LM en | eerie Lc RA_ ere a ay Ar @ 4! Coast. Ens, Kes MR 76-4 (AD- A022 337) Simplified Design Methods of Treated Timber Structures for Shore, Beach, and Marina Construction by — James Ayers and Ralph Stokes MISCELLANEOUS REPORT NO. 76-4 MARCH 1976 DOCUMENT |} COLLECTION / Approved for public release; distribution unlimited. Prepared for ah U.S. ARMY, CORPS OF ENGINEERS COASTAL ENGINEERING RESEARCH CENTER Kingman Building + | Fort Belvoir, Va. 22060 Reprint or republication of any of this material shall give appropriate credit to the U.S. Army Coastal Engineering Research Center. Limited free distribution within the United States of single copies of this publication has been made by this Center. Additional copies are available from: National Technical Information Service ATTN: Operations Division 5285 Port Royal Road Springfield, Virginia 22151 Contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. The findings in this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. IM ii Mon NO UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) PAS READ INSTRUCTIONS REPORT DOCUMENTATION PAGE BEFORE COMPLETING FORM 1. REPORT NUMBER A 2. GOVT ACCESSION NO.| 3. RECIPIENT'S CATALOG NUMBER 4. TITLE (and Subtitle) 5. TYPE OF REPORT & PERIOD COVERED SIMPLIFIED DESIGN METHODS OF TREATED TIMBER STRUCTURES FOR SHORE, BEACH, AND MARINA CONSTRUCTION 7. AUTHOR(s) 8. CONTRACT OR GRANT NUMBER(s, PERFORMING ORG. REPORT NUMBER James Ayers Ralph Stokes #9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK i! i AREA & WORK UNIT NUMBERS American Wood Preservers Institute 1651 Old Meadow Road McLean, Virginia 22101 F31234 11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE Department of the Army March 1976 Coastal Engineering Research Center (CEREN-DE) 13. NUMBER OF PAGES } Kingman Building, Fort Belvoir, Virginia 22060 39 14. MONITORING AGENCY NAME & ADDRESS(if different from Controlling Office) 15. SECURITY CLASS. (of this report) UNCLASSIFIED 15a, DECLASSIFICATION/ DOWNGRADING SCHEDULE Approved for public release; distribution unlimited. 16. DISTRIBUTION STATEMENT (of this Report) 17. DISTRIBUTION STATEMENT (of the abstract entered in Block 20, if different from Report) 18. SUPPLEMENTARY NOTES 119. KEY WORDS (Continue on reverse side if necessary and identify by block number) Design methods Shore protection structures Piers Marine construction Bulkheads Seawalls Pressure-treated timber Groins 120. ABSTRACT (Continue on reverse side if necesaary and identify by block number) Pressure-treated timber has wide application in the waterfront and shore protection structures that are built in marina developments and cther shore l and beach locations bordering on bays, lakes, and river resorts. Because of its strength, durability, and economy, pressure-treated timber is the principal construction material for bulkheads, seawalls, piers, and groins at locations with mild exposure and shallow-to-intermediate water depths. DD 1 en, 1473 Ecortion oF tT Nov6S Is OBSOLETE UNCLASSIFIED i SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered) PREFACE This report is published to provide coastal engineers with simplified technical guidelines on the proper use of treated timber in coastal struc- tures. This study is published under the coastal construction research program of the U.S. Army Coastal Engineering Research Center (CERC). The report was originally prepared in October 1969 by James Ayers and Ralph Stokes for the American Wood Preservers Institute (AWPI), McLean, Virginia. CERC was instrumental in identifying the need for this data and encouraged the AWPI to develop the study. In 1970, AWPI published a condensed version of this report in their Technical Guidelines Series titled, Bulkheads: Destgn and Construction. CERC is publishing the complete manuscript to achieve a wider distribution of these data which are not readily available in other engineering publications. Permission by the AWPI to publish this report is greatly appreciated. This report is published, with only minor editing, as prepared by the authors; results and conclusions are those of the authors and are not necessarily accepted by CERC or the Corps