6,Chapter 13 J. MICHAEL DUNCAN SOIL SLOPE STABILITY ANALYSIS A nalyses of slopes can be divided into two cat- egories: those used to evaluate the stability of slopes and those used to estimate slope movement. Although stability and movement are closely re- lated, two different and distinct types of analyses are almost always used to evaluate them. 1. INTRODUCTION Stability of slopes is usually analyzed by methods of limit equilibrium. These analyses require infor- mation about the strength of the soil, but do not require information about its stress-strain behav- ior. They provide no information about the magnitude of movements of the slope. Movements of slopes are usually analyzed by the finite-element method. Understanding the stress- strain behavior of the soils is required for these analyses, and information regarding the strengths of the soils may also be required. Although these methods define movements and stresses through- out the slope, they do not provide a direct measure of stability, such as the factor of safety calculated by limit equilibrium analyses. The focus in this chapter is on soil slopes and mechanisms involving shear failure within the soil mass. The methods described are applicable to landslides in weak rocks, where the location of the rupture surface is not controlled by existing discon- tinuities within the mass (see also Chapter 21). Analyses of slopes in strong rock, where instability mechanisms are controlled by existing discontinu- ities, are described in Chapter 15. Techniques for evaluating rock strength are discussed in Chapter 14, and those for evaluating soil strength are dis- cussed in Chapter.12. Limit equilibrium and finite-element analyses are described in subsequent sections of this chap- ter. Methods that are useful for practical purposes are emphasized, and their uses are illustrated by examples. 2.MECHANICS OF LIMIT EQUILIBRIUM ANALYSES In limit equilibrium techniques, slope stability is analyzed by first computing the factor of safety. This value must be determined for the surface that is most likely to fail by sliding, the so-called criti- cal slip surface. Iterative procedures are used, each involving the selection of a potential sliding mass, subdivision of this mass into a series of slices, and consideration of the equilibrium of each of these slices by one of several possible computational methods. These methods have varying degrees of computational accuracy depending on the suit- ability of the underlying simplifying assumptions for the situation being analyzed. 2.1 Factor of Safety The factor of safety is defined as the ratio of the shear strength divided by the shear stress required for equilibrium of the slope: 337
SOIL SLOPE STABILITY ANALYSIS
Jun 04, 2023
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