| Description |
The stability of a slope can be evaluated according to its factor of safety. Two approaches used to evaluate the factor of safety include the limit equilibrium method (LEM) and the shear strength reduction technique (SSRT). The LEM determines the factor of safety (FOS) using a force and/or moment equilibrium calculation. The SSRT calculates the strength reduction factor (SRF) using a stress/strain analysis in a numerical model. Comparisons between the FOS and SRF are presented in this dissertation under the same conditions: slope geometry, water level, boundary, constitutive model and material properties. This study aims to evaluate the influence of key input parameters for slope stability analysis on the factor of safety calculations using the LEM and the SSRT, and intend to quantify the difference between the factors of safety generated by each technique in the two-dimensional realm. The variables included in this research are • elastic properties and tensile strength for an associated and nonassociated Mohr-Coulomb material • slope height and slope angle • zone size in the numerical model • dilation angle for nonassociated Mohr-Coulomb material • groundwater level iv This study has determined that the SRF can vary from the FOS by tenths of its value under the same slope conditions. Although the FOS and SRF obtained by this study are in general agreement, the predicted slip surface given by the numerical method can differ from the LEM. It is important to consider that a difference of one or two tenths in the slope stability analysis produces a significant impact on a design acceptance criterion of 1.3, for example. This investigation has concluded that the SRF values are not necessarily always smaller than the FOS, as mentioned by previous references. There is no direct relationship that can be derived between the FOS and the SRF at this point. Hence, caution is advised when designing a slope and determining its stability using either the LEM or the SSRT. Both methods should be considered and analyzed in parallel. In addition, the LEM design acceptance criteria should never be applied to an SSRT design. |
