Shear behaviour of methane hydrate bearing sand with various particle characteristics and fines

It is recognized that methane hydrate (hereafter referred to as MH) is trapped in the sand sediments of alternating sand and mud layers in the turbidite of the Nankai Trough, Japan. The existence of fines within the marine sediment significantly affects its mechanical and physical properties. A series of plane strain compression tests at high pressures were performed in order to investigate the effect of the particle characteristics and fines content of the host sands on the shear behaviour of MH bearing sands. MH bearing sands were artificially produced using rounded glass beads and three other silica sands with different fines contents. A high-pressure low-temperature testing apparatus was equipped with a camera to observe deformation of the specimens during shearing and particle image velocimetry analysis was conducted on pictures taken during the experiments. The experimental results show that strength enhancement due to the bonding effect in MH bearing sand increases with the level of fines content. Values for both the cohesion and friction angle of MH bearing sand composed of Toyoura sand increased along with increasing MH saturation. However, in the case of MH bearing glass beads, only the value for cohesion increased when MH was formed. The maximum shear strain of MH bearing glass beads was mostly concentrated near the shear band. While the maximum shear strains of the three other MH bearing sands were concentrated within the shear band, some was widely distributed in the region outside of the shear band. A rise in the degree of MH saturation increased the angle and narrowed the width of the shear band, regardless of the fines content.