Mechanical behaviors of permafrost-associated methane hydrate-bearing sediments under different mining methods

A series of triaxial tests were conducted to investigate the mechanical behaviors of permafrost-associated methane hydrate-bearing sediments under different mining methods (depressurization/heating under exhaust/non-exhaust conditions, CH4–CO2 replacement). The results indicate that both depressurization and heating will decrease the stability of methane hydrate-bearing sediments containing ice which prepared by a mixture method, due to the loss of bearing capacity of methane hydrates and increasing pore pressure; the sediments dissociated under exhaust conditions present much higher failure strength and elastic modulus than those dissociated under non-exhaust conditions, which means that the instability of hydrate-bearing sediments containing ice is likely to be induced more easily in the low permeability regions in certain conditions; the sediments dissociated by depressurization are more stable than those dissociated by heating, due to the effect of ice re-formation under sub-zero conditions; and the failure strength and elastic modulus of methane hydrate-bearing sediments containing ice (mixture method) are slightly lower than that of the CO2 hydrate-bearing sediments containing ice (mixture method) under various conditions, which means that the layers may possibly keep stable when the methane hydrate is completely replaced by CO2 hydrate.