Coupled Effects of Matrix Friction and Hydrate Saturation on Mechanical Behavior of Hydrate-Bearing Sediments: A 3D DEM Investigation

Natural gas hydrate-bearing sediments (HBS) exhibit mechanical responses governed not only by hydrate saturation but also by the frictional properties of the sediment matrix. However, the coupled effects of sand interparticle friction and hydrate saturation, together with the associated particle-scale mechanisms, remain insufficiently understood. This study employs 3D discrete element method (DEM) simulations to investigate the mechanical behavior of HBS under triaxial shearing, considering sand friction coefficients of μ = 0.3, 0.5, and 0.7 and hydrate saturations of Sh = 0–60%. The results show that sand friction and hydrate saturation jointly control the stress-strain response, stiffness, strength, volumetric deformation, and strain localization of HBS. Increasing Sh promotes the transition from strain hardening to strain softening. Higher μ enhances failure strength and initial stiffness by restricting particle sliding, but also promotes earlier yielding, stronger dilation, displacement heterogeneity, and localized deformation. Particle-scale analysis shows that low-μ systems allow easier particle rearrangement, delaying bond breakage and limiting load-bearing chain buckling. In contrast, high-μ systems intensify particle rotation, displacement transfer, and contact-force anisotropy, although the sensitivity of these responses to μ decreases at high Sh because hydrate cementation becomes dominant. These findings clarify the non-additive coupling between matrix friction and hydrate saturation and provide micromechanical insights for interpreting the geomechanical behavior of HBS.