the proceedings untU such was paid. Under these circumstances the work
was suspended until the following August ; when the said differences ha\ ing
been adjusted, possession of the land was obtained, and the works were
prosecuted with vigour.

Previously to laying the permanent way, a culvert was constructed upon the
invert J throughout the Tunnel, as shewn in section, figure 3, plate 1. The
Tunnel was also Ume-whited twice, with a view of increasing the light;
but this did not answer as was expected.

The monthly rate of progress, during the time the work was in ftill activity,
was as follows. During May, 1841, 104 yards were completed; — June, 185
yards ; — July, 264 yards ; — and August, 228 yards. The bricks were all made
on the ground, and wheeled or carted to the various shafts ; their cost when
thus delivered at the pit's mouth, including waste and aU other expenses incur-
red, was £2 :1s: 6d, per thousand. A portion of the bricks was made during
the ^vinter of 1840, and dried in flues, by coal fires ; which increased the cost
considerably, [See paper by the author, on this subject, read before the
Institution of Civil Engineers, April 25th, 1843.]

The following abstract will shew the whole cost of this important work.

PRACTICAL TUNXELLINO.

ABSTRACT OF THE COST OF BLECHIN6LEY TUNNEU

Materials :

Bricksy • • . •

Cementy • • •

Timber,

Wrought and cast ironwork, and ironmongery

Miscellaneous : including pumps, weighing

machine, broken stone for roads, lime,

ropes, stationery, and all materials not

included under any of the above heads.

Labour :

Mining,

Brickwork

Shafts, heading, and prelimi-
nary works.

Driving the tunnel — ^including \
the hire of gin-horses, and the I
open excavation, for length- i
ing the tunnel, . • /

' Shafts, and preliminary works.
Constructing the tunnel, and \
lengthening the tunnel in (
open excavation, . ;

£ 8. d.

30,409 12 10

11,016 11

11,341 19 2

2,499 3 1

6,555 2 8

3,273 2 8

15,727 7

378 8
11,265 4 11

Miscellaneous :
Including the erection of the tunnel entrances, culvert
through the tunnel, part ballasting the tunnel, construc-
tion of machinery, erection of buildings, carpentry, i
sawing, clerks' and inspectors' wages, &c. &c. . j

8. d.

19,000 9 8

11,643 12 11

6,980 16 6

Deduct estimated value of plant, removed to Saltwood, upon the
completion of Blechingley tunnel

Total Cost of Blechingley Tunnel, . . . :

8. d.

61,911 18 8

37,624 19 1

99,536 17 9
4,300

95,236 17 9

Being at the rate of £71 : 18s : 7d. per lineal yard, for the whole tunnel;
1324 yards in length, or three quarters of a mile and four yards.

BLECHINGLBY TUNNEL.

The foregoing statement sets forth the total cost of the Tunnel^ and the price
per yard forward : the details and expense of each portion of the work will be
given in the following chapters, under theii* respective licads.

The construction of the Tunnel was entrustedn, by Mr. Cubitt, wholly to the
author, who at the same time had charge of the works let to contractors,
extending over nearly fourteen miles of the Railway. Upon its completion, he
proceeded >^dth the plant to Saltwood, to construct a similar Tunnel there. In
the execution of the preliminary works at Saltwood, difficulties of no ordinary
character occurred ; but by overcoming them the work was subsequently made
comparatively easy, as will hereafter be describedp The Board of Directors
afterwards determined upon letting the constriction of the Tunnel (itself) to
contractors ; leaving the author to superintend the same, and look after the
interests of the Company. Under these circumstances, the cost of each portion
of that work cannot be given in detail, as will be done in the case of Bleching*
ley Tunnel, except for the preUminary works; but the total cost will be
supplied ; and, what will be at least as important, the amount or quantity of
labour expended in the construction of various parts of the Tunnel, wiQ be
given, and a comparison be drawn between such statement and the corresjiond-
ing labour at Blechingley*

SALTWOOD TUNNEL-

This Tunnel is also named after the Parish wherein it is situate ; and is 954
yards in length. Its form and dimensions are precisely the same as of that at
Blechingley, except that the versed sine of the invert was made three feet six
inches, instead of three feet. The thickness of the brickwork did not vary so
much, neither was its average thickness so great ; which ^ose from the more
homogeneous character of the ground, after it had been diained by the preli-
minarj* works. The Tunnel is inclined towards Dover, at the rate of twenty
feet per mile, or 1 in 264. An examination of figs, 2 and 3, plate 1, will shew
all that is requisite of these particulars. The former is a longitudinal section ;
and the right-hand half of the latter Lg a cross section of half the tunnel.

The Tunnel is constructed at the top of the middle beds of the Lower Green
Sand ; and is about ninety feet below the surface of the ground. This stratiun
contained, as it usually does, a great body of water, which occasioned the

12 PRACTICAL TUNNSLLINO.

difficulty in sinkiiig the shafts, and driving the heading, that will hereafter be
described.

The sinking of the working-shafts, which were nine feet dear diameter, was
commenced on the 11th of June, 1842, and was carried on in the usual
manner. The earth was raised to the surfcu^ by means of the common wind-
lass, or jack-roU, at which four men could work : and had circumstances
continued favourable, it was intended that no other machinery should have
been used for that purpose, until the sinking and heading were completed ; as
had been previously done at Blechingley. An oak or ehn curb was Inserted
at the bottom of each excavated length, on which the brickwork was carried up
to underpin the preceding curb. The sections of the shaft;, plate 2, shew the
windlass, &c. and the curbs inserted in their places ; and give a correct notion
of the whole. The bottom curb was so placed that the brickwork of the shaft
should terminate eight feet above the level of the intended soffit of the arch.

The difficulties commenced about July 13th; when the ground became a
perfect quicksand. The sinking of the shafts, and driving of the heading,
henceforth became difficult, tedious, and expensive, compared with what had
been expected* Manual labour was insufficient to draw the water to the
surface, and the horse-gins that had been brought from Blechingley were
erected, and barrels holding one hundred gallons were substituted for the
twenty-gallon buckets worked by the men. The average quantity of water
drawn from each shafts during the remainder of July, was 700 gallons per hour,
when it increased to 1600 gallons per hour, which brought with it large por-
tions of sand from the back of the timberings and added to both the difficulty
and danger of the work ; to secure the sand from running, the back of the
polings was, at the time of their insertion, well packed with straw, which let
the water pass, but retained the sand: this kind of packing was subsequently
used throughout the worih:, and in all cases, when properly done, it answered
the purpose.

By the end of August the average quantity of water drawn from each of the
pits amounted to 23 banels of 100 gallons each, per hour ; whilst at the same
time no more tham one^ialf of a cubic yard of sand was raised to the surfiice.
On the 31^ of that month, the quantity of water drawn from Xa 7 pit aver-
aged 37| barrels per hour, which, together with the small quantity of earth
raised^ gare, as the woik of each horse for three hours, 42,637 lbs. raised one
foot hi^ in a minute.

8ALTW00D TUNNEL.

The miners complained much of their employment, and were obliged to have
three, and in some cases four shifts in every twenty-four hours ; they were wet
to the skin in a few minutes after they entered upon their work, and, in many
instances, illness succeeded their constant working in the water. In addition
to the quantity of water, we were troubled with foul air in shafts No. 10 and
13, which prevented the candles burning. (The latter was a supplementary
shaft, to &cilitate the bringing up the heading along the intended open cutting^
and, therefore, is not shewn in the longitudinal section in plate 1). The
headings thus circumstanced were ventilated by an air-machine, or what the
workmen commonly call a Blow-George, fixed at the top of the shafts ; which
is simply a fan-wheel revolving rapidly in a spiral-formed box, driving fresh
air into the workings below, through tubes fixed in the shafts and along
the headings, where the men were at work.

About the end of September, the person who supplied the horses wished to
withdraw them from the works, as so many had been knocked up, and several
had died. Accordingly, endeavours were made to obtain others ; and notices
were issued around the country, advertising for horses ; but the assistance thus
obtained was very trifling, as the numerous carters then in the neighbourhood
declined putting their cattle to the labour. The same party was therefore
prevailed upon to continue his help.

The following statement will shew about the amount of labour exacted from
each horse, at the end of August, at the shafts then at work.

Nnmber of PMMb

railed one foot high

per minute, by each

HotM.

Number of Boon
each Hone worked.

24,475

22,626

24,535

42,687

22,584

30,820

14 PRACTICAL TUNNELLING.

More minute particulars of the difficulties arising from the influx of water,
and of the mode of proceeding whereby they were overcome, will be inserted
in chapters vi. and vii. ; wherein the square timbering and heading driving
are described, — as being a more appropriate place for their insertion.

These exertions were necessary, because it was desirable that the prelimi-
nary works should be got through without having recourse to steam power for
pumping ; as that would at once have involved the Company in a great ex-
pense ; especially, as it appeared probable that if a heading, or adit, could be
made quite through the hill, at the level of the bottom of the tunnel, with an
outlet at the east end leading to the natural drainage of the coxmtry, the whole
of the water would run off from the works, as it collected, and leave them suf-
ficiently dry to admit of the work being proceeded with ; which was as much
as, at that time, appeared reasonable to expect, the proposed inclination of the
tunnel in that direction being ample for the purpose. This, by perseverance,
was accomplished ; but it was not until the end of October that the heading
was completed, and the drainage effected.

The heading, when completed, was altogether 1250 yards in length ; as it
not only extended throughout the length of the tunnel, but also under the
open cutting at the east end, before an outlet could be obtained for the water ;
which there runs off into the valley of Newington, and joins the natural drain-
age of a large district of country that empties itself into the sea, at Hythe.

When the heading was effectually opened, it was considered desirable to
ascertain the quantity of water that was continually passing away from it.
Accordingly, a gauge was fixed at its outlet, which narrowed the opening to
twelve inches in width, and the depth of water flowing over the waste board
(or between the sides of the twelve-inch opening) was noted, from time to time.
At first the depth was five inches ; which indicated a discharge of about 359
gallons per minute, or 21,540 gallons per hour ; but this quantity afterwards
diminished, and for a length of time it averaged four inches in depth, which gave
about 257 gallons per minute, or 15,420 gallons per hour. The first of these
quantities being noted as soon as the heading was completed, confirmed the
accuracy of the registered quantity of water drawn to the surface by horse
power, as will be explained in chapter vii.

The following table shews, approximately, the quantity of water, in gallons,
and in cubic feet, per minute, that passes over a waste board twelve inches
wide.

8ALTW00D TUNNEL.

Deptbonthe

Water, per minute.

mite board,
iainchet.

In Imperial
Gallon!.

In cubic
Feet.

321

5-14

90-8

14-53

167-0

26-71

257-0

41-12

350-2

57-47

472-1

75-54

505-0

95-20

726-9

116-30

867-3

138-77

1015-1

162-42

For any other width of gauge, a proportionate quantity of water will be
discharged.

On the Ist of November the Board of Directors contracted with Messrs.
Grissell and Peto, and Betts and Son, to construct the Tunnel for the sum of
j685,000, exclusive of the entrances, they allowing the Company £3,006 for the
plant and materials, as they then stood upon the ground. The whole to be
completed on or before the 1st day of June 1843, or the Contractors to forfeit
the sum of £50 per day, from that date.

The work was executed under the author's superintendence, as Resident
Engineer, and completed by the time named. The preliminary works that cost
so much labour and anxiety during their construction, ftilly answered the
purposes for which they were designed, and drained the ground more effectually
than was anticipated ; this necessarily facilitated the progress of the work, and
was highly advantageous to the Contractors.

It now only remaias to give an abstract of the cost of this tunnel, before
proceeding to the details of the setting out and the construction of the works.

1ft

PRACTICAL TUNNELLINO.

ABSTRACT OF THE COST OF SALTWOOD TUNNEL.

Expenditure previous to the time that the Works were contracted for.

Materials :

Bricks, including carting.
Cement, ....

Lime, • . • •

Timber, ....

Ironwork and ironmongery,
Straw, ....

Ropes, ....

Cottages, office, store, &c.
Roads along the whole of the works.
Miscellaneous materials.
Plant from Blechingley tunnel, .

Carting and Horse-hire :
Carting on works.
Hire of gin-horses.
Materials from Blechingley tunnel.
Freight, &c

Labour :

Mining, ....

Brickwork, ....

Sawing, ....

Miscellaneous, . . ,

MiscBLLANEOUs Expeoses,
Totals,

For

Preriminary

For

SUMS.

Woriu.

the Tunnel.

f 8. d.

£ 8. d.

3,210 17 3

14,527 12 7

17,738 9 10

• a .

253 2 6

50 14 4

• . •

50 14 4

1,028 9 4

1,420 1 4

3,348 10 8

317 5 5

159 2 2

476 7 7

119 7 10

• . •

119 7 10

8« 8 9

• . .

86* 8

248

310

400 18 7

470 18 7

i 519 2 3

187 17 2

706 19 5

1,433

2,867

4,300

251 9 2

103 15 6

355 4 8

l,5a'> 15 3

• • •

1,585 15 3

315 11 9

631 3 5

946 15 2

120

292 18

412 18

3,477 11 11

217 3 4

•

217 3 4

67 8

...

67 8

706 8 11

682 17 1

1,389 6

70 10

14,608 16 2

21,774 8 4

36,383 4 6

This amount added to the expenditure under the contract, will give the
total cost of the Tunnel, — as follows :

8ALTW00D TUNNEL.

ABSTRACT OF THE COST OF SALTWOOD TUNNEL.

Expenditure under the Contract, after the Preliminaiy Works were completed*

Amount of Contract,
Hoop-bond joints.

Tunnel Entrances:
Excavation,
Brickwork,

£ 8. d.

75 8 9

1,553

Additbnal brickwork, .

„ timber, •

„ labour, •
Hard white bricks, for arch.
Broken stone for ballast, •
Drains, cesspools, kc at ends of Tunnel,

Deductions : —
Tunnel lO; yards short of 964 (the con.

tract length), • • • •

Saving in shafts closed.
Saving upon white brick not carted, •
Bricks for which the Company had pre- >

viously paid, [see last page], • • S

Allow for plant, as per contract.

s. d.

a2 10 8

1,628 8 9

321 15
176 8
358 8
2,948 3 6
99 11 6
386 5 10

825 2 6

223 16 7

14,527 12 7

£ s. d.
i5,0U0

1,660 19 5

4,290 11 10

90,951 11 3

15,612 11 8

75,338 19 7
3,006

£72,332 19 7

Now, if to the above sum be added, the amount expended previous to
letting the contract, as before set forth, and the wages afterwards paid to
inspectors, &c. together with £3,006 — the assumed value of the plant, — the
whole cost of &e tunnel will be shewn.

18 PRACTICAL TUK1CELLIN6.

£ 8. d.

Prelimiiiary Works, and pievions ezpenaes • 96,383 4 ^

PaymenU under contract • • • • 72^332 19 7

Inspection, rent of land, sorting bricks, &c« kc 820 I 5

Assumed vahie of plant • • • • . 3,006

Total Cost of Saltwood Tunnel £112,542 5 6

Being at the rate of £118 per lineal yard for the whole Tunnel ; 953f yards in
length, or half-armile and 73| yards ; but upon a very carefhl admeasurement
the Tunnel proved to be very little short of 954 yards.

The bricks for Saltwood tunnel, had been contracted for previously to the
author's leaving Blechingley ; they were made at Folkestone, averaging five
miles distant from the works; and the cost when delivered, was 51s. per
thousand.

The quantity of bricks used in the construction erf Blechingley and Saltwood
tunnels ; including the entrances, culverts, shaft towers, and all contingent
works, was as follows : —

Blechingley . . 14,606,005 or 11,099 per lineal yard.

Saltwood . . 10,186,246 or 10,677 per lineal yard.

THE OBSERYATOBT. 19

CHAPTER II.

DESCRIPTION OF THE OBSERVATORY. ^THE TRANSIT INSTRUMENT, AND METHOD

OF FIXING, AND ADJUSTING.

Tunnels have generally been made straight from end to end ; and I believe
that the few exceptions (or curved tunnelsj are of comparatively short lengths,
and constructed through good ground, that would admit of a large excavation,
or cavern, to be made throughout their whole extent, or nearly so, without
requiring much timber to support the strata ; consequently there could be but
little difficulty in forming such a timnel to the curve required : but, in heavy
groimd they are made straight, not merely on accoimt of the greater difficulty
of construction otherwise (except in peculiar situations), but, for Railway pur-
poses, it would be considered unsafe for the trains to be passing and repassing
each other in darkness and a confined space, without the advantage of each
engine-fire being visible from the other train for some distance.

The Blechingley and Saltwood Tunnels are both straight, and the centre-
line was careftdly ranged with a transit instrument of thirty inches focal
length, having an object-glass of two and three-quarters inches aperture,
mounted on a cast-iron stand. In order to command a view of every shaft
on the work, the instrument was set up on the most elevated spot of ground,
as near the middle of the tunnel as possible ; and, that the view might be
uninterrupted by the machinery and timber about the shafts, as well as the
earth when brought up from below as the work proceeded, the transit was
elevated considerably above the surface, by the erection of an observatory;
and as such a building is only required during the construction of the tunnel,
it is generally but a temporary erection ; although there are instances of obser-
vatories for such works having been buUt of an expensive character. The
observatories at Blechingley and Saltwood were nearly simUar to each other ;
and the following engraving, shewing that at Saltwood, Avill give the reader a
knowledge of the kind of buUding that will be sufficient for all such purposes,

PRACTICAL TUNNELLING.

and, being composed of brick and timber, it may be taken down at an advanced
period of the work, and the materials used up.

THE OBSERYATORT.

The annexed engraving shews a section of the Salt-
wood Observatory, taken in the direction of the Tunnel,
with the brick pier in the centre, surmounted with the
Transit Instrument. The pier, which was 30 feet high,
was erected over the centre-line of the intended tunnd,
and quite independent of the rest of the building ; so
that any motion given to the building by high winds,
or otherwise, might not be communicated to the pier.
The object to be attained was great steadiness to the
Transit, which could not be ensured so well as by an
erection of brick-work. The dimensions of the pier,
and its counterforts, are given in the engraving. A
flat stone was set on the top of the pier, to which the
iron stand of the Transit was screwed down, as shewn
in detail in the engraving of the instrument itself,
which will be given in the next page.

The building requires but littie description : it was
composed of larch poles, intended for and afterwards
used in the works, stiffened with struts and cross-
pieces; the upper part, or observatory-room, was en-
closed with quartering and feather-edged boards. The
ascent was by steps from below through a trap-door in
the floor ; and the floor was trimmed so as not to touch
the brick pier by about five or six inches. Narrow
openings were made in the sides of the room, in the direction of the tunnel,
through which the observer might look each way for the ranging of the lines ;
these were closed with small sliding shutters, so that one or more of them could
be opened at a time, leaving either a large or small aperture, as occasion might
require. The whole was surmounted by a telegraph, having two arms for the
observer to signal for the ranging lines to be moved either to the right or to the

THE OBSEEVATORY,

left ; and when the line was found to be correct, both arms were extended, thus
denoting that tlie line was to be moved both to the right and to the left at the
same time, — a thing impossible, — it was therefore to be fixed in its then position.
In the engraving (facing the title-page), representing the works above ground
at Blechingley, the telegraph is shewn as signaling to the men setting the
lines on the ranging*frame of the shaft at the right-hand of the picture.

THE TEA^'S1T INSTRUMENT.

« 1

The annexed engraving repre-
sents the Transit Instrument;
which consists of a telescope,
having an axis at right angles
to its length, supported on a cast-
iron stand. This is a standard
instrument in every astronomical
observatory ; where it is adjusted
to describe or define a vertical
chxle passing from the north to
the south points of the horizon,
through the zenith of the place,
and is the best means of observ-
ing the passage of the celestial
bodies across the plane of the
meridian, from which time is correctly derived : hence its name, " Transit In-
strument ;" and, thus employed, it may not inappropriately be called the hmul
which points to the time as shewn by that unerring dial, the starry heavens.
The same construction which renders it the instrument best adapted to trace a
vertical plane for astronomical purposes, makes it equally so to set out a right-
line on the surface of the earth ; or, our problem more properly is, — to find an//
number of points in a straight line connecting two given distant points^ the
ifistrument to be situated also between the given distant points. The line thus
connecting the distant points is the base of a vertical plane of small extent.
To do this, the telescope, a a^, is made to revolve vertically upon u horizontal
axis, B B, the pivots of which are supported by the upright arm?^, c l. oi tlie
iron stand.

22 PBACTICAL TUNNELLING.

It does not appe^ to be necessary in this place to explain how a vertical
circle is described by such an instrument, but that its performance may be
correct it is essential that the optical axis of the telescope, or line of coUimation
as it is called, should be precisely at right angles to the horizontal axis about
which it revolves; and also that the extremities or pivots of the said horizontal
axis where they rest in their bearings on the iron stand be precisely level
with each other.

The telescope resembles those of theodolites and spirit-levels, and for terres-
trial purposes is supplied with a similarly-arranged system of cross wires, the
intersection of the centre wires with each other, represents when in proper
adjustment, the line of coUimation, or optical axis of the telescope. The slide
D, or eye-piece, is movable in or out, to obtain distinct vision of the cross wires;
an adjustment that must be made or verified each time that the instrument
is set up for use, and so long as its eye-piece remains imdisturbed it will
require no repetition for the same eye ; but would, in all probability, require
alteration to suit the eye of another person. In adjusting the eye-piece to
obtain distinct vision of the wires, it will be found that it can be accom-
plished vnth. greater certainty by directing the telescope to a white sheet of
paper, held or fastened at a little distance off, or even pointed to the sky, so
that the wires may appear to be projected on a clear disc.

The screw e gives motion to a rack and pinion, which is the means of dimi-
nishing or increasing the distance between the object and eye-glasses, or rather
I should say, between the object glass and the cross wires, and thereby produces
distinct vision of the distant object to be observed. It should be ascertained
that both of the above adjustments be quite perfect, before any determinate
observation is made, otherwise a parallax will exist, which will prevent
an accurate result being obtained : what is called parallax, in this case, is an
apparent motion between the object viewed and the wires of the telescope, and
is detected when the observer moves his eye up and down, or sideways, while
looking through the telescope. The adjustment of the eye-piece to the wires,
and of the wires to the focus of the object-glass, so as to avoid parallax, requires
a nicety which practice alone will impait to the observer; and which must
always be repeated till it is accomplished.

That the weight of the telescope may not cause the horizontal axis to bend,
the latter is made of two cones, b b, whose bases are connected together (to form
the axis) and to the telescope, by the intervention of a sphere, f, through which

THE TRANSIT IN8TR01ifENT.

the telescope appears to pass ; it in reality however, forms the nucleus of the
instrument, to which the tubes a and a^ forming the telescope, as well as the
two cones fonning the axis b b, are attached. The apex of each cone is finished
with a steel or bell-metal cylindrical pivot, turned and ground upon the axis as
true as possible* Much of the excellence of the instrument depends upon this
being correctly and well done, for if they are not true, the telescope cannot
possibly describe a vertical plane. These pivots work in v-formcd sockets, or
y's, as they are technically called, which surmount the upright arms c c, of
the iron stand.

To test the horizontality of the axis, a spirit-level, h, is placed striding across
the instrument with its standards resting upon the pivots ; for it is clear that if
the pivots of the axis are horizontal (all other things being correct) the telescope
when elevated or depressed, or turned completely over and pointed in the
opposite direction, must continue in the same vertical plane ; when we thus
say *' the telescope," it must be understood to mean the line of coUimation, or
central intersection of the cross wires of a properly adjusted instrument* One
or two thin brass plates aie generally supplied in the box with the instrument,
which may be attached, by a milled-headed screw, to the top of the arms of the
stand. These are notched at their tops to receive a pin fixed in the end of the
tube of the level h, which thus prevents the possibility of the level falling off
the instrument when in use.

The cross wires in the telescope generally consist of a single thread of a
spider's web, which, at the same time that they are extremely fine, are perfectly
opaque, and are not found to be fringed ynth light along their edges, as is
sometimes the case when other fine material is employed. The volume of light
which passes through the telescope in the day-time shews up these cross wires,
but in using the instrument at night to range a distant lamp, or tf need be,
underground, the wires would not be visible, and, therefore, the instrument
would be useless under such circumstances ; to obviate this, and also to enable
the possessor of such an instrument to amuse himself at his leisure, (if he does
nothing more useful), with observing transits of the heavenly bodies, one of the
pivots is perforated through the cone b, and sphere f, and the light from a
lamp or lantern adapted to the top of the stand passes through the said perfo-
ration, and falling on a diagonal reflectorj situated in the sphere, is thence
thrown upon the focus of the instrument, where the wires are fixed, near to
the eye-piece. The reflector is also perforated to allow of the passage of the

24 PRACTICAL TUNKELUNG.

cone of rays in their convei^nce from the object-glass to the said focus, and
thus distinct vision, both of the distant object to \)e viewed and of the cross
wires is obtained by night as well as by day. The detached figore i shews the
lantern in its position when used as above described.

The iron stand is &stened to the stone after it is placed in the required
position, by means of the screws k k, which work into sod^ets previously let
into the stone; the holes in the stand through which the screws pass are
drawn, to allow of a small motion being given to the stand to perfect its adjust-
ment in position, before the screws are made tight.

The adjustments and fixing of the Teansft Instrument. — ^Long before
it is necessary to commence working operations, the direction of the centre-
line of the intended tunnel must be known nearly, and should have ^been
staked out

The most suitable spot must be selected for the Observatory, so as to com-
mand a view of the whole length of the work, and its erection forthwith pro-
ceeded with; also, if possible, a permanent mark should be set up at a distance
from each end of the tunnel precisely in the intended line, for fixture reference
and the occasional adjustment of the transit ; these marks should be placed
where there would be but little chance of their being disturbed or removed.
For this purpose at Bletchingly tunnel I caused to be erected two brick piers,
about five feet high, at the distance of fiill two miles firom each end of the tunnel.
There is an advantage in having them at a great distance, as £Eir as accuracy
is concerned in the adjustment of the transit, but in thick weather they
cannot be seen, and, therefore, other similar marks should also be set up at
shorter distances. All these piers were painted black, with a white line, fix)m
two to six inches wide, (according to their distances,) to denote the precise
line with which the centre of the tunnel was to be coincident throughout its
whole length. A straight line firom the centre of one of the above-described
distant marks, to the centre of the other, (in the opposite direction,) must pass
through the telescope of the transit instrument when set for use, so as to coin-
cide with the line of coUimation. How to fix the telescope in a position to
answer these conditions will be presently described.

To examine and adjust the line of coUimation. — ^When the instrument is
placed on its stand, direct the telescope to some small, distant, well-defined

THE TEANSTT INSTBUMENT.

object^ (the more distant the better,) and bisect it with the central intersection
of the cross mres ; then lift the telescope very carefiilly out of its angular
bearings, or y's, and i^place it with the axis reversed ; point the telescope again
to the same object, and if it be still bisected, the collimation adjustment h
correct ; if not, move the wires one half of the error ^ by turning the small screws^
which hold the diaphragm with the cross \nresnear the eye-end of the telescope,
and the adjustment will be accomplished ; but, as half the deviation may not
have been correctly estimated in moving the wires^ it becomes necessary to
verify the adjustment by moving the telescope the other half, which is done
by turning the screws c c, near the top of one of the arms of the iron stand.
Having thus again bisected the object, reverse the axis as before, and if half
the error has been correctly estimated the object will be bisected upon the
telescope being directed to it ; if not quite correct, the operation of reversing
and correcting half the error, in the same manner, must be gone through again,
until by successive approximations^ the object is found to be bisected in both
positions of the axis. The adjustment wiH then be perfect.

To sei the Aj^i^ of the Telescope truly horhantaJ, — Set the le^el h upon the
pivots of the axis, (as shewn in the engraving,) and by turning a miUed-headed
screw, a, near the top of one of the arms of the stand, raise or depress that y,
and with it the pivot that rests on it, till the spLrit-bubble stands central in its
tube ; now reverse the level, that is turn it end for end, and if the bubble agam
becomes central, it is clear that the axis is horizontal ; but if it should not
become central when reversed, it is equally clear that the axis is not only not
horizontal, but that the level is out of adjustment also. To effect this twofold
adjustment, half the error must be corrected by raising or depressing the screw
a on the stand, and the other half by turning the capstan screws b 6, at one
end of the level, which raises or depresses the spirit-bubble with respect to its
points of support that rest on the telescope pivots* It wiU, however, be obvious
that the axis of the instrument will have been correctly levelled by the first
part of the process, namely, raisinff or (fepressing the screw a^ even though the
error of the level be left untouched ; but it wUl be found convenient to correct
the latter error at the same time, as above described. These corrections, like
those for the adjustment of the line of collimation, ii*equently require to be
made several times before the adjustments are satisfactory ; and when perfect,
the spiiit-bubhle will remain central in the glass tube both before and after its

26 PRACTICAL TUNNELLING.

reversion. Agraduated ivory scale is fixed along the top of the level, by which
the amount of deviation from horizontality can be more correctly determined,
and which scale for astronomical purposes is made to denote the angular devi-
ation of the axis at the moment of observation. The value, in arc, of each
division having been previously determined, a correction due to such enror may
subsequently be computed, and applied to reduce the observation to what it
would have been had the axis been truly horizontal : but such minutie do not
enter into the business of a Mining Engineer.

To fix the TransiUstand on the stone pier, and set the instnmentfar use. — ^The
instrument being set on the stone, move it, stand and all, until the telescope
very nearly coincides with the two distant marks when directed alternately to
them. Having thus approximately placed it, set up the level h, and adjust for
horizontahty (the coUimation adjustment having previously been verified);
now move the instrument very quietly till the telescope coincides with one of
the distant marks, keeping the axis horizontal throughout this part of the
business; then turn the telescope over, and look in the other direction,
— (the obser\'er must always remember to remove the level befi>re he turns the
telescope over, or he will most probably injure, if not destroy it); — see if the
coincidence with the other mark is correct ; if it is not, observe the amount of
de\iation, and as nearly as can be judged move the stand laterally (or sideways)
to correct one half of the deviation, and, by gently pushing one end of the stand
from you, correct the other half. If these movements have been made judiciously,
the telescope will be fi)und, upon reversion, to cut both the distant marks ; or
otherwise they must be repeated till it is accomplished vety nearly, so as easily
to be perfected befi)re the stand is finally screwed down, which must next
be done.

Tlie position of the instrument having thus been approximately settled,
mark on the stone the position of the screw-holes in the bottom of the stand,
luid a mason can let into the stone the screw-sockets, which may be fitstened
with melted lead, plaster, or cement This done, again set the instrument up,
mid insert the screws k k into the sockets, through the holes in the iron stand ;
which again approximately places the instrument in position. This approxi-
mation being now made ^Try close, by repeating the foregoing operation, the
final touch may be put to it, by first carefiilly examining and correcting its
horizontaUty ; making the cross wires intersect one of the distant marks most

THE TRANSIT INSTRUMENT.

carefully, by turning the capstan-headed pushing-screws, c c, on the top of the
other arm of the stand. This gives a horizontal motion to the y, and hence
to the pivot which it carries : now reverse the telescope^ by turning it over on
its axis, and see if the other distant mark is also bisected ; if so, all is well ; if
not, correct half the error by the capstiin screws c r, and gently tap or slide the
stand laterally the other half; — the holes for the screws :k k being drawTi or
made sufficiently large to admit of this small motion being given to the stand.
This adjustment, Mke all the others^ sometimes requires repeating, especially if
not done with delicacy and care. When done, the screws k k may be made

&9t.

The method now described of bringing the instrument exactly into line may
appear rude, and difficult to accomplish, as it requires a nicety of touch which
experience in the use of mathematical instruments (almost) alone imparts to
the observer. To overcome this objection, by imparting mechanically a lateral
motion to the stand, some of them are constructed with a double fi*ame : in
which case, the lower one is first firmly fixed to the stone (approximately in
position), and the upper one is then rectified by means of screw adjustments,
not unlike one of the motions of a slide rest : — which is a great convenience,
but adds considerably to the cost.

When the stone is being fixed on the top of the brick pier, it should be set
correctly level on the upper surface; otherwise much trouble wiH result in
subsequently fixing the instrument.

The foregoing are the adjustments necessary upon the setting up of the
Transit Instrument ; and, although it be ever so correctly done, it mil require
to be verified each time the instrument is used for ranging the lines, to ascer*
tain that no derangement has taken place To prevent this as miich as
possible, except from causes over which the observer has no controul, he should
lock up his observatory when he leaves it, and keep the key in his own pos-
session, to prevent the ingress of ignorant and curious persons, who are too
frequently prompted, although unintentionally, to do mischief.

A Transit Instrument is of all others the best adapted for ranging straight
lines; and for such purposes, where great accuracy has been required, they
have been used for a long time passed r as in the setting out of the base lines
upon which the great trigonometrical sur\'eys have been founded, both in tliis
countr)^ and in distant parts of the globe. Likewise in surveys of small districts.
Even in the prepaiation of parish plans after the manner directed by the

28 PRACTICAL TUNNELLING.

Tithe Commissionjers, an instrument of this kind is highly useful for ranging
accurately the long lines intended for measurement, for it is not sufficient that
the measurements be correct, if the lines have not been set out perfectly
straight.

In setting out about fourteen miles of the South-Eastem Bailway, from
Red-hill in Surrey to Chiddingstone in Kent, through both a hilly and thickly-
wooded coimtry, the author foimd the use of the Transit invaluable for
the purpose. The railway, through this portion, consists of a few long straight
lines which lie nearly in the same straight line; and having found a few
given points on elevated spots, he was enabled, by the superior power of the
Transit Instrument, to range each straight line both ways for long distances,
with the greatest precision. . The instrument used on that occasion was of
small magnitude compared with the one described in the preceding pages : it
was portable, and adapted to a stout tripod stand, which ensured its steadiness ;
and when removed from the stand it could be placed in a conveniently-fonned
box, and carried from spot to spot wherever its use was required. The top of
the stand had also a lateral motion, to enable the centre of the instrument to
be brought readily over any precise spot on the line. Theodolites are now
sometimes made with a transit telescope ; which gives to those valuable instru-
ments a great additional advantage.

The possessor of a Transit Instrument may likewise employ it for astrono-
mical purposes, by placing it on a small brick pier in a garden or yard, and
temporarily covering it over, to preserve it from the weather. For details of
its practical application to such purposes, the reader is referred to a " Treatise
on the Principal Mathematical Instnmients employed in Surveying, Levelling,
and Astronomy," by the author of this work.

SETTING OUT SHAFTS. 29

CHAPTER III.

SETTING OUT THE SHAFTS. RANGING THE LINE BOTH ABOVE AND UNDER

GROUND. TAKING THE LEVELS, AND ESTABLISHING BENCH-MARKS, OR POINTS

OF REFERENCE. ETC.

When the Transit Instrument is in perfect order, as described in the last
chapter, the centre of each shaft may be ranged, and staked out, so that they
may be all in a perfectly straight line. The number of shafts, and hence their
distances apart, will depend upon the speed with which the work is required
to be executed. In ordinary kinds of strata, if the work is required to be
completed in twelve months, the interval between the shafts should not exceed
one hundred yards ; but I believe that about two hundred yards has been the
distance more generally adopted. It will be found convenient to have the
shafts equidistant from each other, unless some peculiar form or circumstances
of the surface call for a different arrangement.

As soon as the shafts are sunk to their proper depth, (the mode of doing
which is described in the following chapters), it becomes necessary to trans-
fer the ranging of the line from above to below the surface of the ground,
either for making the large excavation of the tunnel, or for driving a smaller
heading. When the groimd is quite dry and sound, there is not always a
necessity for the latter, but the excavation of the tunnel may be proceeded
with at once. If, however, there be any quantity of water to contend with, as
is too frequently the case, a heading at the level of the bottom of the intended
work, to serve as a drain, becomes essential ; and indeed, under all circum-
stances, a heading sufficiently large for a man in a stooping posture to pass
along, will be found very convenient to ventilate the works, to form a ready
communication from shaft to shaft, and to ensure accuracy in the levels and
ranging, or setting out, of the work. In this way both objects were attained
with the greatest certainty, at Blechingley and Saltwood ; for in no one of
the junctions, could any deviation from accuracy be detected.

