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土质结构差异较大的层状土入渗过程中易出现指流。为了了解层状土下层介质对指流发生发育的影响,以三种不同粒径的石英砂为下层介质和以砂壤土为上层介质进行了室内积水入渗的染色示踪试验。结果表明,下层介质粒径越大越易出现指流,且指流行进速度越快。指流发生后,入渗过程趋向于稳定,且下层土壤粒径越大,稳定入渗率与累积入渗量越小。采用湿润面积和湿润比描述指流发育的宏观特性,发现湿润面积和平均湿润比都随时间而增大,表明湿润锋趋于均匀。为定量研究层状土入渗中指流发育的分形特征,采用像素点覆盖法编制了计算染色示踪试验中分形维数发育的Matlab程序,对程序进行了验证并计算了四组试验指流发育的计盒维数。结果表明指流分布具有明显的分形特征,下层介质粒径越大计盒维数越小,且计盒维数随时间而增大。
Soil flow in layered soil with large difference in soil structure tends to occur during infiltration. In order to understand the influence of subsoil medium on the development of finger flow, three kinds of quartz sand with different grain sizes were used as the underlayer medium and sandy loam soil as the upper medium to carry out the dyeing tracing test of indoor water infiltration. The results show that the larger the lower media particle size, the more prone to finger flow, and refers to the faster speed of the popular. After the finger flow occurs, the infiltration process tends to be stable, and the larger the particle size of the lower soil, the smaller the steady infiltration rate and cumulative infiltration rate. The wetting area and wetting ratio were used to describe the macroscopic characteristics of finger flow development. It was found that the wetting area and the average wetting ratio both increased with time, indicating that the wetting front tended to be uniform. In order to quantitatively study the fractal characteristics of finger-flow development in layered soil infiltration, a Matlab program for calculating the development of fractal dimension in stained soil samples was developed by pixel point coverage. The program was validated and four sets of experimental finger flow development Box count. The results show that the finger flow distribution has obvious fractal characteristics. The larger the diameter of the lower medium is, the smaller the box dimension is and the larger the box dimension increases with time.