Abstract: The seismic loading on saturated soil deposits induces a decrease in effective stress and a rearrangement of the soil-particle structure, which may both lead to a degradation in undrained stiffness and strength of soils. Only the effective stress influence on small strain shear modulus G_max is considered in seismic response analysis nowadays, and the cyclic shearing induced fabric changes of the soil-particle structure are neglected. In this paper, undrained cyclic triaxial tests were conducted on saturated sands with the shear wave velocity measured by bender element, to study the influences of seismic loading on G_max. And G_max of samples without cyclic loading effects was also investigated for comparison. The test results indicated that G_max under cyclic loading effects is lower than that without such effects at the same effective stress, and also well correlated with the effective stress variation. Hence it is necessary to reinvestigate the determination of G_max in seismic response analysis carefully to predict the ground responses during earthquake more reasonably.

Key words: Cyclic loading, Seismic response analysis, Undrained cyclic triaxial test, Small strain shear modulus, Effective stress, Bender element, Soil-particle structure

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