Stress-strain response and deformation behavior of hydrate-bearing sands under different grain sizes: A particle-scale study using DEM

Natural gas hydrates are crystalline solids found in sediments beneath the seabed and permafrost, which significantly affect the mechanical behavior of sediments. The effect of hydrates often varies for different sediments, which has been captured in some laboratory studies. But the particle-scale information involved is obscure and the underlying mechanisms often rely on assumptions. In this study, discrete element method (DEM) was used to improve understanding of the hydrate effect on the mechanical behavior of different sands. Triaxial compression tests were carried out using DEM on the digital hydrate-bearing sands (HBS) with different grain sizes. Simulation results shows that the large-grain samples often yield earlier and tend to strain-hardening behavior, while hydrate occurrence induces strain-softening behavior. In terms of stress-strain response and porosity changes, the hydrate strengthening on the small-grain samples is much greater than the large-grain samples. Particle-scale observations indicate that particle rotation usually occurs in regions with small particle displacement and is more intense on shear slip surfaces. Hydrate bonds are mainly subjected to tensile failure, and large grain size may hinder bond shear failure. Hydrates restrict the development of radial fabrics and enhance the stress-induced anisotropy, rendering a more stable framework for sediments.