THREE-DIMENSIONAL STABILITY ANALYSIS
Abstract
General methods of three-dimensional slope stability analysis using limit equilibrium concepts and finite element methods are proposed. Two different computer programs based on the limit equilibrium concept, LEMIX and BLOCK3, are developed to analyze rotational and translational slides, respectively. For rotational slides, the failure mass is assumed symmetrical and divided into many vertical columns. The interslice forces are assumed to have the same inclination throughout the mass, and the intercolumn shear forces are assumed to be parallel to the base of the column and a function of their positions. Force and moment equilibrium are satisfied for each column as well as for the total mass. For translational slides, the critical failure surface is assumed according to Rankine's theory and the factor of safety is assumed to be uniform along the total failure surface. The analysis is illustrated for several slope angles, soil parameters, and pore water conditions. The results show that for both translational and rotational slides, the 3-D effect is more significant for cohesive soils with smaller failure lengths. However, a wedge type of failure may result in a smaller factor of safety than that of the 2-D condition. A gently inclined weak layer with lower strength may cause a higher 3-D effect. In rotational slides, the steeper the slope, the less the 3-D effect. Pore water pressures generally cause the 3-D effect to be even more significant. In addition, a 3-D finite element computer program FESPON is also developed. It uses a hyperbolic stress-strain relationship and an incremental technique to simulate the nonlinear behavior of soils. Isoparametric incompatible elements are used to provide good bending characteristics. This program can calculate the local factors of safety at selected points on the failure surface as well as the mean factor of safety for a chosen failure mass. The comparison between limit equilibrium and finite element methods is also conducted for the embankments with the same soil conditions and failure surfaces. The agreement is quite good, with the finite element method predictably yielding higher factor of safety.
Degree
Ph.D.
Subject Area
Civil engineering
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