Problem No. 1. A plate bearing test using a 12-in.-diameter rigid plate is made on a subgrade, as shown in Figure P2.3a. The total load required to cause settling by 0.2 in. is 10,600 lb. After 10 in. of gravel base course is placed on the subgrade, a plate bearing test is made on the top of the base course, as shown in Figure P2.3b. The total load required to cause settling by 0.2 in. is 21,200 lb. Assuming a Poisson ratio of 0.5, determine the thickness of base course required to sustain a 50,000-lb tire exerting a contact pressure of 100 psi over a circular area, as shown in Figure P2.3c, yet maintain a deflection of no more than 0.2 in. 10,600 lb 21,200 lb Rigid Plate Deflects 0.2 in. 50,000 lb 100 psi <-0.2 in. Base E₁ =? 10 in. E₁ h₁ = ? 12 in Subgrade E-? (a) Subgrade E (b) E (c) FIGURE 93