 Caquot and Kerisel [6] modified Muller-Breslau's equations to account for a nonplanar rupture surface.The coefficient of lateral earth pressure, K, is defined as the ratio of the horizontal effective stress, σ’h, to the vertical effective stress, σ’v.The effective stress is the intergranular stress calculated by subtracting the pore pressure from the total stress as described in soil mechanics.