Seepage flow behavior in slopes due to water level change in the reservoir

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Fill-type dams for power generation and irrigation purposes have often experienced severe damages of slope failure due to a rapid draw down of the reservoir water in seasons. This study concerns seepage flow behavior in earth slopes, development of the phreatic surface and distribution of pore water pressure in the dam body and their influence on slope instability, due to the change in the upstream water level in the reservoir. Centrifuge model tests and associated FEM saturated-unsaturated seepage analyses were carried out on several model earth fills to discuss and propose an appropriate procedure of stability evaluation of slopes.The concluding remarks are as follows : (1) The movement of the phreatic surface due to the change in the reservoir water level can roughly be estimated by the centrifuge model tests, and a close agreement was achieved between the behavior in the model tests and that evaluated by the FEM seepage analysis. (2) The development of residual pore-water pressure is really confirmed in model fills due to the rapid draw down of the reservoir water. The accumulation of the residual water pressure is comparatively high in the central part of the fill and its variation has a close correlation to the rate of draw down water level. (3) Stability of model earth fills is largely dependent on the water pressure of the reservoir water as well as the residual pore water pressure developed in the embankment. The overall stability of the fill along a deep sliding surface shows an abrupt decrease as the rate of water table change increases.