Abstract: Methane hydrate bearing sediments(MHBS) are usually found undersea, which is generally categorized into different types, i.e. bond, pore-filling and so on. The mechanical properties of MHBS will be deteriorated as methane hydrate (MH) dissociates and many marine accidents will be caused; thus a lot of attention has been attracted in investigating MHBS properties changes during exploitation. A newly proposed 2D temperature-water pressure-mechanical bond model is implemented into PFC2D, the commercial software of the distinct element method (DEM), to simulate the dissociation of MH by thermal recovery and depressurization using soil in good exhaust and drainage conditions. By comparison with laboratory test results, it is validated that the newly proposed model is applicable to simulate the mechanical behavior of MHBS. At the same time, the micromechanical properties are also analyzed. With temperature increasing during thermal exploitation, the anisotropic degree of total contact distribution increases; the amount of bond contact, whose principal direction is horizontal all the time, decreases and the amount of unbonded contact, whose principal direction is vertical all the time, increases; the value of averaged pure rotation rate (APR) and its concentration degree increases all the time. With back (water) pressure decreasing during exploitation by depressurization, the total contact distribution changes from isotropic to anisotropic with a vertical principal direction, and the value of APR is small and uniformly distributed. After the recovery of back water pressure, the sample is damaged further, and the anisotropic degree of total contact distribution increases. Besides, the value of APR increases and the concentration degree of positive and negative value increases.

Key words: methane hydrate bearing sediment(MHBS), methane hydrate, temperature, back water pressure, macro and micromechanical property