昔格达组黏土岩和粉砂岩现场直剪试验研究

In-situ direct shear test on Xigeda Formation clay stone and siltstone

通过昔格达组黏土岩和粉砂岩自然状态与饱水状态下的现场直接剪切试验,获得不同法向应力及含水率下的剪应力-剪切变形曲线,对这几组曲线特征进行对比分析和总结,采用最小二乘法对自然状态与饱水状态下的抗剪强度参数进行求解。最后,从亲水性矿物化学腐蚀反应的角度出发,分析了水对昔格达组黏土岩和粉砂岩的损伤机理。试验结果表明:昔格达组地层的剪切变形过程可大致分为3个阶段。昔格达组黏土岩和粉砂岩的剪切强度随着法向应力的增大而增大,随着含水率的增大而减小;水对黏聚力的弱化程度比内摩擦角更显著,粉砂岩强度参数衰减幅度比黏土岩大。现场直剪试验测得的强度参数大于室内测试结果,边坡稳定性评价中黏聚力和内摩擦角取值应充分考虑现场试验结果,减少设计的保守性。

In-situ direct shear tests on Xigeda Formation clay stone and siltstone were carried out in natural and saturated state. Relationship curves between shear stress and shear deformation for clay stone with different normal stresses and water contents were obtained. The shear strength parameters were calculated using least square method. The results show that the shear deformation process can be divided into three stages. From the perspective of caustic chemical reactions of hydrotropic minerals, the damage mechanism of Xigeda Formation clay stone and siltstone induced by water was analyzed. The results show that the shear strengths of Xigeda Formation clay stone and siltstone increase with the increase of the normal stress, while they decrease with the increase of water content. The decrease range of cohesion is larger than that of friction angle, and the decrease range of shear strength for siltstone is larger than that for clay stone.The shear strength parameters by in-situ direct shear tests are higher than those by indoor tests. The results got by in-situ direct shear tests must be fully considered in the determination of cohesion and friction angle for the evaluation of the slope stability. The conservativeness in the design will be reduced.