30 PBACTIC^L TUNNELLING.

A common method of transferring the line from the surfkce to the under*
ground works, is by the erection of a ranging-frame over each shaft ; consisting
of three half-timbers framed as a triangle, and supported at the angular points
by stout props. In the engraving of the works above ground at Blechingley,
(&cing the title-page), a ranging-frame is shewn at the shaft on the right hand
of the picture, and some men are represented on the top of the head-gearing of
the gin, adjusting the lines according to the telegraphic signals from the ob-
servatory. The men stand quite free from the ranging-frame, lest they should
by moving it, displace the lines. One side of the frame (or triangle) is fixed
parallel to the line of the timnel, and on each of the other two sides is spiked
a triangular prism-shaped piece, or block, of wood, in such a situation that a
line passing over the projecting arris or angle of such block shall be in the
intended line of the tunnel, and pass down the shaft as close to its side as pos-
sible, without touching the brickwork in its descent. The upper end of the
line is &stened to a nail at the back of the timber, and a heavy plumb-bob is
suspended below, to stretch it perpendicularly. The bob is immersed, or hung in
a vessel of water, the more readily to bring it to rest, and ensure its steadiness.

The line that I used for this purpose was common fishing-line, rather larger
than whip-cord. I am aware that copper wire, and other substitutes, have been
tried, but believe they have not generally been found to answer better than
the common line, which has the advantage of presenting less temptation to be
stolen. That so fine a line may be distinctly seen through the Transit at a
distance, a board, having one side painted white and the other black, was held
up behind the suspended line, and when the white side was turned towards
the observer, the line was rubbed over with charcoal, whereby the observer
had to view a black line upon a white ground ; and when the black side of the
board was used, the line was rubbed over with chalk, when a white line upon
a black ground was presented to view. Sometimes the one, and sometimes the
other, was more easily to be seen : — ^for the shafts near the Observatory, the
black line on the white ground generally answered best ; but for greater dis-
tances the white line upon the black ground was preferred. This might pro-
bably in some measure thus arise. The wires in the telescope being black,
could not so well be distinguished on the dark surface of the board when it
was near, but this eflFect would diminish when the board was further oflF; — the
state of the atmosphere might also have some influence on these different
appearances. Two lines were necessarily suspended down each shaft, on its

EAHGINO THE LINE,

opposite sides ; the one farthest fi'om the obsen^atory was usually ranged first,
and then the nearer one ; after which they were both presented to the observ^er's
\iew at once, by way of test, when, if the prenous ranging of each line sepa-
rately had been quite correct, both would appeal* as one line ; and if such was
not the case, a repetition of the process of ranging each line separately took
place, until the result was satisfactory,

"WTien the signal had been given that each line waa coiTect, a notch was cut
in the vertex of the triangular block where the line passed over it, wliich notch
represented the correct point of suspension of the line, and formed a recess for
it to rest in, retaining it in its proper place. A screw with a capstan head
has been applied to this purpose, which cannot readily be disturbed, as persons
have been found mischievous enough to alter the notches, or cut more of
them, to annoy the parties who might next use the line. These screws no
doubt answer that purpose very well ; but where the ranging-frame is erected
on a spoil bank which is new-made ground, a continual settlement is taking
place, and, consequently, a motion arises in the parts of the ranging
frame which would put the best contrivance out of adjustment: therefore,
as it is necessary freciuently to examine the notches over which the line
passes, a wooden block wiU be found to answer all practical purposes.
The annexed cut shews the appearance of the diagonal or cross
wires of the telescope when bisecting the Hne suspended from
a ranging frame. The vertical Hne «a is the ranging line,
which must be moved to the right or left till it bisects both \ / \ /
the upper and the lower angles of the cross wires, bb andcc, >C^_Jif
of the telescope.

The foregoing method of ranging the lines cannot be satisfactorily used
except in calm weather ; for the wind has so great an effect in forcing the Hues
out of the pcq)endicular, even with a plumb-bob weighing nearly a quarter of
a hundred weight suspended by it, that when the wind is at all high it is next
to impossible to adjust them correctly, and therefore a delay from this cause
wHl frequently take place in so uncertain a climate as ours, which is not only
inconvenient, but, where the ground is hea\T, may be attended with danger.
I allude to a delay in setting the leading frames when the gi-ound has been
excavated ready for the brickwork. These circumstances led to my adoption,
at Salt>vood tunnel, of the iion spikes with holes in them, figured and des-
cribed in the next page.

32 PRACTICAL TUNNELLING.

When the headmg or tunnel is to be commenced, it is necessary to mark, on
opposite sides near the bottom of each shaft, the exact position of the intended
centre line, that in advancing the works in those directions there may be a
certainty not merely of meeting the workings in the opposite directions, from
the other shafts, but that the meeting (or Thirl, as it is called,) may coincide
correctly ; or, in other words, when the tunnel is completed a line stretched
from end to end should pass exactly along the centre of its breadth in all parts;
such a degree of accuracy is not always attained, neither is it so essential for
the heading as it is for the tunnel ; it will be sufficient for the former if it be
so straight that a line stretched along its whole length may be quite free (by
a few inches) from touching its sides ; but the junction of the tunnel should be
strictly correct, and may be so when proper attention is bestowed in ranging
the work and setting the leading frames ; the latter is too ofl;en left to merely
inftelligent labourers, instead of being done by the Resident Engineer himself,
and therefore, it is not surprising that we occasionally hear of such deviations
from accuracy as six, twelve, and even eighteen inches in the meeting of the
work at the junctions of various timnels. To mark at the bottom of the shafts
the direction that the workings are to take, is simply the transference of the
position of the lines, when suspended from above, to the sides of the shafts, by
ranging, and driving spikes or nails ; the hnes having been previously adjusted
to position, in the manner before described ; or by a more simple method,
as follows.

In setting out the shafts for the construction of Saltwood Tunnel, I adopted
a plan which obviated the delay arising from windy weather, &c. and saved
much time, and chance of error afterwards : it was as follows. When ranging
the intended centres of the shafts, (which were nine feet clear dia^
meter), a substantial stake was driven or fixed securely into the ground,
about sixteen feet on each side of the centre of every shaft, and over the
intended centre line of the Tunnel, so that when the shafts were sunk
and bricked, these external stakes were about ten or eleven feet from
their inner, edge. On the top of each stake we drove a spike, made in
the form shewn in the margin (one-half the real size), and ranged
the centre of the hole in the spike accurately with the transit instru-
ment ; this done, wooden caps were screwed over the said spikes, to
prevent their being disturbed. The ranging of each spike can be done,
with the greatest precision, by holding a piece of white paper at a little

RANGING THE LINE,

distance behind it, so that the hole may present a neat white disc for bisec-
tion with the cross wires of the transit ; and, by thns watching the spike as
it is being driven,any deviation to the right or to the left may be corrected by the
man who is driving it, upon giving him the necessary signal with the telegraph.

A line is stretched centrally across the mouth of the shaft, and its ends passed
through the holes in the spikes above described ; it is then to be drawn tight,
and made fast* A plank should next be fixed at each side of the shaft, at right
angles to the line, and so placed that one side of the plank may hang over the
shaft about two or three inches, or sufficiently to keep the line clear of the
brickw^ork when it is suspended from the said plank. The lines may next be
lowered and the plumb-bobs attached at the bottom, and when steady, the lines
may be moved along the edge of the plank until they hang precisely under
the horizontal line which crosses the shaft ; in this position they may be se*
cured by a nail driven into the plank^ and the line twisted around it.

By the adoption of the ranging spikes^ as above described^ it is clear that no
annoyance can arise from windy weather, which so much affects the lines when
suspended from a ranging frame elevated above the shaft, — because they are
wholly sheltered ; and, if care be taken to keep the ranging spikes from dis-
turbance, the lines can be dropped dowTi the shafts at any and at all times,
night or day, for setting the leading frames^ or verifying the position of fixed
marks : an advantage too well known to the practical man to require further
comment*

When the lines and the suspended plumb-bobs have come to rest, and are
steady, nails may be ranged by them, and driven mto the square timbers on
each side at the bottom of the shafts ; thus estabUshing two points in the line
required^ from each of which the workmen may suspend a plumb-line to guide
them in keeping their work in line, and by which they may also correctly fix
other nails more distant fitsm the shafts, as their works recede therefrom*

Some attempts have been made to range the lines below by means of the
Transit instrument itself; for which purpose it was placed over the shaft, and
having been correctly adjusted to position, &c, by some such means as have
been previously described, the telescope was turned vertically downwards,
whereby the observer, (by standing over the instrument,) might look down the
shaft, (the base of the stand being made open for that purpose) ; and thus it
was supposed he might range a line, a wire, lights, enamel discs, or any other
of the many contiivances which Imve been suggested for that purpose. Such

PRACTICAL TUNNELLING.

methods are pretty in theory, butin practice not very likely to answer; for
independent of the difficulty of thus accomplishing the required object, much
time would be consumed, and the result not so satis&ctorily arrived at as by
the method of dropping the lines from the ranging frames, and less advanta^
geous, both as to expedition and certainty, than the method by the ranging
spikes adopted at Saltwood, as before described.

As the miners advance their headings, or recede from the shafts, they must
iix (as before stated) other ranging points from which to suspend more plumb-
lines ; this they do, by looking back, and ranging them with the lines in the
shaft ; and from these new points they range others still more remote, to pre-
vent their deviating from a straight line. When the works at Blechingley
had advanced to this stage, the continual verification of the men's proceedings
became necessary ; and for this purpose the author contrived a candle-holder,
(shewn in the annexed engraving,) which answered
extremely well. It was previously the custom when
ranging several lines at short distances apart, for a man
to stand near each of them with a candle, which he
shaded with one hand to keep the direct light from the
observer, and to throw more light upon the line : this
occupied the time of several men, and was not so satis-
factory as the use of the candle-holders which were
suspended from the same nails that the miners attached
their lines to. Four of these were generally used at one
time, and by raising or lowering them in their racks, a,
the flames of all the candles could be brought to the
same level ; and if the nails from which they were suspended were in the same
straight line, all the four candles would appear but as one, when viewed in a
proper direction ; and, on the other hand, the least deviation from the proper
line in either of the nails under trial was distinctly shewn, especially in the
otherwise darkness of the underground works; and therefore it could be
corrected. This statement may easily be proved, by observing how correctly
any number of candles, of the same height and on the same level, can be
ranged in a line along a passage or corridor, or even on a table. By such
means the work of the miners was kept straight The heading at Blechingley
was remarkably correct : that at Saltwood was not so well done, arising from
the difficulties to be contended with, as already mentioned, and will be hereafter

IGING THI

This

more fiiUy described ; nevertheless, a line conld be^ and was stretched through
the work wthout touching the sides, being nowhere within nine inches thereof,
and therefore it answered all the purposes required-

The annexed cut shews one of the candle^holders
suspended from a nail in the upper cross-piece or cap,
B, of the heading frame, or *' setting/' as it is termed.
The upper part, or rack^ a, — (see last figure) — was
made of thin sheet iron, with a number of holes in it;
the remainder was of iron wire, carrying a socket for
the candle. By means of the rack, the candle could
be raised or lowered to the proper level, and being
hung by a flat plate it was prevented from revolving
and thereby interposing the wire in the line between
the flame and the observer, which would frustrate the desired object,
position is shewn in the right-hand figure of the former engraving.

As soon as the headings were driven from end to end^ the pciinanent ranges
were fixed ; each consisting of a cross-piece, «, — (see last figure) — fixed to
a setting in the heading, at intervals of about thirty or forty feet, and
having marked thereon where the intended centre-line of the tunnel woidd
cross, a block of wood, i, was screwed down, having a hole through it which was
placed in coincidence with the said centre-line mark. By passing a line through
these holes in succession, the centre-line of the tunnel was ranged at all times.
The method of determining the position of the centre marks on the cross-pieces
is by suspending the vertical Hues, as before described, down two or more
consecutive shafts, and stretching a long Hue very tight in the heading ; which
line is then moved to the right or left, until it coincides with or is perpendicu-
larly under the two lines in each shail at the same time, and where the line
then crosses the piece of wood, a, is the position for the central mark, and the
hole in the block, b. When those marks that are near to the shafts are re-
moved by the construction of the side and first leading lengths of the tunnel,
it is convenient to fix in the invert a post of balk timber, with an iron cap,
having a similar hole to those in the blocks above named, centrally arranged,
through which to pass the line when required. When these marks are
fixed all the way through the heading, a number of points will be established
in the centre-line of the tunnel, and therefore the whole, or any portion of the
work can be correctly ranged out whenever require. With such conveniens

36 PRACTICAL TUNNELUNO.

cies at hand, no leading frame should ever be set but by this line to denote the
position of its centre. No further reference need be required to the saibce, or
to the Transit Instrument ; which, however, had better be kept up until near
the completion of the work, or until all chance of its being again required har
passed away, the Observatory may then be taken down, and the materials
worked up. When, however, the tunnel is to be driven without the use of a
heading, frequent reference to the points on the sur&ce will be required.

In perusing the above particulars, it will strike the reader, that if the line
stretched along the heading from whence the central holes in the blocks, &, are
derived, extended the whole length of the tunnel at once, the greatest accuracy
in the result would be obtained : but such a line, when the tunnel is long,
would *sag' too much, and probably break before it could be strained sufficiently
tight ; therefore a line as long as possible, so as to answer these conditions,
should be used, and thus the whole length be ranged piecemeal; which,
having been done with care, and embracing in each length at least two of the
previously-ranged centres, little or no error need arise.

The whole of the foregoing methods and details of ranging the Unes were
not adopted by the author at the first starting of the work ; but suggested
themselves from time to time, as circumstances arose. They are given as
the methods he most approves, and would adopt in future, if ever again
called upon to execute similar works.

THE LEVELS, AND BENCH-MARKS.

Having described the method of keeping the work straight in a horizontal
direction, it remains to explain that of making it correct in a vertical
direction ; or, in other words, preserving the proper level. When the tunnel
is upon the same level throughout, the task is easier than when it is inclined ;
although the latter presents no difficulty, or particular chance of error, to a
careful person. A section of the ground must first be made along the intended
line of the tunnel, and the relative level thereto of some standard bench-mark
determined for future reference. The position of the shafts having been deter-
mined upon, (or even began), a substantial bench-mark should also be esta-
blished opposite to each shaft, but at such a distance therefrom as to be a little
beycmd the area which the spoil-bank and materials used in the course of the
work are likely to cover, so that it may be always accessible for reference.

LEVELS, AND BENCH-MARKS.

For this purpose, large stakes or ends of square timber should be driven or
fixed in the ground^ so as not to be easily disturbed, and an iron spike with a
round head driven in the top, upon which the levelling staff can be held ; and
they may be denoted by the same numbers^ — 1, 2* 3, &c.^ — as the shafts to
which they are opposite* The relative level of these bench-marks with respect
to that of the Railway, at a point immediately under their opposite shafts, must
be determined, and hence, by computation, its height above some given point
in the tunnel may be found, — (the springing, or skewback of the invert was
the point to which preference was given for this purpose) — and registered for
after reference* Thus, at No. 3 shaft at Blechingley, the height of its bench*
mark above the standard datum of the Railway section, as found by levelling,
was 343.78 feet; the formation level of the Railway at a point immediately
under the said shaft, as determined by the section, and computed on the in-
tended gradient, was 249*99 feet above the said datum: therefore 343.78 —
249,99^93,79 feet for the height of No, 3 bench-mark above the formation
level under the centre of No, 3 shaft* But the formation level was L25 below
the intended level of the skewback; therefore 93*79 — 1,25=92*54 feet for
the height of the bench-mark above the intended skewback of the tunnel.
This method of computation was adopted for every shaft, and registered for
future use, as in the following table.

Sb»ft.

FofimtioD

Lrvrlabote

dMnm at

BenchMark

above datnin.

B<geliltark
•bore

Formalioii

Bench-Mark

above

Staple in Shafts

brio*

AboTe or below

Abore

Shtft.

Fonniltittn.

Skewback.

Bench-Harfc.

Skewback.

r«et.

bet.

fc...

tm.

reet,

reet.

feet.

250.37

320.87

70.50

1.25

09.25

— 2.23

67.02

250.18

330.38

80.20

78.95

+ 0.22

79.17

1U9.99

343.78

93.79

92.54

+ 2.70

95.24

240.81

339.64

89.83

88.58

+ 7.38

95.97

249,67

330.68

81.01

79.76

+ 8.61

88.37

240.52

334.04

85.42

84.17

+ 2.73

86,90

249.37

335.28

85.91

84.66

+ 5.71

90.37

240.21

328.85

79.64

78.39

+ 3.63

82.02

249.05

322.98

73.93

72.68

+ 7.35

80.03

248.89

317.54

08.65

67.40

+ 7.08

74.49

248.72

302.33

S8.6I

52.36

+ 14.71

67.0?

39 PRACTICAL TUMNELLINO.

All the dimensions connected with the sinking of the shafts may be taken
sufficiently correct with the common measuring tape ; but for the actual tun*
nelling operations, more certain means must be employed. It is advisable, in
the first instance, to fix a bench-mark at the bottom of every shaft, which shall
represent the intended level of the skewback of the invert, or any other level
that may be chosen. A flat iron spike driven into the timber at the bottom of
the shaft, and projecting sufficiently for the level staff to be held upon, will
answer very well. Having drove this at every shaft, the Engineer should level
through the heading (if there is one) from shaft to shaft, throughout the
whole extent of his work. By this means he will prove how fer he is accurate,
and if as he proceeds along the heading, he fixes at short intervals similar
bench-marks at the proper level for those points where they are fixed, he
will have the means of subsequently checking his work as it proceeds ; and will
relieve himself of all doubt as to the final result of the levels at the several
junctions when they may be effected.

The method adopted for transferring the levels at the sur&ce to the bottom
of the shaft, (or dropping the levels, as it is usually called,) is to drive securely
into the brickwork on the inside and near the top of the shaft a stout horse-
shoe-shaped staple, the circular part of which is left projecting from the brick-
work, and forms a loop for a wooden rod to be passed through to the bottom of
the shaft. The height of the upper edge of the staple above the intended
works below, having first been determined by means of the neighbouring
bench-mark, as shewn by the two last columns of the above table, is the point
from which the required length of rod is to be suspended, so that the bottom
of the rod may represent the level of the invert skewback, or whatever other
level may have been fixed upon. An iron gland is attached to the rod, at the
proper point, which gland is larger than the loop-hole of the staple, and there-
fore rests upon it, and suspends the rod as required.

The wooden rod above spoken of must, from the great length required, con-
sist of a number of pieces which are attached to each other by various contri-
vances ; some of them have been made to screw together, precisely as the old-
fitshioned round 1^ of a spirit level were joined in their middle; but, having
previously witnessed considerable inconvenience and loss of time by this me-
thod, I caused my rods to be connected with a spring catch, or hook and eye,
nearly similar to the hooks we used for suspending the skips from the windlass
ropes fi^r the purpose of lowering them down the pits.

LETfXLING RODS.

The annexed engraving shews the rods used upon
the works, their connecting hook, and the gland*
'Hie rods are shewn by the left-hand figure, with
the gland attached at the point b. The upper right-
hand figure shews the hook, the corresponding eye,
and the ends of the rods to one-half the real size.
The lower right-hand figure shews the form and
make of the gland ; a a are the cheeks which clasp
the rod ; c is the screw for tightening or releasing
them^ which screw is worked by a handle, d, similar
to that of a vice ; e is the hinge by which the cheeks
open to clasp the rods, and when open the screw c;
is drawn quite out of its socket.

The rods were made ten feet long fi"om the inner

edge of the loop or eye, at one end, to the inner
edge of the hook of the other^ or from the two

points of connection ; and when they were sus-
pended in the shaft, each ten-feet rod became as it

were the link of a chain, consequently the whole

woidd be sure to hang perpendicularly, which was

not often the case with those that screwed together.

Each rod was numbered, for convenience in use,

and was hooked on the top of the one previously

lowered ; number 1 having been first lowered, the

succeeding numbers shewed how many tens of feet

had been passed down through the staple; thus,

when number 6 was hooked on, it was evident that

50 feet of rod were already down ; and when any

odd number of feet and decimals of feet had to be

suspended from the staple, as for instance 95/24, the

nine rods were first lowered, and upon the tenth

the odd 5*24 feet was marked, and at that point the gland was screwed to

clasp the rod firmly, the underside of the gland coinciding with the said mark ;

the tenth rod was then hooked on to the ninth, and likewise passed dov^Ti until

stopped by the gland resting on the staple, and the whole then hung

perpendicularly.

40 FBACTICAL TUNNBLUNG*

In all cases both at Blechingley and Saltwood tunnels, when the rods were
suspended in the shafts the bottom of No. 1 rod represented the required level
of the invert skewback, (or springing of the inverted arch,) which was the
standard there adopted, and for the greater convenience of transferring the said
level to any other point, as a ground-mould or bench-mark purposely made,
the lower three feet were graduated exactly as the levelling staff was divided ;
the rod was then illuminated with a candle wherever the line of sight of the
level cut it.

The method of transferring levels fix)m one point to another being so simple
an operation, the reader is doubtless well acquainted therewith ; and therefore
no iitirther explanation of that matter is required. In all instances the rods
were suspended at least three times down every shaft; first, finr establishing a
number of bench-marks through the headings, as before stated ; secondly, for
setting the ground-moulds for every side length ; and thirdly, when the shaft
lengths were completed, to fix an iron bench-mark in the brickwork exactly
at the proper skewback level, at the side of the tunnel under each shaft ; for
although the skewback at that place had then been built and completed,
yet it was considered necessary to fix a proper point on which to hold the
levelling staff at the exact calculated level, for the brickwork (hovirever wdl
done) would be almost sure to vary a small quantity therefix>m. These bench-
marks consiBted of flat iron spikes, projecting about an inch firom the wall into
which they were driven; and from these standard skewback levels all the
subsequent ground-moulds were set, making the calculated aUov^ance for the
rise or foil of the gradient; which would be unnecessary where the tunnel is
to be constructed on the same level throughout.

TRIAL SHAFTS.

CHAPTER IV.

SHAFT SINKING*

THE TRIAL SHAFTS.

The construction of the Blechingley Tunnel commenced with the sinking of
two trial shafts, to ascertain the character of the strata through which the
tunnel was to pass. Instructions for their commencement were given on the
first of February, 1840, and on the third a contract was made, with two men,
to sink and brick the shafts in question. They were to be six feet diameter
in the clear ; the brickwork to be nine inches in thickness ; the bricks to be
laid all headers, properly breaking joint, and to be set in the best grey-stone
lime mortar : the price was to be, — ^for the sinking, eighteen shillings per yard
down, and for the brickwork at the rate of sixteen pounds per rod ; which
prices were founded upon the following estimate.

Excavation :
4.0 cubic yaids in 1 yaid down • at 28 : 6d«
4 oak curbs for a depth of 33 jrards, with plates

and bolts complete . £2. each • . or

per yard down
Props, cbogs, spikes, nails, candles, &c.

Excavation per yard down

BaicKWoax, per rod:

Bricks . 4500 . £2 2 per thousand >
Carting ditto . 10 ,,

Lime

2 12
1^ yard . at ISs.

Carried over

£ s. d.

12 3

4 10

16 1

• • •

11 14

16 3

12 10 3

18 1

PRACTICAL TUNNELLING.

Brought over
Sand . 3 yards . at 2a: 6d. .
Laboar, candles, kc per cubic yard, 5s.

Per rod z=

and .*. per cubic yard =

and 1.8 cubic yards in I yard down

Total Estimate per yard down

£ 8. d.

£ >. d.

12 10 3

18 1

7 6

2 16 7

15 14 4

1 7 9

• ^—

2 11

£ 3 8

The situation of the trial shafts was the same as that of the working shafts
Nob. 1 and 10 — ^fig. 1 plate 1 — as they were subsequently enlai'ged to nine
feet diameter to make working shafts of them. They were designated as the
western and eastern trial shafts; No. 1 being the western, and the other
which afterwards became No. 10, the eastern. They were both commenced
on the seventh of February, 1840, and on the tenth the western shaft was sunk
14 feet, and the eastern 8 feet. My memorandum on that day was as follows:
** At present^ the earth shews no indication of water below the first six feet ; it
is a kind of marl, of a slippery or greasy feel, something resembling fullers*
earth" On the twelfth, the western shaft was sunk 25 feet, when it was no
longer safe, or scarcely practicable, to proceed without inserting the brickwork,
as the last six feet had yielded a considerable quantity of water. Moreover, by
exposure to the atmosphere, particularly if any damp was present, the ground
slaked, or rather dissolved, accompanied with a swelling or heaving movement
This was invariably the case throughout the subsequent operations, and there-
fore it was unsafe to leave a face long exposed to atmospheric action, as such
heaving brought a great weight upon the work, and in a few cases, where the
excavated lengths remained longer than usual for the brickwork, the weight
became such as to break the bars ; which, on this account, were provided of
large dimensions, averaging 14 or 15 inches diameter for the crown, and 12
inches for the side bars, all of oak. The brickwork was commenced upon an
oak curb fidrly bedded on the bottom of the excavation, and set level ; the
inner diameter of the curb (or ring) was that of the intended shaft, — 6 feet ;
its width, 9 inches, to carry that thickness of brickwork ; and its depth, or
thickness, 3 inches : it consisted of several pieces, connected by half-lap joints.

TRIAL SHAFTS,

having an iron plate crossing the joint on each side of the curb, and secured
by four bolts, which passed through tlie timber and both of the iron plates.
Upon this curb the brickwork was carried up to the surface, being weU packed
and rammed with dry earth, wherever there was a vacancy at the back^ to
make it solid.

By the time the brickwork was finished, about 14 feet of water had accumu-
lated in the shaft, which had to be dra^^n out before the work could be re-
sumed. When the sinking had advanced tw^o feet further, a bed of hard
calcareous sandstone, about one foot in tliickness was met with ; — this required
blasting ; — and it was separated from a still harder rock below by about one
inch of sand ; tliis lower rock proved to he two feet in thickness ; next followed
eight inches of brown sand, and three inches of blneish-grey sand ; after which
the clay or shale, the same as that we passed through above the stone, re*
appeared. It was expected that the stone formed a regular bed in the above
situation, where it would have given considerable trauble as it was nearly level
with the top of the tunnel ; it however occasioned only a temporary difficulty,
as it soon clisappeai ed, probably fi^om some dislocation of the strata, as the hill
was full of faults, and had undergone great derangement. This was evident
from the strata lying most abruptly in all directions, as was strikingly shewn
in the open cutting at the west end of the tunnel, and mentioned at page 7.
It is probable that the rock was an outlier from the lower bed of the lower
Green Sand; the Weald Clay in which we were working cropped-ont from
beneath that stratum, about half-a^mile to the north*

The water henceforth flowed into the shaft so fast that but little progress
was made with the sinking ; and during the week ending Febi-uaiy 22nd no
more than 7 feet 6 inches was excavated ; another oak curb was then placed,
of the same dimensions as the former one, and vertically under it ; the upper
one, with its load of brickwork, being supported by raking props, which were
removed as soon as the brickwork was carried up from the lower curb to tlie
under side of the upper one, which was thus under-pinned, and the whole
formed one shaft. This second length of brickwork was set in cement, on
account of the water. WTienever the regulai* courses of brickwork brouglit
up from the lower curb would not exactly fill the space, or fit tight to the
underside of the upper curb» it was generally done by one course of bricks set
on edge; and any small spaces that might tlien be left were filled up by
driving in oak wedges.

44 FRACTICiX TVNKmLINO.

With considerate effort a third length of brickw<H:k was got in, and similarly
secured, and a fonrthlength of excavation was commenced. On February 29th

1 reported as follows.

'^ Bjf perseverance^ and at a considerable expense in drawing water doff amd
nigkt, together with shoring and poling the earth to prevent its falling in, Ihace
succeeded in sinking the western shafi to the depth of iSifeet 6 inches ; at HUs
i^pth so great an influx of water came upon us, that we scarce^ had time to prop
the brickwork before we were compelled to leave the shaft ; this water has
cofUinued to flow so fast that after obtaining larger buckets, and six men
drawing day and night, it could not be kept under ; and at length, finding that
it gained upon us I abandoned it as fruitless unthout more powerful means. I
have therefore lefi the shafi, until bg driving the heading we shall drain the
springs : the water is now within two feet of the surface ; there being full 38
feet of water in the shaft''

Before finally leaving the shaft, sufficient earth was thrown in to fill up the
excavated part below the brickwork, and a foot or two higher, in order to
prevent the earth coming down from the back of the brickwork, which would
have endangered the stability of the whole shaft.

The shaft thus left, was soon filled with water, which ran over in a consi*
derable stream. It was then fenced in to prevent accidents, and remained in
that state for several months, as a dispute with the occupiers of the land about
their compensation, delayed our getting possession thereof imtil the following
August. When possession of the land was obtained, and we were sinking No.

2 working shaft, at a distance of 110 yards to the eastward of the above trial
shaft, we were similarly impeded with water, and, after drawing it for a day or
two, it was observed that the water in the trial shaft had ceased to run over, and
had sunk a little ; taking this hint, men were set to draw as hard as possible at
both the shafts, and in a few days they were drained to the bottom ; aikt,
although we were afterwards more or less troubled with water, yet by drawing
at the two shaft;s we could always prevent its stopping our progress.

The soil through which the eastern trial shaft (afterwards No. 10) was sunk,
waA more nearly uniform, and consisted of day or shale highly indurated ; the
first 25 feet were of a brown colour, the rest to the bottom was of a deep blue^
with an occasional bed of stone about two inches in thickness. (The brown-
coloured day at the western trial shaft terminated at a depth of 18 feet.) We
reached forty-eight feet before we came to water, and were able to sink to 59

TRIAL SHAFTS.

feet (by drawing water), before we placed the curb and commenced bricking
up. This was on February 26th, and the brickwork was level with the surface
of the ground on the 5th of March ; an interval of eight working days inclu-
sive. During this period, seven feet of water cdlected in the shaft, which being
drawn, the sinking was continued to the then full intended depth of 66 feet,
which was completed on the lith of March.

From what has now been stated, it will be evident that the work could not
be done at the price at which it was undertaken ; for in the estimated ex-
pense no such coAtingency as the occurrence of water was provided for ; and
furthermore, the carting of the bricks to the ground cost 20s. per thousand,
instead of 10s. as estimated ; for none could be obtained nearer than seven miles,
and by a hilly road. It justly fell upon the Company to pay these extra
expenses, and the following will shew the actual cost of these shafts ; —

Total outlay, db% yards done

Deduct materials left for future work

Total absolute Cost 4

Estimated cost of 35 V6 yards

fectra cost of carting 24,000 bricks, at lOs.

Extra cost upon the k>wer 15 feet 6 inches of the Western Shaft,
in consequence of water

£ s. d.

202 17 2

20 15 3

£ «. d.
182 1 11

192 14

• • •

120 14 1
12

esteni Shaft, 3

£ 40 7 11

The men having taken to the work at a price per yard down, or running
yard, reckoned at the rate of 2s. 6d. per cubic yard, it may be useful to shew
the amount of their earnings, thereby to judge how far the price was a feir one.
The greater depth of the eastern shaft, where no difficulty occurred that was
not anticipated, wiU give a fidr average ; for it must be remembered that great
progress can be made at first, which necessarily diminishes as the shaft gets
lower. On February the tenth it was down 8 feet, and on the twenty-sixth,
59 feet, — a difference of 17 yards in fourteen working days, averaging 1.2
yards per day, — ^which, at 12s : 3d. per yard, amounted to 14s : 8d. per day, to be

46 PRACTICAL TUNNELLING.

divided among four men, and if we consider the odd 8d. to be the cost of the
candles, it leaves 3s. 6d. per day for each man, supposing their earnings to be
equally divided.

From the sinking of the trial shafts it became evident that the stratum in
which the tunnel was to be formed was the Weald Clay of geologists ; it was
also near its outcrop from beneath the lower Green Sand ; it having been pre^
viously a question whether or not the spur of Tilburstow hill, through which
the tunnel was to be formed, was not included in the green sand stratum. The
shafts ftirther indicated that a considerable quantity of water would, in all pro-
bability be met with in the course of the work, and that the ground would be
heavy ; upon this information, the form most suitable for the tunnel and the
proper dimensions for the brickwork, &c. had to be determined.

TRIAL SHAFT AT SALTWOOD TUNNEL.

The first operation after setting out the centre line of the tunnel, was to sink
a trial shaft, to ascertain the character of the strata beneath the sur&ce ; this
Avas commenced on the 25th April, 1842, and was situated 13 yards from the
centre line of the tunnel, on the south side. It was originally intended, that it
should not only be a trial shaft, but was to have been sunk (if possible) so deep
as to answer the purposes of a well, to supply the works with water during
their progress, in the event of a deficiency of that article.

The shaft, or well, was six feet diameter, clear of the brickwork, which was
nine inches thick, the bricks being laid all headers. The sinking was attempted
by means of a barrel (or drum) curb, which upon being undermined descended^
by its own weight and that of the brickwork (which was constructed upon the
curb, and was carried up as the curb descended) ; In this manner a depth of 46
feet was attained, when the drum getting a little out of the perpendicular, it
stuck fast and could be got no lower, and after a fruitless attempt to liberate it,,
was left in its place, and the sinking resumed beneath in the ordinary mode to a
ftirther depth of 20 ft. 6 in.; when coining upon a quick sand, we were unable to
prop up the brickwork during the process of underpinning, and therefore could
proceed no fiixther by that method. Another curb was then constructed of the
same diameter as the inside of the shaft, namely 6 feet, to continue the sinking
from within the completed brickwork ; but so large a quantity of WBiei wrj^

TEIAL SHAPTt.

given out^ that 8 feet additional depth only were attained, making a total of 75
feet down,

COST OF TRIAL SHAFT AT SALTWOOD TUNNEL.

Carpentry:

Lar^ drum curb •

SmaiJei {lillo . . , *

Platform for work men in the shaft *

Eight curbs or rims . . 12s.

S&icKS: . 17,000 , at 51s.

Labour m excavating and bricking (or steiningj

£ s, d.

£ s. d.

5 5

4 10

J 1 U

4 IG

15 12
43 7

• »

15s, per yard down

18 15

TOTAJ, ,

£77 14

The drum curbs^ and the mode of using them^ will be
understood by reference to the annexed section of part of
the shaft ; which shews the first curb a in the position
where it became immovable ; tlie termination of the
larger portion of the shaft at b ; and the smaller curb
c at the bottom of the shaft. The curbs were made
smooth on the outside, that they might slide down easily ;
were strongly bolted together, and the bottom edge
formed like a wedge (or knife edge) to avoid resistance.
Two plumb-bobs were suspended at right angles to each
other, in the curbs, to guide the workmen in keeping
them perpendicidar. As the brickwork descended with
the curbs it was continued upwards to the surface of the
ground ; thus constantly increasing the load upon the
curb, and of course its tendency downwards, as the
earth was removed from beneath.

