Development of a hybrid limit equilibrium-finite element procedure for three-dimensional slope stability analysis.

摘要

Studies are presented which show that assumptions common to most existing three-dimensional slope stability analysis procedures may produce unacceptable errors in the computed factors of safety. To overcome some of the limitations of existing procedures, a new hybrid limit equilibrium-finite element procedure has been developed for analyzing the stability of slopes along three-dimensional slip surfaces. The displacement based formulation of the finite element method is used to determine the distribution of stress (traction) along potential slip surfaces. The distribution of stress satisfies complete static equilibrium without the need for assumptions about the magnitudes and distributions of forces acting within a slope. In doing so, the hybrid procedure is likely to be much more accurate for analyzing the broad range of three-dimensional problems which are encountered in practice.; Two alternative formulations for determining the distribution of stress on the slip surface were developed and implemented as a part of this work. In the first formulation, the stresses at selected points along the slip surface are computed by interpolation from the gravitational stress field computed using the finite element method. Results from a series of evaluation analyses indicate that the accuracy of the formulation, in terms of both equilibrium and the computed factors of safety, is sensitive to the degree of mesh refinement, the type of element, and the value of Poisson's ratio used in the finite element analysis. In addition, the computational effort required to obtain results with acceptable accuracy often exceeds what is currently practical.; Because of the limitations of the first formulation, the second, "modified" formulation of the hybrid approach was developed. In the modified formulation, the distribution of stress (traction) along potential slip surfaces is computed from finite element nodal forces rather than from finite element stresses. The resulting traction satisfies complete static equilibrium exactly regardless of the degree of mesh refinement, the type of element, or the value of Poisson's ratio. Factors of safety computed using the "modified" hybrid procedure agree very closely with those computed using other complete equilibrium procedures or solutions available for simple problems. The general suitability of the procedure is also demonstrated through application of the hybrid procedure to the Kettleman Hills Landfill case history.