Seismic Coefficients for Pseudostatic Slope Analysis

Pseudostatic analysis is one of the simplest approaches used in earthquake engineering to analyze the seismic response of soil embankments and slopes. However, the choice of seismic coefficients used in the analysis can be arbitrary and generally lacks rationale. To investigate this, a parametric study was performed on a soil embankment of varied geometric characteristics and soil properties subjected to three different strong ground motions obtained during the 1994 Northridge earthquake. The dynamic response of the embankment model was used to calculate seismic coefficient time histories for critical failure surfaces generated through conventional limit equilibrium analysis. FLAC, a two-dimensional explicit finite difference program developed by the Itasca Consulting Group for engineering mechanics computations, was used for the dynamic analysis. The soil behavior was modeled by the Mohr-Coulomb constitutive relationship. Once the seismic coefficient time histories were obtained, a procedure was used to compute weighted average seismic coefficients for each of the time histories. The weighted average seismic coefficients obtained in this fashion were analyzed for possible correlations with the parameters used in the study. The results obtained should provide a more rational approach for selecting seismic coefficients for pseudostatic analysis.