Three-dimensional slope stability analysis by elasto-plastic finite elements

Slope stability analysis is one of the oldest applications in geotechnical engineering, yet it remains one of the most active areas of study in both research and practice. The vast majority of slope stability analyses are performed in two dimensions under the assumption of plane strain conditions. Even when two-dimensional (2D) conditions are not appropriate, three-dimensional (3D) analysis is rarely performed. There are a number of reasons for this. The majority of work on this subject strongly suggests that the 2D factor of safety is conservative (i.e. lower than the ‘true’ 3D factor of safety). Even when 3D may be justified on geometric grounds, the available methods, being often based on extrapolations of 2D ‘methods of slices’ to 3D ‘methods of columns’, are complex, involve numerous assumptions, and are not readily modified to account for realistic boundary conditions in the third dimension such as sloping abutments. The power and versatility of the elasto-plastic finite element approach to slope stability analysis in 2D are well known, and these advantages are even more attractive in 3D. The paper demonstrates some 3D slope stability analyses by finite elements, placing the results in context with 2D solutions and validating the results where possible against alternative methods.