of Engineers. Comments on this publication are invited. Approved for publication in accordance with Public Law 166, 79th Congress, approved 31 July 1945, as supplemented by Public Law 172, 88th Congress, approved 7 November 1963. JAMES L. TR Colonel, Corps of Engineers Commander and Director CONTENTS Page EEN THRO DU CALON tse cumcy ress tenon terer ew actin tau tia Reales y( eS f pspb serge Suvcy aompesuesehy elaborate gee bee mlD. II TIMBER BULKHEADS . ae POM Tee nS BCE Pe oa one 1. Typical Timber Bulkheads Honea whens IRR em ensaboe Gg Na Gun de Ee) 2. Construction Procedures . Romer ets Wor we Pata ee omer ae © San) CSUOTRS ECD Samoa acca so aren tilee ay. ars \ivcie tral. i Uh Svea ne Miia name PE VERT ICALSFACEDSSEAWALLS (OF TREATED! TIMBER) 2) 4 4 4) ee ee 20 1. Design of Timber Seawalls .... Spy eamcdittois Meus Fe. neetic PN el pee oO 2. Treated Timber in Concrete Seawalls Seeiiaria Nairn olindiat ndineyeR clot chy OS IVE SGN ORSGROUNS Se cae hee cee Cee att Me ees ss bt tem eRe ae A Rat NT My eLyPeSiva a0 =: Shier ferndes acigs) ye ESF E SRPEE CRMC tan GeRCL atc tema ROO 2. Location on Shore OL Aree ee cee ae Ta ticct tay at Soman ee) ton else MeN NANgE OO) Se MDUMECTSVONS ec. pemaicwace dl vcviyelaen Ee RAL PLR Roa sPirarae ay omen eee OU APSSo TO TSC at pecker tet Vinioue Soeur wach eat sticks agelesat chy ney ef Wonus Moa an Me: aera OO Bo Specie Se 76 Sees) peutiiis! \s- Seog Rob iwatn cate ceee hee SOU, 6. Advantages of Treated Taner! Se PREC eco heaters ne cay oy Hoe pe NCtING ShORCES! eee Pees ead ee tae Conan carte cee en on: 8. Sizes of Structural Nenbers See RE eet co tiah ech Mae oe OE OF by prcall TaimbereGrodme ways. maetinn fii hs, ey Oey jst cee cee eae Mauer D VE WINGER GPTERSAND WAVE MBARRTER ORS MARUINAG ies cuisincy 2 ate iepo eet er enn Sy 1. Pier Dimensions .. . ribrssactoe sr Mercubehs chp A°) 2. Design of Pier Framing, Supports, and Bracing See ee Crna Aa OLS) ISTO E RASURE 9 GGG Die ctor ea ie: ny erin, tata ae cua em rea rare INDPENDIDXGiiro. charg Sar cere aree cae en cep aceite me Ne Occ eee ad INGE © vaarte ue er a el pera teataaS O) TABLES 1 Unit weights of soils and coefficients of earth pressure .... . 13 2meschedudiesforsesitamatdonsor waveractivonw sy) isi) are cum eis esc say) LO FIGURES iebulicheadadesaon mzeromwaten depth) ewes ental ist een teeta 5s vs cn 6 Zpebuilkheadudesionw. 4 toot water depitlayenn cia) orn ime ry ema thts siren amen 817) Se UL Meza) ClSsrlein Seo Wehesie GIS. Ms Sy Gesge Oo hon Go Oo God ce oo 8 4 Basic vertical dimensions of a bulkhead or seawall ........412 12 13 CONTENTS FIGURES—Continued Pressure diagram for bulkhead . Lateral pressure diagrams . Types of sheet piling . Seawall for moderate wave exposure Seawall for intermediate wave exposure Timber groin General plan of marina pier . Sections of typical marina pier . Floating marina . Page 14 o Ils 18 5 Cll o BY a OS 6 ot 5 Os) 0 SH SIMPLIFIED DESIGN METHODS OF TREATED TIMBER STRUCTURES FOR SHORE, BEACH, AND MARINA CONSTRUCTION by James Ayers and Ralph Stokes I, INTRODUCTION Pressure-treated timber has wide application in the waterfront and shore protection structures that are built in marina developments and other shore and beach locations bordering on bays, lakes, and river resorts. Because of its strength, durability, and economy, pressure- treated timber is the principal construction material for bulkheads, seawalls, piers, and groins at locations with mild exposure and shallow- to-intermediate water depths. II. TIMBER BULKHEADS Bulkheads are boundary structures that separate land from water (Figures 1, 2, and 3). They are built along shorelines and waterways and on the periphery of harbor developments, serving to retain earth usually by means of a vertical wall. The wall is made of timber sheet piles driven into the ground for support against outward movement. The tops of the sheet piles bear against a horizontal distributing member, or wale, connected to an anchor system by steel tie rods. There are two general types of anchor systems. The passive- resistance type (Figures 1 and 2) uses buried timbers located well below the finished ground surface at some distance behind