Simplified Procedure for Effective Stress Anaysis of Ground Response

A review is made of several analytical approaches to the determination of pore-pressure generation and dissipation in saturated sands at level sites during earthquakes and the effects of the resulting pore-pressure buildup on the seismic response of these sites. A simplified procedure is described that uncouples the nonlinearity of the stress-strain relationship of the sand under cyclic shear loading and the gradual stiffness degradation caused by the pore-pressure buildup under the type of loading. It was found that stress reduction between a total stress analysis, where the effective confining pressure is considered to remain constant throughout the earthquake, and an effective stress analysis that accounts for both types of soil nonlinearity did not exceed about 85% under the most severe conditions. Consequently, it is believed that the simplified procedure may be used in conjunction with any ground-response analysis program for the purpose of evaluating ground response including pore-pressure effects.