Abstract: Natural gas hydrate is anticipated to be a potential energy resource. During the mining process from methane hydrate reservoir, the decomposition of methane hydrate can cause risks threatening the safety of engineering and geology. A series of shear tests under different confining pressure conditions was carried out using self-developed low-temperature and high-pressure triaxial apparatus to investigate the mechanical properties of sediments containing methane hydrate under different conditions. The experiment combined with conventional triaxial shear method and multi-stage loading tests was focused on the hydrate decomposition process. It was found that the strength of the sediments was significantly increased due to the presence of hydrates. In the process of depressurization, the strength of sediments was found to be affected by the variations of effective confining pressure and the hydrate saturation. At the early stage, due to the decrease of pore pressure, the effective confining pressure significantly increased, and the shear strength increased as well. In the later stage, the shear strength of samples decreased under high effective confining pressure due to the decrease of hydrate content. The effective confining pressure had a great effect on volumetric strain of the hydrate sediments, and higher effective confining pressure led to obvious shear shrinkage.

Key words: methane hydrate-bearing sediments, depressurization, mechanical properties, triaxial tests