An experimental study of the relationship between water content and strength of unsaturated expansive soil on canal slope
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摘要:
南水北调中线渠首段渠坡土主要为膨胀土，渠坡膨胀土含水率的变化会影响坡体稳定性。为了探究含水率变化对渠坡稳定性影响的具体特征，对采集自南水北调中线渠首段的渠坡膨胀土进行了滴定直剪试验，获得了渠坡膨胀土抗剪强度指标与含水率的关系曲线，试验结果表明：抗剪强度随含水率增加而明显衰减，衰减过程先快后慢；试样初始含水率越低，黏聚力下降越慢，内摩擦角下降越快，不同初始含水率试样的抗剪强度均在增湿至30%左右时产生拐点，此时衰减速率降低并趋于稳定。设计进行了土-水特征曲线法和瞬时剖面法导水率测试试验，获得了非饱和渠坡膨胀土导水率随含水率变化的曲线，试验结果表明：含水率越低，导水率越小，导水率变化速率越快；反之，导水率变化速率越慢，土体含水率趋于稳定。研究成果可用于膨胀土渠坡稳定性与坡体地下水位关系的定量分析，应用在实际工程中可以更有效地获取渠坡非饱和土体中含水率和抗剪强度的分布特征，并获得含水率和抗剪强度随时间的变化规律，为引入土体空间动态抗剪强度分析，建立更准确的膨胀土渠坡稳定性评价模型奠定基础。
Abstract:The soil layer in the canal first section of the Middle Route of the South-to-North Water Transfer Project (MR-SNWTP) is mainly composed of expansive soil, and changes in water content of the expansive soil affect the stability of the slope. In order to make a reasonable assessment of the stability of expansive soil canal slopes, it is necessary to test and analyze the relevant physical and mechanical properties of the expansive soil on canal slopes at different water content. In this paper, titration-direct shear tests are carried out on the expansive soil collected from the canal first section of MR-SNWTP to obtain the relationship between the shear strength parameters and water content of the expansive soil. The test results show that the shear strength decreases significantly with increasing water content, and the decay process starts fast and then slows down. The lower the initial water content of the sample is, the slower the cohesion decreases, and the faster the angle of the internal friction decreases, and the shear strengths of the sample with different initial water content all show an inflection point when the water content increases to about 30%, when the decay rate decreases and becomes stable. Hydraulic conductivity tests based on soil-water characteristic curve method and instantaneous profile method are designed to obtain the hydraulic conductivity-water content curve of unsaturated expansive soil. The test results show that the lower the water content is, the smaller the hydraulic conductivity is and the faster the change rate of hydraulic conductivity is. Conversely, the slower the change rate of hydraulic conductivity is, and the more stable the soil water content tends to be. The research results of this paper can be used for quantitative analysis of the relationship between the stability of the expansive soil canal slopes and the groundwater level of the slopes. In practical applications, they can also be used to effectively obtain the distribution characteristics of water content and shear strength in the unsaturated soil of the canal slope, and to obtain the time variation laws of water content and shear strength, and a more accurate stability evaluation model is established based on spatial dynamic shear strength analysis of the expansive soil of the canal slopes.
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表 1 物理指标与强度指标值
Table 1. Values of physical and strength indicators
指标 含水率/% 干密度/（g·cm−3） 孔隙比 饱和度/% 黏聚力/kPa 内摩擦角/（°） 取值 22.9 1.65 0.76 83 13~23 15~16 
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