Prediction of Undrained Monotonic and Cyclic Liquefaction Behavior of Sand with Fines Based on the Equivalent Granular State Parameter

The undrained behavior of sand with fines under both monotonic and cyclic loading was investigated experimentally by triaxial testing. The testing program covers fines content ranging from 0 to 30%, and a wide range of initial void ratios and confining stresses. The spectrum of cyclic loading includes one- and two-way cyclic loading, and in the latter case, the cyclic loading may be symmetrical or nonsymmetrical. The influence of fines content can be captured by using the equivalent granular void ratio, $e^{\ast }$, in lieu of the void ratio, $e$. All steady-state data points can be described by a single relationship referred to as the equivalent granular steady-state line. This study proposes the concept of the equivalent granular state parameter, ${\psi }^{\ast }$, for capturing the combined effects of the stress state, density state, and fines content. The observed behavior can then be related to $e^{\ast }$ and/or ${\psi }^{\ast }$. Irrespective of fines contents, the behavior under monotonic loading can be classified into three types, and ${\psi }^{\ast }$ is a predictor of the behavior type. Cyclic liquefaction, when triggered by adequate cyclic stress and load cycles, can occur in three different forms. Irrespective of the fines content, ${\psi }^{\ast }$ determines the form of cyclic liquefaction. Furthermore, under certain conditions, the monotonic and cyclic behavior can be correlated.