Cementation Failure Behavior of Consolidated Gas Hydrate-Bearing Sand

The macromechanical properties (strength, stiffness, stress-strain relationship, etc) of the hydrate-bearing sediment are often correlated with the hydrate cementation failure behavior. In this study, a consolidated drained triaxial shear test with X-ray computed tomography was conducted on a hydrate-bearing sediment with a hydrate saturation of 32.1% under 3 MPa effective confining pressure for revealing the cementation failure behavior. The hydrate occurrences were clearly identified to be cementing, grain-coating, prepatchy cluster and patchy cluster. The cementation failure behavior (morphology), deformation evolution (quantitative statistics), and localized shear deformation at different regions of stress-strain curve were observed and analyzed using computed tomography. In the linearity region, the hydrate-cemented clusters moved as a whole, while small hydrate particles would aggregate to the periphery of the clusters. The noncemented sand particles move disorderly during this process. Localized deformation occurred perfectly exhibit an antisymmetric bifurcation pattern. In the plasticity region, the specimen starts to deform plastically; an internal shear band occurs in the specimen. The hydrates begin to shed from the periphery of the cemented structure, and the grinding effect of hydrates begins to occur between sand particles. However, the shedded hydrates will not enter and fill the neighboring pores but hind the movement of sand particles structurally near the original position. In the yielding region, the hydrate-cemented cluster structure is completely damaged and crushed into small pieces; a shear band with a determined thickness and inclination angle was observed.