Application of Critical State Approach to Liquefaction Resistance of Sand–Silt Mixtures under Cyclic Simple Shear Loading

An extensive experimental program of constant-volume (undrained) cyclic simple shear tests was undertaken on Ticino, Italy, sand with different contents of nonplastic fines, ranging from 0% to 40%. The samples were reconstituted by moist tamping and tested with different initial states, including void ratios and effective vertical stresses. Test results confirmed that the concept of equivalent granular void ratio $e^{*}$ is appropriate for the interpretation of the undrained cyclic behavior of sand with different amounts of fines up to the limiting fines content. Because a single trend for critical state (CS) data points was observed in the $e^{*}\text{-}\log (p^{\prime })$ plane (EG-CSL) for different amounts of fines, the cyclic simple shear test results were analyzed within a unified critical state soil mechanics (CSSM) framework in terms of an alternative state parameter, ${\mathrm{\Psi }}^{*}$. A unique correlation between undrained cyclic strength (CRR) and ${\mathrm{\Psi }}^{*}$ was found, irrespective of the fines content and initial state. Although a correlation between the cyclic resistance ratio and the conventional state parameter $\mathrm{\Psi }$ works as well, the procedure based on ${\mathrm{\Psi }}^{*}$ has the advantage that the cyclic behavior of a certain sand with different contents of non plastic fines is described by a single reference curve (EG-CSL). In contrast to previous investigations in the literature, which mainly used triaxial tests, the CRR-${\mathrm{\Psi }}^{*}$ correlation proposed in the present study is based on cyclic simple shear tests, which better represent the real ground conditions under seismic loading.