Rapid Filling-Drawdown Cycling Effects on the Seepage and Slope Stability of PSPS Embankment Dams

The application of Pumped Storage Plants (PSPs) worldwide is growing. For many components of PSPs, such as embankment dams, design guidance and recommendations of several international organizations are applied in lieu of criteria specific to PSPs, even though such guidelines are often formulated for irrigation and water supply dams. As such, their application to the design of components within PSPs, which can have operating regimes that involve daily or weekly oscillations in hydraulic head, may result in overly conservative and uneconomical design outcomes. To further promote the adoption of PSPs, analyses can be undertaken to provide a basis for refining the design criteria for PSP embankment dams. This paper presents an analytical comparison of transient and long-term steady state seepage analyses for an earthfill dam with internal drains. The analysis compares the impacts that both cyclical operational reservoir level oscillations and steady reservoir levels have on the phreatic surface, seepage flux within internal drains, and the upstream slope stability for rapid drawdown conditions. The analysis allowed an accurate definition of the internal water level, which can be used to optimize the drainage and the dam geometry.