Discrete element analysis of macro- and micro- mechanical properties of methane hydrate bearing clay under different salinity

The mechanical behavior of methane hydrate bearing soil is closely related to the characteristics of hydrate phase equilibrium. Compared with sand, clay has smaller pore size and pore size has a great influence on the characteristics of hydrate phase equilibrium. In this paper, a three dimensional thermal-hydro-mechanical-chemical bond contact model for grain-cementing type methane hydrate bearing clay was established by introducing the influence of pore size on the phase equilibrium line. And the numerical simulation of triaxial compression test on methane hydrate bearing clay under different salinity was studied. The macro- and micro-mechanical behaviors such as stress-strain curve, volume strain, the number of bond breakage, the aggregate crushing rate and strength characteristics were analyzed and compared with the mechanical properties of remolded clay. And the enhancement of bond on the mechanical properties of methane hydrate bearing clay is discussed. The results show that : (1) Under low confining pressure, with the increase of salinity, the peak shear strength of methane hydrate bearing clay gradually decreases, and the strain softening are less significant. At the same time, the volume strain shows shear contraction first, then weak dilatation and then shear contraction. Under high confining pressure, it shows strain hardening and shear contraction. (2) With the increase of confining pressure and salinity, the number of bond breakage and the aggregate crushing rate of methane hydrate bearing clay are gradually increased. (3) Finally, through the analysis of the strength characteristics of methane hydrate bearing clay, it is found that its strength envelope presents typical nonlinear characteristics.