含水率对重塑红黏土反复抗剪强度影响试验研究

红黏土性质的稳定与安全生产息息相关，抗剪强度作为红黏土强度特性之一，与红黏土的稳定性密切相关。为探究含水率对红黏土反复抗剪强度的影响，以山西长治地区的重塑红黏土为研究对象进行反复直剪试验。试验结果表明：无竖向压力时，随着剪切次数的增加，抗剪强度减小并趋于稳定值，第2次剪切达到抗剪强度时对应的剪切位移小于第1次剪切时的位移，稳定剪切时对应的剪切位移大于第1次剪切时的位移；抗剪强度与含水率呈负线性关系，且抗剪强度为土体的真黏聚力，随着含水率的增加先增大后减小。当施加竖向压力后，抗剪强度随着含水率的增加而减小；利用抗剪强度表达式拟合得到内摩擦角和黏聚力，其中黏聚力随着含水率的增加先减小后增大；通过真黏聚力计算得出新的内摩擦角，2种分析方法得出的内摩擦角基本接近且均随着含水率的增加而减小，减小幅度逐渐增大。定义黏聚力差异指数比来研究真黏聚力与黏聚力之间的差异，分析得到黏聚力与真黏聚力的差异指数比在0.75~9.96之间，当含水率为19.5%时黏聚力差异指数比达到最小。利用所建立的相关经验公式，能够为红黏土地区矿山岩土勘察、设计和开挖过程中土性参数的合理选取提供一定参考。

Experimental Study on Effect of Water Content on Repeated Shear Strength of Remolded Red Clay

As a special soil，red clay is widely distributed in some areas of China.Due to the engineering problems such as slope cracking，subgrade subsidence and insufficient foundation bearing capacity，the strength characteristics of red clay is one of the main problems concerned by engineers，and the stability of red clay is closely related to safety production.In order to explore the influence of water content on the repeated shear strength of red clay，the repeated direct shear test was carried out on remolded red clay in Changzhi area of Shanxi Province.Because the water content of undisturbed soil in this area is between 17.0% and 23.7%，and the plastic limit water content is 20.34%，considering the law of test results and the influence of plastic limit，soil samples with five water contents of 15.0%，18.0%，19.5%，21.0% and 24.0% were prepared for test.The test results show that when no vertical pressure is applied， repeated direct shear is conducted on the sample，and the test is stopped when the sample’s strength gradually stabilizes.When there is no vertical pressure，the shear strength decreases and tends to be stable with the increase of shear times.The displacement of secondary shear to shear strength is less than that of the first shear，and the stable shear displacement is greater than that of the first shear.In the process of shearing，the shear strength has a negative linear relationship with the water content.When there is no vertical pressure，the shear strength is equal to the cohesion，and the shear strength is defined as the true cohesion.The vertical pressure of 50，100，150 and 200 kPa was applied to carry out the direct shear test.When there is vertical pressure，the shear strength decreases with the increase of water content.The internal friction angle and cohesion of shear strength index were obtained by physical expression fitting，and compared with the internal friction angle obtained by true cohesion and no vertical pressure.The internal friction angle obtained by the two kinds of analysis is basically close，and decreases with the increase of water content，and the decreasing range gradually increases.Due to the dilatancy effect in the test process，the true cohesion first increases and then decreases with the increase of water content，and the cohesion first decreases and then increases with the increase of water content.The contrast analysis shows that the difference of cohesion is obvious，so the difference index ratio of cohesion and true cohesion with vertical pressure is 0.75~9.96，and the change rule of the difference index ratio of cohesion is the same as the fitting cohesion，and the difference index ratio reaches the minimum when the water content is 19.5%.The empirical formula can provide some reference for the reasonable selection of soil parameters in the process of geotechnical investigation，design and excavation of mines in red clay area.