9.1 INTRODUCTION

This Chapter concerns the application of limit analysis techniques to problems involving stability of earth slopes. Since a great variety of conditions may lead to a failure of a soil slope due to its own weight, no more than a discussion of the simple slopes of stability computations will be attempted. The discussion here will be limited to rigid body sliding in cohesive material whose shearing resistance is determined by Coulomb's yield or failure condition. The term rigid body sliding involves a downward and outward movement of a slice of earth as shown in Fig. 9.1, and the sliding occurs along the well-defined, entire surface of contact between the slice and its base.

In order to familiarize the reader with the methods of computation, the individual problems connected with the stability of slopes will be taken up in the following sequence. First we consider the critical height of an inclined slope using a rotational failure mechanism (logarithmic spiral) passing through the toe, because it is similar to that for the stability of a vertical slope described in section 3.2, Chapter 3 (example 3.2). Then we solve in succession the following two problems: (1) the case where the logarithmic spiral failure surface may pass below the toe; and (2) the case where the soil mass may be anisotropic and non-homogeneous. Since the stress fields are not considered in these problems, solutions of the logarithmic spiral mechanism can at best give only upper bounds to the problems. However, the...