the sheet piles. Earth pressure prevents displacement of this type of anchorage. The A- frame anchor (Figure 2) derives its resistance from the structural action of round timber piles arranged in groups. Some piles are verti- cal; others are battered (inclined). Suitable connections between piles enable the A-frame to resist lateral displacement by developing thrust in the batter piles and uplift in the vertical piles. Although either type of anchorage system may be used alone or in combination for any type of bulkhead, the A-frame is generally used for the higher bulk- heads because it develops a greater resistance to the pull of the tie rod, Seawalls are protective retaining structures that occupy an advanced position along a shoreline as barriers to wave attack. Seawalls are not clearly distinguishable from bulkheads. A vertical-faced retaining structure that is subject to direct wave attack of some degree of inten- Sity is classified as a seawall, whereas a similar vertical-faced structure alcrgside a relatively quiet harbor waterfront, with little or very mild wave action, is classified as a bulkhead. te Fa le"\g. drift pin : \"9 tie rod with turnbuckle, |8-6" Ig- ~~ &= 8" wale, 16-O" lg. 5*5%3-O'lg. below, spike and bolt. All bolts, Va"? PLAN EL.*6.0 VE ere eT a EL?5.0O STS = ORNS EMS Std S AER CER Lye ISG a eZ; Tae= Ts. M.A WwW EL.*3.0 =< \ \\fh : First stage of == aC URN NAN \ Seve 7 filling. EEE EL. O28 Vara aS Ae uh mas aot. i ae 28 TO = “Nie 16-0" : | ~~ An AoE” "lA or S10" T +& | 22 * Drain hole sit Thee aoa de sheet piles, 12-O"lg.-“Y @20Ft.ctrs. SECTION Figure 1. Bulkhead design, zero water depth. VYe?boit B12" wale, 14"-0" Iq. lO™*1O"Wole—t A"TP 16-0" lg. fo) x) C14"? tie rod, 2440" ig. 4 ane oe". 65/e'*8" pl., ai 6*/e~ 8" pl., washer fe) washer 0) Two 2«10%2-0- Iq. “splice plates, Four Ve bolts. Ve* bolt Ml Nl Zest Ee GY | 1-5 "BAe 6" EL*5.0 First Sracs MHWEL40 [117 ah Wr Ue “~\OF Filling. == in aoe Sr2.0 Gé F Sus M.L.Ww EL.9.00 ||| | My Seah Fy I Boe \ : \ VA I” dB B*10+0"lg. posts CU | STTS= WIN a= = li 7) 1 H | Wid 4x12%16-O"lg. T+G sheet i Fender piles, ||| piles IS Ft. min. Ig. nt SECTION Figure 2. Bulkhead design, 4-foot water depth. 8% 5/428" pl. washer 10x12" wale, 16-0"lg. Two 2*12*« 2+0"Ig. splice plates. Four Yas bolts M.H.W EL“4.0 Fender piles 5 lea ir 2 js ae flue, ‘ 12%12” wale, 4-O"lg i SE | Oo +BY Lp Ve fbolts | wv O Hl f 1 9) | ( 1%4"% bolt at. 3'«2/4*8"pl.washer 2? Ei Ea —— \} Oo 13/a"# x23" O° 1g. cD || = rod. Thread 6* iT I —— = iss Steel shim plates 4 a PLAN Dap SY’ min. “x Yea)'« +O" stee\ shim plate W%x4.0"lg. bolt Existing pomem XS Wrapping Predominantly granular £351 One pile @ 30t. G'x12"*22+O'lg,, splined sheet Wages Wis \ | piling Wh | i W Wl | SECTION Figure 3. Bulkhead design, 8-foot water depth. 1. Typical Timber Bulkheads. Figure 1 shows a conservatively designed, low bulkhead for instal- lation where the existing grade along the sheet piles is somewhat higher than the low water level. Figure 2 shows an intermediate bulk- head suitable for retaining fill at the site of a marina or for provid- ing a finished waterfront in a housing development. If these bulkheads are located farther inshore, or if the outside water level variations are less than shown in the figures, the heights of bulkheads and lengths of sheet piles may be reduced. The anchorage systems (Figures 1 and 2) depend upon the passive resistance of a mound of earth immediately around the anchor post and wales. The theoretical mound required to develop this passive resis- tance is shown by a dotted'line,. If backfill is placed directly against the sheet-pile bulkhead before this mound of earth is placed around the anchor system, the resulting forces may displace the bulkhead or even push it over, resulting in a costly and disastrous failure. After the mound is placed over the anchorage system, backfill can be deposited against the sheet piles by a dragline, truck dumping, hydraulic pipe- lines, or other suitable methods. Figure 3 shows a bulkhead suitable for the deepwater parts of marinas, or for locations where the existing water depths are 6 to 8 feet and extensive landfills are desirable. The