A fully coupled THMC-MPM framework for modeling phase transition and large deformation in methane hydrate-bearing sediment

Methane hydrate-bearing sediment (MHBS) is a multiphase granular system characterized by complex thermo-hydro-mechanical–chemical (THMC) interactions involving phase transitions and large deformation behavior. Hydrate dissociation weakens sediment strength, potentially initiating geohazards such as submarine landslides. Simultaneously, large deformations in MHBS alter the sediment’s state, influencing hydrate reaction kinetics. Despite recent progress, modeling the coupled processes of hydrate dissociation and large deformation in MHBS remains a significant challenge. This study develops a THMC-coupled material point method (MPM) framework to simulate the pre- to post-failure behavior of MHBS associated with hydrate dissociation. The framework incorporates three key advancements: (i) a six-field governing equation integrated with the Kim–Bishnoi hydrate reaction model to resolve dynamic phase transitions, multiphase interactions, and large deformations; (ii) a strain-softening Mohr–Coulomb model with hydrate saturation-dependent strength to capture sediment mechanical degradation; and (iii) a hybrid explicit–implicit time integration scheme designed to enhance computational efficiency for systems with low permeability and high reaction rates. The framework is validated against Masuda’s hydrate dissociation experiment and an extended Terzaghi consolidation benchmark, before being applied to simulate biaxial compression tests and hydrate dissociation-triggered slope failures. We reveal that (1) shear dilation generates negative excess pore pressure in undrained conditions, triggering hydrate dissociation within the shear bands ; (2) shear heating resulting from rapid, large deformation promotes hydrate dissociation, exacerbating sediment softening; and (3) sediment strength degradation, hydrothermal variations, slope geometry, and other factors collectively shape the dynamic progression of retrogressive failures in MHBS. This work provides a powerful framework for modeling hydrate-related granular mechanics and geohazards.