Shear strength of frozen sand with dissociating pore methane hydrate: An experimental study

Abstract

This paper presents experimental results for peak shear strength of frozen sand containing methane hydrates within the pore space under dissociation at atmospheric pressure. During the experiments, the samples retained metastable pore methane hydrate due to the self-preservation effect. The tested samples were subjected to short-term uniaxial compression at temperatures from −1.8 to −6.5 °C. The gas hydrate component turned out to considerably affect the strength of the host frozen soil: the shear strength of frozen sediments decreased as saturation with metastable gas hydrate became lower. There is some critical hydrate saturation value (~30%) below, which no further strength reduction occurs. Cyclic thawing-freezing increases considerably the strength of frozen samples that contain relict hydrates, primarily because denser ice, with fewer structural defects, forms by freeze back instead of molten porous hydrate-bearing ice. The obtained results indicate that geomechanical properties of frozen sediments correlate with the contents of relict gas hydrate and can be used for detection of hydrate-bearing permafrost layers.