Thermo-hydro-mechanical coupled material point method for modeling freezing and thawing of porous media

Climate warming accelerates permafrost thawing, causing warming-driven disasters like ground collapse and retrogressive thaw slump (RTS). These phenomena, involving intricate multiphysics interactions, phase transitions, nonlinear mechanical responses, and fluid-like deformations, and pose increasing risks to geo-infrastructures in cold regions. This study develops a thermo-hydro-mechanical (THM) coupled single-point three-phase material point method (MPM) to simulate the time-dependent phase transition and large deformation behavior arising from the thawing or freezing of ice/water in porous media. The mathematical framework is established based on the multiphase mixture theory in which the ice phase is treated as a solid constituent playing the role of skeleton together with soil grains. The additional strength due to ice cementation is characterized via an ice saturation-dependent Mohr–Coulomb model. The coupled formulations are solved using a fractional-step-based semi-implicit integration algorithm, which can offer both satisfactory numerical stability and computational efficiency when dealing with nearly incompressible fluids and extremely low permeability conditions in frozen porous media. Two hydro-thermal coupling cases, that is, frozen inclusion thaw and Talik closure/opening, are first benchmarked to show the method can correctly simulate both conduction- and convection-dominated thermal regimes in frozen porous systems. The fully THM responses are further validated by simulating a 1D thaw consolidation and a 2D rock freezing example. Good agreements with experimental results are achieved, and the impact of hydro-thermal variations on the mechanical responses, including thaw settlement and frost heave, are successfully captured. Finally, the predictive capability of the multiphysics MPM framework in simulating thawing-triggered large deformation and failure is demonstrated by modeling an RTS and the settlement of a strip footing on thawing ground.