Slope effects on liquefaction potential and pore pressure generation in earthquake loading

Abstract

Loose, saturated sand or silt deposits can often be susceptible to liquefaction deformations during earthquakes. If these deposits are also on or near slopes or embankments, liquefaction events can lead to damages from lateral spreading or embankment failures. The mechanical study of slope effects and initial static shear stresses on liquefaction resistance is still in development. Furthermore, the literature regarding semi-empirical or Factor of Safety approach to liquefaction site analysis is complicated and presents contradictory results, which often leads professionals to ignore slope effects in engineering liquefaction analyses. However, the standards for characterizing earthquake loading has progressed significantly in the past decades and equipment advances have now made it possible to simulate earthquake loading in soil shear testing. Thus, in addition to summarizing the current standards of liquefaction analyses, this report presents a parametric laboratory study of initial static shear stress on liquefiable sands (with minor emphasis on vertical effective stress, and density). This database is intended to be used as control experimental data on earthquake loading for the development of liquefaction models as part of Next Generation Liquefaction (NGL) project. The parametric program includes a total of 24 simple shear tests on Nevada sands with transient seismic loading on an electromechanical dynamic cyclic simple shear device (EMDCSS). The static shear stress factor (K_α) used in the Simplified Procedure for liquefaction (Seed and Idriss 1975) is empirically investigated under transient loading conditions and corrections for earthquake loading proposed through a regression analysis.