Stability of Earth Slopes

This chapter examines the stability of earth slopes in two-dimensional space using a limit equilibrium method where a mass of soil rotates on a circular or non-circular failure surface at its limit state. On this surface the Mohr-Coulomb failure criterion applies and the shear strength parameters used correspond to the peak strength obtained by a total or effective stress analysis. The factor of safety is defined as the ratio of the shear strength to the mobilized shear stress on the sliding surface required for equilibrium, and is assumed to be constant along the surface. The average value obtained from a traditional circular analysis is a reliable indication of overall slope stability. Problems 9.1 to 9.3 investigate the slope stability in undrained conditions where the factor of safety can be formulated in terms of geometry of the trial circle and undrained cohesion. For a frictional soil, the mass is divided into vertical slices to facilitate the application of the force and moment equilibrium requirements (Problems 9.4 to 9.7). An infinite slope is normally associated with a translational failure parallel to the ground surface. This case has been explained by Problem 9.8. The circular method can also be applied to evaluate a reinforced slope as shown in Problem 9.9. An alternative method to circular solution is the use of wedge mechanisms for both reinforced soil (Problem 9.10) and unreinforced soil (Problem 9.11).