膨胀土干湿循环裂隙演化及其土-水特征曲线研究

Evolution of fissures and bivariate-bimodal soil-water characteristic curves of expansive soil under drying-wetting cycles

周期性的蒸发和降雨作用导致膨胀土裂隙发育,而裂隙对土体的水力及强度特性有很大影响。为研究膨胀土在干湿循环作用下的裂隙发展规律及其土水特征,采用CT扫描技术和图像处理程序定量分析裂隙的发育演化过程;利用压力板仪进行合肥膨胀土土水特征曲线的干湿循环效应试验。研究结果表明:基于CT图像可以得到试样内部裂隙的二维、三维结构及其定量化分析指标;各个裂隙指标的裂隙发育过程可以用logistic函数的生长曲线描述。裂隙对膨胀土的土水特征曲线影响较大,裂隙膨胀土的土水特征曲线呈"双峰"形态;随干湿循环次数增加,膨胀土持水能力降低,不同循环次数的土水特征曲线差异性明显,吸力200~450 k Pa阶段,不同循环次数下膨胀土土水特征曲线逐渐趋于一致;干湿循环对SWCC1和SWCC2特征点(进气值,残余值)的影响程度不同;通过灰色关联法分析发现,平均裂隙宽度、内表面积、平均裂隙长度、体积裂隙度和面积裂隙度均与裂隙膨胀土的持水能力有显著的相关联性;以干湿循环次数和基质吸力为变量建立双峰土水特征曲线模型,采用合肥膨胀土的土水特征曲线试验数据验证了模型的精确性及可靠性,饱和含水率、拟合参数都与干湿循环次数呈良好的相关性。

Periodical evaporation and rainfall cause the development of fractured soil,and the fracture has a strong influence on the hydraulic and strength characteristics of the soil.To study the crack development law and soil-water characteristics of expansive soil under the action of drying-wetting cycles,the CT scanning technique and image processing program are used to analyze the evolution process of fissures.The pressure plate instrument is used to test the soil-water characteristic curves of Hefei expansive soil and to study the effect of drying-wetting cycles.The results show that the CT scan combining with the image processing program can obtain the two-dimensional and three-dimensional structures of the internal crack of the sample and its quantitative analysis index,and the fracture development process of each fracture index can be described by the growth curve of the logistic function.The crack has a strong influence on the soil-water characteristic curve of expansive soil,and the one with cracks is in the form of“double peaks.”With the increase of the number of drying-wetting cycles,the water-holding capacity of expansive soil is reduced,and the difference of soil-water characteristic curves of samples with different cycles is evident.At the high-suction stage,the soil-water characteristic curves of the expansive soil with different cycles gradually become consistent.The influence of drying-wetting cycles on the SWCC1 and SWCC2 feature points(intake value,residual value)is different.It is found that the average fracture width,internal surface area,average fracture length,fissure development degree of volume and fissure development degree of area are significantly correlated with the water-holding capacity of the expansive soil with cracks.The bivariate-bimodal soil-water characteristic curves are established with the number of drying-wetting cycles and the matrix suction as variables.The test data of soil-water characteristic curve(1)s of Hefei expansive soil is used to verify the accuracy and reliability of the model.The saturated water content and fitting parameters are well correlated with the number of drying-wetting cycles.