As the water pressure is equal on both sides of the sheet piling, the 

 net active increase in pressure per foot of depth would equal 93~6i|. = 

 29 pounds. The total active pressure at the foot of the sheet piling 

 woidd equal 



9 X 71 + 29x or 639 + 29x 



where x is the distance from the ground line to the bottom of the pile, 



ii6l. Passive Resistance . - The resistance to the active pressure is 

 provided by the passive resistance of the earth on the dcwndrift side of 

 the groin. Assuming the passive resistance of the piling to overturning 

 at the bottom of the pile would be zero, it would reach a maximum near 

 ground surface. Assuming a uniform variation, the passive resistance per 

 foot of depth would be 



Rp = wh2 tan^gl/2)(90 + 0] (l53) 



where = 25° 



Rp = [110 - (0.6 X 6U)](l)^ (2.J46) = 15'8 pounds. 



At the ground surface the passive resistance would be l58x. 



I4.62 o Length of Sheet Filing to Resist Earth Pressure . - As there 

 are no vertical forces which act against the sheet piling, only two con- 

 ditions of statics must be fulfilled: 



Xh s and2.M - 



From the loading diagram Figure IUTB, the minimum length of pile penetra- 

 tion that would satisfy the condition of JH = can be found by 



5750 ^ 639,- 29x2 ^ 158x2 



Collecting terms 



61pc2 - 639x - 5700 = 



or 



x2 - lOx - 90 = 



X = -b + yb2 - Uac (151,) 



2a 



221 



