閉塞2層砂への雨水浸透に関する実験的研究

Abstract

In order to examine the effect of pore-air on the infiltration phenomena of water intoconfined composite sand column, the experiments of pounded infiltration were carried outby the use of sand column in the lucite cylinder with bottom. The sand column was madeby putting the fine sand on the coarse one or vice versa. For the comparison with theresults of experiments, the unconfined sand columns also were tested.After considering and analysing the results obtained by experiments, the following wasdisclosed for the confined sand column.(1) The case of the fine sand layer on the coarse one.When the wetting front reaches the boundary of two sand layers, the infiltration ratedecreases rapidly, and the moisture content in the upper sand layer and the pore-air press-ure increase rapidly. In the case of a large difference between particle-sizes of two sandlayers, the water flow in the lower coarse sand layer concentrates locally in the cross sectionfor the unconfined column but seems not necessarily to concentrate for the confined column.(2) The case of the coarse sand layer on the fine one.In the case of a small difference between two particle-sizes, when the wetting frontreaches the boundary, the infiltration rate remains constant for some time that is exagg-erated comparing with that in the unconfined column and the rate of change of the pore-air pressure decreases initially. After the time, the former begins to decrease slowly andthe latter increases rapidly. In the case of a large difference between two particle-sizes, when the wetting front reaches the boundary, the infiltration rate rather increases initiallybut decreases rapidly after the time. The pore-air pressure continues to increase rapidlyfrom the initial instant to a certain time. After such a time elapsing, the effect of theupper layer on the penetration of water into the lower one becomes to be similar to thatof the stored water having the same depth as the thickness of the layer.