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) . 



