5.1 INTRODUCTION

Slope failure is defined as the failure of a soil mass forming a slope by downward and/or outward movement. Some existing slopes which have been stable for some time can experience failure due to various reasons, such as occurrence of earthquakes, increased loading on a slope at or close to its crest, removal of earth from the face of a slope to make it steeper, removal of earth close to the toe of a slope, gradual disintegration of the soil forming a slope, and increase of pore water pressure in the soil forming the slope.

The analysis of the stability of a slope or the evaluation of the factor of safety against slope failure needs a thorough knowledge of the shear strength parameters of the soil. In this chapter, it will be assumed that the readers are acquainted with them.

Due to the scope and limitations of this text, only the sta-bility of simple finite slopes will be considered in this chapter.

Figure 5.1 shows a simple finite slope in which the ground surface is horizontal at its foot and at its top. In order to analyze the stability of this type of slope, the critical failure surface has been assumed by various investigators to be a plane, an arc of a circle, or an arc of a logarithmic spiral. Culraann's analysis (1866) for the stability of a simple finite slope is based on the assumption that the critical surface...