Post-liquefaction volumetric compression of sand: mechanism and constitutive model considering the semifluidised state

The recent 2023 Turkey–Syria earthquakes have highlighted that liquefaction-induced settlements can lead to significant damage to overlying infrastructure. During the post-shaking stages, the excess pore water pressures dissipated at the end of the earthquake, resulting in volumetric compression of the soils and ground surface settlement. Laboratory element tests and discrete-element method observations have revealed that the total post-liquefaction volumetric strain of soils primarily consists of resedimentation (under almost zero mean effective stress) and subsequent reconsolidation processes. The resedimentation process contributes significantly to the total volumetric strain. However, existing constitutive models for soil liquefaction underestimate the total post-liquefaction volumetric strain as the resedimentation process is not explicitly modelled. In this study, we utilise the semifluidised state and strain liquefaction factor (SLF) in the SANISAND-Sf model. During post-liquefaction drainage tests, a phenomenological modification is achieved by employing SLF to decrease the elastic modulus in the semifluidised state for achieving a large volumetric strain as the mean effective stress approaches zero. The performance of the modified model is demonstrated by simulating the post-liquefaction volumetric strain of sand and comparing the results with experimental data at an element scale.