anchorage system (Figure 3) is a self-supporting A-frame that does not depend on passive earth resistance. This anchor system is particularly adaptable to filling by the hydraulic method because the backfill can be raised behind the sheet piles without regard for the placement of backfill at the anchorage location, To install the A-frame anchorage, a pile-driving rig is required to drive the piles to specified bearing capacity. At locations with less water level variation than the 4 feet shown, the height of finished grade may be lowered proportionally. For an increase in water level variation, a similar increase in height of finished grade can be made with a corresponding reduction in water depth. The 5-foot vertical distance from finished grade to tie rod level should be maintained. 2. Construction Procedures. The proper sequence for bulkhead construction is: (a) Drive all round timber piles, both vertical and bat- tered; set or drive all posts. (b) Using bolts, attach the horizontal wales for the sheet piles and the anchorage system. (c) Drive sheet piling. (d) Complete all bolted connections and install tie rods. (e) Place the backfill; where passive resistance anchorage systems are used, be certain to place fill over the anchors before backfilling behind the sheet-pile wall. Establish accurate survey lines as a control for the construction of waterfront and shore protection structures, and anchorage systems. Exercise care in locating positions of round piles and posts that sup- port horizontal timbers that will be used as driving guides for sheet piles. In all cases, use a driving guide for sheet piles, preferably the permanent horizontal wale that is attached to the vertical round piling or posts (Figures 1, 2, and 3). It is particularly important to drive the first few sheet piles accurately vertical in all directions. The wall must be plumb and the sheet piles must not be inclined within the plane of the wall. One of the common problems facing piling contractors is "creep," the ten- dency for successive sheet piles to lean more and more in the direction of construction of the wall. The wall can be perfectly plumb, yet piles can lean; this error in alinement tends to accumulate and, if left uncorrected, can create considerable difficulties in driving successive piles. Chellis (1961) has a discussion of this situation and how to correct it. As sheet-pile driving proceeds, place the tongue of each new sheet in the forward position and the groove in tight contact with the tongue of the sheet previously driven. Keep the joints between piles as tight as practicable. Remember that the maximum allowable opening at joints is one-half inch for splined and Wakefield piling, and one-fourth inch for tongue and groove piling. If wider joints appear after the sheet piles have been spiked to the outer wale, cover with treated timber lath to prevent the backfill material from gradually filtering through the cracks and being lost. Wherever passive-resistance anchorage systems are used the anchor- age must be well covered with a mound of earth before backfill material is deposited to any appreciable depth against the piling. Otherwise, the pressures generated by the backfill may disrupt the sheet piling and the anchorage system. Use a predominately granular material for backfill adjacent to the sheet piling and over the anchorage system. Shoreward of the anchorage, a poorer quality filling material may be used unless it is objectionable from the standpoint of foundation support for shore structures, If the hydraulic method is used for backfilling, provide suffi- cient drainage to permit rapid escape of water at the ends of the con- struction area, both to prevent formation of pools and to maintain as low a free water level in the backfill as possible, Although the bulkhead is designed to hold earth, it may not be designed to resist water pressures that can be generated during hydraulic filling. _One method of facilitating drainage is to provide openings through the sheet piling above the level of the outside wale. Space these openings at intervals of about 60 feet to supplement the escape of drainage