An Introduction to Slope Stability Analysis

This publication is concerned with characteristics and critical aspects of the stability of excavation slopes; methods of designing slopes, including field observations and experience, slope stability charts, and detailed analyses; factors of safety; and methods of stabilizing slopes and slides. Excavation slope instability may result from failure to control seepage forces in and at the toe of the slope, too steep slopes for the shear strength of the material being excavated, and insufficient shear strength of subgrade soils. Slope instability may occur suddenly, as the slope is being excavated, or after the slope has been standing for some time. Slope stability analyses are useful in sands, silts, and normally consolidated and overconsolidated clays, but care must be taken to select the correct strength parameter. Failure surfaces are shallow in cohesionless materials and have an approximately circular or sliding wedge shape in clays. The emphasis in this publication is on simple, routine procedures. It does not deal with specialized problems, such as the stability of excavated slopes during earthquakes.