非饱和黏土土体吸力及其对抗剪强度影响试验

非饱和土基质吸力及土-水特征曲线研究对于预测土体的渗流、强度、体变等工程特性具有重要意义。针对合肥典型非饱和黏土,采用滤纸法和温湿度计法开展不同含水率下黏土的吸力试验,同时采用4种预测模型对土-水特征曲线进行对比分析。结果表明,非饱和黏土基质吸力与总吸力均随含水率的升高而降低;当土体处于高含水率时,其吸力随含水率变化速率较低;当土体处于低含水率时,土体吸力随含水率降低迅速升高,呈指数型增长。土体渗透吸力随含水率的增加逐渐增大,达到饱和时渗透吸力基本稳定在750～850 kPa;修正模型兼有较高拟合精度和数值稳定性等特点,适用于计算非饱和黏土基质吸力。最后,结合直剪试验结果可以得出,黏土的黏聚力绝大部分由土颗粒间吸引力所产生,高含水率、低吸力状态下基质吸力对黏聚力的影响占比可达91.13%,而后基质吸力贡献值则逐渐减小直至趋向于0。

Experimental study on the influence of soil suction and shear strength of unsaturated clay

The research on the suction of unsaturated soil matrix and the soil-water characteristic curve is of great significance for predicting the engineering characteristics of soil, such as seepage, strength, and volume deformation. Aiming at typical unsaturated clay of Hefei, the filter paper method and the thermo-hygrometer method are used to carry out the suction test of the weakly expansive clay under different water content. At the same time, four prediction models are used to compare and analyze the soil-water characteristic curve. The results show that both the matrix suction and total suction of the unsaturated clay matrix decrease with the increase of water content; when the soil is at a high water content, the rate of change of the suction with the water content is low; and when the soil is at a low water content, the suction of the soil increases rapidly with the decrease of the water content, showing an exponential growth. The osmotic suction of the soil gradually increases with the increase of the water content, and when it reaches saturation, the osmotic suction is basically stable in the range of 750kPa to 850kPa; the modified FX model has the characteristics of high fitting accuracy and numerical stability, and is suitable for calculating the matrix suction of unsaturated clay. Finally, combined with the results of direct shear test, it can be concluded that the cohesion of clay is mostly caused by the attractive force between soil particles, Under the condition of high water content and low suction, the effect of matrix suction on cohesion can reach 91.13%, and then the contribution of matrix suction gradually decreases until it tends to 0.