water. The final 3 feet of backfill adjacent to the sheet piles should be put into place by earthmoving equipment to avoid hydraulic pressures at the upper parts of the bulkhead. The hydraulic discharge line should be parallel to the bulkhead alinement, not directed at it, and should be located at least 100 feet behind the bulkhead sheet piling. a. Site Conditions. At a construction site, the natural condi- tions that exert the most influence on the design of any waterfront structure are water level variation, wave action, and type of soil. Ice conditions are a special consideration for locations subject to the effects of solid ice sheets, floating icefields, or large icepacks. b. Removal of Poor Quality Soils. Often the natural soil is cap- able of providing the necessary resistance for the lower ends of the sheet piling in seawalls, bulkheads, and groins. However, if the bottom soil is soft silt, mud, or soft clay, it should be removed and replaced with granular materials. In most cases, earthfill is required above the existing ground line for some distance shoreward from the face of the sheet piling. The filling material for a sufficient width to encompass the anchor system should be predominantly granular in nature, even though it may be necessary to transport it from a considerable distance. 3. Design Steps. Several steps are required in the design of an anchored bulkhead as follows: (a) Determine the following basic information (Figure 4): Water depth required (by owner). Water level variation in front of sheet piling. Ground water level behind bulkhead at time of low water level in front. Level of finished grade behind bulkhead. Types of soil available for backfill and for resisting movement of lower ends of sheet piling; unit weights of moist and submerged soils (Table 1). Amount of vertical surcharge loads (if any) anticipated on ground behind bulkhead (determined from proposed use of site). (b) Prepare earth-pressure diagrams for inner and outer faces of sheet piling to obtain resultant pressure diagram (Figures 5 and 6). “[[Temeos IO peoyy[ng & FO SUOTSUSWTp TeOTIIOA JISeg ‘Pp dANSTY Burid yoous jo wopjoq-” Boy 13;0Mm O04 OTP USIPO1SUdq @Anssaid saan = Uy SE WES YELYLLULE™: ee Was dap ta10m ubiseg a8 sc SETS TET iy aoe Sh, S WHH "UI GOL (© \ ee f Se FHNOF NW SLOM,.O1*,.0L~¥ Ne Uts sopruvsdy “ue dope —tHt ae ok ZS pin ae BAVA Jpous-oy ob.107, 1 27 As for bulkheads, the critical design condition is the tendency of the wall to move outward under the driving force of active earth pres- sure and unbalanced water pressure. The combined effects of these forces on seawalls are determined in the same way as for bulkheads. The forces due to oncoming wave action do not establish a critical design condition because any tendency for the wall to move shoreward is resisted by the force of passive earth pressure behind the sheet piles. In locations subject to "rare" occasions of severe storms that raise the general water level by several feet (storm surge), it is not econom- ical or practical to build timber seawalls sufficiently high to prevent wave overtopping. Consequently, it may be necessary to replace eroded backfill after the storm surge recedes. In establishing the allowance for unbalanced water pressure, due consideration should be given to the past history of unusual water levels in a particular locality. For such abnormal conditions, a reduc- tion in the usual safety factors can be tolerated. 2. Treated Timber in.Concrete Seawalls. Figure 9 is a seawall for intermediate exposure to wave action. This is a rigid-type cross section of reinforced concrete with stepped face. The structure is supported on round, treated timber piles and has a treated timber sheet-pile cutoff wall at the toe. This type of sea- wall has been used for exposure to 6-foot waves in storms along the gulf coast. The parapet wall may be added to prevent overtopping if scouring of the backfill material occurs as the result of unusually high wave action during storm surge. Adequate drainage is required behind the seawall for removal of surface water from rain and overtopping waves. IV. DESIGN OF GROINS Groins are fingerlike barrier