Vertical stress increase problem. As shown in Figure 3.27, a continuous footing is designed to support a bearing wall with load of 300 kN/m. The groundwater table is far below the ground surface. The subsoil is homogeneous silty sand with bulk unit weight of 17.5 kN/m³. The width of the wall foundation is B = 1 m, the foundation embedment depth is Df = 0.5 m. Use the following methods to determine the vertical stress increases at z = 0, z = 2.5B, and z = 5B, and calculate the average vertical stress increase in the soil layer below the center of the footing from z = 0 to 5B. Note, z starts from the bottom of the foundation.

(1) Boussinesq method.

(2) Poulos and Davis method.

(3) 2:1 method.