Abstract: To improve the understanding of the mechanical behavior of the gas-hydrate bearing sediments, a series of triaxial compression texts was performed on gas saturated CO2-hydrate-bearing sand. Samples were prepared using the excess gas method, in a modified high-pressure low-temperature triaxial apparatus. The hydrate saturation could be determined readily according to the gas assumption. The repeatability of sample making was analyzed in terms of the hydrate saturation. It was found that samples with high hydrate saturation could be formed from samples with high initial water saturation, however, the repeatability of making samples, which was affected by pore blocking effect, was low. It was shown that the repeatability of making samples with hydrate saturation lower than 40% using the excess gas method was relatively good. The triaxial test results show that the mechanical behavior of hydrate-bearing sand samples depends largely upon the hydrate saturation and the applied net confining pressure. The strength, stiffness, ductility and compressibility of hydrate bearing specimens increase with the effective confining pressure; as hydrate saturation increases, the strength and stiffness of specimens increase, while the ductility and compressibility decrease. In addition, the larger the hydrate saturation, the larger the apparent cohesion, whereas the friction angle remains practically unchanged.

Key words: CO2 hydrate-bearing sand, hydrate saturation, excess gas method, pore blocking effect, mechanical properties