There are various opinions as to the advantages de-
rived from the use of barrel or drum curbs (running
aurbs^ as they are sometimes called,) over the ordinary
mode of propping and underpinning The latter mode
is more generally adopted where the ground is suf-

J»

PRACTICAL TUNNELLING.

iiciently solid to carry the props in safety; in all other cases the drum
curb may be advantageously employed; but it requires much care to
prevent it from setting &st, as it did at Saltwood, which may principally arise
from its getting out of the perpendicular, either from carelessness of the
excavators, or from the earth yielding on one side; neither does it appear
that the work can be more expeditiously done by its use. On the oliier
hand, there is apparently a greater degree of security to the workmen, who
being employed within the drum may perhaps be somewhat less exposed to
danger; but this even is doubtftJ. To those who are unacquainted wilii the
subject, the following particulars of the method of shaft sinking, by props and
imderpinning may not be uninteresting : —

The shaft is first sunk to the frOl diameter of the outside of the intended
brickwork, and as far down as the earth continues to stand safely. When it is
no longer prudent to proceed, a timber curb or flat ring is laid upon the bottom
of the excavation ; this curb or ring has its inner or clear diameter the same as
the intended shaft, and its external diameter as much greater as twice the
intended thickness of the brickwork, for upon its flat surfiuje the bricks are
to be laid. The curb should be made of durable timber, as oak, and formed in
several segments, joined with half-lap joints, secured with a plate on each side,
and four bolts passing through the whole ; upon this curb the brickwork is
carried up to the surface. The sinking is then renewed by excavating the
earth from the centre of the shaft, as far down as may be consistent with safety,
leaving a benching of earth to carry the shaft, as
shewn in the annexed engraving ; a narrow por-
tion of this benching is next cut away as far
back as the brickwork, and a prop inserted rak-
ing either to the front or back of the intended
brickwork ; if to the front, the prop can be saved
and used again, but it is sometimes necessary to
place them raking behind the brickwork, in
which case they are built in and lost. Another
prop is then similarly inserted, and so on until the whole curb and brick-
work, is thus supported. When this is done another similar curb is inserted
perpendicularly under the upper one, and the brickwork carried up to meet or
imderpin it. The work during this operation presents the appearance shewn
in the following sketch. The props, however, are all shewn as raking inwards :

BHAPT SINKING.

one advantage in their raking outwards is,
that they leave more room for the bricklayers
to work. The props may also be set perpendicu-
larly under the upper curb, and the brickwork
completed between any two props before they are
removed ; or the work may be quartered in,
(that is, a quarter completed at a time). Other
methods of proceeding are also occasionally re-
sorted to. The props must rest upon a broad
base, or foot-blocks, and be securely chocked to the curb above, to prevent
motion taking place* As the brickwork proceeds, all vacuities behind ehouhl
be rammed solid with dry earth.

In sinking through, and constructing shafts in the shingle beach upon the
sea coast, at high-water mark, and also about midway between high and low-
water marks, the following method of proceeding was found to answer. Hav-
ing cast out the shingle and sand to a depth of five or six feet, or as far a.s
conveniently practicable, a stout timber curb was laid level upon the bottom
of the excavation, and upon this was built about four feet of brickwork, in
cement; then, during the inten^als of the tides, the shingle was removed
fifom under the curb, by workmen within the shaft, and as they so removed
it, the shaft gradually descended by its own weight, and the bricklayers
continued to build it upwards, so as always to keep it above the level
of the beach around ; which otherwise would have filled the shaft at each
high tide, and have occasioned great loss of time in its removal. This
operation is similar to the sinking by means of a barrel curb, before des-
cribed ; but which would not ansr^ er so well in such loose material as that
on the sea-shore, as it is capable of doing in firm soil.

On another occasion, the author was required to obtain fresh water for the
supply of a large building erected on the sea^shore, to be used as a hotel. The
spot where the building was erected had been left by the sea not many years
before ; the recession of the water, — or rather, the accumidation of shingle, —
having been occasioned by the construction of a pier, for commercial pur-
poses, extending into the sea close by. Upon an examination of the locahty
it appeared clear that within seven or eight yards from the surface, the top
of the middle bed of the Lower Green Sand stratum would be found in situ ;
and therefore there was a reasonable probabOity that a supply of fresh water

PRACTICAL TUNNELLING,

could be obtained from tbat level. But whenever a hole was made in the
ground, which consisted of the beach and sand originally deposited by the Be%
the salt water appeared and disappeared with the rising and falling of the tide,
the sea percolating through the beach (which was there seventeen feet deep),
and rising in the hole to the level of the tidal water. Under these circum*
stances it was necessarj^ to sink a shfLft that should be water-tight, effectually
to exclude the sea w^ater firom entering, and to prevent tlie fresh water that
might rise in it from escaping ; accordingly, a large shaft was first sunk, pn>
tected around mth timber, by having square frames or settings at intervals of
about three feet, and behind these, or between them and the earth (or beach),
upright planks were driven close to each other, in the manner of sheet piling,
some men driving at top while others were removing the earth from under the
piles ; this method was followed quite through the shingle, and answered well,
but it could only be proceeded with at the time of low tide, as otherwise the
salt water filled the timbered shaft. In a manner very similar to tliis, the dif-
ficulties in shaft sinking at Saltw^ood Tunnel were conquered; as will be
explained in a subsequent chapter*

The timbered shaft was sunk quite through the beach fuid silt, and at
eighteen or nineteen feet down, the middle bed of the Lower Green Sand waa
reached ; when, as was expected, a large supply of fresh water was found,
precisely in the same geological level as the water was met with in sinking
the shafts at Saltwood. The brick shaft or well was then commenced upon a
timber curb, sunk into the stratum about three feet below the bottom of the
shingle, and nine-inch brickwork in cement carried up to the surface, and
between the outside of the brickwork and the timber of the shaft the space
was rammed with well-puddled clay, from the bottom to the top ; the planks
being left in the ground, lest their removal should disturb the puddling, and
endanger the letting in of the salt water. The fresh water was admitted into
the well through three pipesj which were built in the brickwork near the
bottom of the shaft : but, a short time afterwards^ the pressure of an extraordi-
nary high tide enabled the sea water to reach these pipes, and thus make the
well water brackish ; whereupon the pipes were closed up, and the whole of
the water from that level excluded ; and by means of boring at the bottom of
the shaft, a plentiful supply of pure water was obtained, which rose in the weU
to within four feet of the surface of the ground.

WORKING SHAFTS. 51

CHAPTER V.

SHAFT SINKING, CONTINUED.

SXCAYATING AND CONSTRUCTING THE WORKING SHAFTS, AND SUPPORTING THE
BRICKWORK BY SHAFT-SILLS AND HANGING-RODS.

The working shafts were 9 feet clear diameter, the brickwork 9 inches in
thickness ; an oak or ehn curb was inserted at the bottom of every length of
brickwork as it progressed downwards, and at the bottom of the brickwork,
where the square timbering of the shaft commenced, a curb of 4 inches in
thickness was used ; the upper ones having been but 3, or 3| inches. These
were to remain permanently in their places. As the sinking proceeded, notes
were taken of every change of strata, which, at the same time that they were
interesting as geological facts, were occasionally useful afterwards. For
instance, in sinking the trial shafts at Saltwood, we passed through a stratum
of clean sharp sand, well adapted for gauging with cement. In the course of
our subsequent work such sand became a desideratum, and all we had to do
was to break through the brickwork of each shaft, at the particular level
pointed out by the memoranda, and a man threw down into the tunnel as much
as was required; excavating it as a driftway. Thus a plentiful supply of
excellent sand was obtained at a cheap rate.

Plate 2 shews two sections of a shaft at Saltwood tunnel, fig. 1 at right
angles to the tunnel, and fig. 2, in the direction thereof; the plan adopted for
suspending the brickwork, and square timbering the lower part of the shaft
is therein represented; likewise, the brickwork, and the timber rings, or
curbs, at a, a, &c. at the bottom of each length. The windlass, together
with the skips for raising the earth and lowering materials — the one
ascending as the other descends — are also shewn. The skips were suspended
firom the rope by a particular form of hook, that prevented' their unshipping
in case of striking against each other in passing, or against the sides of the

PRACTICAL TUNNELLING.

shaft. A further description of the above will be given in a subsequent
chapter.

The following is a copy of the specification drawn up for the guidance of the
bricklayers in constructing the shafts at Saltwood tunnel : —

The brickwork of the shafts is to be nine-inch work, laid all headers. The
shafts are to be nine feet clear diameter, and to be constructed truly cylindrical
and perpendicular. The whole to be laid in mortar composed of one part of stone
lime, and 2^ parts of clean sharp sand, well mixed up with a proper quantity
of water ; the lime to be sift;ed before it is made into mortar. The mortar-
joints to be sufficiently thin to make four courses of work not exceed one foot.
The back of the work to be rammed and well punned, course by course, as the
work proceeds ; so that it shall not be possible to drive the bricks back from
their places by applying any moderate force. Each brick to be dipped in water
previous to its being laid. The bricklayer to find all tools, sieves, tubs, &c. ;
the engineer to find bricks, lime, sand and water.

COST OF THE WORKING SHAFTS PER YARD DOWN.

Excavation : including all tools, gunpowder,
candles, and contingencies

Brickwork: including all labour, candles,)
lowering materials, and contingencies S
Bricks 1.020

Lime . ^ of a yard

Sand . j of a jrard

At Blechingley,

in the

Wddd Cl>y.

At Sdtwood,

ID the

Lower Oreen Sud.

£ 8. d.
1 10

18 9

3 2
4 3
1 4

£ 8. d.
12

2 11
4 3

£5 16 4

£4 11 3

In addition to the above, the cost of the ring curbs must be added, which at
both places was the same, and averaged about one in every three yards down.

WORKING SHAFTS,

iship
r 70 lbs, , at4d.

2 13

1 a

£ 3 19

Timber, and workmanship
Itoowork, — in pkteg,
bolts, and nuts

The above details comprise the cost of the materials and the labour^ actually
consumed in the work ; besides which, there were the windlasses, ropes, books,
skips, planks, and props, &c,, which were part of the general plant of the tunnel
works, but a very small portion of their cost ought justly to be charged to the
shaft sinking^^ — they are included in the total cost of the tunnels.

aUPPOETING OR SUSPENDING THE SHAFTS,

The brickwork of each shaft was carried down to within a few feet of the
intended top of the tunnel ; and from thence through the space intended for
the tunnel, the shaft was continued by means of timber only, having square
frames or settings, at short intervals of depth, and close planking against the
sides of the excavation ; the square settings being supported from each other
with props of round timber, (all of which are shewn in the two sections, plate 2,
and in fig. 1, plate 3.) This timbering was adopted to facilitate the subsequent
excavation, which could not have been so well done if the brickwork had been
continued to the bottom. The square timbering, however, will be explained
next in order after the present subject-

The brickwork of a nine-foot shaft forms a cylinder of great weight, as
it contains 3 tons, t cwt. to every yard in depth, and the friction of its cir*
cumference against the earth is not sufficient to resist its tendency to slide
down, when the ground is removed from under it, to construct the tunnel.
It is therefore usual to support the shafts by some means until that portion of
the tunnel immediately beneath them, commonly called the shaft lengthy is
completed. The shafts are then permanently connected thereto by a curb oi
castiron or brickwork, m shewn in figs. 1 and 2, plate 5, and thus made secure*

The shafts may be secured until they can be permanently luuted to the
tunnel, either by supporting them below, or suspending them from above. At

«4

PBACnCAL TUNNSLLINO.

Blechingley the former plan was adopted, and under each shaft was fixed
at right angles to the direction of the tunnel, a pair of sills, formed of whole
balks, 15 inches square, and 34 feet long ; and upon them was fixed a square
firame of the same kind and scantling of timber, to carry the bottom ring or
curb of wood, and the superincumbent shaft. The under side of the sills were
placed three feet above the top of the intended brickwork of the arch, that the
miners might have plenty of room for their bars, &c., in excavating for
the side lengths.

In consequence of the gradient of the railway of this place being lowered,
after the shaft-sills were fixed, they necessarily were so much higher above
the top of the tunnel ; this however was attended with but little inconvenience.

The annexed engraving shews the sills m^.i

and the square frame in detail, with the
bottom curb, and shaft resting on them.
Fig. 1 is a section of the lower part of the
shaft;, and fig. 2 a plan shewing the shaft
resting on the square frame that is sup-
ported by the sills. The shafts being but
nine feet in diameter, the sills were scarfed
in two places, that they might form three
pieces, for convenience in lowering and fix-
ing them. These scarfings, together with
the glands that connect the square frame
with the siUs, and the necessary iron plates
and bolts, are shewn in the two figures.

For the insertion of the sills, small headings were driven each way from the
shaft, no larger than was sufficient for a man to work in ; and when the sills
were properly placed, and the square frames attached and screwed down by the
glands, and the bolts passing through both the square frtime and the sUls,
the headings were filled with the earth previously excavated, and rammed
solid; a good bottom curb was then placed on the frame, and the brickwork
made good to underpin the part of the shaft previously constructed, and thus
the whole shaft rested on the siUs.

In plate 3 the sills and frames are shewn as fixed ; at figure 1 they appear in
the direction of the tunnel ; and fig. 4, at right angles thereto, a the siUs, h the
frame. The sills are also shewn in each of the figures in plate 4, and in figs. 1

Ky.%

8HAFT-SIIU,

aad 2^ plate 5 ; the last two shew their appearance and position when the
whole was completed.

The stratum of earth through which for the most part the shafts were
sunk at Blechingley, was a hard blue bind (or shale) so highly indurated as to
be when first exposed like rock, which required to be blasted for the econo-
mical working of it. A mass so compact was capable of bearing the weight
of the shafts by means of the sills, when the ground beneath was cut away for
the shaft length, as shewn at figs. 1 and 2^ plate 4, Some assistance however
may mostly be obtained by means of props from the bars of the shaft length,
and from the projecting ends of the crown bars of the side lengths, as shewn at
a, a, a, &c, figs, 1 and 2, plate 4. But in all cases where the ground is not a
solid or compact mass, when for instance it is loose (or quick) sand as was the
case at Saltwood, the use of shaft-sills is injurious rather than beneficial,
because the ground haiTng no cohesion in itself cannot form a foundation for
the sills to rest upon. Under such circumstances they would require to be sup-
ported, and thus produce a source of difficulty and danger of no small magni-
tude : this may be ftiUy understood by reference to plate 4, fig* 2 ; for if the
ground at 6, i, was loose sand, it would be Uable to give way under the siUs
when the excavation was made for the tunneL

These considerations led to the omission of the sills for the shafts at SaJtwood^
and to the suspending them from the surface of the ground by means of
hanging rods, which are generally made of bar iron ; but there being no siutable
material of that kind on the ground^ and for the sake of economy, they were
constructed of wood, as shewn in plate 2, where both a front and side view of
the hangings is given, and their construction rendered plain. A square frame
of whole timber under the brickwork was carried by the hangings, and was
suflficiently stout to prevent any unequal settlement of the shaft. .

The timber of the hangings was larch of a good quality, being the only
available material at hand ; and the pieces were scarfed together to obtain the
proper length, as shewn in the figures, plate 2.

In most of the shafts the hangings stood the pressure without exhibiting any
apparent deficiency of strength ; in one or two they appeared weak for the work ;
and in one case they broke, or rather tore away at the scarfing, but having shewn
previous indication of so doing, any casualty was stopped by timely propping.

This apparent weakness and breakage was chiefly attributable to the follow-
ing cause : — It has been stated that the work w as being done through loose

56 PRACTICAL TUNNELLING.

sand, the ground having in the first instance been saturated with water to a
very great extent ; when the water was subsequently drained therefrom, the
ground was left in a porous state, and yielded in all directions before any
pressure ; and where the lower part of the shafts were sunk and square-timbered,
a great quantity of what was then a quicksand ran into the shaft, and was
removed with the water, leaving large vacuities or caverns in the vicinity,
which were imknown to us, and therefore to the great peril of the shaft so
situated ; for a small amount of lateral or unequal pressure would then throw
an un&ir strain upon the hangings. This was probably, the cause of the
apparent weakness in one or two of the hangings, whilst the others stood
sufficiently firm.

The direct cohesion of larch timber, or the weight that a square inch would
bear without being torn asunder, as stated in Tredgold's Elementary Principles
of Carpentry, page 39, is, according to Rondelet, 10,220 lbs. ; and, according
to Bevan, 8,900 lbs. ; the mean would be 9,560 lbs., which multiplied by the
sectional area in inches of the hanging rods, 9"x6 =54 inches, would give
516,240 lbs. as the weight that would tear each rod asunder ; but it is further
stated, that ^^ the greatest constant load any piece should be allowed to sustain
ought not to exceed one fourth of its computed strength ; therefore, each such
hanging rod should not be loaded with more than 129,060 lbs. or about 57|
tons. The greatest weight of any shaft carried by the two rods was 67 tons,
or 33| tons to each rod, leaving a surplus strength sufficient to have carried
fourteen tons more than it was loaded with.

If iron hangings had been used they would have been made of bar iron,
of a thickness depending on the weight they would have to carry, which would
vary with the different depths of the shafts. In Barlow's Treatise on the
Strength of Materials, page 277, the cohesive strength of good medium iron
is assumed upon good data at 56,000 lbs., or 25 tons per square inch ; and
assuming one-third of that amount as the greatest constant load that should
be applied, it would be 83 tons per square inch, and as four hanging-rods
would be employed, each would have to bear one-fourth of the weight of the
shaft, which in the case above quoted would be 16*75 tons. Now, an iron rod
If inch diameter contains 2-07 square inches; which, multiplied by 8-3 tons,
gives the weight that such a rod wotdd safely carry, namely, rather more than
17 tons: therefore the diameter of the bar employed to carry such a shaft
should not be less than the dimensions above given.

HllfOING-EO0i.

%^ n

The maimer of applying such hanging- ^ %j

rods is shewn in the annexed engraving.
Figure 1 is a section of the shaft ; and figure
2, a plan at the surface of the ground. Two
balks of timber are placed parallel to each
other across the shaft, and two other pieces
axe similarly placed across and at right angles
to them, fonning a square opening (a fig, 2)
to admit the traffic up and down the shaft.
The upper end of each rod terminates in
a strong well-made screw, and passes through
both the balks and a stout iron plate, and is
secured above by a nut ; which screws and
nuts should be carefully made, as the security
of the whole chiefly depends upon them.
Each of the balks should be well bedded on
the ground, to give them a good bearing. The bottom of each rod passes also
through a balk, two of which carry a strong curb, or square setting, upon
wliich the brickwork of the shaft is constructed.

As it would not be practicable to have the hanging-rods in one piece where
there is any great depth of shaft, they must be coupled at diff^erent lengths^ as
may be most convenient. Figures 3 and 4 shew a method of forming these
couplings ; — the one a face, and the other a side view ; — and as the proper
lengths of these hanging-rods can be calculated in the first instance, they may
be contracted for, and made ready for use immediately that they may be
required.

Strong chains would be found a convenient form of hanging ; and as they
could be of an indeflnite length, they would be applicable to any depth of
shaft, and lowered as the shaft was extended downwards. Four chains would
be required in each shaft, and applied in the same manner as the foiu: iron rods
are represented in use in the last figure.

There might be an advantage in the use of chains instead of stout bar iron
for the above purpose, as they would be more manageable, and in all probability
could he more readily appropriated afterwards to other purposes.

The following particulars may be useful, as connected with this subject.

PBACTICAL TtrNNELLINO.

TABLE OF THE COHESIVE STRENGTH OF MATERIALS;
Or, the load in poands that will tear asunder one aqnare indi.

lbs.

Iron — (good medinm)

S6,000

Oak— (English)

14,000

Beech

12,000

Ash . . ,

17,000

Elm

14,000

Mahogany

12,000

Walnut

8,000

Fir

12,000

Ijut:h

9,560

In the erection of Menai Bridge some trials were made of the strength of
ropes used for the hoisting tackle, to get up the main chains. They were as
follows : —

1.— Apiece of 5% inches circumference . . . broke with 6% tons =
2.^A piece of 4iy4 inches circumference, common laid . broke with 4-|V tons =
3.^A piece of 4% inches circumference, of fine yarn, slack laid, broke with 6 tons =

Taking the mean of No. 1 and 2 as a standard, it appears that " good rope
will break vnth a strain of 255 tons per square inch of section" But it ought
not to be strained permanentiy with more than one-third of that, — say three^
fourths of a ton. For temporary purposes it might be loaded with half its
breaking-strain, or 1^ ton per square inch.

For finding the breaking-strain of ropes, the late Dr. Gregory gave the
following rule: —

egir^-tquMg «j. ^ j^^ ,^ ^^^ ^^^ ^^ break the rope.

Which appears to agree well with the experiments at the Menai Bridge : —
take for instance the first example, 5f squared =33- 06, which divided by 5
= 6*61 tons as the breaking strain. The experiment gave a littie more,
namely, 6*75 tons.

SHAFT 8INKIH0,

CHAPTEB VI.

SHAFT SINKING, CONCLUDED.

IXCATTATING AND SQUARE^TIMBEBING THE LOWER PORTION OF THE gHAFTS.

The underside of the shaJt-sills, or of the timber settings carried by the hangings,
was three feet from the intended level of the top of the brickwork of the arch ;
and upon their being made secure, the farther sinking of the shafts through
the intended depth of the tunnel was proceeded mth. Throughout this
space, square settings of timber were placed, at intervals of about six feet, and
propped with rough timber from one to the other ; the intervals were closely
poled, or planked with thiee-inch deals. The cheapest materials that could
be procured for this purpose were six-feet deal-ends. They were placed verti-
cally behind the settings ; which kept them tight against the earth behind ;
with a view to prevent any disturbance of its natural bed,^ — tliis being the great
object to be aimed at in aU the timbering in mining operations : for so long as
the earth can be kept undisturbed in situ, the minimum of pressure Avill be the
result ; but when once a movement takes place, unequal and uncertain w^eight
is immediately thrown upon the timbers, which too often breaks them, causing
a considerable loss both of timber and laboui*, and frequently attended with
danger to the whole of that portion of the excavation, and to the lives of the
workmen. It also frequently happens in argillaceous shales, or what the
miners call *^ blue ground,'* that, upon exposure to the action of the atmos-
phere, or moisture, the earth will swell, or expand. This was the case at
Blechingley ; where, occasionally, in the short interval of six feet between the
square settings in the shaft, the three-inch planks were bulged or forced out
in the middle ; which bulging would probably have gone on until the planks
had broken, had this not been prevented by the insertion of an intermediate
setting. As this happened but in a few instances, it would appear that six

^ PaACnCAL TITNKSIXINO.

feet was a proper distaace for the settings from each other; and the ground
must be very had to require them to be closer: at the same time, it would
seldom be safe or prudent to place them much farther apart ; for the saving
would scarcely compensate any risk, as but little more than the labour in
making the settings is lost, for being so soon released from the shafts the tim-
ber can be advantageously employed during the subsequent works, and the
cost of the labour in making them amounts only to four shillings per setting.

The process of square-timbering, after what has been stated, will be ftilly
understood by reference to plates 2 and 3. In plate 2, figs. 1 and 2, and in
plate 3, fig. 1, the square-timbering is shewn complete. The section, fig*
1, plate 2, is taken across, or at right angles to the direction of the tunnel;
and also shews by the dotted lines the position that the tunnel would occupy
widk respect to the shaft. The opening, or position of the heading is also
shown. Fig. 2 is a section at right angles to the former, or in the direction of
the tunnel ; shewing the arrangement of the timbers in the shaft; and also a
longitudinal section of the heading. Fig. 1, plate 3, is the same upon a
larger scale; and fig. 4, plate 3, shews the upper part of the square-
timbering immediately imder the shaft-sills.

The method of firaming or putting together the square settings is shewn by
figs. 6 and 6 ; a is the stretehing-timber, which is placed across the shaft at
right angles to the tunnel, as at figs. 1 and 2, plate 2: b is the side timber placed
in the direction of the tunnel, as in the figs, plate 2 ; the stretcher, a, has a tenon
at each end, to fix a corresponding mortice in the side timber, b ; making, when
the four pieces are put tc^ether, a clear square opening equal to the diameter of
the shaft above, (in this case, nine feet); but the side pieces were eighteen inches
longer than the stretehers, consequently their ends projected nine inches
beyond the square formed by the four timbers, and stood out like horns,
as shewn at d, figs. 5 and 6. The use of these horns was to form blocks
at the back of the mortices and tenons, to prevent the stretehers from slipping
outwards, when the frame was in its place and the earth excavated from behind,
during the subsequent excavations for the side-lengths of the tunnel. In like
manner the stretehers were prevented from being pressed inwards, by chogs, c,
figs. 5 and 6, which were spiked to the side pieces at one end of each
streteher after it was passed into its place ; that part of the side piece being
cut away, or sloped, to admit the tenon to pass into its mortice, which it other*
wise would not do ; as the excavation should not, in the first instance, be

eQUAEE TIMBERINa.

«1

made so large as to admit the side pieces being opened sufficiently wide
apart to allow both tenons to be admitted into their mortices at the same time.
Several ways have been adopted of framing the settings ; but the one above
described is probably the best, as affording the greatest security to the work

When the ground has been excavated from beneath the shaft-sills to the
proper depth, and the first setting put together, it must be placed exactly under
the shaft, and square with the line of the tunnel ; the earth may then be
removed (or rather pared down, if it will admit of such a process), to allow
the insertion of the three-inch poling-boards, or deal-ends, which should be
driven close to each other, and bedded solid agEdnst the earth behirid, by pack-
ing between the earth and the boards, if more excavation has been made than
was necessary, or wherever a slip has taken place. The rough props, e, e, &c*
plate 2, can then be inserted and wedged tight at their ends ; and, if necessary,
spiked to the square timbers, to prevent their moving.

The work to the fii"st square setting will now be completed ; whereupon the
excavation downwards may be continued through another space of six feet, by
sinking in the middle of the shaft, and leaving a projecting bench of earth
around, on which the first setting rests, in the same manner as explained and
figured at page 48, when describing the shaft sinkiag. When this is done to the
proper depth, the bench is cut away on two sides, for the insertion of the side
pieces of a second setting, which must be placed perpendicularly under the
setting (or settings) already fixed (they being temporarily propped to keep them
from settling during this process.) In like manner the earth is removed for the
insertion of the stretching pieces on the other two sides of the shaft. Some
support may be obtained to the upper setting by temporary raking propSj and
by under-cutting tlie ground for placing the new setting, and subsequently
removing the remainder of the earth to get in the props e (plate 2) and the
poling boards.

In carrying on operations of this kind, so many new circumstances arise
that require different modes of proceeding, even in sinking the same shaft, that
it is only possible in a work like this to explain how it may be done, and how
it has been done, and to state generally that some judgment is necessary to
meet and overcome every difficulty as it arises ; and it may added, watchftalness
also, particularly where the ground is not homogeneous ; as disasters m tunnel
works are seldom rectified at a small cost, and may leave the works in a more
or less precarious state.

62 PRACnCAX TUNNEUJHG.

The forcing operation, or square timbering, was intended to be earned no
lower than the level of the top of the inyert of the tunnel, which was also to
be the level of the bottom of the heading. The setting marked f, plate 2, occu-
pies this position ; but in consequence of meeting with so much water during
the shaft sinking, at both the tunnels, the square timbering was carried down
one setting, or six feet, below the said level, and thus fcrmed a sumph to
collect the water, and for the barrels to dip and fill themselves, as they were
raised and lowered by the machinery above to draw the water to the sur&ce.
The sumph is shewn in aU the figures representing the square timbering of
the shafts.

It may be necessary to explain why in figs. 1 and 2, plate 2, the two settings
B' and c, immediately above the heading, are shewn as being so much nearer
U^ther than the others. This arose firom the use of six-feet deal endsas poling
boards, which required that the said timbers should be placed six feet apart
from centre to centre. Now, if this six-feet interval had been stricdy kept to,
the setting c would have been placed directly across the heading d, which it is
needless to add, could not be allowed ; it was therefore considered better to
place the two settings near to each other, and cut one set of poUngs shorter,
rather than, by equally dividing the space above, to have to cut every set of
polings to correspond thereto, which would have caused needless waste ; or
otherwise, the polings must have overlapped each other behind, which would
have been troublesome to do, and at the same time not so sound nor workman-
like a job.

In the above manner the work of shaft-sinking was carried on, and satis&c-
torily completed at Blechingley tunnel. The quantity of water in the shafts
was various ; in some it caused delay, in others none worth naming. The jack-
rolls, or windlasses, were sufficient for raising both the earth and water, during
which time the horse-gins were being made. The price paid for the work, in-
cluding aU labour in drawing earth and water, candles, gunpowder, and all
tools, was £4 per yard down. At Saltwood it was commenced at 30s. per yard,
and could have been done for that sum, had the sand kept dry, and as easy to
get as at first ; but when the water appeared in such abundance, of course the
work cost much more. It had been the intention to have proceeded at Salt-
wood in the same manner as at Blechingley, but this was prevented by the great
quantity of water, which rendered the ground a complete quicksand. The diffi-
culties met with, and the method of overcoming them, will now be described.

VATEE BABHELS.

The ainkiiig of the shafts at Saltwood was commenced on the 11th of June,
1842, and was carried on without intermission or difficulty until about the
13th of July ; when water began to appear^ at a depth varying from sixty to
sixty-five feet down* Small barrels were at first used to draw the water,
alternately with a skip of earth ; but, as the water increased, a second barrel
w*aa used at each shaft, and very soon the whole time of the men was taken
up in drawing water only ; it was therefore evident that the means then
employed were inadequate to keep the water under, and enable the work to
proceed. It was therefore resolved at once to fix up the Horstvgins, and
apply much larger water barrels than could be worked by manual labour.
Th€ gins were those made for, and used at the works at Blechinglcyj and now
required considerable repairs, which were done as fast as they arrived upon the
ground from that place. All the pits, therefore^ could not be got to work for
some time, but were proceeded with one by one, as the gins could be prepared
and fixed.

The HorsC'gins will be described hereafter ; but the large Water Barrels,
with the manner of mounting them for use, is b

shewn in the annexed engraving, a a are two ^^

centres, about which the barrel revolves when
suspended by the large iron bale. The ring b
has a double motion, by turning in its socket,
and the socket turning in the bale. Strong
ii*on straps pass down the sides, and are crossed
imderneath tixe barrel, to strengthen it for car-
rying its weighty burthen ; one of these straps
is secured to the centre, a, and passes under
the barrel to the opposite centre, whereby the
whole weight is in a measure taken from the
bottom of the barrel, and thrown upon the bale.
The centres, a a, are placed below the centre ' -*^^ >

of gravity of the barrel, which therefore will readily tip over, and empty its
contents, when raised to the top of the shaft; where a trough is placed to
receive and carry off the water. By this method, the barrel need not be landed,
but, as soon as it reaches the proper height, the banksman clips the top of the
barrel with a hook, and releases the bolt, c, which slides upon the bale, and fits
into a socket in the barrel to prevent its revolving until it is required to do so ;

04 PRACTICAL TUNNELLING.

and as soon as it is thus released, the barrel may be turned over towards the
trough, and emptied, without any apparent exertion bemg required. When
emptied, it is placed upright, and the bolt, c, pressed into its place to keep it
erect ; and it is again lowered, to fill itself in the sumph below. The ring,
B, is secured to the end of the gin«rope by means of a shackle shewn in the
axmexed cut ; the rope thus yields and bends as soon as the barrel reaches the
bottom, to allow it to roll over, and fill, without any risk of its becoming
detached. The same shackles were used throughout the subsequent works;
for when the barrels were not attached to them the large
skips for raising the earth — (which will be described, with
the gins, &c. in chap, viii.) — ^were suspended therefix)m, by
means of a chain. The rope was 6^ inches in circumfe-
rence, and cost 50s. per cwt.

The dimensions of the water barrels are given in the en-
graving ; the weight of each was 1 cwt. 2 qrs. 6 lbs. ; the
ironwork weighed 3 qrs. 20 lbs. ; and when ftdl of water
the whole weighed 1,310 lbs. : and as they held 100 gallons, the weight of
that quantity of water was 1,032 lbs. which gives 10*32 lbs. per gallon, which
is about the usually estimated weight of a gallon of water. These determina-
tions have been arrived at, by weighing the parts and the whole, on an excel-
lent weighing-machine by Pooley and Son.

When the barrels had been got to work, and the shaft emptied, the sinkp
ing was resumed and carried on without intermission. The ground we were
excavating, was a dark-coloured sand and clay, nearly black, (but which
became lighter as it dried). The quantity of water it held made it of the^
consistency of soft mud, and as fiist as we shovelled it into the skips, the
space firom whence it was taken was almost instantly filled up again by
fresh sand running from the back of the polings around the shaft. In this
way we struggled with the work for some time, trying innumerable schemes to
counteract the blowing or running of the sand, but to no purpose; for, in
several instances, after a fortnight's work we were less advanced than when we
began. At length, the following method suggested itself, after the repeated
fitilure of other plans. This was called sumjdiing; and its adoption was
attended with success.

The plan was to drive the deal-ends, as if they had been sheet piles, bdiind
the square settings, and remove the earth frt>m the area of the shaft, as they

BITMPHING.

were driven. But, finding it impossible so to do» this operation was preceded
by l inkin g a sumph, about six feet square, at the middle of the bottom of the
shaft, which was always kept as much lower than the ends of the said piles as
was practicable, so that the sumph sinking and pile drilling were continued
together. By this means the water was tended to the sumph, and the earth
above and around was left in a firmer state ; for, it must be mentioned, the
water followed us in our descent, — or, in other words, the ground was drained
to the level of our workings, and left compai'atively dry, except in a few case$
whicb were influenced by the upper s]>rings. T^Tien this was done, the deal-
ends being inserted behind the last square setting, were driven down by beetles
(like piles behind a waling timber) ; at the same time the ground was sho-
velled from under them to admit of then* descent. The earth was kept suffi-
ciently dry for this purpose, by drawing water from the sumph as fast as the
barrels could be worked, occavsionally disengaging one of them, to hook on and
send up a skip full of earth. As the pile dri\dng proceeded, the sinking of the
sumph was continued, in order to keep the drainage as much as possible below
the lower ends of the piles, and also that the barrels might dip and fill them-
selves ; and when five or six feet were thus gsdned, another square setting was
inserted, as might be found to be necessary ; and thus tlie work was continued
to the bottom.

The making of the sumph w as the difficulty ; and this was done as shewn
in the annexed engraving, which is a plan or section of the shaft at the
level where the sumphing commenced* a, a, are
the side pieces, and b, b, the stretching pieces of
the square timbers ; c, c, c, c, are the upright
polings or deal-ends at the back of the square
timbers; a, a, &c., are sections of the uprigbt
props between the square setting, a, a, b, B, and
the one above it ; the shaded space represents
the bottom of the shaft ; and the space enclosed
within the four sides, n, e, f, g, is the sumph.

To make the sumph, two planks, d and e, were
placed on their edges, parallel to each other, ha\ing triangidar pieces, or chogs,
ej e^ e, «, securely spiked to them near their ends ; between and at right angles
to them two other planks, f and g, were placed, which were kept from being
pressed inwards, by the chogs, e, e, &c* When all four planks (or deal-ends)

66 PRACTICAL TUNNSLLINO.

were thus placed, they formed a square frame nine inches deep, The area was
then cleared of the sand and water, by two men, the one shovelling the
sand into a skip, the other baling the water into the barrel, at the same
time that two other men with beetles drove down the four planks; for it
was impossible to clear the area within the planks, without at the same tim^
di^iving them lower, as the earth ran in so rapidly from behind 9s to fill the
space immediately. When the planks were driven their whole depth (nine
inches), four other planks were similarly placed upon them, a^id all secured
together, so as to make a box twice the depth that a plank is wide, or eighteen
inches. The sinking proceeded as before, and when they weire down to the
level of the bottom of the shaft, they formed a sumph, 18 inches deep. A third
rand a fourth set of planks were then placed above them, and lowered likewise,
and so on till a sumph several feet deep was attained, for the barrels to dip and
draw off the water, whUe some progress was being made with driving the
polings or deal-ends behind the settings, as before described. This, together
with the sumph«sinking was then continued, as nearly as possible simultaneously
until the required depth of shaft was obtained. Behind every poling-board
in the shaft, and wherever there was any space, a packing of straw was rammed
tight, which had a good effect in preventing the live sand from running. The
extensive use of this kind of packing was of the most essential service. The
state of the work at this time, and throughout the subsequent driving of the
heiKling, was so injurious to the health of the workmen, that about one eighth
of the whole number was under medical treatment for rheimiatism, ague, or
dysentery ; which, however, proved fatal to but one.

BEIVTKG HEADINGS-

CHAPTER VIL
DHiYiNa THE headings; and experiments upon horse fqwer.

When the shafta were completed, the Heading or Adit was commencetl.
The same dimensions were adopted^ and the same settings used, both at Bh -
ehingley and Saltwood tunnels. At the former place the work was done with
comparatively but little trouble: the water that appeared passed into the
sumph at the bottom of the nearest shaft ; and, there being no great quantity,
the drawing of it to the surface delayed the general work but very little. At
Saltwood it was otherwise : there the difficulties continued until the heading
was completed through the hiU, when the water ran off into the natural w atei*
courses of the country, — previously to which it all had to he drawTi to the
surface by horse power^ as already described. It remains to state a few parti-
culars as to the heading itself.

Figure 1 of the subjoined engi*aving shew^s a transverse section, and fig. 2,
a longitudinal section of the heading.

