南海水合物黏土沉积物力学特性试验模拟研究

利用自行研制的含水合物沉积物合成、分解与力学性质测量一体化试验设备,以南海水合物区域的海底粉质黏土作为骨架,制备含水合物沉积物样品,并对其进行了三轴压缩试验研究,获得了水合物分解前后的应力应变曲线和抗剪强度特性. 结果表明:在水合物饱和度0%~45% 的范围内,水合物沉积物的应力应变曲线均表现为弹塑性变形,存在明显的应变硬化现象;抗剪强度、内摩擦角和黏聚力随水合物饱和度的增加而增加. 相对而言,内摩擦角随饱和度增加幅度较小,其他参数在水合物饱和度超过25% 时,呈陡然增高趋势;水合物分解后导致抗剪强度最大可降低为初始的1/4,不同初始饱和度条件下水合物完全分解后沉积物的抗剪强度基本相等,并大于同等围压条件下初始不含水合物的沉积物抗剪强度.

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.