APPENDIX B-Continued 



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Flg. 2: Bulkhead design, four-foot water depth. 



from the standpoint of foundation support for shore 

 structures. 



If the hydraulic method is used tor backfilling, pro- 

 vide sufficient drainage to permit rapid escape of 

 water at the ends of the construction 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 gen- 

 erated during hydraulic tilling. 



One method of facilitating drainage is to provide 

 openings through the sheet piling above the level ot 

 the outside wale Space these openings at intervals 

 of about 60 feet to supplement the escape of drain- 

 age water The final three feet of backfill adjacent to 

 the sheet piles should be put into place by earth mov- 

 ing equipment to avoid hydrau'ic pressures at the upper 

 portions ot the bulkhead. The hydraulic discharge line 

 should be parallel to the bulkhead alignment, not 

 directed at it, and should be located at least 100 feet 

 behind the bulkhead sheet piling. 



DESIGN STEPS 



At a construction site, the natural conditions 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 

 tor locations subject to the effects ot solid ice sheets, 

 floating ice fields, or large ice packs. 



Removal Ot Poor Quality Soils 



Often the natural soil is capable 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, earth fill is required above the exist- 

 ing ground line for some distance shoreward from the 

 face of the sheet piling The filling material for a sutfi- 

 cient 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, (continued, part II) 



309 



