Cyclic Stress History Effects On Small-strain Shear Modulus Of Silt

Present seismic response analysis, a hyperbolic model proposed by Hardin & Drnevich is widely used for describing the nonlinear stress-strain relationship. The small strain shear modulus G_max is the most significant important dynamic property of soils in the Hardin-Drnevich model. The seismic cyclic loading on saturated soil deposits not only induces a decrease in effective stress and a increase in pore water pressure, but also a rearrangement of the soil skeleton which may also lead to a degradation in undrained stiffness and strength of soils. However, only the contribution of effective stress reduction to G_max degradation is considered in the Hardin-Drnevich model, and that of soil fabric change is neglected.Silts are susceptible to liquefaction showed by field performance data during earthquakes. The cyclic behavior of silts has been investigated only on a very limit scale. In this paper, undrained cyclic triaxial tests were conducted on isotropically consolidated saturated silts. Liquefaction characteristics of silt under dynamic loads are analyzed on the basis of the results. Meanwhile, the shear wave velocity is measured intermittently by bender element during cyclic liquefaction to study the influences of seismic cyclic loading history on small strain shear modulus G_max during earthquake. The test results presented herein indicate that present seismic response analyses may overestimate the value of small strain shear modulus G_max without considering the influence of seismic cyclic loading history. The test results indicate that the further reduction of small shear modulus G_max was obviously influenced by the cyclic shear stress ratio and the relative density and initial small shear modulus G_max influence the small shear modulus during cyclic liquefaction together.