Effect of relative density of sand confined with clay under the impact of liquefaction

Abstract Soil profiles often exhibit both liquefiable and non-liquefiable layers; the impact of a confined liquefiable layer on seismic response remains a subject of ongoing research. This study investigates the influence of liquefaction on the seismic response of a free-field soil profile subjected to various earthquake excitations. The profile comprises liquefiable sand layers with different relative densities (35%, 55%, and 75%) confined with non-liquefiable clay layers. A non-linear dynamic analysis utilizing PLAXIS 2D and the PM4Sand model was employed to evaluate the liquefaction soil's response under seismic loading. The analysis reveals a frequency-dependent filtering effect exerted by liquefaction on earthquake waves. The soil's relative density plays a critical role, where lower densities promoting de-amplification across most frequencies, while higher densities can lead to selective de-amplification or even amplification within specific frequency ranges. Furthermore, the confining effect of the upper clay layer can elevate pore pressure ratios, potentially triggering liquefaction throughout the entire sand layer, resulting in reduced peak ground acceleration (PGA) compared to models without this layer. Moreover, excluding a clay crust resulted in smaller final displacements compared to those including one.