APPENDIX B-Continued 



lO- or 4- . IS' 



TONGUE AND GROOVE 



Fig. 5: Types ol sheet piling. 



materials into which sheet piles are driven. Granular 

 materials have several characteristics that make them 

 desirable The active pressures they exert on bulk- 

 heads are considerably less than those exerted by 

 silts and clays or even by sands that are 'contami- 

 nated" with silt or clay Granular materials can develop 

 a higher passive resistance, permitting ttie use ol 

 shorter sheet piles 



It IS often preferable to bring granular materials to 

 the construction site by truck or other conveyance 

 rather than to backfill with silt or clay. In the final 

 analysis, a judgment is required. A designer must 

 determine whether it is more economical or otherwise 

 more desirable to increase the thicknesses of materials 

 in the bulkhead rather than to transport granular 

 materials from far distances Fortunately, granular 

 materials are quite often readily available near bodies 

 of water 



Granular material also promotes drainage behind 

 the bulkhead and is less likely to be eroded away 

 through minor fissures in the bulkhead as the water 

 level rises and falls The drainage is advantageous 

 wherever the backfill is to be used for roadways, side- 

 walks, parks, yards, and so on Grass and plants will 

 grow better irr a soil that is moderately well drained: 

 the granular material will not shrink and swell with 

 alternate drying and wetting to the same degree that 

 clay will The backfilled area is not likely to resemble 

 a marshy bog where drainage is provided through 

 granular materials Where lawns and other plantings 

 are required, a relatively thin layer of top soil can be 

 placed over the granular malerial. 



Where the material at the shoreline is silt or clay, 

 the passive resistance will be very low. This will require 

 lengthening the sheet piling to obtain sufficient passive 

 resistance to avert a failure The greater length ol 

 sheet piling induces a higher degree of bending in the 

 piling, requiring a thicker piling than would otherwise 

 be needed 



Under these circumstances, the designer should 

 consider removing the poor soil and replacing it with 

 a granular material, such as clean sand. The cost is 

 often far less than that of providing thicker materials 

 and more elaborate anchorage systems for the 

 bulkhead. 



SURCHARGE (Step 1g) 



Where the backfill behind a bulkhead will be used for 

 supporting loads above and beyond that of the earth 

 Itself, for example a road or street subject to automo- 

 bile tratlic. the effect of these additional forces must 

 be considered in the design of the bulkhead To sim- 

 plify the design, lighter loadings are translated into 

 surcharges for convenience in design Surcharges 

 are uniform loadings applied to the surface of the 

 finished elevation Lateral earth pressures resulting 

 from surcharges are calculated in the same manner 

 as the lateral earth pressure of the soil behind the 

 bulkhead itself. 



The magnitude of the surcharge depends upon the 

 use to which the land adjacent to the bulkhead will 

 be put Only a very small surcharge would be required 

 tor a footpath, heavier surcharges for light vehicles. 

 Where automobile and truck loadings will occur, refer 

 to authoritative texts, such as the AASHO Bridge Spe- 

 cilications. for load data (continued, port III) 



REFERENCES 



1 Chellis. Robert D,, Pile Foundations. lilcGraw- 

 Hili, 1961 



2 U S Army— Coastal Engineering Research 

 Center, Shore Protection. Planning and Design, Tech- 

 nical Report No 4. Third Edition, 1966 



3 Terzaghi, Karl, 'Anchored Bulkheads," Trans- 

 actions. ASC£ 1954 (Vol 119) pp, 1243 to 1324, 



314 



