Preliminary investigation on parameter inversion for three-dimensional distinct element modeling of methane hydrate

Marine sandy sediments containing pore-filling type methane hydrate particles can be considered as a class of special granular materials which present apparent discontinuity characteristics. To numerically simulate such materials, the distinct element method (DEM) can be used by modeling methane hydrate particles as groups of spheres cemented together and filled into the pores of soil skeleton. The model parameters for inter-particle bonds within an individual hydrate particle are investigated through parameter inversion against the existing laboratory triaxial compression (TC) test results of methane hydrate blocks under various confining pressures. The results indicate that a loose packing with low inter-particle friction needs to be used for the simulated methane hydrate block. When the inter-particle friction coefficient is equal to or less than 0.0, the friction angle obtained from the unbounded sample is less than that of the experimental tests. The bond stiffness varying in a very small range can adequately capture the elastic behavior of methane hydrate under different confining pressures at the same temperature. Because the interaction between stiffness parameters and bond strength parameters is small, it is assumed that the two types of parameters should be independent. The relationships between micro bond strength parameters and macro parameters (internal friction angle and cohesion) are established by conducting TC tests on choosing different micro bond strength parameters. The methane hydrate shows volume contraction, then dilatancy. And the characteristic dilatancy increases with the decrease of the confining pressure. With the increase of the axial strain, the grain contact direction deflects