Similar sections may also be observed in most of the plates at the end of tbi^
work. The clear dimensions of the heading was 4 feet 8 inches high ; 3 fet^t

PRACTICAL TUKKELLING.

wide at bottom, and 2 feet 7 inches at the top. Such were the dimensions
of the frames or settings, which were made of round larch timber* The caps^
Bj and the sides, a a, were from five to six inches diameter, and the sills, e, four
inches ; the sides were tenoned into mortices in the caps and sills ; they were
placed at intervals of two or three feet apart, according to the character of the
ground to be supported* The sides were closed by poling-boards, e, from ^ to
one inch thick ; and the top, d, with poling not less than one inch in thick-
ness. At Saltwood, the bottom under the sills was also poled quite close, and
the whole packed with straw, to prevent the running of the sand, which but
for the floor of poling-boards would have blown up from below, and filled the
heading. In each of the above figures, the ranging-setting, and candle^holders,
described at page 34, ai*e shewn.

The annexed en-
graving shews the
manner of making
the necessaiy exca-
vation, and removing
the earth from the
heading to the shaft,
which was done by
means of a skip, upon wheels, which ran upon a temporary railway. For this
purpose, the rails consisted simply of strips of iron, one inch wide and | inch
thick, screwed down at the edges of long pieces of common fir scantling,
4 inches by 3 ; which was spiked down to the sills of the square settings, and
answered all the pui-poses required.

The cost of the settings complete, ready for use, delivered on the works, was
four shillings and sixpence per setting; and for inch poling-boards, from
thirteen shillings and ninepence to sixteen shillings per hundred feet super,
also delivered.

The driving and timbering of the heading at Blechingley cost thirty shiUings
per yard forward, including aU labour, candles, gunpowder, and water draw-
ing. At Saltwood, the cost of the labour was the same ; the water drawing
being an additional expensCp

An inspection of the engravings at the end of the work may lead to the
remark tliat the headings were driven at the level of the top of the invert ;
and a question might arise as to the reason for taking that level, in preference

DRIVING HEADINGS. 69

to others. The object in so doing was to keep the drainage of the works at
all times free ; namely, upon the same level in the finished portions of the
work as in the headings at the unfinished parts ; and the only interruption
thereto arose when the ground was excavated for a new length of brickwork ;
in which case, the water was carried across this twelve-feet space in a wooden
shoot, and what little leaked into the excavation was baled out by the brick-
layers' labourers. If the heading had been placed at a lower level, the works
would have been always under water to the level of the top of the invert, as
soon as any portion of it was completed, and a continued annoyance and
expense would have been the result, independently of the greater risk of having
unsound work from the effects of the water. Had the heading been driven
altogether below the invert, and a culvert constructed before the tunnel works
had been begun, a great additional outlay would have beeii the consequence ;
and the culvert thus made under ground, in so confined a space, would probably
have been badly done, and there would have been an unsound foundation for
the invert of the tunnel : moreover, none of the advantages of the heading for
the purposes of ventilation, ranging the lines, and levelling, would have been
obtained. On the other hand, if the heading had been driven at the level of
the top of the tunnel, all its advantages in draining the works would have been
lost ; the ranging by the method of lines along the heading, for setting the
ground-moulds, as explained in chapter iii, would have been less conveniently
done, and with greater uncertainty as to its accuracy. If, therefore, there is
not a certainty of the ground being quite dry (which is rarely to be expected),
such a situation for a heading appears to have but few advantages to
recommend it.

HORSE POWER.

During the progress of water-drawing, there appeared an opportunity of
obtaining some results as to the power of horses. Having found it desirable
to ascertain the amount of labour performed at the various shafts, in order to
determine from day to day, not only whether the difficulties were increasing
or diminishing, but also correctly to fix the duration of horse-labour at each
working, — otherwise there would have been opportunities of deception and
misrepresentation, — all the horses being hired (at the price of 7s. per diem)

PRAcncAL rxnxvmx^Q.

BeiddM whichy it appeared that bjr keeping a daily register of the work
actually performed by the horses in each given time^ there would be cdQlected
a qtumtity of fitcts relative to horse poweor that might prove tiseful, in assigning
an Approximate value to that uncertain co-effident. The register— which
extended from August 25th to October 24th — ^was kept by my friend and
assistant, Mr. P. N. Brockedon, in the manner shewn in the following table,
which is a copy of the register of work done at nine shafts, on the 17th of
September, 1842; and is sufficiently explanatory of the mode adopted in
arriving at the results.

SALTWOOD TUNNEL.— WORK DONE BY THE HORSES IN THE
For the twenty-foar hours ending 6 a. m. September 17th, 1842.

GINS,

No.

Number raised during
24 boiirt, of

Average Number
per bour, of

Weig'ht in Pounds raised
per bour, of

Total NumbeD of

Pounds raised the

iull heigrht.

Height

NiiBber of Pounds

raised on« Foot high

per Minute.

Time
that

of
Shaft.

Water
Barreb.

Lar^
Skips.

Small
Skipi.

Water
Boneb.

Large
Skips.

Small
Skipi.

Water
Barrels,

eoch
1310 lbs.

Laqj*
Skips,

each
1060 lbs.

Small

Skip.,

each

500 IIm.

per
Hour.

per
Minute.

raised,
in feet.

two
Horses.

(Mb
Horae.

each
Hone

•rork-
ed, io
Houn.

Not in
operation

•

398

100

16-6

0-2

21.740

210

2,100

24,056

400,9

38,086

19,043

649

27-0

35,370

3,150

38,520

642,0

110

70,620

35,310

725

30-2

2-0

39,562

2,100

41,662

694,4

108

74,995

37,498

647

270

2-2

35,370

2,310

37,680

028,0

107

67,196

33,598

693

28-9

37,859

2,520

40,379

673,0

103

69,319

34,660

446

18-6

8-8

24,366

3,990

28,356

472,6

101

47,733

23,866

605

25-2

2-3

33,012

2,415

35,427

590,4

100

59,040

29,520

420

17-5

22,925

1,680

24,005

410,1

100

41,010

20,505

333

13-9

1-8

18,209

1,890

20,099

335,0

31,825

15,913

BOBBIN POW]^

Upon thje c(»npletion of jthe water-drawii^, namely, when the shafts and
headmg were finished, — ^the following mew results were obtained as the
power of horses working a given number of hours per diem: —

Horses working three hours per diem, mean of 112 results,=32,943 lbs.
raised one foot high in a minute.

Horses working four hours per diem, mean of 4 results,=:37,151 lb&
raised one foot high in a minute.

Horses working four-and-half hours per diem, mean of 12 results,=27,056 lbs.
raised one foot high in a minute.

Horses working six hours per diem, mean of 212 results,=24,360 lbs.
raised one foot high in a minute.

Horses working eight hours per diem, mean of 4 results,s;=23,412 lbs.
raised one foot high in a minute.

In the determination of the value of horse power from the above results, the
three and six-hour experiments alone should be adopted. The other results
were more or less objectionable, from a variety of causes over which there
could be no controul; and are therefore of less practical value.

The following table of estimates of horse power wUl afford some means
of comparison with the above results.

Name.

PouDdt raised

1 foot hisrh
in a Minute.

Moan of
Work.

Autharity.

Boulton and Wait .

33,000

Robison's Mech. PhiL, toL ii., p.l45.

Tredgold . .

27,000

Tredgold OB Bailioads, p. 69.

Desagulier

44,000

Ditto

27,500

Not stated.

Sauveur

34,020

{ Dr. Gregory's Mathematics for
( Practical Men, p. 183.

Moore, for Society of Arts

21,120

Not stated.

Smeaton

22,000

Not stated.

72 PRACTICAL TUNNELLING,

These are higher results than were given by the average of the Saltwood
experiments, and more nearly accord with the maximum there obtained:
which was as follows: —

Horses working 3 hours

= 47,895 lbs.

Horses working 4 hours

• •

. 30,604

Horses working 4\^ hours .

• •

. 35,300

Horses working 6 hours

• •

. 36,810

Horses working 8 hours

• •

. 36,630

But with such high results, or any thing approaching thereto, the horses sunk
under the excessive fatigue, and eleven of them died. Nearly one hundred
horses were employed, — which were supplied by Mr. Bichard Lewis, of
Folkestone; — ^they were of good quality; their average height was 16 hands
:J inch, and their weight about 10| cwts., and they cost from £20 to £40
each. They had as much com as they could eat, and were well attended to.

The total quantity of work done by the horses, and its cost, was as under : —

Registered quantity of water drawn 104 feet, the average height, ) ^^

28,220,800 gallons S "" ^^^'

Ditto, ditto, earth 3,500 yards, . 1 ton 6 cwt. per yard = 4,550

Total weight drawn to the surface . . . 133,055 tons.

Total cost of horse labour, including a boy to drive each horse . . £1,585 : 15s : 3d.
Or, 2*85 pence per ton, the average height of 104 feet.

A paper upon the subject of horse power, containing the fiill particulars of
the Saltwood experiments, by the author of this work, was read before the
Institution of Civil Engineers, on the evening of March the 14th, 1843.

FOEM AND DIMENSIONS OF TUNNELS.

CHAPTER VIIL

FORM AND DIMENSIONS OF BLECHINGLEY AND SAXTWOOD TUNNELS, DESCRIPTION

OF THE SKIPS, ETC. AND THE HOBS&.GINS EMPLOYED IN THE CONSTRUCTION
OF THE WORKS.

The tbrm aiid the several dimensions of these Tunnels, as they were constructed,
are shewn at fig* 3, plate L The figure is divided into two parts by a vertical
line : the left-hand half shews a transverse section of Blechingley tunnel ; and
Uie righ^liand half shews a similar section of Saltwood tunnel : the only dit
fereuce, in the two sections, being, that the inverted arch of Saltwood tuunc^l
had a rise, or versed sine, of three feet sLx inclies ; whereas that of Blechingley
was hut three feet. This difference was thought necessary, to ensure sufficient
stability in the former.

The figure of each tunnel, from the springing of the invert on the one side,
over head, to the same point on the opposite side, was elliptical, and described
with arcs of circles whose radii was 31 feet, 15 feet, and 9 feet. Tlie small
circles, and the dotted lines, shew the various centres and the extent of the
said arcs. The invert of Blechingley tunnel, mth a rise of three feet, Wd^
struck with a radius of 22 feet 1| inch ; and that of Saltwood tunnel, vrith a
rise of three feet sis inches, was struck with a radius of 19 feet 5| inches.

The thickness of the brickwork of the invert of the shaft and side lengths in

both tunnels, and, for the first leading length at Saltwood tunnel, was 2 feet 3

inches; and for the remainder, 18 inches was considered ample. The side

walls and arch at Blechingley tunnel were 3 feet thick for the shaft and side

lengths: tliis was, however, reduced to 1 foot 10| inches, wherever the ground

was sufficiently sound and undisturbed to admit of it being safely done. At

Saltwood tunnel, the shaft, side, and first leading lengths were 3 feet, or four

bricks thick ; and the remainder of the work 2 feet 3 inches, or three bricks

thick. The whole work of both tunnels was set in cement,

74 PEACTICAL TUNNKLLINO.

The clear height from the upper surfiu^ of the rails to the crown of the arch
was 21 feet, and the clear width at 5 feet above the said level was 24 feet. The
skewbacks and footings were also of brick ; and at Blechingley wedge-formed
bricks were made for this purpose, as shown in section at fig. 2, plate 6.

On the right hand half of the figure are shewn a number of horizontal lines
drawn at intervals of one foot from the exterior crown of the arch downwards,
and the length on each line (in feet and inches) from the centre vertical line
to the exterior of the brickwork throughout the whole depth of the work is
given. Also from the same point (the external crown of the arch) oblique lines
are drawn to the extremities of the said horizontal lines, and the length of such
oblique lines are given at the outside of the figure on the right hand. By these
two sets of lines it will at once be seen that the figure of the tunnel could be
laid down independent of the radii given on the left of the figures ; their appli-
sation was, however, to guide the miners in excavating the earth to the correct
dimensions : for, as they commenced at the top and worked downwards, they
had this guide in taking out sufficient earth to admit the insertion of the tunnel
without removing more than was necessar)'. A plumb-line was hung from the
roof in the centre of the tunnel, and upon this line a knot was tied at every 12
inches of its length. A tape, to represent the corresponding line on the work-
ing section above spoken of, was stretched horizontally from any one knot to
the extent of the excavation, at right angles to the line of tunnel, which deter-
mined whether or not sufficient earth had been removed : thus at 8 feet down
it required a space 12 feet 2 inches to be removed on each side of the line, and
as a check, another distance to the same point was occasionally measured from
the intended crown of the arch which is marked outside of the curve in the
figure ; at 8 feet down, this oblique distance was 14 feet 6f inches.

The dimensions furnished to the miners were those of the outside of the
intended brickwork ; they had therefore to excavate still farther, to receive the
timbers that were required to support the earth. These extra dimensions were
supplied by themselves, at the time ; dependent upon the substance of the
timbers necessary, together with the requisite allowance for subsidence; as
the character of the ground might have pointed out. This extra space for the
timber, &c., beyond that required for the brickwork of the tunnel, will be
readily understood upon reference to such plates, at the end of the volume, as
contain transverse sections of the finished tunnel ; of which there are several
examples given.

SKIPS AND HOOKS,

BESCRIPTION OF THE SKIPS, ETC,

53ifi common windlass, or jack-roU, as she^vTi placed across the top of the
shafts, in plate 2, bus the only machinery employed for raising the eaith and
lowering materials, throughout the sinking and heading-driving at BIcchingley,
The Gins (or "Wliims) were not erected until the actual tunnelling operations
were commenced ; Avhen more powcrfiil means had become necessary. The
same windlasses, &c, were subsequently employed in sinking at Saltwood tun-
nel ; but were there obliged to be Ifdd a&side before the sinking was completed,
on account of the great flow of water requuing more efficient means to keep
it under, as already explained.

As the windlasses were adapted for manual labour, a smaller quantity of
earth could only be drawn up at one tune than was subsequently raised when
horse power was employed. The most comenient sized skip to be used with
the windlasses is represented in the
annexed engraving. They w^ere made
of inch elm^ and weighed 84 lbs, ; but
when filled with wet earth, as that at
Saltwood^ weighed upon an average 500
lbs. J and required four men to raise
them. The skips were attached by their

bales to the ropes, by means of a hook, whichj at the same time that it aff'orde^l
facilities for releasing it, both at the bottom and top of the shaft,— (the former
for filling the skip, and the latter for emptying it.) — was contri\ed so as not to
be liberated durmg its ascent or descent^ as such an accident woidd be likely
to prove fatal to the men below. Several schemes were tried for this purpose,
and the two found to answer best are shewn in the minexed engraving;
wherein both a side and end view of each
are given. The left-hand hook is secured
from unshipping, by means of an iron pin
passed through the return of the hook
above a loop dropped over for the pur-
jrase: and the right-hand figure shews
how the like security was obtained, by
a spring acting against a continuation

PEACrrCAL TtTKNELLING,

of the hook, which is thus converted into a ring. This is very similar to the
hooks of the hanging-rods represented at page 39. The real dimensions liotli
of the skips and the hooks, are given in the above cuts.

At a subsequent period of the work, when the Gins were set up, and liorne
power applied to raise the earth, the larger-sized skips were used. These ure
represented in the annexed engraving, where the real dimensions are al^^i

given. These were not suspended from the rope by a bale, as were the above
described for the smaller skips, but the iron bands terminated in loops, or eyes,
one on each of the two opposite sides of the skip, as at a, a. These loops received
the hooks of a chain made of f inch iron, that wm attached to the end of the
rope by a shackle, which is represented at page 64, where the method of sus-
pending the water barrels is described. The wheels and axles are attached, for
the purpose of running the skips along a temporary railway laid under ground
from the several faces of the work to the shaft, and also upon a similar rail-
way, above ground, from the top of the shaft; to the tip of the spoil-bank,
where the earth raised was deposited. There was no necessity for such an
appendage to the smaller skips, because they had to be removed but a few feet,
either below or above, and were sufficiently light to be easily shiftied by
hand : on the contrary, the large skips were too Iiea^y for men to move about,
except upon wheels; and the distances they had to be moved continually
increased^ as the works advanced. ITiey were made of l^inch elm; and
when empty weighed 140 lbs., and when full of wet earth 1050 lbs.

78 FBACTICAL TUNNSLLING.

A is the span-beam, with a bearing of 39 feet; 16 inches in depth in the
middle, and 8 inches thick, b is the horse arm, 35 feet 8 inches long ; and,
as first made for Blechingley works, consisted of one piece, 12 inches by 7,
passed through a mortice in the drum shaft, d. But finding this mode of con-
struction to be too weak to stand the strain for a length of time, the horse
arms were subsequently trussed, and consisted of two pieces, each 1 foot 2
Inches by 4 inches, notched into and bolted to two opposite sides of the drum
shaft, D ; where they measured across, from outside to outside, 2 feet ; and then
the truss was gradually narrowed near the ends, where they measured 1 foot 4
inches, and were blocked apart, and bolted together through the blocks, be-
tween the centre and the extremities, c is the drum, 9 feet diameter, and 2
feet 6 inches deep, divided into two parts by a fillet roimd the middle of the
cylindrical part of the drum, to separate the ascending and descending ropes.
The ropes were prevented from working off the drum, by horns projecting
aroimd the top and bottom, twelve in number, made of four by four-inch stuff,
and jutting out about ten inches ; the inner side of the projection being sloped
off. D is the drum-shaft, 13 feet 6 inches long, and 1 foot 2 inches square : to
this the horse-arm is securely bolted at four feet from its top, and steadied by
stays of 4 by 4-inch scantling, from its lower part ; to these stays the driving
boys tied one end of a small cord, which served as a rein to the horses, as shevra
in the engravings. Above the horse-arm, and resting on it, the drum was
secured by the shaft passing through it, the frame of the drum was made square
in the centre for that purpose ; the lower frame of the drum was steadied from
the shaft at right angles to the horse-arm, by stays, similar to those last des-
cribed. The shaft rotates on two spindles of two-inch round iron, one end being
squared and turned both ways, at right angles, to secure a firm hold in the
shaft. The top spindle worked in a socket formed by straps bolted to the
span-beam, and the bottom spindle worked in a bell-metal cup. The top of
the shaft had one hoop, 2 inches by |-inch, driven on after the spindle was
fixed; and the bottom of the shaft in like manner had two hoops. The
weight of the top spindle was 28 lbs. ; the bottom spindle, 25 lbs. ; the straps
for the top spindle, 18 lbs. ; the three hoops, 21 lbs. ; and the brass or bell-
metal cup, 13 lbs.

The horses were harnessed to shafts attached to a perpendicular piece, 8
inches by 10 inches ; its top forming the end of the truss of the hors&^irm.

HOB8E OIN& 79

ficom which it was pendant : it was also steadied thereto by means of braces,
as shewn in the engravings. The harness shafts were made to reyolye on a
spindle at the bottom of the perpendicular piece last named, whereby the
horses could be turned round, and proceed in the opposite direction, to
reverse the action of the machinery; which was necessary, at every as-
cent and descent of the ropes, — the one ascending as the other descends,
and vice versa. It would, however, have been more convenient had the
machinery of the Gin been so contrived that the alternate ascending and
descending action of the ropes could have been effected without the neces^
sity of turning the horses round.

The span-beam, a, was supported at each end by a triangular frame —
shewn in the last engraving — the base of which was 13 feet long, and
was steadied with props. e is the pit frame, placed on each side of
the shaft, at a distance of 24 feet 6 inches from the drum shaft. This
carries the head-gearing, or frames, in which are mounted the pulley
wheels or sheaves, which were of cast iron, 3 feet in diameter, and
weighing 1 cwt. 3 qrs. The spindle upon which the sheave revolved
was of wrought iron, 2 inches diameter; and worked in a bell-metal
box, or plummer-block, weighing about 3| lbs. k was a pole, of which
there were two, called jackanapes poles because they carry what are tech-
nically called the jackanapes, g, g, whose use was to keep the rope straight
in passing from the drum to the head gearing, and had small friction rollers
for it to work upon. These jackanapes were pendulous, and therefore
they vibrated or yielded as the ropes moved ; which was necessary, because
the ropes continually changed their levels as they woimd round the drum,
or vice versa.

H shews the trough into which the water barrels emptied themselves
when tilted, — as described at page 63; from which trough the water
was passed into proper drains, and was not allowed to soak into the
ground. i shews the platform, made to run upon flange wheels, which
worked upon rails, whereby it could be drawn over the shaft to cover it when
necessary, for greater security in landing the skips ftdl of earth, as they
were raised to the surface; the skips were then rolled away, on temporary
rails, to the spoil-bank, and emptied of their contents. But, when the
wet earth was brought up, at Saltwood Tunnel, during the sinking and
water drawing, it was generally emptied into barrows, and wheeled away.

80 PRACTICAL TUNNELLING.

This was being done when the sketches for the foregoing engravings
were taken, and which accounts for their being shewn therein.

The pit firame, and head gearing, were made of oak; the frame of
the drum, of oak, and the covering of ehn; the jackanapes poles were
of larch ; the horse shafts of ash ; and the rest of the Gin, of Dantzic
timber.

For the greater preservation of the ropes, they might be tarred, and
payed over with coarse canvass tarred. Some such covering is requisite
for economy's sake, as the wear upon the rope is considerable. It may
be worth remarking, that the recently invented wire ropes would in aU
probability be appUcable to the purposes now under consideration, not
only on account of their a]>parent greater durability, but to prevent the
possibility of wicked persons cutting or otherwise injuring the ropes to
cause accidents by their breaking when loaded. Such a circumstance
occurred at Balcombe Tunnel, upon the Brighton Railway; where a rope
having wilfully been cut, broke at a time when several men in a skip
were suspended by it; whereupon they fell to the bottom of the shaft,
and one of them was killed. This, unhappily, is not a soUtary instance,
as the same kind of injury was done to one of the ropes at Blechingley
Tunnel, but was fortunately discovered before that it was again put into
use. Too great care cannot be exercised where there is so large a body
of men congregated together; and some of whom are too apt to indulge
vindictive feelings from motives of revenge.

CONSTRUCTION OF THE TUNNELS*

CHAPTER IX.

CONSTRUCTION OF THE TUNNELS.
THE SIDE LENGTHS. EXCAVATION AND TIMBERING,

le excavations for the tunnels at Blechingley and Saltvvood were carried on
in a similar manner. One description of the general process will therefore
suffice; with such occasional particulars of any peculiarity in the circumstancea
of either, as may have arisen in the course of those works.

The work was commence<l by removing some of the polings, or deal ends,
from behbid the two top settings of the square timbering of the shafts ; and
driving a narrow heading, about twelve feet long, at the top, and in the middle
of the intended tunneL Where the ground is good, and will stand without
much timbering, the top heading (as it is usually called) may have rather large
dimensions ; but must be hmited in this respect where the ground is loose or
treacherous. The headings at Blecliingley and Saltwood were sufficiently high
for a man to stand upright in, and about three feet in width. In some of the
headings at the former tunnel no poling boards were required in so small an
excavation, but at the latter place they were in all cases necessary. No regular
system of framing was used^ but pieces of poling boards were put up and
secured in the best and most convenient manner, wherever the earth shewed
symptoms of falling in, but so arranged (where it was possible) as to form part
of the subsequent roof of the excavation. The top of this heading was so much
above the intended soffit of the arch of the tunnel, as to admit the proposed
thickness of the brickwork, and that of the crown bars, packing, and poUng
hoards, togotlier with the allowance of sever^ inches for the settlement of the
timber which is certain to take place when more of the excavation is made,
and before the brickwork can be inserted to take the weight, and relieve the
bars of their burthen. This allowance should never be omitted, for when such
settlement takes place, and no room has been previously left for its occurrence,
a part or the whole of the crown bars in sinking occupy the position of the

PRACTICAL TUNNELUNGL

intended brickwork ; and therefore, in order to insert a tunnel of the required
dimensions, the bars and poling boards must be raised to their proper level ;
which is only to be done piecemeal, by removing the earth over each bar, and
then raising them one at a time : this involves considerable labour and care,
and no trifling expense.

When the heading is driven, it is widened at the top along one side, to form,
as it were, a shelf, upon which a crown bar may be laid lengthways. When
this is done, the centre crown bar is placed along the top heading, and supported
against the roof, by an upright prop at the remote end, and by resting it on the
square timbering of the shaft at the near end ; poling boards are then arranged
above the two bars to carry the earth. This is shewn in the
annexed section of the top heading. A similar excavation or
shelf is next made on the other side of the centre crown bar,
and a third bar placed thereon, and poling boards inserted
above, as in the first instance ; a narrow sUp of ground is
next removed from under the remote ends of the two side
crown bars, to the bottom of the heading ; and rough props
inserted to support them in the same manner that the centre
crown bar is supported ; their other ends being in like man-
ner supported by the square timbers of the shaft. The earth
may next be removed from under the two side bars, which
leaves the heading much wider than before.

Sometimes, when the top heading is wide enough, two crown bars are inserted
and poled above, and the insertion of the side bars (by excavating a shelf to the
right and left, as before described,) is then proceeded
with, in the manner shewn in the annexed engraving.
The bars are kept at the proper distance apart, by in-
serting five or six struts between every two bars, as
shewn in the next engraving, page 83, also at s, s, &c.
in fig. 2 plate 3, and in each plate that contains a trans-
verse section of the timbering of the tunnel. The tempo-
rary props, at the remote end of the bars, rest upon flat
foot-blocks, to prevent the superincumbent weight
pressing them down. The foot-blocks are either placed
at the bottom of the heading, or the ground is dug up
to admit of their base standing upon the intended level of the under-side of the

GETTING IN THE TOPS.

top sill. In either case, they are placed feu enough outwards to admit there-
after of the sill being placed in front of them, — The dotted portion of the prop*?
and foot^blocks, in the above cuts, shews the end of the props so placed below
the bottom or floor of the heading : however, it is not always that the giound
will allow of this being done in the first instance. The perpendicular face of
the work is secured from falling in, by the insertion of poling-boards across it,
at the back of the props, as shewn iti the last figure*

In the manner above described, bar after bar is inserted to the right and left
of the top heading ; propped and strutted from the ground and fit)m each
oihrn ; and tlie poling-boards inserted both in the roof and against the face of
the excavation, the bars being so airanged as to follow nearly the intendetl
%ure of the timnel : or rather, such an arrangement is preserved as wUl he
best suited for the subsequent insertion of the brickwork, — as will be hereafter
explained.

The annexed engraving shews
a section of the work in this
stage of progressj winch is tech-
nically called '' getting in the
top."

From what has above been
stated, together with an exami-
nation and comparison of the
engravings, it may be hoped
that the matter has been sufli-
ciently explained to require no
ftirther observations*

It has been stated above, that the near end of the crown-bars is at first tcm-
|>orarily supported or propped from the square timbers in the shafts ; it mutt
however be observed, that, by so doing, a great weight is thvovm upon the
square timbers in addition to that of the brickwork of the shaft, which is all
that it is designed to carry, and in which it is materially assisted by the hang-
ing-rods, or shaft-sills described in the preceding chapters ; and, for this reason,
the square timbers should be as speedily as possible relieved from the weight
of the bars, and whatever pressure of earth they may be sustaining: — this is
finally done, when the top sill next the shaft is inserted in its place, by prop-
ping every bar therefrom. Wlien the ground is good, there is no danger in

'"^&.

PRACTICAL TUNNELLING,

temporarily supporting the near ends of the crown-bars from the square tim^
hers ; but where it is soft, or yielding, it is unsafe thus to load them ; for, under
.^uch circumstances, the ground, instead of steadying the square timbers, h
liable to give under the pressure ; and when once the square timbers get out
of the perpendicular they would require no great additional weight to force
them in, and the yielding or soft ground wliich would thus lead to the acci-^
dent» would follow from behind the shaft, and in all probability bring the
shaft down with it.

This was precisely the kind of accident that occurred, in one instance, upon
first starting the Saltwood tunnel. The sand had become extremely porous,
and consequently yielding, by the draining of the water therefrom, to a great
extent, as described in the preceding chapters. Not only was the earth jiorous,
by the absence of the water, but large spaces (in some instances, complete
caverns) had been formed behind and around the squai'e timbers, by the sand
having run into the shaft, and been drawn to the surface with the water-
Under such circumstances, it was no wonder that half the weight of the first
side lengths being tlirown ui>on the square timbers (in consequence of the
bars haring been propped therefrom), should have caused their downfall,
and the destruction of the shaft; the porous nature of the ground, and
the existence of the caverns, being unknown at the time. The necessity
of relieving the square timbers from the weight of the bars, as speedily as pos-
sible, cannot be too strongly impressed upon the reader ; and such relief may
he obtained to a great extent, if not wholly, by temporarily propping, upon
planks or timber laid across the then floor of the excavation, near the shaft, or
at the middle of the length, or both, as circumstanceB or the progress of the
work will atlmit of, during the removal of the
earth for, and the insertion of the shaft top siU,
D fig. 1, plate 3; which should be got into its
place as speedily as possible.

The manner of forming the roof of the exca*
vation by poling-boards overlapping each other
behind the bars, is shevni in the adjoining en-
graving j where a miner is represented as prcv
paring for the insertion of another bar.

A completely arched roof of timber is con-
structed, in the manner now described, and

TNSERTrON OF THE SILLS*

shewn in the upper portion of fig, 2, plate 3, above the sill, a, a ; btit, as
at present explained, it is left supported at the face by props resting
upon the earth, at the level of the under side of the top sills^ each prop stand-
ing upon a broad base in the form of a foot-bloek, to prevent its being pressed
into the ground, which would cause the roof to give way : therefore, as soon m
the whole of the bars to the intended level of the sills are inserted, or even
sooner if possible, the sills themselves should be got into their places. The
bars are longer than the first length of brickwork is intended to be^ so that, at
the face of the excavation, the top sill, a, may be placed in front of the advanced
props, and as soon as the sill is placed, another prop may be fixed from the sill
to support each bar. These props, therefore, stand in front of the ad^^anced
props, which are hid in the section, fig. 2, plate 3, but are shei^Ti in the longi-
tudinal section, fig. 1, plate 3 ; where a is the top face sill, — f the croT^ii bar,
— G the advanced prop, corresponding to those shewn in the cuts at pages 82
and 83, and h the permanent prop. In a similar manner the sill, d, next the
shaft, is inserted, and the bars propped therefrom, as i, fig. 1.

The sills (which are called miners* sills, to distinguish them from the cental
Hills, to be hereafter spoken of), are made of whole balk, 12 or 14 inches
square, according to the nature of the ground ; or, in other words, the sc^ant-
ling for the timber of the sills must depend upon the weight or
pressure they are intended to sustain or resist. Their length was
about 36 feet, in two pieces, scarfed together in their middles^
and secured with iron plates, bolts^ and glands, as shewn at
fig. 2, plate 3, where a a is the top sill, and c c the lower sill.
The weight of the iron work for the scarfing of each sill was
1 cwt. 2 qrs. 14 lbs,; and the price paid for labour, including
sawing, was 43, 6d. per scarf. Each scarf was five feet in length.

When the sills are well bedded in their places, they should be
set level, and the props from them to the bars, above, be driven
or wedged tight, and secured from the chance of disturbance
by driving a peculiarly formed spike, called a brob^ of wrought
iron, (as figured, half the real size, in the margin,) around the
ends of the props into the bars and the sills. The brobs are
shewn in their places, in figs. 1 and 2, plate 3 ; and in most of
the engravings where their use is required. The tops will now
have been completely got in, and the whole weight of the bars.

8$ P&iLCTICiJi TUNNSLUNO.

with that of the ear& preasing on them, will be 8upiK»i:ed by the sills, which
by their greater length present a large base, and no settlement can take place in
any one bar or prop but must equally affect the idude, unless the sUls should
have been unsoundly bedded in the first instance, or subsequently unequally
propped when the earth is removed from below, in the further progress of
the work. At this rtage of the work the stretchers m h, plate 3, should be
inserted, to prevent the sills from being pressed inwards by the earth against
the foce of the work. The right hand portion of fig. 1, plate 3, shews the
excavation with its timbering ready for the reception of the brickwork, as it
appears longitudinally, or in the direction of the tunnel ; fig. 2 shews the
appearance of the same timbering, as seen at right angles to the former ; and
by a comparison of the two figures, the corresponding parts in each may
readily be distinguished.

When the top sills are in their places, and the roof finished as above des-
cribed, the excavation downwards, for the insertion of a second sill may be
proceeded with. So much care is not required in this part of the work as in
getting in the tc^ A narrow passage should first be made along the middle
(rf the length, corresponding with the top heading before described, and tempo-
rary raking props, k k, fig. 1, resting upon foot-blocks, should be placed under
the sills, to carry them till they can be propped from the next low6r sill, after its
insertion. The temporary, or, more properly speaking, advanced props, k k,
rake outwards,, to admit of the sUl being placed and adjusted vertically under,
and in all ways parallel to the one above ; whereby when the final props, p p,
are inserted between them, the lower sill will receive its weight in a manner
best calculated to sustain it. For the insertion of each raking prop, a narrow
space is first excavated from under the siU, which leaves between the places so
excavated, a pillar (or pilast^) of earth, that supports the siU until some of the
raking props, x k, are secured in their places. The remaining earth may then
gradually be r^noved, and other raking props inserted, until sufficient stability
i^ secured to the sill above.

What has now been stated relates only to the face sill. The mode of proceed-
ing for the corresponding sill, e, (plate 3, fig. 1,) adjoining the square timbers
of the shaft, is s(Mnewhat different, inasmuch as raking props cannot be in this
case applied, excepting near the extremities, on accoimt of the open space
forming the shaft. The support required for carrying the upper sills and the
.tops may be obtained by tempwary props raking inwards, placed where they

INSERTION or THB 8ILL8<

are not in the way of the insertion of the eiUs ; or if 8o, they mnst then be
shifted to anoOier place. And where there is confidence in the stability of the
square timbering of the shafts a portion of the weight niight be temporarily
carried by propping the &ill from them, as shewn at i^ fig. 1, plate 3 ; but this
mode of proceeding is best avoided, unless the circumstances of the case compel
the miner to have recourse thereto, for reasons before explained.

As soon as the upper slQs are temporarily secured, and the earth cleared
away from under them to the proper level, the second sills may be inserted,
and the upright or permanent props p' p' be fixed betw^een the bottom and top
sills. These props should be set perpendicularly and vertically under the upper
ones, which cannot be done unless the sills are truly under each otlier. When
tliis set of props is inserted and properly secured with brobs, the remainder of
the earth in the length down to the level of the second sill, may be removed ;
and as the sides are excavated to the required form and dimensions of the
tuimcl, by hanging a centre line as described at page 74, additional baiB,
poling boards and props may be inserted to support the earth. Stretchers also,
from sill to sill in the direction of the tunnel, as shewn at m m, &c, plate 3,
must be mserted, to prevent the sills from collapsing by the pressure of the
earth on either face of the excavation.

In all cases, except where tlie ground is good, the faces of the excavation, ae
well as the roof, should be poled behind the advanced or raking props, more or
less close, according to the character of the earth ; and where it is running
sand they should be well packed behind, and at the joints, with straw ; which
at Saltwood proved a valuable auxiliary.

The section, fig. 2, plate 3, shews the arrangement of all the timbers des-
cribed between the top sUl, a a, and the bottom siU, c c. This arrangement
is precisely that followed at Blechingley; but at Saltwood a third sill was
used, which was placed immediately over the top of the heading. The second
sill was placed midway between the upper and the lower one — see plate S —
whicli represents a section through the middle of the side lengths at Saltwood,
and shews the three sills, and the mode of timbering there adopted ; and which
in aU probability would be suitable for the heaviest ground that occurs in ordi^
nary practice. Such a peculiar situation as that of the Thames Timnel of course
forms an exception ; so extraordinary a work required means to be employed
that were in like manner, out of the common way, and could only have been
supplied by such a master-mind as liis who executed it-^ir M. I Brunei

PEACTICAL TUNNELLING,

When a third siU is used, the mode of excavating between it and the one
above is precisely the same as that just described,

Tlie following engraving shews the excavation going forward for the second
siU; but it is likewise intended to represent the work in a more advanced

■f

TUT.

