A Generalized Critical State Model for Gas Hydrate-Bearing Sediments

Abstract

Methane gas hydrate, usually found beneath permafrost and in marine continental margin sediments worldwide, has attracted interest as a possible energy resource and as a potential agent in climate change and seafloor instability. Here, in order to describe the mechanical behavior of gas hydrate-bearing sediments (GHBS), an elastoplastic model is proposed based on the framework of a critical state model. The presence of gas hydrate can increase yield stress, enhancing the cohesion, peak strength and stiffness of the sediments. Therefore, GHBS is considered as the bonded material in the proposed model. A new bonding strength parameter is introduced into the yield function to evaluate the effect of gas hydrate on the yield behavior of the earth materials. Bonding strength of the GHBS subjected to mechanical loading and/or hydrate dissociation may be drastically reduced, causing strain softening after peak strength. Dilatancy is assumed to be a function of the bonding strength and the stress ratio, instead of the single parameter stress ratio, which can reflect the direction of plastic strain increment more realistically. The proposed model can transform into the modified Cam Clay model when hydrate saturation reduces to zero. Finally, the proposed model has been used to predict the stress-strain behaviors of GHBS in triaxial tests, and it is demonstrated that the proposed model has the capability to describe the behavior of GHBS.