降雨条件下非饱和膨胀土中优先流发育机理的试验研究

Soil fissures and small cracks generally develop as a result of soil shirnkage during the swell-shrink process. The rainfall infiltrates quickly into the soil along the preferential paths, i.e., soil fissures and cracks, which are vital to groundwater recharge and stability of the expansive soil sides, however, how does the preferential flow develop in expansive soil and which factors control have not been reported so far. Therefore, the mechanism of preferential flow in the expansive soil under different rainfall intensities and duration, and the number of swell-shrink processes in a laboratory, will be sutied. The impact of the number of swell-shrink process, rainfall intensities and druation on the preferential flow in the distributed soil corns will be observated by a X-ray computed tomography (CT) in a mecro scale , and three-dimensional reconstruction of the preferential flow will also be conducted. And the results of the expriments will be verified by the Brilliant Blue FCF tracing tests. The cures of effluent volume at the bottom of soil columns vs. time will be uesed to quantify preferential flow in the expansive soil, and to anlyse the mechanism of preferential flow together with the data of CT. The analytical results will improve the understanding of preferential flow in the expansive soil, and will be important to the development of no-expansive and expansive soil infitration theroys.

膨胀土在干湿循环过程中产生裂隙，导致降雨快速入渗深部土壤形成优先流。因优先流对膨胀土壤水入渗补给过程与膨胀土边坡的稳定性产生重要影响而受到广泛关注，但其发育规律与机理尚不清楚。本项目拟开展降雨条件下膨胀土壤中优先流演变机制的试验研究。利用CT技术，研究重塑膨胀土在不同降雨强度与历时和不同干湿循环次数下优先流发育的动态特征，构建三维优先流发育模式，从细观尺度研究降雨过程中优先流动态发育特征、降雨条件和干湿循环次数对优先流发育的影响，并结合亮蓝染色试验和土柱底部出流体积-时间关系曲线的分析结果，综合研究优先流发育机理。该研究成果将弥补目前对膨胀土壤中优先流机理研究的不足，促进土壤水入渗理论的发展，对膨胀土渗流理论的研究具有重要意义，为膨胀土区土壤水入渗补给和边坡稳定性的机理研究提供重要科学依据。

膨胀土干湿循环形成裂隙，为优先流现象发育提供重要条件。本项目采用优先流理论，利用自制降雨-CT物理模型研究了降雨条件下非饱和膨胀土优先流现象发育机理。研究结果表明：（1）膨胀土体裂隙发育受干湿循环次数的增加而增加，但其主大裂隙则随干湿循环次数增加而减弱；（2）降雨试验过程中，膨胀土中裂隙会缓慢闭合，降雨入渗速率显著降低，且膨胀饱和渗透系数随干湿循环次数的增加而逐渐增加；（3）在降雨过程中，膨胀土裂隙均是由上至下逐渐缩小或闭合，但降雨入渗能力尚未达到裂隙优先导水能力时，膨胀土裂隙的优先导水速率随降雨的动态变化相对较小；（4）随着干湿循环次数增加，土壤裂隙发育，在降雨过程中其吸水能力越强，裂隙更容易因土壤膨胀而收缩，影响裂隙的优先导水能力；（5）在降雨过程中优先导水能力出现了波动跳跃的动态特征，这表明膨胀土的膨胀土性是非线性的；（6）降雨强度越大，膨胀土可吸收的降雨越多，土体膨胀程度越大，对大孔隙的膨胀挤压程度越大，优先通道形态发生变化，影响优先流的形成与发育；（7）膨胀土优先通道直径越大，土壤初始含水量越低，其优先导水能力越强。本项目研究成果对提高非饱和膨胀土水分迁移机理的认识具有重要科学意义。