' I I I I

iUl

^i^^^

.^.^^V^y^

state, namely, the construction of the leading lengths ; and, as such, it will be
again referred to in a subsequent chapter. But, although it does not rejire-
sent the work quite as it would proceed for a side lengthy yet, by examining
and comparing it with what has been stated, some help may be obtained in
understanding the present descriptions.

After all the sills required for each length are inserted^ the excavating and
timbering of the lower portion of the length is very simple. A gullet, or
narrow passage, should be excavated down to the level of the skewback of the
inverted arch tliroiigh the length, similar to the narrow passage described
at page 86, and which is there represented as corresponding with the top

EXCAVATION FOR INVEET. 89

heading previously described. The gullet must then be widened out to the full
width of the tunnel ; and as the earth is removed from the vicinity of the bot-
tom sills, care must be taken to prop them in the most convenient manner that
the state of the works will admit of, whilst the earth is gradually being removed
from under them, to admit of upright props being there placed to carry the
weight. But temporary propping must first be resorted to, (in this, as in
almost every instance of tunnelling operations,) because the permanent (or
final) props cannot be got into their places until the ground has been excavated
beneath the level of the skewback, in a proper figure for the reception of the
inverted arch ; which must be the next and last operation of the miner, pre*
vious to the bricklayers entering upon the constructive part of the business.

In plate 3, and in most of the engravings at the end of the work, the timber-
ing of the lower portion of the side lengths is shewn : and, after what has now
been described, together with an inspection and comparison of the figures in the
several engravings, no difiiculty can arise in comprehending the whole of it.

Considerable care is necessary in shaping the ground for the inverted arch ;
for it is as important that it be constructed of as true a figure as the arch
overhead is required to be ; and which the bricklayers cannot do in a sound
and satisfactory manner imless the ground is correctiy shaped for its reception.

In the figures at plate 3, and some others, the timbering is shewn as if con-
tinned down to the bottom, — at least to the skewback level. This was in all
cases necessary at Saltwood, but only in some instances at Blechingley ; for
there the ground was occasionally so good as to stand, for the short time that
it was required to do, without any timber below the level of the bottom sill,
as shewn in plate 6.

When the excavation of the side length is complete for the reception of thr
brickwork, it presents the appearances shewn in section at fig. 2 ; and the right
side of the shaft, at fig. 1, plate 3. Before, however, describing the construc-
tion of the side lengths in brickwork, the following particulars, shewing the
amount of labour expended in the excavation of the side lengths, both at
Blechingley and Saltwood, may be useftd and interesting.

PRACTICAL TUNNELLING.

NUMBER OF MEN AND HORSES, AND THE NUMBER OF SHIFTS
employed in the Excavation of the Side Length at Blechingley.

Number of Shaft.

Hiaen.

LabouKn.

Honet.

Shifts.

West

East

Ill
93

109
100

29
22

26
21

West
East

122
105

109
100

28
22

25
21

West
East

95
66

106
90

30
20

21
15

West
East

122
100

127
110

42
27

29
26

West
East

107
103

113
96

33
33

26
24

' 5

West
East

85
81

80
75

22
30

18
18

West
East

94
76

36
27

24
19

West

East

100

100
59

30
24

27
19

West

East

83
65

20
15

West

East

24
28

20
18

West

East

111
03

104

26
20

West

132

119

Mean of the whole twenty-three lengths :

Number of Miners, . . . per length

„ Labourers,

„ Horses,

„ Shifts,

96-2
95-0
28-9
221

LABOUB IN EXCAVAtlON.

Through a misunderstanding on the part of the person who noted the
amount of labour expended on the works, the particulars of the first side
lengths at Saltwood were not recorded ; but those of six of the second side
lengths were noted, and are given in the following table.

NUMBER OF MEN AND HORSES
employed in excayatiDg six of the second Side Lengths at Saltwood.

Number of Men and
Horwfl employed in
driTing top Heading.

i
I

To top Sill.

To middle Sill.

To bottom Sill.

Invert.

Total.

3
2
2
2
2

Not
3

wor

14
13
23
21
13

18
20
34
29
24

8
8

21
22
19

18
11

27
28
25
21
16

8
7
6
4

16
18
14
14
16

22
23
17
18
23

6
6
5
6
6

13
12
13
14
15

3
3
4
4
4

63
63
69
66
52

ked.

83
86
93
86
81

26
24
27
25
2JJ

Mean of the whole six lengths : —

Number of Miners, .
„ Labourers,

„ Horses, .

per length

61-6
86-1
25-0

As the above statistical observaticms upon the side lengths at Saltwood
were made in so much detail through each stage of the work, it may be useful
to draw therefrom the following average amount of labour expended upon
each portion or subdivision of the work.

PRACTICAL TUNNEIXINO.

AVERAGE AMOUNT OF LABOUR

expended in each portion of the excavation and timbering the six Side Lengths at Saltwood Tunnel.

Gettingr in the Topi.

Middle
Sill.

Bottom
Sill.

iDTCrt.

Total.

Top Heading.

Top Sill.

2-33
3-33
l-OO

16-50

25-33

7-66

17-00

2216

6-50

15-66

21-16

5-83

10-16

14-16

4-00

61-65
8614
24-09

Miners

Labourers

Horses

The amount of labour, and hence the cost of getting in the tops, —
which is always the most costly part of miner's work, in tunnelling opera-
tions, — ^may be found from the sum of the two first columns of the above table.

By comparing the results of the preceding tables, pages 90 and 91, it
appears that less labour was required for the excavation of the side lengths at
Saltwood than at Blechingley. This arose from the unexpectedly more favour-
able character of the ground after that it had been so effectually drained by
the construction of the headings. The comparison is shewn in the following
table; but more extended remarks upon this subject will be made in a
subsequent chapter, when there will be an opportunity of making a fairer
comparison by means of the results of the leading lengths.

BleebiDglry.

Saltwood.

Difierencr.

Miners,

06-2

61-6

34-6

Labourers, .

95-0

861

8-9

Horses,

28-9

25-0

3-9

Shifts,

22-1

•

Upon examining the preceding table for Blechingley, it will be observed
that the west side length of each pit (which was the first that was excavated)

COST OF LABOUR,

occupied more time and labour than the east or second excavated length.
This may appear remarkable^ as it would naturally be expected that the two
corresponding lengths in each pit would give a similar result, inasmuch as they
were excavated by the same men^ and under similar circumstances. It may,
however, be accounted for, by supposing that at the first opening of new ground
which was understood to be heavy, a greater degree of caution was used by the
workmen, and, consequently, their proceedings were slower than when, by
c-ompleting one length, they had become famiMar with the peculiarities of
the soil.

When it is stated that the work required 96*2 minors, 95 labourers, &c, it is
meant that the labour was equal to 96"2 miners working one day (or shift), or
one miner working 96 2 days.

The cost to the Contractors for excavating the side lengths at Blechingley
would, upon an average, be as follows : —

£ s.

Miners, , * 96^2 days

al6s.

28 17

Labouterst, . . 95*0

at3s:6d. .

16 12

Horses, . . 28-9

at 7s.

10 2

Candles, , . 4 dozen

at 6s: fid, .

1 6

Gunpowder* . 114 cwt.

at 46s.

2 17

Totils, and sharpening picks, wedges^ Stc,

i * »

1 5

Contractors* Stiperinti^ndene^*, . 22 days

. at 78. .

7 14

Clejiring up tlie work when completed.

per length
•TAt

£68 19

Thus the cost to the Contractor averaged £68 : 19 : 6 per length of 12 feet.

In making the engagement with the gangers, or subcontractors, a price per
lineal yard, for the side and shaft lengths taken together, was agreed upon,
which price was £15, or £60 for each side length; they to find aO manual
and horse labour, candles, gunpowder, working tools, &c. Now it was well
known that at sucli a price no profit could be derived from the side lengthig ;
as the working expenses would, upon an average, exceed such price, which
was proved by the result, as shewn above; but taken together with the
sliaft lengths, which, at the same time that they were longer than the side
lengths, required much less time and labour ta construct^ they yielded a fair

94 PRACTICAL TUNNELLING.

amount of profit. When the particulars of the shaft lengths have been
given, this subject will be recurred to, for comparison between the actual
average cost, and the price paid to the contractors.

When the leading lengths were in progress, the miners obtained a bonus, in
a charge to the bricklayers of £S per length for lowering their materials, as
bricks, cement, &c. to the underground works ; which was done by loading
the descending skip, at the time that the earth from the excavation was being
raised in the other. This yielded a profit of about £2 — ^the third poimd
being paid for extra labour in loading the bricks, &c. and the loss of time
occasioned to the miners' own work. But during the construction of the side
and shaft lengths no such profit could be obtained, because the excavation was
at a total stand, whilst the bricklayers were at work in each of these three
lengths; whereas, during the progress of the leading work, the bricklayers
would be proceeding at one end, from the shaft, whilst the miners would be
progressing at the other, and vice versa, whereby the earth excavated by the
latter could be raised to the surface at the same time, and by the same power,
that the materials of the former were lowered.

The observations made of the side lengths at Saltwood, as given at page 91,
comprising as they do but one set of side lengths only, are, perhaps, not suffi-
ciently extensive to warrant an investigation of their average cost to the sub-
contractor, as done above in the case of Blechingley ; but if it be found
desirable, such cost may be deduced by the aid of the above investigation
of the side lengths at Blechingley, and of that which will be given in a subse-
sequent chapter upon the leading lengths at Saltwood. The item for the
gunpowder must be omitted from such an investigation, as none of that
material was used in the last-mentioned work. The quantity of candles
consumed, and the charge for superintendence must also be taken in pro-
portion to the comparative quantity of time consumed in executing the work.

« /

THE TUNNELS-

C H A P T E R X,

CONBTRUCTIOK OF THE TUNNIXS, COJITINUED.

THE SIDE LENGTHS. BRICKWORK.

The first tiling to be done as soon as the excavation is completed, is to set a
ground mould at each end of the length, to guide the bricklayers in construct-
ing the inverted arch to the required form and dimension : — n fig* 2, plate 3,
shews a ground mould as set iq its place ready for the bricklayers to work.
It forms part of what is called a leading frame^ of which e e are the side walljc.
or, rather, the moulds to which the side walls are constructed* f and g an*
stretchers, or cross bars, which connect the parts of the frame together, and
keep them at their proper distance apart ; and thus altogether these several
p€u1;s form the leading frame, and, placed upright against the timbered face of
the excavation, as shewn at oo, fig, 1, plate 3, guides the bricklayers in carry-
ing on the work.

The inverted arch is built in front of or against the ground mould d, the
two ends of which are formed as at u and constitute the skewbaek, from which
the side walls of the tunnel spring. The points where the curve of each side
wall meets that of the invert mould as at a^ is the part idluded to in chapter iii.
page 37, &c* as the " invert skmvhack^'' when describing the requisite levelling
operations. At fig. 2, plate 3, and at plate 8, (which represent the side lengths
of the two tunnels under consideration,) it will be observed that the ground
moulds are not embedded on the ground, but elevated nine inches above it,
and propped in that position, in several places, by bricks laid flatways on each
other, and wedged up to the proper level ; this was done for all the side length**
at both tunnelsj and also for tlie first leading lengths at Saltwood. By refer-
ence to the transverse sections, ^ 3, plate 1^ it wiU be seen that the brickwork
of the side and shaft lengths * was thicker than in the leading work. This is
the usual practice, because these lengths have always more work to do.

96 PRACTICAL TUNNELLING.

being liable to be tried with greater strains than the other portions, parti-
cularly the side lengths when first constructed, for they then remain a long
time before they receive any assistance from the adjoining work.

The ground moulds were made of Dantzic timber, 3 inches thick, and in two
parts, scarfed and united in the middle by iron plates and bolts, as shewn at 6,
fig. 2, plate 3. It would have been better to have made these in one piece, but in
that form they could not have been got down the shafts into their places ; their
length being too great to admit of their turning the angle from the shaft into
the excavation through the confined spaces between the timbers ; but where
shafts of a larger diameter are used such groimd moulds may then be got down
whole. The stretcher, g, was in one piece, 5 inches by 3 inches, and was
made to drop into a socket at each end, formed by iron plates at the skew-
back, as will be shewn more fiilly in the engraving on the next page, i, i,
are two upright pieces, or plumb rules, fitted between the stretcher, g, and
the invert mould, d, by mortices and tenons ; their use was to give stability to
that part of the frame. By their plumb lines the ground mould was set
upright, and would, if all its parts had been made very correctly, have de^
termined when the mould was truly level ; but it was never depended on for
that purpose, as the spirit level, when placed in the length, was both a correct
and ready means of so doing. Upon the stretcher, g, and upon the groimd
mould, the centre line was marked with a saw kirf, to enable it to be placed
centrally under the ranging line, when stretched along the heading for this
purpose, as explained at pages 35 and 36. In each side length there was of
necessity two leading frames used for the starting of the work ; after which,
one only was required in each length, as the brickwork already constructed
answered the purpose of the other. On the right hand side of the shaft,
fig. 1, an end view, or section, of the leading frames is shewn, at o o, as set
against the back and front of the excavation, ready for the bricklayers.

The side walls of the tunnel were built outside of the moulds e e, or between
the moulds and the earth ; the intervening timber (the bars, &c.) shewn in the
engraving fig. 2, were removed as the brickwork was advanced upwards. These
wall moulds were also made of Dantzic, 3 inches in thickness, and were fitted
on the skewback of the ground mould, by having at their lower end an iron
cap, containing mortises that fitted on the corresponding iron tenons, on the
plates of the skewback of the ground mould ; by this means it could be shipped
or uni^pped most readily. The subjoined engraving shews this part at large.

LEADING FBAMEa.

iM^i

%* I

a J. a

Fig. 1 is an elevation, and
fig. 2 a plan, of that part of
the leading frame which forms
the skewback of the inverted
arch, or the point where the
side walls rise, or spring, fironi
the invert.

A is the cap before spoken
of, on the lower end of the
side waU moulds, having mor^
tises at the under side, which

drop over two iron tenons, a a (shewn by the dotted lines), which rise above
a plate screwed down to the invert moidd, at its skewback. b, fig, 1, is the
skewback plate ,^ — there being a corresponding one at the other side of the in-
veit mould. These plates are so formed as to make the socket into which the
end of the stretcher, g, is dropped ; its ends being made to correspond thereto,
by a cap^ c, which is bolted through the wood. At e, fig. 2, is shewn, in plan,
the end of the stretcher when in the socket above spoken of ; ^ is an iron pin
passing through the socket, above the end of the stretcher, and retains it in its
place. The pin is secured, against working out, by a cotter, A, on the other
side, and, firom being mislaid or lost when not in use, by a chain attached to a
staple, at/.

The top bar, or upper stretcher, of the leading frame, f, plate 3, served
to connect the upper part of the frame, and to keep the top ends of the
side wall moulds at the proper distance apart. It w^as in one piece, 5 inches
by 3 inches, and was notched into the side walls, and secured thereto by iron
plates, which were bolted t« the stretcher, and projected over the moiJds on
e-ach side, A pin was then passed through the overlapping ends and the
moulds, similarly to the pin ff in the last engraving, and was in like manner
secured from being lost, when not in use, by chains attached by staples to
the mould*

Above the leading frame, in fig. 2, plate 3, there is a dotted cur\ ed line that
etews the intended underside of the brickwork, or the position that the tunnel
would occupy with respect to the timbering of the excavation ; fig» 3 is a
cmss section of the brickwork of the side length when completed, with the
centres and laggins under the arch ; and the timbering of the face of the exca-

98 PRACTICAL TUNNELLING.

vation, also the crown bars, f f, &c., above the arch, intended to be drawn
forward when the leading lengths shall be proceeded with, or left to remain,
according to circumstances. Between each of these bars, a pier, c, or what
is called a packing, is built, as the work proceeds, to relieve the bars from
the superincumbent pressure, if it should be deemed advisable to draw them.
The left hand side of the shaft, fig. 1, shews a longitudinal section of the above
described length in brickwork.

It has been before stated that in each of the side lengths, two leading frames
were required to start the construction of the tunnel. These ground moulds
required to be careftQly set, and secured in position, so that the centre line
marked thereon might coincide with the intended centre of the tunnel, and
that they might also be at their proper relative level. For this purpose the
level of the skewback of the invert was adopted in all cases, as before stated.
The method of setting these leading frames or ground moulds was as follows : —

Afl;er being lowered and put together, they were approximately placed
against each face of the excavation ; the hanging rods were then suspended ftom
above, to obtain the levels, as described in chapter iu, page 37, &c., and Uie
ranging Une was stretched along the heading on each side of the shaft, (being
passed through two or more holes in the ranging blocks, 6, described at page
35,) representing the intended central Une of the tunnel, with which the centre
mark of each leading frame should coincide. A spirit level was then set up in
a convenient part of the excavation, to determine the levels of the skewbacks by
the hangmg rods, the bottoms of which were graduated, as at a in the engrav-
ing, page 39, similarly to a levelling staff. If this had not been done, a
staff must have been held alongside the rod, which would not have been so
satisfactory an operation. To determine the levels of the ground moulds, a
staff divided like the hanging rods was held thereon, and by directing the level
to each, alternately, it could be ascertained if the mould was too high or too
low ; in either case it was adjusted to the proper level by means of wedges,
and, if necessary, more earth was removed from under it. A lighted candle
held near the staff, or rod, was sufficient to render the graduations distinctly
visible.

In the above manner the ground moulds were set exactly in line and at the
proper level ; but in addition thereto it was necessary that the plane, or face,
of the leading frame should be perpendicular, and be at right angles to the
centre line, the former was regulated by the plumb lines, 1 1, fig. 2, plate 3, and

SETTING THE GKOUND MOULDS.

the latter was determined as follows : — ^A ntiil was driven into some timber at
the shaft end of the lengthy exactly in the centre line* and firom thence was
measured the distances to the skewback points at each end of the mould. If
the two measurements were equal, the mould would be coiTectly square ; but
if the distance of the central nail to one end of the mould was greater than the
distance to the other end, it was a proof that tlie mould was not at right angles
to the centre line ; and, therefore, one end was moved inward, or the other
end outwards, or both, until the distance from the said central naU, to any
assumed point on the mould (as the edge of the skewback) wa$ the same.

This explanation will be better understood ,

by reference to the annexed plan. Let a, b, s±

represent the centre line of the tunnel; c, o, f \ ; / I

one of the ground moulds ; b, a nail (as above j

described) in the centime line. From this nail j

the distance b d must be equal to the distance : ^ i y'' j

B Cj in order that the mould, c d, be at right »*

angles to the line a, b ; if it be not so, the

mould must be so moved uutil it answers these conditions, in order that it

may be correct*

When one of the moulds is set square, the other may be brought parallel
thereto by simply moving it, until its two ends be equidistant from the two ends
of the one already fixed. Thus, in the engraving, if e f represent the second
ground mould, it must be moved until its centre coincides with the centre line
A B, and the distances of its ends, e and f, are equidistant from the ends c and
D of the other mould respectively. When both the ground moulds are set
straight^ levels and square^ they may be secured in their places with respect U\
each other, and prevented from collapsing or expanding, by means of narrow
pieces of board nailed from one to the other near to gg^^m^^a^^^^^^m.
their ends ; and also, with respect to their position u w

in the tunnel^ by a kind of holdfast, called a dog, f |

(shewn in the annexed cut), driven into the mould
and into the adjoining timbers, wherever it may be
convenient. This kind of holdfast is very useful in
such like operations* They consist of a piece of
round iron, with pointed ends turned up at right
angles to their length, and in some of them at right angles to each othii :

100 PRiiCTICAL TUNNELLING.

these points, or spurs, can then be driven into the timber in opposite directions.
A number of them, of various sizes and degrees of strength, should always be
at hand, to be appUed as circumstances may require.

During tihe early proceedings at Blechingley, the first ground moulds were
ranged centrally, by suspending two lines down each shaft, from the ranging
frame described at page 30, and by moving the mould until the two lines
were seen to cut its centre, where a lighted candle was placed. This was but
an imcertain and imsatisfactory mode of proceeding, even when all circum-
stances were favorable; but when, from thick weather, the lines could not
be tested above by the transit ; or, if tested, could not be depended upon,
by reason of high winds forcing them out of the perpendicular, it became so
doubtfril that it would have been imprudent to adjust by them at all, —
consequently, it occasionally happened that a delay took place in setting
the moulds, — and thus a large excavation was left for some time to the
strength of the timbers only to carry the earth; which, in unfavourable
ground, to say the least of it, was hazardous. This kind of delay led to
the fixing of posts securely in the invert, and adjusting to each of them an
iron cap, with a central hole through which to pass a Une to another central
point, fixed at a distance in the heading, whereby the line was passed over
each groimd mould that would require adjusting ; and having thus obtained
central as well as level points below, the work could be carried on without
delay, or dependence on the contingencies of the weather; and led, at
Saltwood, to the contrivance and adoption, in the first instance, of the rangiiig
spikes described and figured at page 32.

It may not be thought unnecessary to recapitulate the points to be attended
to in setting the ground moulds.

1st — ^The furthest mould from the shaft should be fixed.

2d — ^It must be upright, as determined by the plumb lines attached to it.

3d — ^Its centre must coincide with the centre line of the tunnel, as deter-
mined by the ranging lines.

4th — ^Each end must be set to the same level ; which level is to be derived
from bench marks already established below, or from the hanging rods
suspended in the shaft for that purpose. In tranferring the levels to
the skewback, due allowance must be made for the rise or fall of the
tunnel (if any) according to the gradient.

SETTING THE GEOUND MOULDS.

101

5th — It must be at right angles to the line of tunnel; as deter-
mined by measuring from a distant central nail to each end of
the mould.

6th — In the side lengths, the back, or second mouldy must be set parallel
to the first, by placing it so that its ends may be equidistant from the
ends of the mould first set.

When the two ground moulds are set, the miners should tiim the giound
correctly to receive the brickwork of the inverted 6irch, This they can do, by
fi)llowing the line of the under side of the moulds.

After the completion of the side lengths, only one leading frame is rcqiiii-ed
to go forward on each side of the shafts, as the work advances; because the
brickwork already inserted becomes, as it were, the back moidd to be worked
from ; therefore, as in each shaft four leading frames are required at first, and
subsequently only two, the work may be so arranged as to obviate the necessity
of making double the number of frames. This may be done by fixing those
ground moulds that are next to the timbering of the shafts at a little
distance therefrom, by means of wedges, which may be eased and drawn
after the brickwork is in, and thus the frame may be set free; for
otherwise the brickwork would jam the frame so tightly against the
timbers that it would be impossible to set them at libeity until the
shaft lengths were excavated, which is never done until both the side
lengths are completed.

If, however, it should be considered the more secure method to build tight
against the mould and the timbers, to steady them when the ground is heav)% the
moulds must remain until released after the completion of the shaft lengths ;
under which circumstances, additional leading frames must be made, or some
of the shafts remain till the side and shaft lengths of others be finished. No
moulds are required for the shaft lengths, as the brickwork of the two side
lengths must be worked to.

Upon the fiice of the ground moulds and side waUs every course of bricks
was distinctly marked (or cut in) to which the bricklayers were required to
work. These lines were determined by the size of the bricks to be used ; and
unless rigidly adhered to, there would have been great irregularity in the
courses at the junction of length upon length, which would have been bad in
appearance and deficient in strength.

102 PRACTICAL TUNNELLING.

The invert was constructed with concentric half-brick rings, bonded, in each
case where the joints became flush, excepting about six feet on each side from
the springing at the angle of the skewback, which was constructed in English
bond. At Blechingley the bricks for the skewback were made of a suitable
shape, but at Saltwood the common bricks were cut for that purpose. In some
instances stone has been employed, whereby the skewback is made in one piece
for lengths of about three feet ; but this method was considered too expensive
for the tunnels under consideration.

When the invert and skewback were completed, the side wall moulds were
set up, by simply placing them in the situation shewn in fig. 2, and at o o, fig.
1, plate 3 ; and fixing the cross bar or stretcher f, at the top ; thus completing
the leading frame, which was then set upright by the plumb Unes x x, and also
central, by suspending from e a plumb bob d^ which should hang vertical over
the centre line, as marked on the lower stretcher g ; it was then secured in its
position by dogs driven into it and some of the props and sills, and by pieces of
board wherever they could be advantageously attached.

The brickwork of the side walls to the springing of the arch, was then con-
structed in English bond, with neatly drawn joints. As the brickwork advan-
ced, the bars that had supported the earth were removed, together with as much
of the poling boards as could be got out. At Blechingley the work was built
soUd against the earth wherever there was more space than was necessary for
the insertion of the intended thickness of the brickwork ; but at Saltwood, such
vacuities were rammed solid as the work advanced. Whichever of these
plans may be adopted, it is of great importance that it should be carefrdly
executed ; it should therefore, in all cases, be well attended to.

When the walls were up springing high, the centres were set for turning the
arch. The form, and all the particulars relative to them will be reserved for a
separate chapter, and it is therefore only necessary in this place to refer to fig.
3, plate 3, for their appearance when set, and of the brickwork of the side
lengths completed, The left-hand portion of fig. 1 is a longitudinal section of
the same work.

The brickwork of the arch consisted of a series of concentric half-brick rings ;
and where the joints became flush and straight, a heading, or bonding course,
was inserted throughout the length of the arch ; and care was taken that the
bricklayers should preserve the true form of the arch in every ring of which
it was composed.

BRiCKWOElt,

103

The manner of removing the bars which supported the earth,
as tlie upper part of the side walls and the arch was advanced,
is shevra in the adjoining cut; where the brickwork^ a, is
represented as brought up as far as the bar, b ; and, before
it can be advanced any further, the bar must be removetL The
brickwork is built close up to the poling board, c, which re-
tains the earthy and also overlaps the front of the poUng, D ; it is therefore
cleex that the brickwork would hold both the polings in their places, and tlu^
bar which before held them might be removed without danger ; foi*, even when
the ground is bad* no movement could well take place in it before the brick-
work would be fiirther advanced, and render the poHng board, d, still more
secure. In no case should the bars be removed until the brickwork is ready
to supply its place, without delay. In this way each of the side bars were
removed, one by one, and laid aside to be used in the further progress of the
work. A considerable number of poling boards were necessarily built in,
where the ground was not good, and their removal could not be effected
without risk.

The brickwork of the arcli was brought up equally on each side, towards
the crown, until it assumed the shape shewn in fig, 3, plate 7 ; where a a is
the brickwork of the arch. At this stage of the work, the laggins c e, which
are rabbeted on the top of their inner edge, are placed on the centres. In
these rabbets, cross laggins, rf, about 18 inches wide, are placed, one at a time,
beginning at one end of the length. A bricklayer, then (standing with hin
head and shoulders between the two sides of the brickwork, a a) keys in the
arch over the first short cross or keying-iu laggin ; which done, he places a
second cross laggin in tlie rabbets of the long laggins, c c, and in Uke manner
keys in that portion of the arch ; he then places a third cross laggin, and key.^
in, as before, retreating backwards along the narrow space between a a, as his
work advances, until the whole of the length is completely keyed in. ITiese
kejing-in laggins are also represented in the annexed cut, — which is a section
through the laggins, — where a is the top of a
centre rib ; b 6, ordinary laggins, wluch were
battens, 12 feet long, 6 inches wide, and 3 inches
thick ; f c, are the rabbeted laggins extending
the whole of the twelve-feet length ; and rf, one of the ke)ing-in laggins fitting
in the rabbets.

.£_tf

104 PRACTICAL TUNNELLING.

Fig. 4, plate 7, is a longitudinal section, shewing the same work, and also
the maimer in which the end of a length is left, with respect to the timber
props and bars, f is the projecting end of a bar, to be drawn forward for the
next length ; 6 is the back prop, and h the permanent prop, as described at
page 85. The whole of the brickwork was set in Boman cement.

Upon an inspection of fig. 3, plate 3, seven crown bars appear to have been
built in, and coimterforts or packings of brickwork, c c, constructed between
each two of them. In all cases these bars were closed in above the arch, and
remained there imtil the shaft lengths were completed, because they could not
have been previously drawn ; and no good purpose could be answered by so
doing; on the contrary, the disturbing of them might have endangered the
rest of the work. When, however, the first leading length was excavated,
these bars were, in some instances, drawn forward, to be used for the crown of
such length. The maimer of doing this will be explained in a subsequent
chapter, when describing the leading work. But in every case where symp-
toms of much pressure were present, it was considered prudent to leave the
bars of the side lengths wholly undisturbed ; as it was better to lose them than
run any risk by their removal.

The bricklayers should be closely watched during the whole time they are
at work, to see that they do it in a sound and satis&ctory manner ; as upon
their labours the ftiture stability of the tunnel depends. In no part should
more attention be paid than while they are constructing the invert, for as much
depends upon its strength as upon the arch above ; and too frequently this is
considered by the workmen as of minor importance ; and as it is more out of
sight when done than other portions of the work, it has a corresponding chance
of being slurred over. In many cases, the low price that the men are paid
for their task work leads to their hurrying it over to make up their wages,
and in other cases, where they have been well paid, unless they have been
looked after, the chance of making greater gains has been their inducement to
slight their work. The system of sub-letting the work, and then again sub-
letting it in detail, wherever it is practised, invariably has an injurious effect
upon the soimdness of the construction.

The price paid for the brickwork at Blechingley was £4 : 10s. per rod ;
which included the setting and moving forward the centres, — all tools, candles,
and the lowering of the materials from the surfece to the underground works,
procuring water where required, &c.

BRICKWORK.

105

TABLE SHEWING THE PROGRESS OF THE BRICKWORK

in the ooiutraction of the Side Leng^ at Blechinglejr TnnneL

NomberofSlMft.

Oroaod MoaU

Kt.

Side WalU
SpriiViofhirb.

Areh

Keyed

in>

*« I East

Mardi 25
AprU 14

March 27
April 17

March 31
Apra 22

* I East

March 13
April 2

March
April

16
5

March 19
April 8

"* ' East

April 2
April 19

April
April

4
21

April 7
April 24

** ^ East

March 1
March 22

March
March

4
24

March 7
Mardi 26

A $ West
* \ East

March 12
March 31

March
April

14
3

March 17
April 5

. < West
<* ^ East

April 29
May 14

May
May

1
15

May 4
May 18

<t 5 West
« J East.

April 14
April 29

April
May

April 18
May 4

- 5 West
^ I East

May 6
May 22

May
May

8
24

May 11
May 26

" ^ East

May 12

May 25

May
May

May 17
May 29

" ' East

April 14
April 30

16
1

April 18
May 4

"' ^ East

April 7
April 24

April
April

9
26

April 12
April 88

11 West

March 22

Mardi

Maicfa 27

106

PRACTICAL TUNNELLING.

From the preceding table the following mean results are obtained :

Tianeeenpied

Time occupied

Total Time

iBMttiiirtlM

ooeapiedn

Ihaft.

«rtelav«rtud

Cealraand

ooortraetiif.

Side Walb.

tnniiar the Arch.

Lcogtba

Oi^t.

THj*.

2-6

4'5

■

3-0

6-0

2-0

3-0

5-0

2'&

2«

5-0

2-5

5-0

1-5

3-0

4-5

2«

2-5

2-0

2«

4-5

2«

1-5

2-&

4-0

2H)

2-5

4-5

2-0

3-0

5-0

Mean result of the whole table :

Time occupied in the constmctioii of the Invert and Side Walls
Time occupied in setting the Centres, and turning the Arch

Total time occupied in constructing a Side Length

Days
2-13

4-96

The number of men and horses employed in the above work was not

LABOUR IN BBICKWOBK*

Tor reasoiiB stated at page 91, the particulars of the brickwork dt iihe &rst
side lengths at Saltwood were not recorded; but the following table gives
all the requisite information respecting the second side lengths.

TABLE SHEWING THE TIME AND FORCE
employed in the construction of ten Side Lengths at Saltwood Tunnel.

Wert

Number of Hen

Nunbtr of Mem

Number of Men

ToMlNuBberof

Side

uidllaMO

aodHonei

and Horses

MeDudHonn
compIetiDf the

Leogfths.

Onmiid
Mould*

Kt.

oa the Infcrt.

Springmy

on the Side Walb.

Keyed
in.

the Areh.

Leg^.

1
1

]

■

Nov.23

NoT.26

Decl

12i

26i

«i

40i

91J

19J

I7i

17.;

NoT.30

Notwor

ked.

•

18;

Dec. 2

17;

Nov.26

Notwor

ked.

•

■.

Dec. 3

loa

PRACTICAL TUNNELLING.

Frmn the preceding table the following mean results are obtained :

Time occupied in the constnictioii of the Invert and Side WaUs
Time occupied in setting the Centres, and taming the Arch

Total time occupied in constructing a Side Length

Days
3-2
41

7-8

MEAN OP THE FORCE EMPLOYED:

Bricklayers

Labourers

Horses

,.--^

Inveft.

Side Widli.

Aiefa.

Total Id Uii«tb.

9-90

9-85

16-40

36-15

23-50

21-05

87-80

82-75

4-63

4-60

8-20

17-43

By comparing the results of the tables at pages 105 and 107, it will be seen
that more time was taken by the bricklayers in the construction of the side
lengths at Saltwood than was employed for the similar work, at Blechingley :
the former occupying 7*3 days, and the latter but 4*96 days.

SHAFT LENGTHS.

109

CHAPTER XL

CON^aUCTION OF THE TUNNELS, CONTrNUED,
THE SHAFT LENGTHS- EXCAVATION AND BRICKWOBK,

EXCAVATION,

Upon the completion of the second side length, the excavation of the earth
from under the shafts for the insertion of the shaft length of brickwork, should
be proceeded with, as rapidly as circumstances, and sufficient care for the
safety of the shaft, ivill admit of This, like the other portions of the excava-
tion, is commenced at the top, and continued downwards. As the whole space
beneath the shaft, to the full width of the tunnel, must be cleared away^ it is
evident that the square timbers, which had hitherto assisted in carrying the
shaft, must be removed also : their removal leaves the shaft to be supported*
or suspended, wholly by the shaft sills, as at Blechingley ; or by the hanging
rods, as at Saltwood ; or by whatever other means may have been resorted to
for that purpose. It is therefore incumbent on the miner to provide, as
speedily as possible, other means of assisting to resist the downward tendency
of the shaft, until it can be securely connected vrith the crown of the tunnel,
by means of a curb of brick or cast iron. The only support that can be given
thereto, (without encumbering the space where the men are at work), is by
propping from the projecting ends of the crown bars of the side lengths, and
from the upper bars of the shaft length, as they are inserted ; and in this way
ample strength may be obtained for the purpose.

The mode of timbering a shaft length is very simple ; and consists in placing
the bars with their ends resting on the back of the arch of the two side lengths
already completed, and poling behind them, to secure the earth from moving,
Plate 4 represents a shaft length, as completed ready for the bricklayers ; —
fig. 1 is a longitudinal section, and fig. 2 a transverse section through the
middle of the length ; and, consequently, each section is taken through the

110 PRACTICAL TX7NNBLUNO.

centre of the shaft. Fig. 1 shews the two finished side lengths, a a% and the
wide space between them (or the shaft length) supported by the timbers, as
above described, b b b, &c. are the bars, whose ends are passed behind the
brickwork of the lengths a and a', whereby they are secured in their places.
s s s^ &c. are the short stretchers between the bars, which keep them steady,
and connect them for mutual support. The poling boards are also shewn in
place, c c, are the crown bars of the side length, the ends of which project
beyond their own brickwork, and thus supply a base, from which to prop the
sills, or curb, that carries the shaft. At Blechingley, the under sides of the
shaft sills were thus supported ; and at Saltwood, in the absence of such sills,
the suspended square frame, or setting, upon which the wooden curb temporarily
rested, was supported, a, a, shews two of the props thus carried by the ends
of the crown bars (c) of the side length. In addition to this, more help may
be obtained, by propping from the upper bars of the shaft lengthy as shewn at
a' a\ fig. 1, which are props supported by the upper bar, b'. In this way the
shafts were supported, both at Blechingley and Saltwood, imtil the brickwork
could be completed to take the weight of the shaft.

The transverse section, fig. 2, plate 4, being taken through the middle of
the length, cuts through the bars, b b, &c., and shews an end view of the
brickwork of the side length a a, which is left in toothings to be united with
that of the shaft length. The same letters of reference in the two sections
refer to corresponding parts of the work.

