2017 Volume 70 Issue 4 Pages 3-12
Previous reports showed that the pipe flow and entrapped air have effects on the slope stability. Although a variety of studies indicated the role of the pipe flow on the rise of soil pore water pressure in hillslope, several effects, such as branch of soil pipe, entrapped air, has not been examined. In this paper, we conducted a bench-scale model experiment to clarify effects of branch of soil pipe and entrapped air on soil pore water pressure. We used the model which was composed of soil layer, artificial rainfall simulator, and artificial soil pipe in soil layer. We set up five conditions of model experiment, 1) no soil pipe, 2) only one pipe, 3) three pipes which joined into single pipe in middle of soil layer, 4) only one pipe with silica sand layer, 5) three pipes which joined into single pipe in middle of soil layer with silica sand layer. Silica sand layer was installed at the surface to prevent air escaping from soil layer. Under these conditions, we changed the water supplying level with time. The results showed that the spatial variation in drainage capacity of soil pipe, such as confluence of the soil pipe gave impact on soil pore water pressure distribution. So, the soil pore water pressure dramatically increased at the point where drainage capacity of soil pipe was smaller than that of upslope. Moreover, entrapped air enhanced the increase of soil pore water pressure at the point where drainage capacity of soil pipe was smaller than that of upslope.