structures built perpendicular to the shoreline for extending and maintaining a protective beach. At locations where the supply of sediments is not sufficiently large to fill a groin system without causing erosion of downdrift shores, artificial filling for the groin system is required so that the natural supply of sediments in transport may pass without reduction in volume. Lawsuits by owners of eroded property may be expected. ils Types. Groins are classified as impermeable, or permeable corresponding to their tightness as barriers to sediment movement, The current flow is completely obstructed by impermeable groins. Openings through permeable groins permit partial current flow and passage of a part of the sus- pended sediments past the barrier, often resulting in deposits on both sides of the groin. The sizes and spacings of the openings are some- times varied to increase the flow progressively from shore to the seaward 28 Land side SOF | Sa Reinforced concrete fe —= SSS _— —_ —_——_ __ 4°27 T+G Sheet Piles —~ SECTION Figure 9. Seawall for intermediate wave exposure. Os) end. The degree of obstruction designed for the barrier must take into account the needs of shoreline segments for littoral materials down- drift from the particular area. In order to protect a long shoreline segment, groins are built in series as systems of barriers. 2. Location on Shore. The suspended sediments travel along the foreshore in a band width extending from the breaker zone to the limit of wave uprush, Because the predominant part of sediments travel in the zone shoreward of the 6-foot-depth contour, groins are located at the inner margin of this band. Groins should be rooted in the shore landward of the crest of the beach berm sufficiently far to prevent flanking by littoral cur- rents during storm wave attack at times of abnormally high water levels. Connection to a bulkhead or revetment is desirable. The outer ends are usually extended as far as the 6-foot-depth contour at low tide. 3. Dimensions. The range in usual lengths extends from some minimum value less than 100 feet to a maximum of several hundred feet. Heights of groins vary with wave conditions and the degree of obstruction permissible, considering the material requirements of other shore segments downdrift of the particular groin system. 4. Profile. Three sections are recognized along the length of a groin, namely the horizontal-shore section, the intermediate-sloped section and the outer-horizontal section. The horizontal-shore section should be secured to a bulkhead or keyed into ground that is not disturbed by attack of severe storm waves. The shore section should extend, as a minimum height, to the level of normal wave uprush above high water. The maximum height required to retain all material reaching this section of the groin is the level of maximum wave uprush during all but the least frequent storms. The top of the intermediate section matches the levels of the hori- zontal-shore section and the outer section. It is parallel to, and corresponds in length with the slope anticipated for the foreshore as a result of material retention by the structure, The outer section extends seaward from the intermediate-sloped section to such a length as is required to contain the intersection of the proposed beach slope updrift of the groin with the existing bottom. The top of the outer section is established as nearly as practicable at the MLW level, usually about 1 foot above it. 5. Spacing. The fillet of sand trapped between groins tends to stabilize along 30 an alinement perpendicular to the predominant direction of wave attack as established by the direction of the orthogonals in a wave refraction diagram. The spacing between groins of a system should be correlated with the length of the groins so that the final stabilized alinement of the fillet between groins will provide the minimum width of beach desired at the updrift groin with a sufficient margin of safety to pre- vent flanking of the updrift groin, The distance between adjacent groins is in the range from one to three times the total groin length. 