Essentials of Soil Mechanics and Foundations 7th Edition David McCarthy An oil storage tank 50 ft in diameter imposes a maximum loading of 2500 psf onto the ground surface where the tank is supported. The soil underlying the tank has a unit weight of 125 pcf. For a point 25 ft below the ground surface, compute the effective vertical stress when the tank is empty and when the tank is full, at location beneath the center and the edge of the tank. Assume that Boussinesq conditions apply