Investigating the mechanical behavior of grain-coating type methane hydrate bearing sediment in true triaxial compression tests by distinct element method

Methane hydrate is viewed as one of the potential energy resources to alleviate the current and future energy needs. Sediments containing methane hydrate are referred to as methane hydrate bearing sediments. In laboratory tests, the methane hydrate bearing sediments are commonly synthesized by the gas saturated method, and their mechanical properties are tested under simple stress path. When the gas saturated method is used to form the methane hydrate bearing sediments, methane hydrate tends to generate at the surface and meniscus of particles, namely the grain-coating type methane hydrate bearing sediments. In this study, to obtain the mechanical behavior of grain-coating type methane hydrate bearing sediment subjected to complex stress paths, a discrete element method simulation scheme accounting for three particle-scale mechanisms of grain-coating type methane hydrate bearing sediments, i.e. cementation, particle enlargement and particle angulation, along with the experimental data of pure methane hydrate that indicate the strong correlation between the mechanical property of pure methane hydrate and the pore pressure/ambient temperature, is adopted to explore the mechanical behavior of grain-coating type methane hydrate bearing sediments under true triaxial compression tests. The results show that: (1) the discrete element method simulation scheme accounting for microscopic mechanism is effective to simulate the mechanical property of grain-coating type methane hydrate bearing sediments; (2) the cementation effect of methane hydrate in the grain-coating type methane hydrate bearing sediments is weak and the mechanical behavior of grain-coating type methane hydrate bearing sediments in true triaxial compression tests is similar to that of cohesionless granular materials; (3) in true triaxial compression tests, the peak and residual deviator stresses of methane hydrate bearing sediments are larger under a lower value of intermediate principal stress ratio. The Lade-Duncan criterion can be used to describe the strength of grain-coating methane hydrate bearing sediments.