6. Advantages of Treated Timber, Marine-treated timber is a recognized construction material for building groins. It has the requisite strength to resist the applied forces at locations with mild to moderate wave action. There is the distinct advantage in withstanding abrasion from sand driven by the wind without ill effects. The marine treatment provides an effective protection for the timber against marine borers. Ho Acting Forces. The two significant forces to be considered in design of groins are earth pressure and wave action. The ordinary methods of computing earth pressure from granular materials are applicable. The magnitude of forces from earth pressure depend on the differential in level of the material on the two sides of the sheet piling. For an impermeable barrier wall, the maximum differential would occur at a time when the accretion fillet has about reached its stabilized depth updrift of the groin and the deposit of material on the downdrift side has only begun. The height differential in sand level on the two sides of a permeable groin would be considerably less than for an impermeable groin. Three types of wave action are: (a) Reflected oscillatory motion (nonbreaking waves) ; (b) breaking waves; (c) broken waves (onrush). For a discussion of methods for computing wave forces for the three types of wave action and illustrative examples, see U.S. Army, Corps of Engineers, Coastal Engineering Research Center (1973). 8. Sizes of Structural Members. The conventional method of arriving at the sizes of members is to follow successful examples from past engineering experience for similar environmental conditions. Whereas this method does not lend itself to close design tolerances, approximate cou )utations can be made to investi- gate the strengths of the component parts shown for an existing design in relation to the environmental conditions expected at a particular location. 3| 9. Typical Timber Groin. Figure 10 illustrates a typical groin of the impermeable type us- ing marine-treated timber throughout as the construction material. A vertical wall of timber sheet piling is framed into a system of hori- zontal timber wales and round vertical piles to form a tight barrier. The structure is supported laterally by the combined bending strength of the sheet piles and the round vertical piles, all of which derive their fixity from penetration into the earth bottom. The timber wales and the round piles serve to distribute the load from waves traveling along the wall, and thus limit the deflection of the local length loaded at a particular time and prevent opening of the joints between adjacent sheet piles. The penetration of the round piles should satisfy two requirements, a minimum bearing capacity of 10 tons and a minimum penetration of 10 feet. The sheet piles are made of two, 3-inch-thick timber staggered to produce a shiplap type of joint between sheets. Losses of material through joints in adjacent sheets are not so critical as in bulkheads. Some groins are deliberately made permeable. However, even if tight joints are desirable to prevent loss of material placed artificially to fill the groin, there is no paving to be undermined as is the case in many bulkheads. The two boards are spiked together for handling purposes and act only as individual planks in bending. V. FINGER PIER AND WAVE BARRIER FOR MARINA In marinas where the tide range is 4 feet or less, the piers are supported on piling at a fixed elevation. However, for sites with higher tidal ranges, floating piers are used for the greater conve- nience afforded in gaining access to boats. A conventional arrangement of pile-supported berthing facilities for small boats in a marina is illustrated in Figure 11. The berths for individual boats are laid out at right angles to, and on both sides of a finger pier. The pier may have a T-head at the outshore end where, as is often the case, the water depth is greater than that alongside the pier proper in order to accommodate the larger boats with deeper draft. Figure 12 shows sections through a typical marina pier. Vertical timber planking is used to form a wall for the length of the T-head. This wall acts as a barrier to the passage