层状土入渗试验中指流发育的分形特征及入渗规律

Fractal characteristics of finger flow and infiltration laws in layered soil

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。

Finger flow may occur in layered soil with distinct difference in soil texture. To understand the influence of the subsoil on the occurrence and development of finger flow in layered soil, laboratory dye infiltration experiments were carried outusing sandy loam as the topsoil, and quartz sand as the subsoil with three particle sizes. The results show that the larger the difference between the soil texture of the topsoil and subsoil, the easier the occurrence of finger flow and the faster the finger advancement. After the occurrence of finger flow, the infiltration process tends to be stabilized, and steady infiltration rate and cumulative infiltration amount decrease with increasing of the particle size of the subsoil. Wetted area and wetted proportion were used to describe the macroscopical character of the finger flow. Both wetted area and mean wetted proportion increase with time, and wetting front tends to be uniform. The Matlab Software was used to calculate box counting dimension of finger flow at different time. The results show that the finger flow has obvious fractal features, and the box counting dimension increases with time and tends to decrease with increasing of the particle size of the subsoil.