MPM formulations for the coupled thermo-hydro-mechanical behaviour of saturated and unsaturated soils

Frictional heating-induced excess pore water pressure is a significant factor contributing to the rapid movement of landslides. Although some studies have explored the thermal effects on fully saturated soil slopes, this study focuses on unsaturated soils and employs a thermo-hydro-mechanical (THM) coupled material point method (MPM) to simulate large deformation problems involving frictional heating. The THM coupling effects are accounted for by adopting a void ratio and temperature-dependent soil water retention curve (SWRC) and permeability function, and by considering the influence of void ratio and degree of saturation on thermal conductivity. The mechanical behaviour incorporates unsaturation effects, as well as thermal strain and strain hardening/softening. The MPM simulations are validated against experimental and analytical results, and parametric studies are conducted to investigate the influence of frictional heating on landslide mobility across different soil types and initial moisture conditions. The results indicate that the effects of frictional heating on the mobility of landslides involving soil with higher water retention capacity are less pronounced. For a given soil, when the initial water content is relatively low, the increase in landslide displacement caused by frictional heating becomes less significant as the water content increases. However, the opposite trend occurs when the soil is close to saturation.