Strength behaviors of CH4 hydrate-bearing silty sediments during thermal decomposition

Predicting the mechanical response of methane hydrate-bearing sediments prior to and during gas production enable appropriate design and anticipate risk due to extraction process of methane from deep-ocean and permafrost setting. In this study, a series of triaxial drained shear tests followed by hydrate dissociation were performed on artificial hydrate-bearing silty sediments at given porosity and stress conditions. The peak strength of HBSS increases exponentially with hydrate saturation, which signifies proportional loss of strength due to hydrate dissociation by thermal decomposition. The peak strength of partially dissociated sediments is slightly lower than the strength of sediments with similar hydrate saturation freshly formed. The enhancement effect of CH4 hydrate on the strength behaviors of HBSS would be more obvious under higher effective confining pressures. The peak strength increase of HBSS was not only due to the increase in cohesion component but also frictional component for a given hydrate saturation and porosity. Thermal decomposition of HBSS is governed directly by its hydrate saturation rather than the confining stress, although with higher confining stress the dissipation of the released gas is affected by the permeability of the sediments thus slightly prolonging the dissociation process.