Triaxial shear tests and statistical analyses of damage for methane hydrate-bearing sediments

Any perturbation to the thermodynamic equilibrium by exploitation may push out hydrate-bearing sediments (HBS) out of the stability zone, thus inducing hydrate dissociation, loss of cementation, which, in turn, can cause submarine landslides and loss of platform foundations during gas extraction operations. Therefore, a thorough understanding of mechanical properties of HBS is of great importance for stability analyses under different environmental conditions. A series of drained triaxial shear tests were carried out on a self-developed apparatus with the samples prepared by gas diffusion method, in which the time domain reflectometry technique was used in measurement of hydrate saturations in real time. A meso-mechanical and mixed model for the elastic modulus of HBS was proposed based on the classical series and parallel models, including the parameter of statistical force transfer paths between particles in HBS. A constitutive model of HBS was improved by coupling the statistical damage theory and the Mohr-Coulomb failure criterion. It is shown that the stress-strain curve changes from strain-hardening into strain-softening with the increase of hydrate saturation and the decrease of effective confining pressure; the secant modulus and the peak strength of HBS increase when the hydrate saturation and the effective confining pressure increase; the cohesion of HBS increases obviously with the increase of hydrate content, and the internal friction angle changed little with the increase of hydrate amount; the proposed mixed model for elastic modulus and the constitutive model of HBS are both reasonable and feasible. © 2016, Editorial Office of Chinese Journal of Theoretical and Applied Mechanics. All right reserved.