The constitutive behavior and dissociation effect of hydrate-bearing sediment within a granular thermodynamic framework

Considering the energy dissipation caused by hydrate dissociation and granular rearrangement at the micro level, a multiphase constitutive model of hydrate-bearing sediment is established within a granular thermodynamic framework. This model incorporates the nonlinear expression of bonding stress into the elastic energy density function, considers the relative velocities of the gas and liquid phases in terms of the solid phase in the dissipative force system, and introduces the coupling effect of heat conduction into the migration coefficient matrix to capture the complex behavior of the sediment. Defining the migration coefficient matrix and elastic energy function, the effective stress is obtained and is suitable for constant hydrate saturation and hydrate dissociation conditions. Dilatancy equations are improved by considering the effect of compactness, bonding stress, and hydrate saturation. Meanwhile, the calculation method of bonding stress is suitable for both strong and weak cementation conditions. The deduced model is validated against the test results conducted on natural and synthetic samples under different hydrate saturations, sediment porosities, and hydrate habits and can effectively capture the strain hardening and softening as well as the dilatancy properties of the sediments and the loading path effect.