Modelling Liquefaction-induced Large Deformations with a Two-Point MPM Framework for Unsaturated Soils
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This study presents a three-phase, two-point Material Point Method (MPM) formulation for simulating large deformation behaviour in unsaturated soils. The solid phase is modelled with one set of material points, while the liquid and gas phases share another, enabling the capture of phase interactions and relative motions in porous media. A u–U formulation is adopted, allowing independent tracking of solid and fluid displacements. This eliminates the need to handle advection between the solid and liquid phases, enhancing numerical stability under large relative deformations. Advection between liquid and gas phases is neglected. The method is validated through simulations of both small and large deformation scenarios. Its effectiveness is further demonstrated by modelling seismic-induced liquefaction beneath an unsaturated embankment, capturing pore pressure buildup, liquefaction onset, and post-liquefaction deformation, as well as rapid pore pressure dissipation in permeable layers. The proposed framework offers a robust and versatile tool for analysing unsaturated soils in multiphase, large-deformation geotechnical problems.