During the excavation for the shaft length, the centres that axe imder the
side lengths, a and a', together with the timbers connected therewith, should
remain undisturbed ; but the miners' sills (d and e, fig. 1, plate 3,) which were
against the shaft, must be removed, with the earth that they abutted against ;
and in doing this, the stretchers m m, (plate 3,) between the miners' sills
must also be removed. But before the removal of either the sills or the
stretchers, it is necessary to secure the timbers of the fiu» of the excavation
from* the possibility of their being forced inwards by the pressure of the earth
behind (especially if it should, as at Blechingley, expand). This security is to
be obtained by fixing two raking props, d d, plate 4, against the lower miners'
sill ; the upper end of the prop being cut in the form of a bird's mouth, to
receive the angle of the sill ; and strongly hooped, to prevent its splitting ; the
lower end must be firmly bedded, and wedged into a hole made for th^t pur-
pose in the brickwork of the inverted arch.

SHAFT LENGTHS.

Ill

Figs. 1 and 2, plate 4, shew the raking props in place, of which there were
always two against the lower sill at each &ce ; and, at Blechingley, there was
occasionally a necessity for two others to be set against the upper sill, and
which are shewn in plates 6 and 7. At Saltwood it was generally found suffi-
cient to use one pair of rakers against the middle sill only ; but in all cases,
after the completion of the side and shaft lengths, and in advancing the
leading work, four rakers were invariably used, at both the tunnels, iar the
two upper sills, at every &ce of the excavation.

Nothing more need be added, as to the mode of doing this part of the work;
it remains therefore to shew the time and force employed as given in chap, ix,
page 90, for the side lengths.

NUMBER OF MEN AND HORSES, AND THE NUMBER OF SHIFTS,
employed in the exctvatioii of the Shaft Lengths at Blechingky.

NaalMTof
Shaft.

Mioen.

Laboaren.

Honn.

Sbifti.

Not

noted.

•

112

PRACTICAL TUNNELLING.

Mean of the whole eleven lengths :

Number of Miners, 45*8

„ Labourers, 45*8

Horses, 15-0

Shifts, 11-3

From the preceding results, the average cost to the ganger, or subcon-
tractor, may be deduced, in the same manner as done for the side lengths at
page 93 ; thus —

Miners,

46-8 days

at 68.

Labourers,

45-8

at3s:6d.

Horses,

15-0

at 7s.

Candles,

2 dozen

atGsrGd.

Gunpowder,

1 cwt.

at 468.

Tools, and sharpening picks, wedges, &c.,
Contractors* Superintendence, 11*3 days . at 7s.
Clearing up the work when completed, . per length

Total

£ 8.

13 14

5 5

2 16

1 5

3 19

£35 18

At page 93 it has been shewn, that the excavation of the side lengths alone,
at £15 per lineal yard, would have been a losing concern; but it was there
stated, that taken together with the shaft lengths a fair profit was obtained ;
this may now be shewn as follows : —

COST OF EXCAVATION :

Two Side Lengths, each £68 : 19 : 6 = £137 19
ShaA Length, as above . ==: 35 18 2

Total Cost to the Ganger = £ 173 17 2

The side lengths were each 12 feet in length, and the shaft lengths averaged
14 feet, making 38 feet for the three lengths ; which, at £15 per yard, or £5
per foot, gave £190 to be received by the ganger for the work, which cost

LABOUR IN EXCAVATION.

113

upon an average, £173:17:2; leaving a dear profitof £16:2: 10, or at the
rate of about 8| per cent.

The following table will shew the amount of labour, &c., consumed in the
excavation of six shaft lengths at Saltwood : —

NUMBER OF MEN AND HORSES
employed in the Excavation of six of the Shaft Lengths at SaltwoocL

Nonberof
Shaft.

Minen.

Honet.

40.

Not wo

rked.

•

Mean of the whole six lengths :

Number of Miners,
„ Labourers,

,, Horses,

50*5
19-7

By comparing the above table with that at page 111, it will be seen, that
more labour was expended upon the shaft lengths at Saltwood than was
required for the similar work at Blechingley ; and that such a result is the
reverse of that obtained by comparing the labour of the side lengths, as at
page 92 ; and also is contrary to the result of a comparison of the leading
work, as wiU appear in the next chapter. The greater amount of labour
required for the shaft lengths at Saltwood must have arisen fix)m the circum-
stance, that greater caution, and expenditure of time, was there required, in
removing the timbers about the shaft; in timbering the length; and in
making all solid, where the running of the sand, during the shaft sinking, had
left large vacuities.

114 PaAOTICAL TUNNBLUKO.

BRICKWORK.

After what has been stated in chap, x., but little remains to be said of the
brickwork of the shaft lengths. The sumphs under the shafts were careftdly
filled solid with dry earth, or with concrete, according to circumstances, and
upon this the inverted arch was constructed.

When the side walls were built, the arch was turned upon four centre ribs,
a, a, a, a, fig. 1, plate 5, in which the mode of executing the brickwork of the
shaft length is shewn. The three ribs under each of the side lengths were left
in their places, undisturbed, until the shaft length, and also the first leading
length, were completed. At Blechingley there were ten centre ribs used in
every shaft ; five in each direction ; so that when the four ribs were lowered
for turning the shaft length, they were not again raised to the sur&ce, (except
for the purpose of repairs^) until the work was completed. These four ribs,
together with the three under each side length, made the required ten ; of
which five were advanced, as the work proceeded, in one direction, and the
other five in the opposite direction.

It has sometimes been the practice, for the sake of economy, to use but six
centre ribs in a shaft, instead of ten ; and for the purpose of turning the shaft
length, to remove the two back ribs, b 6, fig. 1, plate 5, from each of the side
lengths, and place them under the shaft length, in the position a a, &c. ; then
to re-adjust the two ribs c c, nearest the edge of the shaft, to take the ends of
the laggins for the shaft length to be turned upon. By this practice the side
lengths are left without any assistance, at a time when they are least of all
capable of bearing any great strain ; and while thus standing alone, and un»
fiupportedt (hey have to can|r, not only the weight of earth that is fiurly their
dua, but .also the weight or pressure of the earth upon the bars of the shaft
length ; and in addition thereto, have to sustain the weight of the shaft itself.

The sa&st practice is in the use of the greater number of ribs ; and those
were arranged as shewn at fig. 1, plate 5. The three ribs under each side
length remaining undisturbed, were a great assistance to the brickwork in
resisting any great pressure. And fturther, the two ribs, b 6, on each side,
were continued in their places until the first leading length each way was also

CtJftfiS.

completed ; for as three ribs only were required for each leading lengthy two
of the four ribs, a a, were moved forward each way from under the shaft to the
advanced work, and the back rib, e, was all that was taken from (or disturbed
in,) the side length to make the three ribs required for turning the arch of the
first leading length- And ftirthermore^ the ribs b b were still continued in
their places, undisturbed, until the side walls of a second leading length were
constructed, and ready for the centres ; which walls acted as buttresses against
the new work when the two ribs h b were removed ; and were well calculated
to resist any tendency to derangement in the work-
in the foregoing manner the side lengths were well sustained during the
whole time they were exposed to more than their fair share of pressure ; and
the same mode of advancing the work^ with five centre ribs each way from the
shafts, was carried on throughout the tunnel at Blechingley, without the least
accident, or imdue settlement, in the arch or side walls.

To determine upon the adoption of the use of either ten or six centre ribs,
depends upon whether or not it be considered, that the extra expense attend-
ing the former method, more than counterbalances the risk incurred by using
six ribs only ; the risk not being confined to the construction of the shaft
length, but lasting until the work is finished. And it is not improbable that
the cost of setting to rights one broken length, would exceed the whole extra
cost of the centres, laggins, &c., for any one shaft; independent of the doubt
(to say the least of it) that attends all work done where there exists any chance
of failure.

When the arch is turned the shaft is permanently connected therewith by a
curb, either of brickwork, or cast iron made and put together in segments*
The former was used in the works now under consideration, and is shewn at
figs, 1 and 9, plate 5, For these curbs the bricks were purposely made of the
required shape ; the angular bricks, where the shaft joins the soffit of the
arch, were made large and rounded off, as shewn in the engraving ; these bull-
nosed bricks, (as they were called by the workmen,) not only gave the work a
better appearance when finished, but the arris being thus taken off, it did not
injure the gin rope, in its subsequent ascending and descending ; neither was
the curb so liable to sustain injury by the striking of the skips. This subject
will be enlarged upon in a fiittu-e chapter, and a description, with an engraring,
of the iron curbs, will be given.

116

PRACTICAL TUNNELLING.

The annexed table shews the amount of labour required in constructing the
curb at each shaft of Blechingley TunneL

NUMBER OF MEN AND HORSES
employed in oonitructing the Brick Curbs to the Shafts at Blechingley TunneL

Mambcror
Shaft.

Brickla;en.

Laboureri.

HOIMI.

67-7

59-0

20H>

72-7

93-5

18-3

59-5

72-5

17-0

fSO-0

74-3

22*5

64-7

78-3

21-3

66-7

65-0

18-0

73*7

93-0

21*3

77-7

820

22-0

68-7

1010

16-0

64-7

65-7

17-3

eoo

69-3

17-3

Mean of the whole eleven shafts :

Bricklayers, 66*9

Labourers, 77*6

Horses, 19-2

The five bars nearest to the crown, of the shaft length, were built in, and
left, — as shewn in the transverse section, fig. 2, plate 5. In this plate the
maimer of finishing the shaft, where it joins the arch of the tunnel, and of
underpinning the shaft sills, at Blechingley, are ftdly shewn.

At E, fig. 2, is shewn the manner in which the skewback of the invert of
the tunnel was constructed, as regards the form and arrangement of the bricks.

I^ADING LENGTHS.

117

CHAPTER X I L

CONSTEUCTION OF THE TUNNEL, CONCLUDED.
THE LEADINO AND THE JUNCTION LENGTHS. EXCAVATION ANO BarCKWORE,

THE LEADING LENGTHS.

When the shaft length is completed, — the curb inserted, — and the brickwork
made good to the shaft,— the centre ribs and the laggins may be removed from
beneath it; but those under the side lengths should not be disturbed until
after the first length forward is completed, for prudential reasons, explained
when treating of setting the centres for the shaft lengths, at page 114, and
which will again be alluded to when the centres, and method of using them»
is described in a subsequent chapter*

The side lengths at Blechingley and Saltwood were twelve feet long, and so
situated as to leave between them, upon an average, fourteen feet for the shaft
length ; the three lengths making together thirty-eight feet of tunnel under
every shaft, from which to carry on the work in both directions. Wlien this
portion of the work is done, the difficulties of the tunnel may be said to be
over; as the subsequent proceedings are comparatively straightforward and
safe : at all events, there can be but few natural difficulties that cannot be
foreseen, and consequently their effects provided for, or guarded against;
unless by injudicious proceedings, or absolute carelessness, difficulties and
dangers arise which otherwise would not have existed.

Previously to commencing the leading lengths, it is requisite to construct a
platform over the invert of the lengths already completed, as showm at f p,
plate 9 : and which platform must be continued each way, as the work advances.
It is made of planks, laid on sleepers or transverse timbers, placed across the
invert, so as to leave a free channel for the water to pass along the invert, to be
drained oiF through the heading ; or, in cases whore the water is not abundant,
it may hence be conducted to a proper receptacle or sumph, convenient for the

118 PKACVicAL Tumnoxmo.

frorkmen to me it in mixing tfaeir cement or mortar ; for where th^re is no
water in the tnnnel, the conveyance of that material to the shafts fi>r the brick-
layers* use, forms a considerable item of expenditore. This was partly the case
at Blechingley ; the water, which was in abundance at first, diminished in
quantity as the work advanced, and towards the last, (except at the west end)
the land springs appeared to have been drained neariy dry.

The more immediate use of the platform is to make a uniform plane, on
which to lay down, a temporary double line of rails, to run the wheeled skips
(described at page 76) upon, from the &ice of the excavation to the shafts, and
the empty skips back again ; one line being used as a going, and the other as a
returning road. The rails, at Blechingley, consisted of pieces of quartering^
with hoop iron fastened along the inner edge of the upper surfitce, for the
wheels to run upon, and were before named at page 68: the roads so formed
were frequently out of order, and in all probability it would have been better,
in the first instance, to have provided some Ught wrought iron ndlway bars for
the purpose, which although much more expensive in their first cost would have
saved a deal of annoyance afterwards. The platform is shewn in the engraving
page 88, where one man is represented as pushing a loaded skip towards the
shaft, and another filling an empty skip with the debris cast down by the men
above, who are excavating fi>r the insertion of the second sUl of a leading length.

The process of driving a leadiog length is nearly the same as that described
for a side length ; with this di£fer«M)e, that the bars in that case have to be
propped, and supported, at both thdr ends, whereas, in the leading work, they
only require such assistance at their remote end, or against the fiu^e of the
excavation; thenear or back aiid of each bar, being left to rest behind, cur upon
the briokworic of the arch already turned.

The work is commenced by getting in the top, in the manner described as
for the side loigth* A top heading is driven in the middle line of the tonnd,
for the insertion of the crown bars, and is thai wid^ied oat to the li^t and
h^ and the bars inaorted one by one down to the levd of the top siDL It will
be remMnbared, that the crown bars for the leading Imgdis were described as
left above die brickwork of the side logth, to be drawn out (of their odb) to
form die roof of the leading work, kngOi after length; hywiadimMam, H^
same bars travel akmg the rooftotiie next jnnctioii, unless bj aocidaiit amy ef
dMiagetbrokm^orskidLfostinacMaepaitQftkeir joomey;
an gSMnlly boih in, and kft. It is, hawefer, not tiie safest of

DRAWfKO BAR9.

119

draw the crown bars irom the side lengths at aU^ but to build them in, and
leave them, unless the ground is very good, when their removal would be
attended with perfect safety. They were mostly left in at Blechingley ; as
their value was of trifling importance, compared with any risk to the security
of the work that cairicd the jshafts, through disturbing tlie earth thereabouts ;
for, although the space from whence each bar is drawn is, professedly^ rammed
solid with earth, by a man standing at the end where it is drawn, using a
long-handled punner^ — yet, however well and carefully this may be done, it
would, in most cases, be better that the bars were built in, than that the sur*
rounding earth should be in any degree disturbed : and, too often, if the men
«re not watched, they wiU omit the ramming altogether, as their neglect can*
not be detected afterwards.

€

'%\X

-— ^

llic above engra\Hng represents the process of drawing the crown bars,
whether fiom over the side or any subsequent leading length. The top heading
is shewii as having been already driven, and one bar a drawn forwards, and its
advanced end resting upon the shelf of earth b, preparatory to its being propped ;
the ground is also shewn as ready for another bar, c, which the men are draw-
ing from over the brickwork of the last turned length, d ; the leading centre

120 PRACTICAL TUNNELLING.

rib, E, is shown in section under the brickwork, also an end view f of the top
sill, and the upper end of its raking prop o.

The drawing of the bars can mostly be accomplished with crow bars, used as
levers, as shewn in the above engraving, which brings them forward by little
and little, till the larger portion of them is advanced, and then they come out
easily enough; but if, during their confinement above the brickwork, any
particular settiement has taken place, the bars will frequentiy be jammed in
extremely tight ; the only way then to release them is by the use of one or
. more screw jacks placed horizontally against the arch, and lashing chains passed
over these and also roimd the projecting ends of the bars, when upon working
the screws, the bars are released. If however, the resistance is too great to
be overcome in this manner, the bars are left and built in ; for where a settie-
ment has been so great as to cause such an eflTect, it wouldprobably be unwise
to draw the bars at all, were it even possible to do so, lest a movement be given
to the earth that would be liable to produce results &r more costiy than the
value of a few bars.

When the bars are drawn, great care should be taken, as before stated, that
the space from whence they are removed is packed and rammed solid with earth;
for the danger of leaving an empty space above the ^xch is too obvious to need
any remarks. It is also of importance that attention be paid to the amount of
sinking that takes place in the top of each length whilst standing in timber, in
order that the leading ends of the bars for the succeeding lengths may be raised
sufficiently high above their required level to allow for their sinking, before the
arch is turned.

It will be easily understood that where so large an excavation is entirely
supported by timbers, in comparatively small pieces, resting upon and pressing
against each other, without being one piece of framework well braced together,
that there must be some general or particular settiement in its parts ; and this
as might be expected takes place very much in the roof If, therefore, the
bars are raised sufficiently high above their required level, and such settiement
takes place, they will merely descend to their proper places ; and if the amount
of sinking that is thus provided for does not occur, it is but of littie conse-
quence, as the space can be packed solid, and a more correct allowance for it
be made in friture. If^ however, sufficient allowance has not been made, the
bars will sink into the space that must be occupied by the brickwork of the
arch; in which case, when the arch is brought up to that place the bars must

EXCAVATION FOE SILLS,

121

be raised, by excavating above them by little and little, which is attended with
inconvenience, and additional expense. The arch forms the gauge to direct
the miners in placing the bars. This subject has been named before, in con-
neidoti with the side lengths, — page 81,^ — but its importance in every stage
of the work will be sufficient excuse for referring to it again.

The engraWng at page 88 is a section of the tunnel, with a leading length
in progress. The last two completed lengths are left resting on five centre
ribs, supported by their props. The whole of the timbering of the top of the
new length is represented as complete down to the first sill ; and the excava-
tion is proceeding for the insertion of a second sUl, which is shewn as standing
in its last place against the toothing end of the finished length, supported by
its props ; fi-om whence it wiU be shifted forward, as soon as the excavation is
ready for its reception.

The whole of the operation of timbering and bricking the leading work is
shewn in plates 6 and 1. Fig. 1, plate 6, is a section through the timbering at
the line a b, fig. 2, and shews the fiice of the excavation, with its sills, bars,
props, &c. &c.^ with a leadiug fi^me, o, set ready for the bricklayers : fig, 2 is a
longitudinal section of the same thing. It will be observed that the timbering
is not shewn to extend lower than the bottom sill, except in the central part,
R, around the heading of the tunnel This is the manner in which a large
portion of Blecliingley tunnel was done ; the ground being sufficiently good
for the lower parts to stand without assistance, during the short time it was
exposed, until the brickwork w as inserted ; but this in no case applied to the
upper parts, which had a much longer time to stand before it could be perma-
nently closed in. It was always the rule, never to let a length w ait for the
bricklayers, but to have them and their materials ready to proceed immediately
that the excavators had done, and the ground mould set : thus the lower part
of the length being the last exposed, and the first closed in, stood but a short
time without assistance.

The leaving the lower part of the excavation without being timbered was
not general throughout the tunnel, and in no case around the heading, where
the ground was always loose, having been previoudy disturbed when the head-
ing was driven. The method and extent of timbering about the heading is
shewn at r, fig. 1, plate 6, At Saltwood tunnel, as w^eli as in some parts of that
tt Blechingley, the timbering w^as continued to the bottom, m it must be in all
looie ground — and is showii in plate 8, and several other engravings.

122 PRACTICAL TUNNELLING.

The timbeiiiig of the side and leading lengths are nearly similar to each other,
with this diief difference ; that in the former several stretchers were fixed from
sill to siU, horizontally, along the length, as described at page 86, to keep the
back and forward sill from collapsing, or the &jce of the excavation being
pressed inwards ; but in the leading lengths, no back sills are required, as the
completed brickwork makes all secure over head, at that end of the excavation ;
in order therefore to prevent the pressure of the earth forcing the sills and timber
of the face inwards, and bringing destruction upon the whole length, two
raking props are applied to each sill, notched at the upper end to fit its angle,
and wedged at the lower end in a hole purposely left, or made, in the invert ; and
thus the thrust of the fiwe is resisted. An inspection of each figure repre-
senting the leading work will make the explanation perfectly dear, d d and
d' d% in each of the figures in plate 6, are the raking props. These raking
props have also been previously alluded to at page 110.

A longitudinal section, showing the brickwork of a length completed, is
shewn at figure 1, plate 7 ; and figure 2 is a transverse section taken across the
said length, or on the hne a b fig. 1.

After all that has been before stated respecting the manner of excavating and
constructing the side lengths, it would be but a recapitulation to go through
the details of that of the leading work ; the modus operandi, in both cases,
being so similar that an inspection of the plates 6 and 7, afi;er reading what
has before been stated, must show to every intelligent reader the whole business.

Before closing this part of the subject it should be observed, that where the
forward ends of the bars, in the leading lengths, abut against the fiice of the
excavation, they should be well chogged, or rather, tightly wedged, against the
earth, allowing the bar no interval or room to play in the direction of its length.
This is especially necessary where the groimd is loose, as sand ; or yielding, as
soft clay ; for as the tendency of all leading work is to settle, or press forwards,
in the direction that the work is being driven, the earth in firont of the said
bars is liable to yield when the pressure is great, and if it does yield the whole
length goes forward that much, and is liable to drag the last turned length
Mith it ; and thereby cause a firacture in the brickwork where it joined the
preceding length.

This kind of accident occurred at Saltwood tunnel, where the negligent
workmen had even left a space between the ends of the bars, and the fitce of
the work, which caused the lengths, so circumstanced, to go forward and drag

aXJANTITY OP TIMBER.

with them the last length of brickwork, breaking it away from the preceding
work, and brought so much weight thereon, as not only to break the brickwork,
but also to break the bars themselves ; none of which accidents occurred after
that care was taken that the ends of the timbers were closely abutted, (by
wedges if necessary,} to the face of the work. It must here be again impressed
upon the practical man, the necessity of always keeping the work tight against
the earth, to prevent the possibility of its moving ; and it should be an inva^
riable rule, never to leave a vacuity behind the work*

The quantity of timber required for any tunnel work will depend upon the
character of the ground. In the works at Blechingley, which have been
described, two miners' sills only were used ; the ground at that place was neithsr
good^ nor, taken as a whole, very bad ; if it had been a little hea\ier, or in other
words, have pressed more heavily on the work, three siUs would have been used
in each feice instead of two* The extensive use of timber is to be avoided as
much as possible where it can be safely omitted, because it increases the cost of
the works, not only by the price of the timber, but for additional labour in
inserting and removing it. In no place should be practised a penny vdse eco-
nomy in the use of materials, as that frequently results in pounds of subsequent
expenditure. Experience and judgment will decide as to the extent of timber-
ing necessary.

When three sills are employed, as at Saltwood tunnel, the mode of operation
need not be altered from that already set forth ; and an inspection of plate 8^
which represents the timbering adopted at Saltwood tunnel, mth what has
already been stated, will give aU the infonnation necessary for the working
%vith three sills ; a, b, c, are the three miners' sills ; a, a, &c. &c. shew the
position of the stretchers, this being a side length ; but in other respects, it is
the same as was adopted for the leading work, except the omission of the raking
props.

Where the circumstances are such that the ground will stand with but little
or no timbering, as is mostly the case with rock and chalk, the operation of tun-
nelling is of the simplest character. The only thing necessary to guard against
is the first displacement of the strata ; which can generally be prevented with
very sHght timbering, judiciously placed; if this is not watched, and done in
time, a slip of the rock will frequently bring in so much as to leave a great
cavern, which must be filed solid behind the work to make it secure from
fiiture danger. The annexed engraving shews the manner of timbering in

dtt

134

PRACTICAL TUNKSLLINO.

constructing tunnels of this description ; and is similar to that adopted by Mr.
Wright, in the construction of the Abbot's Cliff Tunnd, which A^as niade
through thie lower chalk between Folkestone and Dover. The sides are first
excavated^ leaving a pillar in the
middle, which serves as a base to prop lu 30
the roof ftom, and also to support the
centres for turning the arch when the
side walls are up ; the pillar may then
be cut away. But where an invert is
to be inserted this mode of proceeding
is inconvenient, 6nd requires great care
in propping the arch, during the con-
struction of the invert and the side
walls for the underpinning of the said
arch; because the central pillar that
was left to carry the props and centres
must be removed, before the invert can be commenced ; and that must be
completed before the side walls can be constructed. This method has been prac-
tised to a limited extent, namely, excavating and constructing the tunnel from
the top down to the springing ; or, in other words, constructing the arch first,
then excavating the lower parts, and, by constructing the invert and side
walls, underpin the arch. Such a method of proceeding is better suited for
rock and chalk timnels, when no invert is required, than for heavy ground,
where an invert is indispensible ; in which latter case considerable risk at*
tends the operation. It was however accomplished very successfully by Mr.
Daniel Frazer, in a large portion of the MarteUo tunnel, which he constructed
near Folkestone, for the contractors, Messrs. Grissel and Peto, through the
junction of the chalk, upper green sand, and the gault ; which latter stratum
appeared in the lower part of a portion of the tunnel.

Having now described the modus operandi of proceeding with the leading
lengths, it wiU be necessary to give the particulars of the amount of
labour consumed, and the cost of the work.

FOBCE EMPIjOTKD AT BUBCHIKOLET.

125

NUMBER OP MEN AND HORSES, AND THE NUMBER OP 8HIPTS
emiriojed in the excavatioii of the Leading Lengths at Blechingley TunneL

Number

Number of

Leuflrtht
conttmcted
from each

Avenge Numbn

r in faeh Shaft of

Shaft.

MiDO*.

Labooren.

Bonn.

Sbifli.

521

71-7

151

14-3

42-8

53-9

12-5

11-8

47.3

65-8

14-7

9-0

531

87-8

16-8

9-5

51-7

78-4

18-4

10-1

51-3

79-1

17-4

9-6

52-4

72-4

18-2

11-0

48-5

63-5

14-8

8-8

30-5

54-3

12-4

6-9

51-6

70-4

16-5

9-4

64-5

74-8

18-5

10-5

88-8

112-7

30-8

25-4

Mean of the whole two hundred and forty lengths :

Number of Miners, . . . per length . 52*2

„ Labourers, 70-1

„ Horses, . . . . . . 16*5

Shifts 10-8

126 PRACTICAL TUNNELLING.

The number of workmen employed in a length will vary in different parts
of the work as it advances. In driving the top heading, one or two miners
and one labourer only can be employed ; then, in getting in the tops and
before they have commenced drawing the earth, the numbers will be about
three or four miners and three labourers; and when the earth is being
drawn to the sur&ce, the greatest force can be put on, which amounts to
about five miners, three labourers attending upon them, one hooker-on,
and four banksmen.

Upon inspecting the preceding table it will be seen that No. 11 shaft
employed the greatest force, and took the most time; this arose from the
ground being so very heavy where it was shallow, near the entrance of the
tunnel, as described in the general particulars of the tunnel, at pages
7 and 8.

It may also be observed, that the amount of labour for the leading work is
much less than that for the side lengths, as given at page 90, although it
may, at first sight, appear that as the lengths were nearly of similar dimen-
sions such a difference ought not to exist ; but it must be remembered, that
at the first starting of all works a deal of time is lost in preparation, &c. ;
and, on this occasion, all the timber had to be lowered down, and prepared
for the side lengths, which was not the case afterwards.

Previously to letting the labour, by contract, to the respective gangers,
(each of whom was to have no more than one shaft), the following estimate
was made of the probable average expense of executing the work of the
leading lengths.

ORIGINAL B8TIMATB.

127

ESTIMATE OF THE COST OF EXCAVATING

the Leading Lengths at Blechingiej Tnnnd.

£ s. d.

Driving top heading, and taking out timber, 4 yards, . at 1^.

4 miners getting in tops, . 4 shifts (extra) 6s.

4 16

Remainder of length, or drawing the earth ; say 8 shifts

for the following force : —

4 miners . 66. .

1 4

1 mongrel 4s : 6d.

4 6

3 fillers ds:6d.

10 6

4 banksmen . ds:6d.

1 hooker-on . . 38.

2 horses and drivers Ts.

Cost of labour per shift

3 10

which multiplied by 8 shifts = .

Powder and candles ....

Tools, &c .....

1 5

Superintendence, . 8 shifts, . , Ts.

2 16

Total for each length

£ 42 17

which, divided by 4, gives £10: 14s : 3d. per lineal yard.

The price contracted to be paid to the gangers, for the excavation, varied
from £10 : 10s. upwards, per lineal yard, according to the supposed character
of the ground, at the different shafts. The average was about JBll. Some
portion of the work yielded a deal of water, and was extremely heavy;
which brought up the average, as above stated.

By means of the table at page 125, the average cost to the contractor may
be ascertained, and compared with the contract price and the estimate given
above.

128

PRACTICAI. TUNNELUNO.

AVERAGE COST OF EXCAVATING

the Leading Lengths at Blediingley.

Miners,

52*2 days

at 68.

Labourers,

70-1

atd8:6d.

Horses, and drivers.

16-5

at 7s/

Candles,

3 dozen

at66:6d.

Gunpowder,

1 cwt.

Tools, and sharpening picks, wedges, &c.
Contractors* Superintendence, 10*8 days at 7s.

Clearing up the work when completed, . per length

Total

which, divided by 4, gives £10: lis : 3d. per lineal yard.

£ 8.

15 13

12 5

5 15

2 6

I 5

3 15

£42 5

Thus the cost to the contractor averaged £42 : 5s : Id. per length, and the
amount he received averaged £4A: — ^leaving a profit of £1: 14s : lid. To
this may be added j63, which the bricklayers paid to the miner, per length, for
lowering bricks, cement, and sand, down the shaft, at the same time that they
were raising the earth to the surface ; this, however, would require one or two
additional labourers, to load the bricks, &c. into the skips, and would take one
pound away from the three, leaving £2 to be added to the above £1 : 14fl: lid.;
making together £3 : 14s : lid. as the profit per length : being at the rate of
about 8| per cent.

The above is about the average result of the works at Blechingley ; — ^in some
cases the work did not cost so much money to execute it, and in some it cost
more. There were several cases in which the contract price would not cover the
outlay, and the gangers at such shafts gave up the work. Upon the whole, the
above statement appears to be a fidr representation of the cost of executing
the work at Blechingley.

The following statement comprises a similar investigation of the works at
Saltwood.

FORCE BMPLOTBD AT 6ALTW00D.

129

AVERAGE NUMBER OF MEN AND HORSES, AND THE NUMBER OF SHIFTS

employed in the excayation of the Leading Lengths at Saltwood Tunnel.

Number

Shaft.

Number of
Lengths

from each
Shaft.

Miuen.

UboiBcn.

Hotfa.

Number of Shi^

Before

drawing

earth.

While

drawii^

earth.

Total.

45-3

SO'3

12-8

3-3

7-2

10-5

421

501

15-3

2-5

7-2

9-7

30-2

54-3

15-3

2-7

9-8

: 36-5

54-7

14-4

3-2

6-6

9-8

33-3

50-6

13-2

8-8

Not wor

ked.

•

34-3

53-6

14-0

2-5

6-5

34-6

S0«

13-4

6-2

8-9

34-6

53-3

13-8

2-9

6-2

9-1

34-3

55-2

14-3

2-8

6*3

9-1

35*3

571

14-8

6-6

9-7

34-7

56-3

14-5

6-4

9-5

Mean of the whole one hundred and ninety-two lengths :

Number of Miners^ per length 96*8

M Labomrersy * . v • • ^*^

,, Horses, 14*1

Shifts, ...... 9-4

The preceding table shews the aven^ amount of labour and time expended
in the construction of the leading lengths at Saltwood Tunnel. The cost
thereof would be approximately as follows :

130

PKACnCAI. TOmfELUNO.

AVERAGE COST OF EXCAVATING

the Leading Lengths at Saltwood Tunnel

Miner*,

36-8 days .

at 5s.

Labouren,

at 3s :3d.

Honea, and drivers,

141

at 78.

Candles,

2V4 dozen

at6s:6d.

Tools, and iharpening picks, wedges, Sec,
Contractors* Superintendence, 9 days • at 7s.
Clearing up the work when completed, . per length

Total « . .

8 12

£27 19

whiohf divided by 4, gives £6 : 198 : 9d. per lineal yard.

The price of the miners* and labourers' wages are put above at 5s. and Ss: 3d.
per diem ; whereas, for the same class of men, in the investigation of the cost
of Blechingley they were reckoned at 6s. and 3s: 6d. The &ct was as stated,
in each case ; for wages were higher at the time Blechingley Tunnel was in
hand than they were two years later, when Saltwood Tunnel was constructed ;
because that so many similar works were proceeding at the time the former
tunnel was made, which led to a demand for men who were accustomed to the
work ; whereas, two years later no such demand for workmen existed.

At Saltwood, the contractors supplied the horse power themselves, and let
th^ manual labour, only, to the subcontractors.

A small poortioii of the Saltwood Tunnel was driven firmn the open cutting at
tiM^ wt>at twl, as the excavation was completed at a suffidoitly early time for
th^ purpose. SeT» lengths of tunnd were constracted firran tiie intended
fiite^ or Hitrance to the tunnd, when a junction was ^fe<^ed with tiie workings
tiiat had proceeded in the opposite direction firran Na 1 shaft.1

TW »ode of proceeding with the worii firom an apea cutting is tiie same as
for ^ oidiiiary kaduig lengths previously descnbed; bat considenble care i$
required in timbering the fiice of the excmTation^ before the dnving of tiie tun-
m1 i» cowoaeiiced^ to prevent its folHng io^ and causing inoonvenienoe and

182

PKACTICAL TVmrELUMG.

Number of Lengths,

,9 Miners, • •

34-3

„ Labourers,

Horses,

Shifts, . . .

By placing the mean results of the tables in pages 125 and 129 in juxta-
position, it wiU be seen how much more labour was required in the excavation
of the leading work at Blechingley, than was necessary at Saltwood. This
could not arise from any difference in the skill of the workmen, as a lai^e por-
tion of the same men were employed in both cades ; and all the gangers, or
subcontractors at Blechingley were the most experienced men that could be
found : the difference arose from the varied character of the ground in the two
cases. At Blechingley it was a strong blue clay, highly indurated into a hard
shale or bind requiring the aid of gunpowder to get it and when exposed to
moisture, or the air, it swelled and afterwards slaked ; there was also some water
to contend with. At Saltwood after that the preliminary works were completed,
which had drained off the water most effectually, the ground was a dry sand,
except at the level of the invert, where but little trouble was experienced
from the water, as the heading afforded so excellent a means of letting it off.
Admitting, therefore, that equal skill was employed in both cases, the following
table will shew the amount of labour required for excavating the leading work,
in the two kinds of earth, and may serve as a usefrd guide in friture operations.

Blue Shale.

Di7 8«id.

DiAereaeein

fcTourof

Sud.

AppcDximete

Ratio of the

SandtotheShde.

Miners,

52^

36-8

15-4

0-7 \

Labourers,

70-1

53-0

171

0-7 i .etD,

H«»8es,

16-5

14-1

2-4

0-8 ( 0-8

Shifts,

10*8

9-4

1-4

0-9 j

Or the amount of labour and time required to excavate for tunnelling
through dry sand, may be said to be approximately eight-tenths of that
required to do the same work in blue clay or bind.

BRICKWORK, LBADINO LEHOTHS.

183

BRICKLAYERS WORK FOR THE LEADING LENGTHS.

Upon the subject of the Bricklayers' work but little need be stated in addition
to the particulars given in chapter x., where the construction of the side lengths
is described; except to give the following table of the work done at Bleching-
ley. The reason that there is so Uttle variation in the amount of labour and
time required for the brickwork arises from the tact that the circumstances are
nearly always alike ; this kind of work not being subject to such vicissitudes
as that of the miners.

AVERAGE TIME TAKEN BY THE BRICKLAYERS

to turn twelve feet Leading Lengths at Blecbingley TuaeL

Nnmber

of
ShtA.

Nonber

of
LncO..

tbeq>riagiBffor
the Arab.

FroBtlM

Arch
to Kejring-in.

Tot>L

Force mpiojcd

Briekkyen.

Labooicn.

D*]n.

D.yfc

Day*.

