DESIGN OF RETAINING WALLS. 235 



and the minimum pressure is 



p = 3,220 2,700 - + 520 Ib. per sq. ft. 



The allowable pressure was 6,000 Ib. per sq. ft., so that the pressure is safe for a compact gravel. 

 Where the walls were supported on the mushy clay it was necessary to extend the projection of 

 the footing on the front side and to bring the resultant F to the center of the wall. 



FIG. 9. RETAINING WALL, WEST ALAMEDA AVENUE SUBWAY. 



4. Upward Pressure on Front Projection of Foundation. Where projections are used on the 

 foundations of retaining walls it may be necessary to reinforce the base to prevent the projection 

 breaking off in line with the face of the wall. The bending moment of the upward pressure about 

 the front face of the wall from Fig. 9 is 



M = M5.920 + 4.120) X 4 X 2.1 X 12 

 = 506,000 in-lb. 



The tension on the concrete at the bottom of the footing will be 



/ = M -c/I = M -d/2l = (506,000 X 27)7157,464 

 = 88 Ib. per sq. in. 



Since the ultimate strength of the concrete in tension is approximately 200 Ib. per sq. in., 