of short surface waves moving toward shore. In some cases, the vertical planking is driven into the harbor bottom and is supported laterally at the top by the pier structure, If the wave action is only surface chop, the wall does not extend to the harbor bottom; the planks are entirely supported from the pier deck. Section B-B through the pier head indicates a round 32 NOILOAS ‘uTOI3 JoquT], “QT ean3ty NWl1d wel OML: SS[OM,O1X.Q Pesinbes sr [lz pu KNH'W 2000072492. MH'W 2A0q0 9.2.79 33 Wave POLES) eyes 2m ‘ze ue Bae ioe poeta | ea ae i 21° «65° ee ea ———— -- Ss] ——— | 1850; =o a ; @ e 10’ 40% + ul 4 oN: | beam == r ———— Ge 5'«10° eet ewe Bulkhead Nofe:- See FIG. IZfor Sections A-A and 8-B Figure 11. General plan of marina pier. 34 ‘zetd eurzew Teotdd} Fo suot}s9eg “ZT saNsTy G-G NOILOAS W-V NOILOAS 1 | poainbe $I paul by SA49.0501 © SHU a Pp ALE L ALT EY 1: ef nat ai y) Sh Sw YIP = N= (ely YW=EDGYEMaWSESIWENS oO S-13 SHOP g.%Al , [94,2 0OML SHOP" gt] .O2e HIS Val "SE[OF> gti 4,9» Se ek A= ess pe Se coos wT pn ; ‘Gene ee (es! SHOE g.1 Ol. OMLF Z| — a QQ spas eat SALD,Of 2.2 xe c a O e134 M H W Ha fey | tit Sxebuls1s .Ol*.2 | OL. 1a | | buiy2ep,gx2 ald O‘Ol 1a LL 35 vertical pile (shown dotted on Figure 12). If wave action in the range of 2- to 3-foot heights occurs at the site, an additional pile in each bent to carry lateral loads should be provided. Plank barriers are to be considered only as supplements to any primary wave protection neces- sary for the marina site. A layout plan for a floating marina with sections through the boat walkways is shown in Figure 13. 1, Pier Dimensions. The pier length is established in accordance with the number and widths of berths which are to be built alongside. The typical pier width is usually 8 or 9 feet wide. The pier deck is located a minimum of 3 feet above the mean high water level. 2. Design of Pier Framing, Supports, and Bracing. The framing arrangements, and the minimum thicknesses and sizes of members for deck planking and bracing timbers, are guided largely by conventional practice. The deck stringers are proportioned for a design uniform live load of 75 pounds per square foot of deck area. The pile bents are spaced to suit the design of the deck stringers, with two piles in each bent. The specified deck loading usually does not determine the number and spacing of supporting piles, which are driven to a minimum bearing capacity of 10 tons, or minimum penetration of 10 feet. 36 “eCUTIeW BUTICOTY “ET sansTYy AYVMYMIVM LVOG JAIM ,b YO AVMAIVM LVYOS 3GIM ,€ NYHL NOILOSAS JGIM ,9 NYHL NOILIDAS LVOI4S JNAYALSAI10d Ll SS eS AU Saw) cf ) an era? qj } ANN Ratt VNIYVWW ONILVO14 JO NV 1d QV3SHWINE YSGWIL Ge J1ld YOHINY YSGWIL el [01 Ge 37 LITERATURE CITED CHELLIS, R.D., Pile Foundations, McGraw-Hill, New York, 1961, pp. 332-333. TERZAGHI, K., Theoretteal Sotl Mechanics, Wiley and Sons, New York, 1943, epprid2s=25ie TERZAGHI, K., "Anchored Bulkheads,"' Transactions, Amertcan Soctety of Ctvtl Engineers, Vol. 119, 1954, pp. 1243-1324. U.S. ARMY, CORPS OF ENGINEERS, COASTAL ENGINEERING RESEARCH CENTER, Shore Protectton Manual, Vols. I, II, and III, Stock No. 08022- 00077, U.S. Government Printing Office, Washington, D.C., 1973, 1,160 pp. 38 APPENDIX GLOSSARY accretion fillet — a deposit of sediments by littoral currents. downdrift — the predominant direction of movement of littoral materials. littoral — pertaining to a seashore or coastal region. littoral current — a nearshore current, primarily caused by wave action. orthogonal — perpendicular to the direction of wave crests. spline — a long wooden strip which fits into a recess in the face of a timber member and extents out beyond the face as a tongue. updrift — the direction opposite to downdrift. 39 £09 7=9/ .0u au gon’ €0¢0L “y-9/ ‘ou J10odeiI snosueTTeosTy *Ieque) YyoIeesey BuTiseuTsuq Teyseog *S*f : SeTzesg “TIT *zoyjne jupof fydqey ‘seyolg “IT ‘eTITL *I ‘poon *y ‘*uotjz0030A4d atoys *€ *seinjzonajzs usapoom *Z “*uoTJONAJSUOD pue usTsa *f *syjdeap rt07eA 7b TPouiszUT-O}-MOTTeYS pue sinsodxs pTTW YIFM suOTIeIOT We suTOA’ pue ‘szetd ‘sTTemess ‘speeyyrtnqg toy 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