of passive pressure applied on the x-iall face would 'u.: greater than the increase 

 of active pressure applied at the wall back,and the net rate of change or pressure 

 is given by 



R = R - R 

 o a 



80 



(97) 

 3.00 - 0.33] 



= 21U pounds per square foot per foot of depth 

 = rate of decrease of outward pressures 



33O0 The noint on the loading diagrajn at vrhich the isarth pressures would 

 be zero is labeled G and its distance h^- below the dredged bottom may be found 

 by dividing pg by R„ 



hj.pg/R-ll (98) 



= 2,36 feet 



= depth of i'.ero loading point below the dredged bottom. 



331 • The magnitude of the concentrated force (T) on the wall due to the 

 deadman is dependent on the depth of penetration of the pile. 



332. Pile Length. - A pile which is just long enough to support the 



backfill will have a leirger cross section than one, somewhat longer, which is 



designed for minimum bending moment. The choice between the tt-io is a matter 

 of economics^ 



3^^" Pile De sign -- Mini mum Pile Ijength . - For optimum pile design, the 

 point of aoplication of the deadman thrust should be such that the bending 

 moment at this point equals the maximum bending moment in +he pile below it. 

 To attain this optimum, design, the maxim.um moment below an assumed point of 

 application must be found and compared xfith that at the ast,amed point. If 

 these moments are not eaual, the process must be repeated. For the purpose 

 of this illustrative problem, only the methods of calculating the bending 

 m.oments will be carried out. 



33U. Assuming the point of application (C) of the deadman tension (T) 

 to be 1 foot above the low i/«.ter line, the moiaent M of all the forces about 

 this point between the surface and noint C is given by 



162 



