A10-ft-tall concrete wall with a vertical back is to be backfilled with a silty sand that has a unit weight of 122 lb/ft^3, an effective cohesion of 0, and an effective friction angle of 32 degree. the ground behind the wall will be level. using rankine's method, compute the normal force per foot acting on the back of the wall. assume the wall moves sufficiently to develop the active condition in the soil. also, draw a pressure diagram and indicate the lateral earth pressure acting at the bottom of the wall.