Mechanical and deformation behavior of layered hydrate-bearing clayey-silty sediments: different effective confining pressures and clay content analyses

The layered distribution of hydrates significantly influences the mechanical properties of hydrate-bearing sediments (HBS). A comprehensive understanding of the mechanical and deformation behaviors of layered HBS is essential for the safe and effective exploitation of hydrates. In this study, marine clay from the South China Sea and quartz sand were used to simulate hydrate-bearing clayey-silty sediments, and layered hydrate-bearing clayey-silty sediments (LHBCSS) were prepared. A series of consolidated-drained triaxial tests were conducted, and the results were compared with those from homogeneous hydrate-bearing clayey-silty sediments (HHBCSS) to analyze the differences in mechanical properties and deformation characteristics. The shear strength and deformation behavior of LHBCSS were further investigated. The results show that the layered distribution of hydrates reduces the initial stiffness and strength of HBS, while promoting strain hardening in the specimens. The failure strength of LHBCSS is significantly influenced by the effective confining pressure, with the clay content having no obvious effect. However, the clay content is negatively correlated with the secant modulus (E₅₀). The internal friction angle of the LHBCSS is higher than that of the HHBCSS, and the cohesion of the LHBCSS gradually increases with the clay content. The layered hydrate distribution causes the volumetric strain of HBS to favor shear contraction. The maximum shear dilatation rate of LHBCSS is notably lower than that of HHBCSS, and the clay content has a minimal effect on the critical stress ratio of LHBCSS. The layered distribution of hydrates alters the stress behavior between the upper and lower layers of the specimen, with the low hydrate saturation layer having a greater influence on the overall strength and deformation characteristics of the HBS.