Approximately 90% of gas hydrates are buried in fine-grained sediments on earth, especially in the South China Sea. The potential instability of the fine-grained sediments induced by hydrate dissociation requires us to investigate the shear strength and pore pressure response of the sediments during the hydrate recovery. To date, most of studies focused on the undrained mechanical behavior of gas hydrate-bearing sand or gas hydrate-free clay, and few studies examined gas hydrate-bearing fine-grained sediments. According to the low-permeability and water-saturated characteristics of the sediments in the South China Sea, we performed a series of undrained triaxial shear tests on water-saturated methane hydrate-bearing clayey-silty sediments in this area. The experiment results show that the failure strength of methane hydrate-bearing sediments (MHBSs) increases with the increase in hydrate saturation and initial effective mean stress. The excess pore water pressure of MHBSs remains positive during shear. The cohesion in Mohr-Coulomb model increases with the increase in hydrate saturation, while the internal friction angle in Mohr-Coulomb model has little dependence on the hydrate saturation.

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Natural gas hydrate has always been the focus of scientists' research as a kind of clean energy. There is a causal relationship between the thorough study of mechanical properties of hydrate-bearing sediments (HBSs) and the realization of the utilization of hydrate resources. We conducted a series of mechanical experiments on HBSs at different temperatures and effective confining pressures in this work. Experimental data showed that the samples' mechanical properties have a remarkable correlation with temperature and effective confining pressure. The strength of HBSs is positively correlated to effective confining pressure and negatively correlated to temperature. Furthermore, the samples' stress−strain behaviors shifted from hardening to softening with decreasing effective confining pressure and temperature. By assessment of the Mohr strength envelope, the cohesion linearly increased with decreasing temperature. A simple relationship among confining pressure, temperature, and strength was established. Moreover, the fitted failure point line was influenced by the temperature of the samples. The presence of hydrate solids in the sample pores weakened the samples' compressibility. The samples' dilatancy showed a negative correlation with temperature, and the maximum dilatancy and peak strength did not occur at the same strain level.

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