Vertical stress increase problem. As shown in Figure 3.27, a square spread footing is designed to support a column. The load on the column , including the foundation weight, is 600 kN. The dimensions of the foundation are B × B = 1.2 m × 1.2 m, and the foundation embedment is Df = 0.6 m. The subsoil is homogeneous silty sand with bulk unit weight of 18 kN/m³. 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 that z starts from the bottom of the foundation.

(1) Boussinesq method.

(2) Poulos and Davis method.

 (3) 2:1 method.