(b) Active pressiires may be computed by use of relationship; 



h tan^ (2^) (87) 



a 2 



where w =. the unit weight of the material 



h = the height (including the equivalent height due to surcharge 

 if any) of the fill 



= the internal friction angle of the fill material. 



The point of application of the resultant thrust will be through the 

 centroid of the pressiire diagram drawn from this relationship; 



(c) Maximum passive pressure may be computed by use of the 

 relationship: , 



Pp = w h tan^ (22JX^) (88) 



The point of application of the resultant thrust will be through the 

 centroid of the pressure diagram which may be drawn from this relation- 

 ship. The application of these relationships to the design of sheet 

 pile bulkheads is illustrated in the following example. 



32ij.. Design problem . - It is desired to construct a bulkhead in a 

 protected anchorage where the maximum tidal variation is 3 feet. The 

 anchorage is to be dredged to a depth of 6 feet below extreme low water. 

 The original ground line is 3 feet below extreme low water ^ but the 

 area is to be backfilled to 10 feet above the original ground line or h 

 feet above maximum high water. A surcharge load of 1^0 pounds per square 

 foot is to be designed for, 



325. The fill material has a drained unit weight of 120 pounds per 

 cubic foot with an internal friction angle (0) of 30'=, Its saturated 

 unit weight is lUO povmds per cubic foot, and its submerged unit weight 

 is 75 pounds per cubic foot, both with an internal friction angle of 

 25°. The undisturbed ground has a submerged weight of 80 pounds per 

 cubic foot with an internal friction angle of 30°, 



326. Figure IO6 is a diagram of the desired placement for the 

 proposed sheet pile bulkhead. For design purposes, it mil be assiuned that 

 the backfill is saturated to the high water linoo The heights h_, h , and 

 h , refer respectively to the backfill height above the high water line 

 and the original ground line. The height h, refers to the height of the 

 original ground above the dredged bottom. The corresponding unit weights 

 and internal friction angles are w^ , and , Wp and 0„, w and and w. 



and 0, , 



158 



