Subsurface Water Movement and Downslope Deformation in Model-Slope Tests by Artificial Rainfall

The flowslide is reproduced by the quasi-real scale model-slope tests on river sand by artificial rainfall, in which subsurface water movement and downslope deformation are carefully monitored. The rainfall at the intensity of 100 mm/hour on the specimen formed at loose state (9.0-metre long, 1.0-metre wide, 0.5metre deep) have brought about the failure at 2,931 sec after the onset of sprinkling. Firstly, the pore-fluid has descended gradually leading to the parallel wetting-front to the base, and the sand specimen has been susceptible to the vertical contraction. From 300 sec before the failure, the equi-potential lines started to bend normally to the model-slope base and the pore-fluid has been subject to downslope flow. At the same time, the soil strain in deep layer has considerably started. The most severe creep deformation has been produced in the deep layer among the upper slope portion on steep slope and the failure has been initiated within this section. The excess pore-pressure has not been observed in the source area. Whereas, severe excessive pressure head has been generated due to the collision of the failed upper slope-mass, leading to liquidization. It suggests that the dependence of flowslide generation must be on the dynamic changes in pore-pressure not in the source area but in the compressed lower slope-section.