Mechanical properties of the interstratified hydrate-bearing sediment in permafrost zones

Natural gas hydrate (NGH) is a promising energy for the future since the huge-reserve and clean-burning. Currently, countries such as China, Japan, Canada, and the United States have conducted the marine NGH field trials successfully. While the exploiting cost of permafrost hydrate-bearing sediment (HBS) could be lower considering the rental costs of platform, personnel transportation, etc. The development of permafrost NGH can also serve as a strategic alternative. Clarifying the mechanical properties of permafrost HBS is crucial for the safety exploitation assessment, while the hydrate mainly distribute to be interstratified due to the sedimentation history. In this study, 23 triaxial tests were conducted to investigate the effects of confining pressure, hydrate layer inclination and thickness on the mechanical properties of permafrost interlayered HBS. The results showed that the specimens mainly exhibited strain softening and secondary hardening at high strain (7%). With the increasing confining pressure, the strength increased and then decreased with a threshold around 5 MPa. The strength and cohesion increased with increasing inclination and thickness, while the internal friction angle was insensitive to inclination and thickness.