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

发电和灌溉用的填埋式大坝，由于库水在季节的快速下泄，经常遭受严重的边坡破坏。研究了水库上游水位变化对土坡渗流特性、坝体潜水面发育、坝体孔压分布及其对边坡失稳的影响。对几种模型填土进行了离心机模型试验和有限元饱和-非饱和渗流分析，探讨并提出了合适的边坡稳定性评价方法。结论如下：(1)通过离心机模型试验可以大致估算出库水位变化引起的潜水面移动，模型试验结果与有限元渗流分析结果吻合较好。(2)由于库水的快速下沉，模型充填体中残余孔压的发展确实得到了证实。残馀水压力在填方中部积聚较大，其变化与水位下降速率密切相关。(3)模型填土的稳定性在很大程度上取决于库水的水压力和路堤内发育的残余孔压。深层滑动面填方的整体稳定性随地下水位变化率的增加而急剧下降。

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.