不同细颗粒含量甲烷水合物沉积物三轴剪切试验研究

海域试开采区域含水合物沉积物的粒度分析结果表明水合物沉积物骨架由粗、细颗粒混合构成,通过开展多组低温、高压三轴排水剪切试验研究细颗粒含量和密度对含甲烷水合物沉积物和无水合物沉积物的强度和变形特性的影响。试验结果表明,含水合物沉积物抗剪强度及剪胀性都随细粒含量提高而显著增强。这是由于细颗粒含量增加改变了颗粒间水合物的样貌和分布特征,形成了由水合物包裹着粗颗粒-细颗粒的团簇状集合体。然而,细颗粒含量对无水合物沉积物的强度和变形特性的影响却表现出相反趋势。另外,含水合物沉积物的剪胀关系可以使用修正剑桥模型中的剪胀关系式进行描述。结果表明,剪胀关系的拟合曲线依赖于水合物饱和度的大小。通过对比研究发现,天然水合物和实验室合成水合物试样在较高饱和度时的峰值摩擦角大小及其伴随水合物饱和度的增长趋势存在差异,这种差异主要来源于水合物在沉积物骨架颗粒孔隙中不同的赋存模式及分布特征。

Experimental study on mechanical characteristics of gas hydrate-bearing sands containing different fines

The skeleton structure of gas hydrate-bearing sediments from ocean gas exploitation is composed of coarse grains and fines.A series of low-temperature and high-pressure triaxial drained shear tests are performed to examine the effects of fines and density on the strength and deformation properties of host sands with and without gas hydrate.The results imply that the shear strength and dilation tendency increase with a rise in fines.The rise in fines alerts hydrate morphology and distribution pattern among sand grains.The cluster of coarse grains and fines bonded by hydrate are formed in samples.The shear behavior of host sands exhibits opposite varying tendency with the increasing fines.Moreover,the stress-dilatancy relationship can be modeled using the equation adopted by the modified Cam-clay model and is dependent on hydrate saturation.At a larger hydrate saturation level,the natural samples own a higher peak friction angle and larger increasing speed with the level of gas hydrate than the gas hydrate-bearing samples synthetized in laboratory.The difference is originated from the nucleation mode and distribution pattern of hydrate mass among sand grains.