Influence of seismic cyclic loading history on small strain shear modulus of saturated sands

Small strain shear modulus Gmax is a key parameter together with the state of stress and shear strain amplitude for predicting the dynamic behavior of soils. Although the seismic cyclic loading on saturated soil deposits induces a decrease in effective stress and a rearrangement of the soil skeleton which may both lead to a degradation in undrained stiffness and strength of soils, only the contribution of effective stress reduction to Gmax degradation is considered in the Hardin and Richart equation which is widely used in seismic response analysis nowadays, and that of soil fabric change is neglected. In this paper, undrained cyclic triaxial tests were conducted on normally and isotropically consolidated saturated sands with the shear wave velocity measured intermittently by bender element during cyclic liquefaction, to study the influences of seismic cyclic loading history on small strain shear modulus Gmax during earthquake. And the Gmax values of samples without such influences were investigated for comparison. The tests results indicate that Gmax of sand under high amplitude seismic cyclic loading history influences is moderately lower than the corresponding value of non-cyclic loading effects at the same effective stress. Hence it is necessary to reinvestigate the determination of Gmax in seismic response analysis carefully to predict the ground responses more reasonably.