A discrete element simulation considering liquid bridge force to investigate the mechanical behaviors of methane hydrate-bearing clayey silt sediments

Abstract

For the safe exploration of natural gas hydrate, an understanding of the mechanical behaviors of methane hydrate-bearing sediments is essential. To date, the majority of the related research has focused on the mechanical properties of sandy sediments; research on fine sediments containing clay or silt is very limited, although more than 90% of gas hydrates are found in clay or silt. In this study, a novel discrete element method (DEM) model considering liquid bridge forces caused by the capillary water effect among particles is proposed and is used to simulate methane hydrate-bearing clayey silt sediments with pore-filling distribution. A series of DEM simulations of drained biaxial compression tests under different confining pressures is performed to investigate the mechanical behavior (i.e., the stress-strain relationship, the volumetric response, and strength properties such as friction angle and cohesion) of samples with different hydrate saturations. The numerical results reveal that methane hydrate-bearing clayey silt sediments are characterized by strain-hardening behavior with shear contraction. In addition, the liquid bridge forceincreases with methane hydrate saturation, which considerably enhances cohesion while making no significant contribution to the internal friction angles. The presence of methane hydrates in the pores can increase the failure strength of the sediments, while the initial stiffness is slightly affected by methane hydrate saturation when the latter ranges from 10% to 30%.