2*3

2-6

4-9

2-9

1-9

2-4

4-3

1-8

2-2

4-0

1-9

2-4

4-3

1-7

4-2

I'd

2'2

4-0

1-7

2-5

4-2

i-e

2-1

2-0

2-5

1-7

3-8

3-0

5*0

134 PRACtlCAL TUNNELLING.

Mean result of the preceding table :

Days

Time occupied in the construction of the Invert and Side WaUs • • 1*88

Time occupied in setting the Centres, and turning the Ardi • > 2*42

Total time occupied in constructing a leading Length • • • - 4*90

The brickwork of a leading length iis shewn in plate 7 ; wherein fig. 1 is a
longitudinal section ; and fig. 2 a transverse section taken on the line a b fig. 1
—each representing the work as it appears as soon as the arch is keyed-in, and
ready for the miners to commence excavating for another length onwards. In
each of the figures the crown bars are shewn at f, the packings in brickwork
at Cj the props at o and h. b' is the arch of the length last completed, and a^ is
the arch of the preceding length ; the line of junction between the two lengths
being where the ends of the two sets of laggins meet, as at/, ff. a\ h\ c", are
the three centre ribs, supporting the laggins upon which the last length wqb
turned ; and d! e\ shew the leading and middle ribs under the laggins of the
preceding length, the third or back centre rib having been moved onward to
the position C. The two ribs d' e' were left to remain imdisturbed in the posi-
tion shewn in the engraving, until the side walls of an additi(mal length were
built, when they with the lagging, sills, props, &c., were moved onwards, as
named at page 115. d and d^ are the raking props to the upper and lower
sUls. The wedges or slack blocks, the half timbers, and the props, (all of
which belong to the centering), will be referred to and explained in chapter xiv,
which will be devoted to the particulars of the centres. Figs. 3 and 4 have
already been referred to at page 103 ; where the brickwork is generally des-
cribed, under the head of the side lengths.

IDNCTION LENGTHS,

135

THE JUNCTION LENGTHS,

In the manner now described the tunnei works are usually carried on in
lengths, as they are called, of 9, 10, or 12 feet; as the nature of the ground will
admit of- Twelve feet is a convenient length, in all cases where it can be
adopted with safety ; and this is done both ways firom each shaft, till the work-
ings meet; the last length, or space required to join the two workings, is called
the junction (or thirUng.) The length of the junctions should be brought as
near to that of the ordinary lengths as possible, so that the same timbers may
be used ; for if they be much longer, the same bars will not reach across from
brickwork to brickwork, to take a bearing for the support of the earth ; and if
they be much shorter^ there wiU be a difficulty in drawing the last crown bars
from the last length each way : and, what is of more consequence, if the earth
left between the workings which form the junction is but a mere thin partition,
it will probably give way before the last two leading lengths are turned ; and
this might be productive of at least unpleasant consequences. It is the safer
practice when approaching the junction to stop'one of the workings, and advance
to it in one direction only ; for if the work be carried on at both sides, there is
great probabihty of disturbing so narrow a wall of earth as would then be left
for the junction length.

The only timbers required for a junction length are bars, and poling boards.
The bars rest on the brickwork of the preceding lengths, and are built in, as
the work advances. The side walls, and the arch, are constructed in the usual
manner, together with the keying-in of the crown, as described at page 103, by
the bricklayers inserting one cross lagging at a time, and closing each space
over the said lagging, till at last he reduces the space to such small dimensions
that he no longer can stand with his head and shoulderg in it, to do the work,^
as shewn in the engraving on the next page ; he is therefore obliged in this
last small piece to turn the top ring of the arch first, by fitting, and wedging
his bricks tight, in the best manner that he is able, passing them witli his hand
and arm up the opening, and bonding the top into the next lower ring, by
some of the bricks put as headers ; then setting the next lower course, or ring,
bonding as before, and wedging it up tight; and so on with each course,

13^

TUACSICAL TUNN;BI4|ING.

until the opening in the bottom course, or soffit of the arch, will only be

sufficient to receive one brick put endways into it; which brick, if neces-

atttry, must be tightly wedged into its place, with wooden or iron wedges, and

the work will be finished. The whole of this finfd closing the work should be

done with cement of the best quality.

The space or opening left for tiliis process

need not exceed the dimensions of two

CX08S, or keying i^, laggins. The an*

noxed engraving represents a bricklayer,

in the act of passing a brick up into its

place^ through a hole kft by the omis*

wm of two cross laggins, in the maimer

above described. The closing portion, if

properly done, is never likely to &11 out,

because its sides are splayed from the

op^ng upwards, each course being

wider than the lower one ; they are also

bonded into eaoh other, as well as into

the toothings of the arch at each end of

the aperture, and the hurt brick is wedged or rammed tight into its place so as

^ot easily to be dislodged, added to which there is the adhesion of the cement,

which, if good, and properly gauged, possesses great strength.

ENTEANCES.

137

CHAPTER XIIL

TUNNEL ENTRANCES, SHAFT TOWERS, AND CULVERT THROUGH THE TUNNEL,

TUNNEL ENTRANCES,

It is unnecessary to state much upon the subject of the entrances; as it
would answer but little purpose except to swell the volume. The designs
for such constructions should be massivcj to be suitable as approaches to works
presenting the appearance of gloom, solidity, and strength. A light and
highly decorated structure, however elegant, and well adapted for other
purposes, would be very unsuitable in such a situation : it is plainness com-
bined vrith boldness, and massivenesa \^ithout heaviness, that in a tunnel
entrance constitutes elegance ; and, at the smne time^ is the most economical.
The above conditions may be answered without cramping the taste of the
Engineer, so far as taste enters into the composition of such designs; for
architectural display, in such works, would be as much misplaced as the
massiveness of engineering works would be^ if applied to the elegant and
tastefully-designed structures of the Architect. Upon the London and Bir-
mingham, and upon the Great Western, milways, there are several very
suitable structures of this kind.

The engraving on the following page represents the eastern entrance to
Blechingley Tunnel ; where the slopes of the open cutting are uniformly 2
to 1, The western entrance is similar in design ; but the slopes of the open
excavation differ from the slopes at the east end, — being 1| to 1 on the north
side, and (by means of level bencWngs, is) 2 to 1 on the south side ; which
arrangement of the slopes w as occasioned by the tendency of the strata to slip
on the one side of the cutting, more than the other, and arises from its dipping
from south to north, and from the general disturbance of the beds, as explained
at page 6* The quantity of brickwork in the wiag widls of tlie one entrance
is, consequently, greater than in the other : they are, however, similar in every
other respect.

138

PRACTICAL TUNNELLING.

An inspection of the engraving will render it unnecessary to go into a
minute description of the entrance^ as the design is fiilly shewn in all its
parts. The whole is cx)mposed of bricks ; no stone whatever being used in
the construction- Not but the use of stone for the string course, and the
coping, would liave been preferable to bricks for those purposes ; but no good
material of that kind could be obtained in the neighbourhood^ and its cost
when conveyed from London (about 24 miles, by land carriage, over a hilly
country,) the nearest place from whence good stone could be procm-edj would

-~ >- ..^^

It/*

y^^

L'^/'flUP*

rpHiJid

probably have been greater than was due to the difference in the comparative
quality of stone and bricks, for that purpose*

The plan of the wing walls is circular, being struck with a radius of tliirty
feet, and battered three inches to one foot* The pilasters are six feet, and
the plinth of the pilasters six feet six inches wide. The space between the
pilasters, for the entrance of the tunnel, is 28 feet ; and as the tunnel is 24 feet
wide, the arch shews on the outside a thickness of 2 feet, and is formed of five
half-brick rings- The space between the external contour of the finished arch.

BALTWOOB TUNNm«

It#

at the crown, and the underside of the string course, is one foot ; the string
consists of four courses of brickwork ; and the height of the parapet, from the
string to the under side of ttie coping, is three feet The thickness of the
coping is one foot three inches. A brick open drain, along the back of the
[jarapet, conducts the rain water to similar drains made down the slopes, and
hence to the water channels alongside the railway, where it joins the drainage
firom the culvert within the tunnel, (to be presently described), and passes off
to the natural drainage of the country, at the tailing out of the open cutting.

The Saltwood entrance differs materially from that constructed at Blechingley,
and IB shewn in the above engraving. The left-hand half of the figure
represents the elevation of half the entrance ; and the right-hand half shews
a nection of the same>

The mng wails are not curvilinear^ as at Blechingley, but are built straight,
or parallel to the line of railway, and follow the slope of the excavation ; they
alno batter at the rate of two and half inches to one foot. The dimensions of
the wing walls, parapets, &c, are given in the above engraving.

140

PBACTICAL TUNNELLING,

The follovring engraving is a section taken through the centre of the end
of the tunnel ; and shews a side elevation of the wing wall ; and also a section
of the barrel drain which conducts the water from the culvert that is con-
structed on the invert of the tunnel, throughout its length, similar to the one
at Blechingley. A drain is also made along the back of the parapet and winj^
walls, to conduct the surface water to the proper drainage. By comparing the
various parts of the preceding engraving with the corresponding parts of the
following engraving, the details of the construction wiU be clearly apparent.

The erection of the entrances was paid for by the rod, of 306 cubic feet.
The price per rod is not the same in all places; chiefly arising from the
variation in the price of bricks. The quantity of brickwork in such entrances
and wing walls as at Saltwood, — where the slope of the earth is 1| to 1 —
amounts to 40 rods; and where the sloix? is 2 to 1, it wiU amount to 51 rods.
This is reckoning for the work as shewn in the above engraving ; but wber*^
there is additional work, as counterforts to the walls, &c. it will of course*
exceed this. The quantity of brickwork in the Blechingley entrance amounted
to 65 rods, — *the slope being 2 to 1, — and the wing walls being much larger
than those at Saltwood, in all their dimensions.

SHAFT T0WEB8*

141

THE SHAFT TOWERS.

At Blechingley Tunnel, aU the shafts (with the exception of No, 11) were
left open, for the purposes of ventilation ; and at Saltwood, five were left o])en
for the same purpose ; the others were closed by doming them just above the
arch of the tunnel, and filling them with earth to tlie surface* For the pre-
vention of accidents, the brickwork of the shafts was carried up to some height
above the surface of the ground, in the form of a tower^ as shewn in the an-
nexed engraving, and then covered in with an iron grating ; which prevents

stones falling down, if thrown for that purpose by mischievous persons. Tlie
domed shape of the grating not only gives it strength, but woiUd cause such
stones to roll oflf again.

The towers at Blechingley and Saltwood were raised 12 feet above tlie h vel
of the spoil-bank, or where the brickwork of the shaft terminated. The >^hafts
were of nine-inch work, but the towers were foui teen inches thick ; therefore,
where the towers commenced they saUed over, outwards, 4| inches, a$ shewn

149 FEACnCAL TUHKELLIKG.

in ttio above engraving. The towers diminish upwards, from 9 feet at bottom
U} 7 feet 10 inches, inside dimensions, at the top.

I1ii9 iron grating was made with a cast-iron circular ring, or plate, 9 inches
wide, and an inch in thickness ; with a lip around the inner edge that fits into
t\w shaft, and keeps the grating from sliding from its bed. The plate was cast
in halves, dovetailed together, when set in its place, as shewn in the right-hand
flgnro of the last engraving.

An arched rib passed over the grating, which was bolted to the plate, and
bolng also in two parts, was united in the middle by a half-lap joint, and a
l)olt and nut. The wires forming the grating were five-eighths diameter, and
were rivotiHl on each side, at the under side of the plate, and in the centre
|huim(hI through the arched rib before named, which strengthened them, and
kept thcni equidistant apart The cost of each grating, complete and delivered,
was £6 : lOs.

TH£ CULVSRT.

AUuig the oentre of the invert of the tunnel, a culvort was oonstnicted to
(Hirry off the water^ both at Bledungley and Saltwood; its fixm and position is
nhtc^wu at A in the «tigiavuig page 139 of the sec^ioii of half the entmioe c£
SaltwtH^d tuniieL It was described with a radius ot 2 feet 3 mdiea from the
r^\tn> i^ the in^mri, and was thatefoie not quite a senkiide, becanae of the
ri«iiv( <^ the iiiT^tt on Mdi side of its cmtre. Hie bridnradL was Snsdiesin
thickiiMs; and^ at Meciaai;^^pwycrfy radiating or wf dy i Amp ilbneb wqe
mmW fbr il.— a»y w«fe K^ iMhm loiig, 4 iMhm tittck aft tke tsck^ and
SiiKliMattlieiKiffrstdKaBdSiMhmiiibnftddL TofenaOeaRkil Replied
^ of tlMW brides; aad 90 w«e wed ia eronr jaid feravdL as Aaafertlsr
tmwl ( l^kM ywds lsi«^ IIMM wfR wed lA ti^
TrW^ biica&$ Mrt 9wl

TW" wkdsef the Wicss ^

bml»^ «ra MMlHt kaaiL tea tke^ivki^fwt Wcmletia^

CULVERT,

In order to facilitate the work, a centre was contrived 24 feet long for turning
the culvert. This centre was fitted to a strong horizontal frame of the same
length, and 3 feet 3 inches wide ; and the whole was fitted to a similar frame, or
itage, moveable upon rollers. The annexed engraving shows this culveit
centre. Fig. 1, is a longitudinal section shewing six feet of its leading end,
and fig. 2 is the elevation of the leading end. The lagging are shown at a,

I\f.3

J'S'^

which were made of inch deal. The centre ribs are shown at b, b, and were
six in number^ made of one and a half inch stuflF, and strengthened at the top
by cross pieces c. The upper frame is shewn at d, and e is the lower frame :
the upper one is moveable upon the lower one, by sliding up the inclined
planes, f of which there are six on each side. WTien the upper frame is lying
close upon the lower one^ these inclined planes or notches resemble scarf joints.
The frames are made of fir, 3 inches square, and are strengthened by cross
ties, o, and diagonal braces.

The lower frame is moveable on twelve rollers, u, &c., (six on each side,) by
which means it can easily be drawn forward, as the work advances, i, is a
winch, the turning of which gives motion to a screw that is attached to the
upper frame, w hile its thread works in a socket attached to the lower frame ;
when the screw is turned, it draws the upper frame forwards or causes it to
slide lengthways upon the lower frame ; but in consequence of its being
notched, as it were, into the lower frame, in the manner of a saw-tooth rack,
it must necessarily slide up these inclined planes ; thus partaking of a com-
pound motion, rising upwards as it advances forward ; and when a reverse
motion is given to the screw by turning the winch i the contrary way^ the up-
per frame, with the centre, will recede to its former position, and in so doing
it will descend the inclined planes, and hence take a lower leveL k shews
one of six iron guides that partake of the motion of the centre, and keep it
from moving sideways while it is being wound up, or the reverse.

t44

PRACTICAL TUNNELLING.

By this contrivance the business of setting and easing the centre was greatly
facilitated, and withal it was made twice the length that culvert centres
usually are, thereby enabling the workmen to get on &ster. In using it,
the centre was first placed in position ; the winch i was then turned, till the
segment was raised to the required level ; and upon this the arch was constructed,
which completed a length of 24 feet: now, by reversing the action of the
winch, the centre was lowered from under the brickwork, and was therefore
released from its pressure ; whereupon it was drawn forwards by two men
(nearly, biit not quite,) from under the 24 feet of culvert already completed ; and
being placed in line, motion was again given to the winch until the centre was
raised once more to the proper level, which could now be known by the end of
the centre fitting up to and under the completed length ; a second portion of
the culvert was then turned, and the centre raised and moved forward, as
before. In this manner the work proceeded rapidly, as the easing, removing
and resetting the centre did not occupy more than two minutes ; and when
the men got accustomed to it, they did it in but littie more than a minute.

The following table shews the amount of labour, and the cost of constructing
the culvert through Blechingley timnel — 1324 yards lineal — ^with the radiating
bricks, and the above-described centre.

Carting bricks
Lowering bricks and mortar
Turning culvert
Loading brick carts, 8cc.
Wheeling bricks at top

,» in tunnel

Making mortar
Banking

Total

Honn.

Bricklayer!.

Labourers.

D.,..

D-y.

Days.

•

43»4

681^

151%

16714

252^4

30%

11414

151%

614)4

CnTLYBRT.

146

ACTUAL COST.

120,000 Bricks, including waste,
75 bushels of Cement,
48 yards of Lime, .

Materials J 06 yards of Sand, .

consumed i Carting ditto
Carting Water

at 50s. per thousands
at ls:8d. per bushel =
at 13s. per yard =
at Is. per yard =

at 2s. per yard =

Labour

Candles

Horses
Bricklayers,
, Labourers,

410 lbs, at Oi^d.

. li4V4 days, at 7s.
. 151% days, at 6s.
614^ days, at3s:dd.

Centre, as above described
Total

800

4 16

45 10

99 16

550

12 11

£560 12 11

Being at the rate of 8s : 5|d. per yard forward.

The weight of iron work to the centre, including axles to the rollers, *was
181 pounds.

Had the culvert at Blechingley been buUt in two rings, with common bricks,
it would have taken 264 to a yard forward, or 350,000 in the whole.

When the tunnel at Blechingley was completed, it was cleared out from end
to end, and the invert examined and made good where the raker-holes and
props had injured it. A scaffold was made to run upon wheels along the tun-
nel, by means of which all parts of the arch and side walls were carefully exar
mined, and its shape tested by a mould. Afterwards, the whole was lime-
whited, with a view to add to the light of the tunnel ; which, as before stated,
was but of little service. The ballast for both tunnels was mostly the debris
from the brickyards, and the broken stone dug up from the temporary roads
made on the works above. These were thrown down the shafts, and spread at
the bottom. On the top of this rough ballast, a coat of finer material was
used, about a foot in thickness, to bed the sleepers in ; and the permanent way

was then finally laid.

».»

146 PRACTICAL Tl^lUfSLLINO.

By means of the culvert above described, the whole of the water that might
find its way into the timnel was effectually carried off. The rough ballast that
formed the bottom stratum was sufficiently porous to allow the water to pass
to the culvert, which being built with the end joints of the bricks dry, admitted
of the water percolating into the barrel of it, from whence it passed off" to the
drainage at the open end of the tunnel.

Towards the west end of the tunnel a considerable quantity of water en-
tered through the roof at one place, and appeared likely to continue to do so : —
it was, therefore, necessary to provide for conducting it to the under drainage,
instead of allowing it to drop into the tunnel. This was accomplished by cutting
a chase in the brickwork of the side walls, and, from the top of the said chase
making a similar cut in the soffit of the arch to where the water was found to
enter ; then, concealing the chase or gutter, by bedding flat tiles in the front,
to make the Walls and arch of the tunnel appear perfect ; this left a conduit or
channel behind the tiles, to collect the water that entered the tunnel, and con-
duct it down the sides, to the invert, and from thence to the culvert, by a small
drain. The tUes wmre set in cement, and the whole of the &€e was then plas-
tered with the same material.

When the water enters at more than one place, but at no great distances
apart, it can all be gathered into one general drain, by cutting oblique chases
to coHect, and lead it to one or more outlets.

At the Martello Tunnel, near Folkestone, where a great quantity of water
enters tiirough the roof, it is conducted to the sides, by lining the roof
with sheets of corrugated zinc.

CENTBES.

CHAPTER XIV-

THE CENTRES OP OEDINAEY CONSTRUCTION, AND FEAZEE S PATENT CENTEES.

In the preceding chapters all particulars of the centres were omitted wheti
deaciibing the brickwork ; an important and interesting part of the sub-
ject; the reason for so doing was to prevent confusion by introducing so
many subjects together ; and as the account of the centres, and the method of
using them, would occupy considerable space, it appeared better, for the
general clearness of the subject, that it should be reserved for a subsequent
chapter ; it being sufficient for the purpose of describing the brickwork, to
state that the centres were set up, and the arch turned upon them. The
particulars of the centres mil now be given.

The centre ribs, that were made for and used in the construction of Ble-
chingley Tunnel, were essentially the same as is commonly used in such
Works. It is frequently the case that contractors carry on their work vritli
one set of centre ribs only, which must be taken from under the green brick-
work to be set forward each time the arch of a new length is to be turned.
As this mode of proceeding appeared objectionahle, two sets both of centres
and laggins were used upon the works under consideration ; by which means
all danger and injury thereto was prevented ; and although the additional cost
of such set of materials was considerable, yet it probably saved a much larger
sum that would have been incurred in repairing broken work ; and ensured a
sound tunnel.

When the Blechingley Tunnel was completed, the plant and other mate-
rials were conveyed to Saltwood, for the purpose of being again used, and the
centres were partially so : but upon that tunnel being let by contract, and the
TOUtractors having appointed Mr* Joseph Frazer as their representative, that
gentleman introduced his patent centres; thus aiFording ample means for
observing and estimating the comparative merits of his centres, and those of

148 PRACTICAL TUNNELLING.

the ordinary construction ; especially as they were being worked under the
superintendence of Mr. Frazer himself. Particular attention was, therefore,
paid to the subject, that the result might be satisfactory. A description of
each system of centres, with the cost of their construction, will be given ;
and a comparison drawn between them.

THE BLECHINGLET CENTRES. — ^PLATE 9.

For each shaft of the tunnel there were required 10 centre ribs, 4
sets of laggins, 6 centre siUs, 16 half-timbers, 40 props, and 40 pair of
slack blocks or wedges; to these may be added a few wedges, and
chocks, or chogs, &c. ; the timber for which is generally obtained from the
offid timber, which always collects in abundance on such large works, and
therefore is not necessary to name in an estimate. The above quantity of
materials is required for working from each shaft in both directions ; conse-
quently one half the above materials form a complete set, as used at Bleching-
ley, for working in one direction, or as it is called " one end of the shaft.''
This will be described, as being all that is essential to the present purpose. It
must be supposed that the side and shaft lengths are completed, and that the
centres are about to be applied to construct the arch of the leading work.

At each end of a shaft, five centre ribs are required ; two of them must
have no tie beam, as that would interfere with the raking props ; — these were
called segment or leading centres; — ^their construction and dimensions are
shewn at large, fig. 3, plate 9 : they consist of two segments, and when put
together for use, are joined along the line a, i, and also by the moveable tie c ;
this tie prevents the spreading or contraction of the segments. This form of
centre was found to be particularly convenient and strong, and as the only
doubt about its utility, for all tunnel purposes, might appear to be the want of
a complete tie beam at the bottom, this desideratum, if such it is, might be
supplied by a moveable piece, or iron screw tie, to connect the point d to the
opposite point d' ; if this were appUed it probably would, in addition to the
convenience of shifting and resetting, sustain any amount of pressure ever
likely to occur, either vertically or laterally, and also all ordinary wear and
tear, and damage from the blasting of rock, and therefore would require little
(h: no repairs throughout a job. There is, however, an objection to moveable

BLECHINGLET CENTRES,

pieces* as they are apt to be mislaid and lost ; but to prevent this, the men
employed in the gang for shifting the centres should each be fined when a
piece is lost, not merely to pay the value of the material, but also loss of time
sustained by the bricklayers and others, in consequence of such neglect* At
Blechingley the strength of these ribs was fully tested ; for^ as they were the
leading ribs, they were exposeii to the greatest eifects of the blasting, yet they
never required any repairs ; and after removal to Saltwood, by land and water
carriage, they were uninjured ; it would therefore appear that they are pre^
ferable to most of the ordinary centering.

The other three ribs were differently constructed, and were called scarf or
queen-post centres. Fig. 4 represents them: in construction they are well
calculated to sustain heavy weights* This form of centre has been before used
in tunnels, as on the Birmingham and Brighton lines of railway. The tie
beam is a great security against the spreading or contracting of its span ; but
it is liable to interfere mth the raking props, supporting the face of the
excavation. Another objection to this form of centre is, that it is not well
adapted to withstand the side blows to which it is exposed (particularly if used
as a leading centre) when the miners are blasting rock or other material in the
forward length* The extent of the repairs at Blechingley was considerable,
not only arising from this cause, but being taken so completely to pieces each
time they were shifted, they were more liable to injury, particularly in the
scarf joint; whereas the segment centre is not so completely taken to pieces,
for each of its two segments will pass through an opening of 5 feet 6 inches
in width..

Setting and Shifting the Centres. — As the Bricklayers bring up the
side walls, they leave holes about 13 inches deep (a figs. 1 & 2, plate 9) at the
proper places, for the reception of the ends of the sills ; a in fig. 2 shews the
hole from whence a sill has been removed forward. When the walls are at
their full height, the sills, which are in two parts scarfed together in the
middle, as shewn at a fig. 1 , are set in their places, and joined together at the
scarf; the plates are then bolted, and the glands secured. Fig. 1 shews the
sills, A^ stretching across the tunnel, carrj^ing the centres; and they likewise
are shewn in section at a a a fig. 2. Each sill has two props b b under it, the
bottoms of the props are wedged on the invert, and their tops fit into a collar
spiked to the under side of the sill as shewn at fig. 5, where a is the sill, b the
prop, and e the collar ; the first and third figures are an end and side view.

150 PRACTICAL TUNNBIJuING.

and the middle figure is a {dan of the under side of the sill, shewing the pn^
B nearly surrounded with the collar e. The half timbers, c c, &c. were next
laid on the siUs nearly at right angles thereto : by comparing figs. 1 and 2,
their situation and arrangement under the centres will be obvious. Each
half timber was propped in the middle, or inmiediately under where the centre
ribs take their bearing upon the half timber, as shewn at o o, &c. Instead of
sills to support the centre, sometimes tressels are used ; but at Blechingley
the sills were adopted, as the most preferable mode.

The centres were next put together across the half timbers, and when set up
in their required places, were raised to the proper level by the slack blocks or
wedges £ e, &c., and also at large in fig. 6, where the wedges are shewn both
in a side and end view. Upon the centres the laggings were laid, and thoreon
the arch turned.

It may be well here to call attention to the oblique manner in which the
half timbers are placed^ as represented in the engraving ; one end of each of
the middle half timbers, and the slack blocks, are imder the heel of the leading
rib, as at 6 6 (fig. 1) ; whilst the other end of the same half timbers is under
the queen post of the scarf centre, as at c c ; and as the queen posts in that
kind of centre are nearer the centre of the tunnel than the heel of the seg-
ment, or leading centre, such oblique positions of the half timbers is necessary
to take those important bearings of the two ribs.

The setting of the three centre ribs, as above described, is all that is
required for each of the side lengths ; where they ought to remain after the
arch is turned, during the time that the shaft length is completed, and also the
first leading length each way ; when the one nearest the shaft will be taken
forwards without disturbing the other two. By referring to plate 4, fig. 1 —
where the side lengths are shewn as complete, and the excavation for the shaft
length ready for the brickwork, — ^it will be observed that each side length has
all its three centre ribs remaining under it ; and by referring to plate 5, fig. 1,
the same shaft length is represented as complete : in this case it will be seen
that each of the side lengths still has its three centre ribs imdisturbed, and
that the arch of the shaft length has been turned upon four additional centre
ribs, two of which will be carried each way for the leading lengths, to make up
the five centres required on each side of the shaft, as described at page 114.

Upon the completion of the shaft length, the centres and laggings were
removed fix^m under it, and a leading length on one side commenced ; and as

ILICHIKOLET ClKTimb

soon as the side walls were up springing high, the centres ^ t ctp set without
disturbing those in the side lengthy except tlie hack one of nil (iitniit*st the
shaft) which was brought forward. Fig, 1, plate 9, in a cn\m i^ec tion of the
tunnel, shewing the work in this state, and figure 2 is a longitudinal siTtioo of
the same; the cross section being taken near the lace of the excavatitm
through the line f, g, looking toivards the completed portion of the tiiniu*h
The brickwork is she^Ti as being above springing high, and pArt of tb(^ nrrh
turned, as at h h» six of the laggings on each side having been already laid on
the centres.

Figure 2 shews the five centre ribs in use at one time ; three undtT the
length in progress, and two supporting the laggings under the last turned
length ; the third or back rib, having been moved forward for use umh^r the
advanced work. When the arch is completed the whole five ribn nniiain
unmoved, under the two lengths, (as shewn in fig, 2i) during tht? whole of the
time another length forward is excavated ; antt also until the invert ami Mitle
walls of the same are constructed ; thereby materially assisting the nc^w brick-
work to sustain whatever pressure it may have to bear» not oidy from the
earth above itself, but one half the weight of the newly excavated length ; as
may be seen in fig. 2, where the brickwork k has to carry hidf the wc^ight of
the new length, because one end of all tlie bars rest upon it near its enil, im ni
L. Furthermore the invert and side walls being constnicted before any of the
centre ribs are removed, they form a buttress against tin* complett*d work, that
prevents any tendency in those lengths to slide forward and «eparat/3 from the
preceding work; for it sometimes happens that nearly a whole length will
move onward, and leave an open joint between itMQlt and the length it had
separated from ; for in all these operations the work has a tendency, aw before
stated^ to press forward in the direction tliat it is beitig carried on. Nr^ne of
the support of the arch of the two preceding lengths were ever disturln^d at
Blechingley Tunnel, till wanted for a third length ; for although the back rib
of aU was moved forward as in fig. 2, yet the laggins of the mul back length
were kept tight up to the arch by the remaining two ribs, so that two lengths
of 12 feet each, or 24 feet of completed work^ nrmained with its full ftupjiort,
not only till the next length was excavated, but until the next mde wmUi wire
Up ready for the centres.

Under these cooditaoiis every limgth was well able to bear the mperiiieum'
bent weight, tintfl it received aiiiitaiice from the neigbboiiring adraadog

162

PRACTICAL TUNNELLINa

length ; the construction of which to the springing height necessarily occupied
some days, and therefore the cement had time to harden before the weight
came upon the arch after the removal of the centre ribs ; which is an import-
ant advantage.

But when, firom motives of economy, three ribs and one set of laggins only
are used, the whole support must be removed firom under the first length before
a second one can be turned, and again must be in like manner removed firom
the second before the third can be constructed, leaving the back work without
support ; which occasionally causes it to give way, — the bricks to crush, — and
firequently the two last lengths to be separated fix)m each other ; and if the
arch does not come in, it is often bulged in various directions, and conse-
quently unsightly, if not unsafe. Enough has now been stated to shew that,
in heavy ground at least, the cheapest method of proceeding is not the best, or,
at all events, not the safest.

The cost of setting the centres and removing them forward was included in
the price of the brickwork, namely j64 : 10s. per rod. This work was performed
by a gang of men who devoted their whole time to it, and contracted with the
several bricklayers to do this part of their work : and thus, by constant prac-
tice they obtained a readiness in its execution.

The price paid by the bricklayers at first was £S per set, but this was sub-
sequently reduced to £2 : 10s. — ^the centre setters finding all necessary tools,
candles, &c.

The following will shew the total cost of a double set of centres, and the
requisite materials for one end of a shaft, the work proceeding as at Blechingley
tunnel.

2 leading or segment centres,

3 scarf ditto, . .
2 sets of lagans,

2 sets of keying ditto,

3 centre sills, and ironwork complete
8 half timbers,

14 props,
6 collars,
40 slack blocks.

Total Cost of Materials,

at £10 12 11 each

9 4 6
6 10

3 19

£87 18

FRAZERS PATENT CENTRES.

The preceding prices were paid at Blechingley, in 184L But subsequently
the duty on foreign timber has been greatly reduced, and therefore the same
materials at the present time, 1844, would not cost so much by a considemble
amount.

FRAZEE's PATENT CENTRES. PLATES 10 AND 11*

A set of Mr. Frazer's centres consists of three ribs, which are represented
as in use, in plates 10 and II . In fig, I plate 10, which is a transverse
s^ection of Saltwood tunnel, they appear^ as viewed from the face of an ad-
vanced or leading length, when such length is completely excavated, and
timbered ready for the bricklayers to commence the construction of the invert.
The centres are in the position they held when the arch of the last length of
brickwork was turned, and therefore they appear to be supporting the said
arch. Fig, 2 is a longitudinal section of a portion of the tunnel, shewing the
same state of the work, and consequently at a time when the centres are at
rest, waiting to be advanced onward as soon as the invert, of the next length,
and the side walls thereof, up to the height of the springing of the arch, are
constructed. Fig 1, plate 11, is also a longitudinal section, shewing the in-
vert» and side walls ; and the centres advanced, and adjusted to their places,
ready for the bricklayers to commence upon the arch.

The three ribs are distinguished in the following description by the letters a
B and c ; A being the leading rib, b the middle rib, and c the back rib. Each
rib is constructed of elm timber, 4| inches in thickness, and 16 inches wide ;
and consists of four pieces scaifed together, as shewn in figures 1 and 4, plate
10, In the ordinary construction of centres, the ribs when the laggms are upon
them are all of one size, and of the same span and rise as the under side (or
soflSt) of the intended arch ; but in Mr, Frasser's centres all the three ribs differ
from each other in dimensions of their radii, and the middle rib is the only one
that acts in the same way as centres of ordinary character, namely, ha>ing the
laggins and the arch immediately resting upon the rib, and consequently, with
the laggins, is of the same dimensions as the arch (in the clear). The leading
rib is larger, and the back rib smafinr, than the said dimensions. Each rib wiU
now be described separately.

164 PRACTICAL TUNMELUNO.

The leading rib ▲ is 12^ inches larger radius to its outer edge than the
under side of the arch, and 3^ inches less radius to its inner edge; both
edges are covered with half-inch iron plate, bolted quite through the rib, ae^
fig. 4, where the plates are shewn at a a, and the bolts at 6 6 &c ; the platQ on
the under side is 6 inches wide, and is placed to project 2 inches over one side
of the wood, forming a flange for the laggins ( which are 3 inches thick) to
rest upon, as shewn in section, figs. 2 and 5 ; the former, being a longitudinal
section taken along the centre of the tunnel, shews the keying^n laggins, rest-
ing upon the flange, and the latter shews the long laggins so resting, wherein a
is the rib, d the iron plate projectmg over the rib, inwards, upon which projec-
tion the laggms, e, rest.

When the laggins are in their places their upper surface forms the core or
bed upon which the arch is to be constructed. The leading rib when set, must
be its whole thickness in advance of the end of the intended length of Imck*
work, and therefinre it will stand in front of, or, cover 12^ inches of the toothing
end of the same ; this forms a convenient mould, to guide the toothings of the
work as they are brought up, the same being set out, and chocks of wood being
nailed thereon, compels the bricklayers to keep their work regular. The chocks
are shewn at c c c, &c., fig 4, which figure shews the inner face of the rib.

The ribs b and c rest upon and are fixed to a trestle o, on each side of the
tunnel ; but it will be seen figs. 1 and 4, plate 10, and fig. 2, plate 11, that the
leading rib, a, is supported by wedges or slack blocks, <f , upon the end of the
brickwork of the side walls e, which for this purpose is carried up nine inches
longer than the arch of the said length is intended to be. This, Mr. Frazer
states, was all the support that he ever found necessary, to carry the said rib
and its superincumbent weight ; but at Saltwood tunnel, where the grbimd
was heavy, and the bricks none of the best quality, the weight presdng upon
the said rib, occasionally broke off the end of the brickwork upon which it
r^ted ; in cases, however, where all circumstances are favourable, the plan of
resting the rib upon the end of the brickwork may perhaps be sufficient, but it
would certainly appear to be by no means a safe method of proceeding without
the support of the props f, which will next be described.

This prop is represented at f, figs. 1 & 2, plate 10, and at large figs. 2 & 3,
plate 11 ; the upper part of the two latter figures shews two views of the top
of the Bald prop supporting the rib a, and the lower part shews the manner in
which the prop is supported upon the invert, part of the skewback of the

FRAZEHS FATEMT CENTRES.

155

invert being cut away to receiye an iron block, g, for the square end of a cap-
stan-headed screw-bolt, /, to rest upon, the screw of the said bolt being the
means of tightening up the prop when set in its place under the rib ; die
ibot of the rib is held between two iron cheeks g #7, which are fastened to the
top of the prop by a bolt h and a collar t, figs. 2 & 3, plate 1 1, The end of the
upper slackblock passes between the iron cheeks, and appears at k^ figs. 2 & 3,
thus affording facilities for striking the same when the rib is to be eased ; the
under slackblock does not extend within the iron cheeks, but is cut off at about
the level of the brickwork, as at Z, fig. 2.

' Before the prop can be applied to the rib to assist the brickwork in carrying
it, the rib must first be set, and tightened up, or adjusted in its place, ready
for the reception of the laggins and the brickwork; such adjustment being
effected by driving or easing the slackblock or wedges^ because the prop
is in the way of any alteration of the smd wedges, after it is fixed and
tightened up to the heel of the rib, by the screw /*, at the bottom of the prop.

