SPF-MHBS: a stress partition constitutive framework for methane hydrate-bearing sediments

A constitutive framework based on the concept of stress partition, referred to as SPF-MHBS (stress partition framework for methane hydrate-bearing sediment), is proposed to capture the mechanical behavior of methane hydrate-bearing sediments (MHBS) both with and without methane hydrate (MH) dissociation. Inspired by the effective stress principle, MHBS is treated as a composite material with the sediment matrix and MH as two individual components in SPF-MHBS. The effective stress of MHBS is jointly carried by the sediment matrix and MH under the assumption that the two components are subjected to the same strain. A significant advantage of this approach is that the deformation of MHBS caused by MH phase change can be naturally reflected due to stress transfer between the two components. Within SPF-MHBS, the choice of constitutive model for each of the two components is flexible, depending on test evidence and application purpose. A specific model developed within this framework is calibrated in this study based on a limited number of triaxial tests without MH dissociation. The calibrated model is then used to simulate the mechanical behavior of MHBS under a wide range of conditions, including different MH saturation, temperature, pore pressure, sediment density, and confining pressure, showing good agreement with test results. More importantly, the model is able to appropriately simulate the deformation of MHBS under both heating- and depressurization-induced MH dissociation conditions. All of the simulations of the tests on the same material are conducted using a same set of model parameters, highlighting the general applicability of the model.