Method for Estimating Postcyclic Undrained Secant Modulus of Clays

Abstract

This paper outlines methods for predicting changes in the undrained secant modulus for saturated clays after cyclic loading, but prior to the dissipation of cyclically induced excess pore pressures. The equations are developed using relationships between the relative stiffness for normally consolidated (NC) and overconsolidated (OC) soils originally predicted by the concept of critical state soil mechanics. The experimental parameters used in the proposed equations are easily determined from the results of laboratory tests or as a function of the plasticity index. The proposed methods were applied to the results from cyclic triaxial tests previously carried out by the writers and other researchers on various clays. The methods show good agreement, and it is suggested that they are valid for the prediction of the undrained stiffness of clays after cyclic loading.