A state-dependent subloading constitutive model with unified hardening function for gas hydrate-bearing sediments

Abstract

Natural gas hydrate in ocean sediments and permafrost areas may become a significant potential energy resource. Since the hydrate dissociation may affect the stability of production wells and even lead to geological hazards, it is essential to study the mechanical properties of gas hydrate-bearing sediments (GHBS) for the efficient and safe extraction of gas hydrate. This study presents an extended subloading Modified Cam-Clay model for clayey-silty and sandy GHBS. The state-dependent unified hardening function and equivalent skeleton void ratio are newly introduced to consider the coupled effects of stress level, void ratio, dilatancy, and hydrate saturation on the mechanical behavior of GHBS. Based on the theory of hyperelasticity, an elastic constitutive relation accounting for the influences of cementation caused by hydrate formation and sediment structure change caused by hydrate dissociation is established by using a stiffness evolution function related to hydrate saturation. The bonding and debonding law of strength reflecting the hydrate cementation and its degradation are used. The model is applied to simulate different triaxial tests of GHBS, and its performance in predicting the isotropic compression, strain hardening and softening, shear contraction and dilation, and collapse induced by hydrate dissociation is investigated.