Thermodynamic model of coupled temperature and pressure effects for hydrate-bearing sediments within particle rearrangement theory

The mechanical properties of hydrate-bearing sediments are significantly influenced by changes in temperature and water pressure. Based on the particle rearrangement theory, a thermodynamic model that couples temperature and pressure, incorporating the dilation equation considering the effects of hydrate saturation and introducing the bond degradation parameters caused by shear and volumetric strains, is developed to describe the mechanical behaviors of hydrate-bearing sediments. The numerical simulation results are compared with the laboratory experiments to explore the effects of confining pressure, hydrate saturation and the temperature-pressure coupling coefficient on the mechanical properties of sediments from both macroscopic and microscopic perspectives. Finally, the sensitivity analyses are conducted on the stiffness coefficient and bond degradation parameter. The results indicate that the introduction of a temperature-pressure coupling coefficient in the model effectively describes the relationship between the mechanical properties of sediments and temperature and water pressure during deposition. Decreasing environmental temperature and increasing water pressure enhance the bond strength and stiffness of hydrates at the microscopic level, resulting in the increased peak strength, strain softening and shear dilation at the macroscopic level. Increasing the stiffness coefficient γ enhances the peak strength of sediments by increasing the initial stiffness of sediments. The bond degradation parameter enhances the strain-softening behaviors of sediments by increasing the rate of bond degradation.