Strength estimation and stress–dilatancy characteristics of natural gas hydrate-bearing sediments under high effective confining pressure.

Gas production by depressurization can significantly increase the effective stress in hydrate-bearing sediments. Therefore, strength and deformation characteristics of sediments under high effective confining pressure should be fully understood before large-scale extraction. In this study, a series of triaxial tests on artificial methane hydrate-bearing specimens were conducted under effective confining pressures of 0.2–20 MPa, and the effects of effective confining pressure and hydrate saturation on the strength parameters and the stress–dilatancy characteristics were discussed. The results demonstrate that the strength and stiffness of hydrate-bearing sediments increase with increasing effective confining pressure. Shearing under high effective confining pressure leads to significant breakage of host particles, which is independent of the hydrate saturation. The increase in the effective confining pressure decreases the internal friction angle while increasing the cohesion of hydrate-bearing sediments. By linking the effective confining pressure and hydrate saturation with strength parameters of Mohr–Coulomb criterion and Drucker–Prager criterion, the strength of sediments in a high range of effective stress can be accurately predicted. With increasing effective confining pressure, the shear–dilation transfers to shear–contraction, the critical stress ratio gradually decreases to attain a constant value, and the effects of hydrate saturation and effective stress on the dilatancy characteristics gradually become less notable. [ABSTRACT FROM AUTHOR]