EXPERIMENTAL STUDY ON THE STATIC MECHANICAL PROPERTIES OF HYDRATE-BEARING SILTY-CLAY IN THE SOUTH CHINA SEA

By using an integrated experimental apparatus for syntheses of hydrate-bearing sediment (HBS) and tri-axial mechanical tests, a series of static tests were conducted on the silty-clay containing tetra-hydro-furan (THF) hydrate. The samples were prepared with the silty-clay obtained from the South China Sea where gas hydrate has been found. The stress-strain curves before and after hydrate dissociation and the strength parameters were obtained. It is shown that the hydrate-bearing silty-clay behaves as elastic-plastic failure and obvious strain hardening. The failure stress (the stress difference of the maximum and minimum stresses), internal friction angle and cohesion increase with the rise of hydrate saturation. The internal friction angle increases a little bit with the rise of hydrate saturation, while the other parameters increase rapidly once the hydrate saturation is over 25%, which is agreed well with the change of hydrate occurrence form in the pore of HBS. The dissociation of hydrate can cause the sediment's strength decrease to be 1/4 of the initial value. The strengths of the sediments after hydrate dissociation at different initial hydrate saturations are almost the same and larger than that of the sediment initially without hydrate.