杭州湾浅层储气砂土应力路径试验研究

Experimental study of stress path of shallow gassy sand of Hangzhou Bay

利用GDS非饱和三轴试验系统开展了杭州湾储气砂土主动压缩、被动压缩、主动伸长与被动伸长等4种应力路径试验研究,以论证应力路径对非饱和砂土的变形性状与强度特性影响。结果表明,在卸荷应力路径被动压缩与被动伸长下非饱和砂土的应力-应变曲线呈明显的应变软化性状,而加荷应力路径主动压缩与主动伸长则分别表现为轻度应变软化及显著应变硬化变形特征;非饱和砂土的强度参数在卸荷与加荷应力路径中也存在差异,前者的有效凝聚力高于后者,而内摩擦角则相反;但其表观凝聚力与基质吸力关系在不同应力路径下均可用乘幂函数τus=a(ua-uw)b有效描述,而试验参数a、b值不同,公式τ=c′+(σn-ua)tan′+a(ua-uw)b可合理地用于表述非饱和砂土的强度特性。

In order to reveal the influences of stress path on the deformation behavior and strength characteristic of unsaturated sand, the four kinds of stress path experimental study of conventional triaxial compression （CTC）, reduced triaxial compression （RTC）, conventional triaxial extension （CTE） and reduced triaxial extension （RTE） on shallow gassy sand from the Hangzhou Bay is carded out by GDS unsaturated triaxial system. The results show that the stress-strain relationship of unsaturated sand in unloading stress paths of RTC and RTE appears strain softening, and the light strain softening and significant strain hardening deformation behaviors for loading stress paths of CTC and CTE relatively. The shear strength parameters of unsaturated sand are also different under the condition of unloading and loading stress paths, the effective cohesion value of the former is higher than the latter; and the internal friction angle is the opposite. However, the relationships between the apparent cohesion and the matric suction in various stress paths of unsaturated sand are effectively described by the power function τus=a（ua-uw）^b, and the test parameters of a and b are different. Therefore, the shear strength formula τ=c＇＋（σn-ua）tanφ＇＋a（ua-uw）^b can be used to express the strength characteristic of unsaturated sand reasonably.