359 • Final P ile Designo - Vlhen designed for inirj.mtuii length, the 

 maximuin bending moment in the pile was IL '^ 56h5 foot pounds per foot of wall, 

 and the length needed was 18.8 feet. >rnen designed for miniimim bending 

 moment;! ^'t, was reduced to SjlOO foot-pounds per foot of wall, but the 

 length needed for this reduced moment was 22 a8 feet, an increase of h feet. 

 The lightest pile section which can withstand a moment of 5,100 foot-pounds 

 per foot of wall is an W 12$ wliicb with a section modulus of 5«i| is good 

 for a bending moment of 6^,300 foot-pounds per foot. Since this is larger 

 than the maxLiffUBi moment which would occur in the pile when designed for 

 minimujn lengthy no saving is introduced by designing for minimum ifnoiTient. 



360„ Accordingly^ the design pile would be an MP 115 (or an MZ 22 

 which has the same weight per square foot of wall but f^reatly increased 

 strength) and the total pile length would be 18,8 (1?) feet. 



-^^-'' I)eadrnan Designo - If the backfill is such that dcjpendable passive 

 resistance would be developed, either an intermittent or a. continuous deadman 

 could be used instead of one {s^r) of sheet pile which would probably be 

 more expensive, T^e deadman may be of reinforced concrete, steel, timber, 

 or any other material which would develop the required tie rod tensions 

 over the life of the structure. The size of deadman required maj'" be found 

 by reference to Figure 113. 



362 o The deadman would experience an active pressure on its back 

 (the side farthest from the bulkhead wall) which would increase at the 

 rate 



90 - ^ 

 R ^ w., tan'" (~.^:^»~±) 

 a J. ^ 2 ' 



and a passive pressure on its front which would increase at the rate of 

 2/^°~^ll 



R ~ tf, tan 

 p J 





assuming the entire deadmsji to be above the line of permanent saturation. 

 The total rate of pressure increase then is 



(132) 



= 120 Q.OO - 0.33^ 



~ 321 pounds per square foot per foot of depth. 



363 » The total earth pressure on the deadman, given by the area of 

 the trapezoid p K L p^ must equal the tie-rod tension per unit width of 



175 



