Temperature and Pore Pressure Dependencies of the Mechanical Behavior of Methane Hydrate–Bearing Fine-Grained Sediment

In the South China Sea, a significant amount of methane hydrate exists in the sediment containing fine-grained soil. Increasing temperature and/or decreasing pore pressure can remarkably degrade the mechanical characteristics of this methane hydrate–bearing fine-grained sediment (HBFS). In this study, several compression tests under triaxial stress condition on HBFS are performed with changing temperature and pore pressure. The experimental results reveal that the HBFS specimen has an enhanced stiffness and failure strength characteristic under lower temperature and/or higher pore pressure conditions. An improved phase state parameter H is presented as a characterization for the temperature and pore pressure condition, which considers the capillary effect for HBFS with wide pore size distribution. The secant modulus and failure strength tend to linearly increase with the rising improved phase state parameter H. The internal friction angle is independent of the temperature and pore pressure, while the cohesion exhibits a significantly linear increase with the rising improved phase state parameter H. In addition, the shear–dilatancy curve shifts to the right with the rising improved state parameter H owing to the enhanced cementing strength of hydrate–soil cluster. These research findings are beneficial for grasping the mechanical behavior of HBFS. Furthermore, this research also provides data support for building the constitutive model of HBFS during methane hydrate recovery.