Stability Analyses of the 1981 San Luis Dam Slide

Abstract

The 1981 upstream slope failure in San Luis Dam in California, USA, is analyzed for stability and deformations in two- and three-dimensions using continuum-mechanics-based analysis procedures implemented in the computer programs FLAC and FLAC3D. The analysis results (failure surface, factor of safety, and displacements) from the continuum models are in general agreement with the field data. In addition, two-dimensional slope stability analysis results using a modified form of limit-equilibrium-based Spencer’s procedure for variable factor of safety implemented in the computer program SSTAB2 are included. Overall, the analysis results supplement the previously reported failure analyses. The paper serves three primary functions: (1) it documents results of a different analysis of the 1981 San Luis Dam slope failure; (2) it demonstrates the use of 2-D and 3-D continuum models to study the onset of instability, failure surface geometry and location, and permanent displacements associated with slope failures; and (3) it demonstrates the use of variable factor of safety to identify location of instability initiation, and progression of instability in a soil deposit. In addition, the paper demonstrates the benefits of three-dimensional analysis for complex conditions in dam engineering practice.