Cyclic behavior and liquefaction resistance of silty sands with presence of initial static shear stress

摘要

The liquefaction resistance of silty sands and the potential effect of initial static shear stress are major concerns in seismic design of dams and embankments. This paper presents a systematic experimental study on non-plastic silty sands to address these concerns. It is shown that the concept of threshold alpha (alpha(th)) proposed by Yang and Sze (2011) to characterize the impact of a (representing the initial static shear stress level) on cyclic resistance (CRR) of clean sands is applicable to silty sands as well. When alpha alpha(th), CRR increases with increasing a, otherwise it decreases with increasing alpha. The threshold a is affected by the initial packing density, the initial effective confining pressure and the fines content. An improved state dependency of the threshold alpha, which is regardless of fines content, is proposed in the framework of critical state soil mechanics by using the state parameter (psi). An analysis platform, known as CRR-psi platform and developed based on clean sand data, is shown to have the capability of characterizing the state dependence of CRR for sands with varying fines contents. This platform in conjunction with the unified alpha(th)-psi correlation provides a unified and consistent framework for understanding the complicated effects of initial static shear stress on soil liquefaction and for quantifying such effects for engineering practice.