The middle rib, b, (and ako the back rib c) stands upon, and are perma*
nently fixed by brackets, and straps and bolts to the trestles d, as shewn at figs.
6 and 7, plate 10, and moves forward with it upon the rollers fli,fig8p 1 2, plat«
10, and 1, plate 11 ; the under side of the middle rib is covered with half^inch
plate iron in one piece, bolted through, as shewn in fig. 7, plate 10, which gives
strength to the arched rib, in the same manner as the struts* &c. apply in
centres of the ordinary^ construction. The bolt and nut are shewn at large fig,
9. The laggins e e^ &c. rest flat upon the upper edge of the middle rib, and
therefore the radius of this rib must be the same as of the arch, all but three
inches (the thickness of the intervening laggins,) and, as before observed,
it m the only rib of the three that carries its load like the centres of the
common kind.

The back rib c, is also strengthened with a covering of half-inch iron in one
piece on its under side, bolted through like the middle rib, with this difference,
that patent screws, fig, 12, are substituted for everj^ alternate bolt, as they^
are cheaper than the bolts ■ between each bolt, and screw, a hole is made
quite through the rib, to receive the stem of a bearing iron, n, n, &c, fig. 6,
and at large, fig, 10; and there are as many bearing irons as there are to
be laggins. It will be seen, fig, 6, that the laggins do not rest upon the back
rib itself, but upon the bearing irons, which project from the timber, or upper
edge of die rib ; the amount of projection being regulated as may be required

156 FRACTICAL TUNNELUNO.

to press the laggins to their proper level, by means of adjusting screws, a o &c,
which are tapped into the half-inch iron plate, and act upon the stems of Urn
bearing irons; and, conversely, the reversing of the said screws, lower the
bearing irons, and ease the laggins from under the brickwork, one by one, to be
removed forward.

As before stated, the ribs, b and c, are permanently fixed at their footings to
the trestles d ; they are also steadied at their crown by the irons, h h', as
shewn fig. 2, plate 10, and fig. 1, plate 11. The»e irons are moveable at one end,
which, forming a hook, drops into an eye screwed into the side of the rib;
the bricklayer, by imhooking either of the irons can put them out of their
way, when the work advances towards the crown of the arch ; each iron, how-
ever, can only be unhooked at one end, the other end being permanently
fiB^tened by the eye to the other rib, so that when unhooked by the workmen,
they hang down, as shewn at h', fig 2, plate 10. If they were not so attached
to the ribs they would very soon be mislaid and lost.

The trestles d, with their load, move upon rollers, m, and half-timbers, i i,
figs. 1 and 2, plate 10, and fig. 1, plate 11, laid longitudinally, as a kind of tram-
way for the rollers to run upon : the half-timbers are held in their places on
the skewback of the invert, by bricks or blocks let therein for that purpose.

Setting and Shifting the Centres. — In setting these centres for the turn-
ing of the arch, the leading rib must first be set in its place, and wedged
up, on the end of the brickwork, e, until it is at the correct level ; the prop, f,
is then to be placed, and screwed up tight under the heel of the centre, which
will readily be understood by those who have attended to the previous descrip-
tion ; next, the trestles d are rolled forwards until the ribs b and c are advanced
to their proper places ; when this is done, three pair of wedges and blocks, k k
K, are placed between each trestle and the half timbers, and by their use the
trestles are lifted up, until the top of the middle rib is upon a level with the iron
flange of the rib a, thus forming two level bearings for the laggins ; next, the
bearing irons of the rib c must be pressed outwards, by the adjusting screws
0, until the top of each of them is also upon the same level ; so that when the
laggins are placed one by one upon the three ribs, they will bed solidly upon
them all ; the adjustment of the bearing irons or of the three ribs may be
tested by passing a laggin over each of the irons and the other two ribs in
succession, for the first length of the brickwork ; but in all succeeding work

sinrrNG centres*

1S7

iheir adjustment is regulated by the brickwork last completed, as will be
shewn presently. The three bearings of each laggin^ when the ribs are
adjusted for the intended arch, is as follows: — 1st, upon the iron flange of the
leading rib^ 2ndly upon the middle rib itself j and 3rdly upon the bearing irons
of the back rib ; when this is all made correct, the centres will be ready for the
bricklayers to turn the arch, and by whom the laggina are laid on one by one
as the work advances.

When the arch is completed the miners again take to the work, and excavate
and timber another length, as shewn fig, 2, plate 10 ; as soon as this is done the
bricklayers re-enter and construct the invert and side walls to the springing
height; the centres have then to be advanced for turning the arch. Fig, 1
plate 1 1 shews this stage of the work ; the side walls are represented m up,
and the centres in their places ; four laggings are also shewn as drawn
forward, and the work of the arch commenced. The detail of the method of
moving forward the centres now remains to be given,

*. First a rib, called a jack rib, l, is fixed under the laggins^ in the rear of the
back rib c, fig, 2, plate 10 ; this jack rib consists of an iron plate, 1 inch in
thickness, and about 2| inches wide, which is bent into the form of the arch of
the tunnel. Fig, 8, plate lOj shews a portion of the jack rib upon a larger
scale, wherein it ^ill be seen that, opposite to every alternate joint of the
laggins, a screw is tapped into and passes through the rib ; which screws have
their outer end finished as a loop, whereby they may be turned with a lever ;
their inner ends are finished with a square head driven on to the end of the
screw, and are similar in appearance to the ends of the bearing irons of the
back rib c before described, but not so stout^ neither do they revolve, as the
screw is turned round.

The screws being placed opposite every alternate joint of the laggins, it is
clear that only half the number of screws that there are laggins, are required,
as each screw presses against two of them at a time, and exerts quite sufficient
force to retain the laggins in their places when the ribs b and c arc removed
fit>m under them ; and which is all that is required of the jack rib. ITiis
arrangement is fully shewn at fig. 8, r r, &c, , are the screws passing through
the iron plate, s that forms the rib, the square end of each screw pressing two
laggins, e e, &c,, at their joints, against the brickwork of the arch m, The jack
rib terminates with a screw, o, which works in sockets, as shewn in the figure^
and its extremity rests upon an iron bar, n, about two feet long and four

158 VRAtriCAh TUNNELLING.

inches wide, driven temporarily into the brickwork, for the purpose of car-
rying the rib. J

The jack rib will be understood to be only a flat iron arch, springing fironi
the iron support, n, on each side ; and its use is simply to support the batk
ends of the laggins by means of its screws, r r &c., when the trestles d, mth
tiiie two ribs b and c, are removed firom under them by lowering of the wedges
K. The other ends of the laggins are, at the same time supported by the
leading rib a, independently of the tresdes, and therefore, under such circtmi-
stances, the laggins will continue undisturbed. They would, however, no
longer be of use in preventing the arch above them from giving way, if it
should be subjected to extraordinary pressure before the cement is well
hardened ; the leading rib being the only part of the centering that would
afibrd assistance in such a case. The use of the screw o fig. 8, itf for the
adjustment of the jack rib to its required elevation under the arch, or the
laggins.

As soon as the jack rib is fixed, and its screws r r &c. adjusted, to take the
ends of the lag^^s or press them against the brickwork, of the arch ; the iron
bar H' is unhooked, and left to hang down, as shewn at fig. 2 plate 10, and the
wedges k, k^ &c. are eased, whereby the tresdes are lowered, and their roUers
mm^ rest upon the wooden tramway laid for their reception; which tramway
being then continued in the direction that the work is proceeding, the tresdes
are roUed onwards ; and with them, of course, the middle and back ribs b and
c, which are thus advanced to their proper position for the turning of a new
length of the arch. When the ribs b and c are lowered as above described,
the middle rib, b, easily passes under the leading rib a, which would yet remain
in its place, under the toothing end of the last-turned arch.

It will be remembered, that the leading rib, a, was described as placed in
front of the brickwork of the arch, its iron plate carrying the ends of the lag-
gins ; this arrangement, which is shewn in section at figs. 2 and 5, plate 10, is
contrived in order to keep as much clear headway as possible, for the passing of
the middle rib under it, when that rib is advanced, with the tresdes, to the
next forward length.

The tresdes, with the ribs, are moved forwards until the back rib, c, nearly
abuts against the rear edge of the leading rib, a, or, more particularly, it is
moved till it is within six inches of the ends of the laggins, when they are again
wedged up to a proper levd, as before ; the bearing irons of the back rib c, are

SETTING CENTRES.

159

then pressed, by their screws, home to the laggina of the arch^ which afford
them^ and the superincumbent brickwork^ the same support at that end that
had hitherto been obtained from the leading rib a ; whereupon the said leading
rib may be relei^ed, by easing the wedges rf, at its springing, and moved
onwards by passing it over the rib b ; it is then to be fixed as before, on the
end of the brickwork of the newly-constructed side walls, and adjusted, toge^
ther with the rib b, to their proper level, which may be proved by ascertaining
that the laggins of the arch already completed, if produced^ would fit on the
ribs A, B, in the same straight line. The props f, &c. must then be again
fixed on each side, to support the heels of the rib a.

When the centres are set, and adjusted to their proper level, as above des^
cribed, they are ready to receive the brickwork of the arcli ; for wliich purpose,
the same set of laggins are again used, they being drawn forwards from their
last place, one or two at a time, as they are wanted, beginning at the springing.
One of the screws, of the jack rib, and the corresponding screw or bearing iron
of the back rib c, are eased, which releases the laggins against which they
pressed, and admits of their being drawn forward to their places on the ad-
vanced centres ; the screw of the bearing iron of the back rib is then again
tightened, which presses the rear end of the laggin tight against the arch,
or under the tootliing end of the last-turned length. The three bearings of
each laggin, as it is so advanced and placed, will be as in the former case,
(If the centres are correctly adjusted in position) on the iron flange of the
leading rib a, o/i the middle rib itself] and oti the bearing irons of the back
rib. Upon the laggins as they arc thus drawn forwards, the bricklayers
construct the arch.

From the account above given, it wiU be obvious that (in using these centres)
flo soon as the arch of one length is completed, it remains supported by its
centres and laggins, until another length is prepared by the miners, and the
invert and side walls thereof are built ; whereupon the two centres b and c, are
removed from under the said arch, leaving its toothing end only, supported ;
for the jack rib does nothing more than keep the laggins from falling down.
The back rib c, is next brought under the toothing end, and its bearing irons
screwed up tight to the laggins, which enables the leading rib a, to be released*
and carried forwards ; so that, from the time that the side walls of a second
length are constructed, the last turned arch receives no support, except under
its toothing ends.

160

PRACTICAL TUNNELLING.

The following table shews the total cost of a complete set of Frazer's patent
oentres and the necessary materials for one end of a shaft, as used at Saltwood
tunnel.

Leading rib»

Middle rib»

Back rib.

Jack rib,

Irons for ribs,

2 props for leading ribs, . £13 2 eadi

2 trostles, . . 8 18 10 each

I set of laggins,— eame as at Blechinglej

1 set of keying-in ditto— ditto

Total Cost of Materials,

■.

9 11

17 17

6 10

£60 15

COMPARISON.

A double set of Blechingley centres, with all the necessary materials to be
used, as already described, cost, as stated at page 152, the sum of £87 : 18: Id.
If a single set be employed, as they might be with safety, where the ground is
light, (and which is the plan frequently followed by contractors), the cost
would be £50 : 6 : lid. ; which exceeds half of the above sum, because more
than one-half of that quantity of materials would be required.

The cost of a corresponding set of the patent centres would be, as shewn
aboTe, £60: 15: lOd. (the prices of the materials being taken alike in both
estimates, for the sake of correct comparison). The patent centres would
therefore be less costly than a double set of ordinary centres, by £27 : 2 : 3d.,
and more costly than a single set, by £10: 8: lid.

It may also be considered, that, when the work is completed, and the centres
laid aside, the sills, hal£>timbers, and props, used with the ordinary centres,
would be worth more money, as timber, than the pieces forming the trestles,
&C. of the patent ooitres; because they would be less cut up into small pieces.
Tlie former, indeed, would be nearly as YaluaUe as whoi first put into use for

C0MPABT80N.

161

those purposes, if proper care had been taken of them. The real deduction
from their original Taluo would be the usual charge for use and waste.

^Vhere the ground is heavy, the use of a single set of materials of the
ordinary construction^ has been explained, in the preceding pages^ as being an
unsound mode of proceeding ; but this Is by no means the case when the
ground is light ; for then one set of centres will be sufficient

The patent centres, when used in hea^v^' ground, do not afford anything hke
the support to the brickwork, that is derived from the use of a double set of
those of the ordinary construction. This opinion would be arrived at by the
perusal of the preceding pages, and is in accordance with the author *s ex-
perience, and obsen-^ation of their use, at Saltwood tunnel.

For ground that is light, the patent centres are well adapted^ and even when
the ground is moderately hea^y they may be advantageously employed, for they
afford more security to the work than a single set of the ordinary materials,
although they faU much short, in that particular of a double set.

The great advantages the patent centres appear to possess over centres of the
ordinary construction, is in the total absence of queen posts^ and struts, &c.,
(which form the framework of the lEist-named centres), they therefore leave a
large open space for the scaffolding and materials of the bricklayers, who can
get at their work with greater facihty, by having so much more room tlian is
afforded by the ordinary centres. Another advantage, and which in tunnel-
ling through rock, where much blasting is necessary, is great, — namely, that
the debiis from the explosion is less likely to disturb or injure these centres ;
whereas, with the other kind of centres, it is likely to do much mischief, and
occasion considerable outlay in repairs.

Independently of the difference in the first cost of the two kinds of centres,
it does not appear to the author that any money is saved in the subsequent
use of the patent centres ; both kinds being equal in this respect.

Although it would appear^ from the above statement^ that a set of the patent
centres, and necessary materials, are rather more expensive, in their first cost,
than a single set of centres and materials of the ordinary construction^ yet there
can be no doubt that they are greatly superior thereto, in their practical appli-
cation; for although one set of centres and materials will be sufficient for
tunnel works in light ground, yet there is no ground so perfectly homogeneous
in character throughout a hill, but in some parts, from faults, or local disturb-
ance of the beds, vn\l prove heavier than other portions of the same strata.

162 PRACTICAL TUNNELLING.

When this case occurs, and the pajtent centres are in use, no cause for alarm
need be apprehended, there being sufficient provision therein to withstand the
effects of moderately heavy ground. The difference of the original cost ought
therefore, not, to be considered, as compared with the greater security obtained
by the use of them.

It must, however, be understood that the author's strong recommendation of
Mr. Frazer's centres is limited to light or moderately heavy ground; for where
the earth is very heavy, the use of a double set of i;aaterials of the ordinary
construction is greatly superior thereto. Under such circumstances, the extra
cost in the original outlay would be nothing, in comparison with the superior
advantages to the security of the work during its construction. In short, those
who have had experience in tunnelling in heavy ground would consider no
expense (within reasonable Umits) too great, to secure the work from such
casualties as it is liable to under those circumstances.

MISCELLANEOUS.

163

CHAPTER XV.

CAST-IRON SHAFT CUBES. CUTTING BRICKS. WEIGHT OF BKICKWOBK.

BHICKMAKI^'G CONTRACT* ETC.

When describing the brick curbs that connect the shafts with the soffit of
the arch of the tunnel, it was stated (at page 115) that the subject woidd be
again returned to, in order to describe the curbs of cast iron. The reason
why those particulars were not inserted in that part of the work, was on
account of an unavoidable delay in the preparation of the engraving, and it
was deemed unad\isable to delay the printing untU that was done, as there
would remain the present opportunity to supply the omission.

Curbs of cast iron were used by Mr.Stephenson, in the tunnels on the London
and Birmingham Railway, and the engraving, plate 12, represents them in
detail.

Fig. 1, is a plan of the curb, as it is fixed ready for the support of the shaft.
It is made in four segments, which are fitted and bolted together at a, 6, c, d.
The clear diameter of the cbrcular area, formed by the curb, is the same as that
of the shafts, nine feet ; and the top of the curb is a level surface (or flat ring)
1 foot 3 inches wide, and upon this the brickwork of the shaft rests. The
dotted circular line shews the junction of the curb with the brickwork, as it
appears from below, and corresponds with the point e in each of the other figures.

The brickwork of the shaft is built flush with the inner edge of the curb.

Fig. 2, is a section taken through the curb, upon the line a, b, of the plan,
or at right angles to the direction of the tunnel. (This section corresponds
with that of the brick curb, shewn at fig* 2, plate 5.) The under side of the
figure represents the soffit of the arch, and the line ef is the skewback sup-
ported by the brickwork of the tunnel, e. The line e f is, in this part of the
curb, at its greatest obliquity, or makes its greatest angle with a vertical line ;
from thence its obliquity gradually diminishes (each way) throughout a quarter
of a circle, or, to the crown of the arch ia the direction of the tunnel, where
the line ef becomes pei-pendicular.

164 PRACTICAL TUNNELLING.

Fig. 3, is a section on the line c d, of the plan, and is at right angles to the
section in fig. 2. The line « /, in this figure, where it joins the brickwork of
the arch £, is, as above stated perpendicular. (This section corresponds with
that of the brick curb shewn at fig. 1, plate 5.)

Fig. 4, is a back view of the curb, looking at it in the direction a b, and
shews the manner in which it is formed to abut against the courses of the
brickwork of the arch.

Fig. 5, is also a similar back view, but taken in the direction c o, or at right
angles to the last figure.

The curb is cast with chambers, in order to combine lightness with the re-
quisite strength.

A plan of the brick curb is given at fig. 3, plate 5, and by comparison of the
two sections in that plate, with the engraving, plate 12, together with what has
been stated upon the subject, there can be no difficulty in comprehending the
whole of its details.

CUTTING OF BRICKS.

In several parts of the preceding pages, it has been stated that when wedge-
formed bricks were required for particular purposes, as for the skewback of
the tunnel invert, they were either moulded to the required shape, or the com-
mon bricks were cut for that purpose ; when the latter plan was adopted, they
were cut in the following manner, which saved a deal of time as well as waste
of the material. A number of them was placed in a box (which was pur-
posely contrived) and then wedged, or screwed up tight ; they were then cut
with a stone-mason's saw, working through a saw kirf in the opposite sides of
the box, at the required angle, in a similar manner that a joiner cuts the
mitres of his mouldings. This method answered very well, and had been pre-
viously used by the author, for cutting bricks to the proper angle for the face
of oblique arches.

MISCELLANEOUS. 165

WEIGHT OF BRICKWORK.

An experiment was tried, on September 3d, 1842, to determine the weight
of a cubic yard of brickwork. On the works at Saltwood there was an excel-
lent weighing-machine, by Pooley and Son, upon which the experiments were
tried.

BRICKWORK IN CEMENT.

Ton cwt. qn. Ibi.
A cubic yard of dry bricks . . (384) = 1 2 1 20
Sand, water, and cement for ditto ... 0624

Total weight of a cubic yard of brickwork in cement =1 8 3 24
BRICKWORK IN MORTAR.

Ton cwt. qn. Ibt.
Bricks, . as above • • . 1 2 1 20

Mortar for ditto ..*.... 0418

Total weight of one cubic yard of brickwork in mortar = 16 3

BRICKMAKING CONTRACT.

The following is a copy of an agreement made with one of the contractors
for the brickmaking at Blechingley : —

Memorandum of an agreement made this I9th day of March, 1841, between
William Chaplin, brickmaker, of the one part, and Frederick Walter Simms,
on behalf of the South-Eastem Railway Company, of the other part. The
said William Chaplin agrees to dig, make, bum, and deliver, as many bricks
as the said Frederick Walter Simms, or other the Resident Engineer to the
said Railway Company shall require, without intermission, at or near to the

166

PRACfTlCAL TUIiNELLlNG,

proposed Blechingley Timnel^ on the line of the said Railway, and upon such
land or lands as the said Frederick Walter Simms may require, and to find at
his own expense aU labour, tools, utensils, horses, and every material except
coals, that may be required in and for the production of kiln-burnt bricks,
of the best quality, and also to buUd and maintain in repair all necessary kilns
for the burning of the said bricks, he finding all labour and materials for
that purpose, with the exception of bricks, which are to be found or provided
by the said Company, — ^for and in consideration of the sum of fourteen shillings
per thousand, for all bricks which he may deliver from the kilns ; and the said
Frederick Walter Simms, agrees, on the part of the said South-Eastem Railway
Company, to pay to the said William Chaplin the sum of fourteen shillings per
thousand, for so many bricks delivered from the kilns as the said Frederick
Walter Simms may require ; the said South-Eastem Railway Company to find
coals, and to pay the duty only, and to allow the said William Chaplin the use
of such soft bricks as may be required to build the kilns and maintain them in
repair, and to sink a well if required. And it is hereby further agreed, that no
payment shall be made to or required by the said William Chaplin, on account
of any work in progress, or bricks in the course of making ; but that he shall be
paid only for such bricks as shall have been pre\dously delivered to the said
Frederick Walter Simms, as above specified. And it is also ftirther agreed^
that the bricks shall be of the best possible quality, and of the largest dimen-
sions allowed by act of parliament ; and that if the said William Chaplin and
the said Frederick Walter Simms shall disagree upon any point regarding the
quality of the bricks, or the mode of carrying on the work, or upon any other
matter whatsoever, the question in dispute shall be referred to Williiim Cubitt,
esquire, or other the Engineer-in-chief to the said South-Eastem Railway Com-
pany for the time being, whose decision shall in aU cases be binding and con-
clusive ; and that, if the said Engineer-in-chicf should think proper to put an
end to this agreement, and determine the connexion between the said William
Chaplin and the said South-Eastern Railway Company, before that a sufficient
number of bricks shall have been made or provided for the said proposed
tunnel, whether made by the said William Chaplin, or otherwise, he shall be
at liberty to do so, upon the said Company taking the unfinished stock, and the
materials that may be upon the ground, at a fair valuation, unless the cause of
the said Engineer determining and ending of this agreement shall be or shall

BBlCKMAKmO.

161

have beeu. occQMoQ^d by neglect on the part of &e said Wiiliam Chaplin to
push forward the work enteuoited] to Im care with the utmost possible expedih
tioDL ; or ^ Y^ cball hii.ye executed any part or parte; of the said work in an
ii^ftcj^nt or UBLWorkmanlike manner; or from any other reasonable cajuse, —
then, and in such case, it shaU be at the option of &e Engineer whether or not
the said Company shall take to the said materials. In case of a valuation of the
mat^aU bec(»ning necessary, such valuation shall be made by two referees,
one to be appointed by the. said William Chaplia and the other by the said
Company, or by an umpire to be appointed by- sudi two. referees in case they
should disagzeie;' and in case o£ either of the parties n^^lecting to appoint a
referee within seven days after-being required in writing by the other of the
said parties so to do, then at a valuation to be made by the referee of the other
of the said parties alone, whose decision shall be binding and conclusive.
In witness, &c.

ESTIMATED COST OF HORSE-POWER EMPLOYED IN WORKING THE GINS
during^ the Shaft-sinkings and Water-drawings at Saltwood Tunnel 1842.

Expense of 67 horses, and attendants, in twenty-four hours.

2 quarters 1 bushel of beans.

•

38s« per quarter

2 quarters 1 bushel of oats,

•

25s. „

50 trusses of hay,

£5 : lOs. pel

'ton of 40 trusses

40 trusses of straw,

• •

8d, per truss

Shoeing^ each horse.

• •

per diem Id.

Farrier's expenses.

p^borse

.. 3d.

Stablingr,

per horse

„ 8d.

Harness and repairs.

per horse

.. 3d.

12 stablemen.

• .

„ 38. each

18 g^-boys.

• •

M Is :3d. each

18 ditto,

. per

night Is : 6d. each

2 13

1
1

16
2

£21

/yj^__^-^^/^

4...

Being at the rate of 6s : BiW. per diem for each horse.

168 PRACTICAL TUNNELLING.

They were supplied with as much food as they could eat, not only in the
stable but at every interval of rest during the time of working.

The average time made by each horse was I'll shifts per diem, which at 7s.
per shift, gave 7s : 9fod. as the earning of each horse. Leaving Is : 2|d. per
diem to cover contingencies arising from the death or depreciation in the value
of the cattle.

The above table will give a good approximation to the quantity of food con-
sumed by horses when working hard, and of the general expenses attending
that kind of work. The cost of the com and hay will of course vary from time
to time. When the works were executed, in which the horses above referred
to were employed, the price of grain, &c. was very high.

169

APPENDIX.

BLECHINGLET TUNNEL SICK FUND.

Where a large body of men are collected together, as upon the works of a
tunnel, there will be sure to arise considerable sickness among them, as
well as occasional accidents. To provide for, and defray, the expenses of the
necessary medical attendance, &c. it is the usual practice to raise a fund by
means of a small contribution from the weekly earning of every one employed
upon the work; and therefore a set of rules are necessary, to provide for its
proper distribution. The following are the rules and r^ulations of the
Sick Fund that was established at Blechingley Tunnel; which, upon the
whole, were found to answer very well ; Irat,'^ in th^^ course of time, two
additional rules were found requisite, and were accordingly added: these
are annexed below. Besides these, there appears to require an alteration in
the third rule, which enacts that ^ members jiball contribute alike, namely,
" sixpence per week." This would have been better if it had required each
man to pay a per centage on his earnings, as for instance, one iarthing, or
one hal^nny in the shilling, according to the requirement of the sick list.
Such an arrangei^ei^t would have been more equitable than the one adopted.

There should also have been a small fine attached to Hie non-attendance
of the Committee-men at the appointed time of meeting, as their want of
regularity in this respect gave additional trouble to the Treasurer, and to
the Clerk who kept the accounts of the ftmd.

Except what has now been stated, with the two additional rules before
named, nothing more appeared wanting to make the r^ulations complete ;
and with a view to their being usefrQ on any similar occasion, they are inserted
in this volume.

170 APPENDIX.

RULES AND BEOULATIONS.

1. This Fund it to be fonned by subscription of Workmen emplojed in the ooostractioo of
Bleching^ley Tunnel, or in connexion therewith, for their temporary relief in sickness and in case of
accidents, and for the payment of Medical assistance.

2. A Committee of Management shall be appointed by Mr. F.W. Simms, the Resident Engineer ;
to consist of five, who shall be Masters of workmen, or Contractors of works on the Tunnel, three of
whom shall be a quorum ; and who shall meet once a week at least, and shall have the management
of the Sick Fund, and regulate the proceedings under the superintendence of the said Mr.F. W,
Simms, who is constituted Treasurer of the Fund.

3. Every man now employed, or to be employed on the works of the Tunnel, shall pay sixpence
per week to the Treasurer ; except in case of his having had no more than diree dajrs* employment,
then he shall not be required to pay any subscription.

4. Every man must be on the books, and pay two weeks' subscriptions, before he will be entitled
to any benefit from the Fund, in the event of bodily sickness ; but he will immediately be entitled
to the benefit of the Fund, in the event of personal injury received while in the actual execution of
his work.

5. The allowance to sick members, from the Fund, shall be twelve shillings per week, exclusive
of Medical attendance, in manner following.

A sick member shall be entitled to receive the full allowance for six consecutive weeks ; then
if the sickness should continue, he shall be entitled to half-pay for the next following three
weeks, when his claim upon the Fund shall cease.

No member shall be entitled to benefit from the Fund, unless his illness or accident is certified
in writing by the Medical Attendant ; and if such illness or accident is, in the opinion of the
Medical Attendant, or can be proved to be, to the satisfaction of the Committee, occasioned
by intemperance, or any other immorality, such member shall forfeit all claim to relief in
respect of such illness.

Any member receiving personal injury in the regular course of his employment upon the works
of the Tunnel, or in connexion therewith, so as to incapacitate him from attending thereto,
such member shall be entitled to full allowance for a period of six weeks ; and then if he is
unable from the above cause, to return to his work, such member shall be entitled to half-
allowance for a second period of six weeks if his case requires it, when his claim upon the
Fund shall cease.

Any member receiving an injury, and being removed to an Hospital, shall, while being an in-
patient, receive an allowance of three shillings per week, to pay Hospital fees, &c. : but such
allowance shall not exceed twelve weeks. But if he should be an out-patient, and has no
otiier maintenance, he shall receive pay as before mentioned for members receiving personal
injuries.

The Committee, with the consent of Mr. Simms, shall have power to alter the foregoing limita-
tions of allowance in any particular case, when circumstances appear to them to require a
departure from the general rule.

APPENDIX.

171

6p Iq the event of a member dying, hU representatireA^ or those entrusted with his funeml, slmll
be entitled to receive the full amount that such deceased member shall have subscribed to the Fund
(exclusive of the sums such member may have received during his illness) in aid towards defraying
the expenses of his funeral. Any member leaving his employment, or being discharged, shall have
no claim upon the Fund,

7» The Committee shall have power to increase or diminish the subscript ions of the members,

and of reducing the Sick Pay, according to the state of the fundsi and the claims thereupon : and

shall also make and determine all contracts with the Medical Man for attendance and medicines^

All proceedings and determinations of the Committee relative to the management of this Fund

must be reported to Mr* Simms, the Treaaurer, and conhnned by hira, before they can be

acted upon ; and when so confirmed shall be finaL

The Cummittae shall prepare, for the information of the members, a Balance Sheet of the state

of the affairs of the Fund once a mouthy or oftener if they shall be so directed by the Treasurer,

8. If at the expiration of the works on the Tunnel, or when it may be considered expedient to
discontinue this Fund, there should be any funds left in hand, such funds shall be paid for the
beueHt of the widows and orphans of men who may have lost their life by accident on the works;
and those who by accident may have been incapacitated from earning their own living : or otherwise
to be given to whatever Hospital or Dispensary for the relief of the sick Poor that the Committee^
with the consent of Mr^ SimmSj may think proper,

9. Every Master Workman, Foreman, or Ganger* must give a list of the names of the men
employed by or under him, at the Tunnel OSBcCr every Thursday evening by six o* clock, or in
default thereof forfeit one shilling for the first hour, and sixpence for the second and every subse-
quent hour that elapses after the above time before he so delivers his list, which forfeit is to be the
property of the clerk who may have been kept waiting at the office to receive the said list.

Additional Regulations made subsequently to the above.

Any sick member found drinking in a public house shall thenceforward forfeit all claim upon the
sick fund, in respect of that illness,

Upon its being ascertained that any member has been, and continues to be, subject to any sick-
ness periodically, or otherwise, the Committee to have power, at their discretion, to return to such
memljer the full amount he may have subscribed to the Fund, during the time of his membership,
and to declare him to be a member no longer^

172 APPENDIX.

HIGHGATE TUNNEL.

It will probably be in the recollection of many persons living, that, early in
the present century, an attempt was made to construct a tunnel through the
London Clay at Highgate Hill, for the purpose of making a more easy commu-
nication between HoUoway and Rnchley. The attempt, however, failed ; and
the result was the construction of the open cutting, which forms the present
Highgate Archway road. The failure appears to have arisen in a great measure
from the want of experience on the part of the Engineers who had charge of
the work, more especially as they had such very difficult and heavy ground to
work in as the London Clay. Those who have witnessed the trouble and diffi-
culty that has been recently experienced in working in that treacherous soil
will be less surprised at a failure in such a work thirty years ago.

Li the year 1811, while the works at Highgate were progressing, the Com-
mittee of Management thought it necessary to obtain the opinion of the late
John Rennie, Esq., as to the correctness of their mode of proceeding, as difficul-
ties began to appear. That truly eminent Engineer examined and reported upon
the works, which report the author has much pleasure in communicating, not
only because it will throw some light upon the probable cause of the failure of
the work ; but also it will dispel the erroneous opinion that too generally pre-
vails, namely, that Mr. Rennie was the Engineer to the said work ; whereas the
fact was otherwise. The author believes that Mr. Nash, the Architect, was the
principal, and a Mr. Vazie, the resident Engineer. It may at the present day
be a matter of surprise that an Architect should undertake the construction of
a tunnel ; but so late as August 17th, 1812, there appeared in the Star, a Lon-
don newspaper, an advertisement from the Regent's Canal Company, addressed
to " Architects and Engineers," offering a premium of fifty guineas for the best
design for a timnel that was to be made (and afterwards was made) imder the
town of Islington ; in which advertisement it was stated that the Company
were " anxious to have the best information which science and practice can
afford on the subject."

APPENDIX. 173

MR. RENNIE'iS REPORT.

London, Dec. 27th, 181 1.
Gentlemen,

I examined the Archway at Highgate on Saturday last, and it appears
to me there are several parts of the Work which may be altered with much advantage to render the
stability more certain, and the works more perfect than they will be if the present mode of execution
is adhered to.

First. On examining the arch already finished, thete are two places in which a weakness
appears: first, in the upper part of the arch, between the top and side; and in the inverted arch,
about three feet from the junction with the side arch.

Second. The manner in which the bricks are laid, and the bonding of the work together.

Third. The dimensions of the cast-iron skewplate.

Fourth. The mode of proceeding to the south, in the progress of the work.

Lastly. The kind of mortar which ought to be used in the brickwork.

As to the first.— It is quite clear to me that, owing to the swelling of the clay, the whole of the
ellipsis is very much compressed ; but the upper part, being more curved, is better able to resist
that great pressure than any of the other parts ; and, therefore, the clay that rests thereon being
unable to push it down, slips off a little on each side, and the flat part between the top and sides
is thereby charged with this additional load, and yields a little. To prevent this, I advise that in
forming the centre this part should be curved about an inch and a half more in proportion than the
rest, so that when compressed by the incumbent weight it will come to the form I have drawn it.

In like manner the inverted arch yields, within three or four feet of the iron skewplate. This part
should also be increased in its curvation about two inches or two inches and a half, when first built,
so that by the compression it will come to what I have drawn it. The inverted arch need not be
more than eighteen inches thick in the middle, but it should gradually increase to two-and-half
bricks as it approaches the skewplates, and continue so to the said plates.

The manner in which the bricks are laid in the arch is by no means calculated to produce the
greatest strength ; for, as the radius of curvature increases the width of the brickwork at the out-
side, unless the bricks were radiated they would not bend in the extrados and intrados equally to
resist the pressure : the length of the extrados towards the top of the arch is greater than the
intrados, by about three inches on every two feet ; so much thicker will therefore be the mortar-
joints ; and mortar, being more compressible than the bricks, when green will yield in proportion.
The arch should, therefore, be laid in single rows throughout the whole thickness, until the length
in the extrados (or outside) admits of one brick in thickness being inserted there ; at which
place or places the bricks should be laid lengthways, to bind the different rings together ; and so
continuing round the whole. By this mode the arch will be equally solid throughout, and the im-
mense pressure which is now exerted on the intrados (or inside), so as to flush the bricks, will
thereby be avoided : and very great care should be taken in making the whole brickwork solid,
with as thin joints as it is possible, to make them lie fair in each other.

174 APPENDIX,

Third. The cast-iron skewplates should be made the whole breadth of the joint between the
inverted and side arch. This was so represented, in stone, in the section I made.

Fourth. It would not be advisable to proceed southward with the present arch until the water
has been thoroughly drained off. For this purpose, two new pits should be sunk ; and the work
carried on from these to a junction with the present work.

Lastly. For nine inches from the extrados (or outside) the cement should be all Roman cement,
of the best quality : — from thence to the intrados it should be one part of Roman cement to one of
lime, with the proportion of sand. Perhaps Mr, Charles Wyatt, the maker of Roman cement, may
know better than me how much lime and sand the Roman cement will bear, as I have not been
accustomed to use it mixed.

The extrados, or back of the arch, should have a good coat of Roman cement over it, to prevent
the penetration of the water, and between the arch and what is cut out, clay should be rammed as
hard as possible, so as to make the action as nearly equal as can be.

In addition to the queries which I understand were put distinctly to me by the Committee, I

must beg leave to remark, that when I gave the thickness of the brickwork in my section, it was

expressly understood that that was the least thickness which ought to be given on the supposition

that the clay was perfectly firm and hard where such arch was to be made, but whenever the clay is

deficient, and does not answer the description, an additional thickness was to be given, and this at

the discretion of the Superintendent, as the nature of the clay should appear — some places will

require to be made 2% bricks, some 3, others 3^, and perhaps some may even require 4 bricks.

This, however, can only be ascertained by careful examination ; and the Superintendent should be

attentive, and decide with judgment ; on which decision the success of the work will in a great

measure depend.

I am.

Gentlemen,

Your most humble Servant,

JOHN RENNIE,
To the Committee of Management

of the Higfagate Archway.

THE END,

W. TirrBll, PRIIfTBB, HTTHB.

Lontfitiniinal Si'ttiorts.

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