Optimization of Seepage Prevention Form of the Zhen’an Pumped Storage Power Station

The main dam of the upper reservoir of Zhen'an pumped storage power station in Shaanxi Province, China, is a concrete face rockfill dam with height of 125.90m and crest length of 363.00m. The in-situ drilling and geological prospecting show that the groundwater level is higher than the normal water level in part of the left bank and the reservoir tail, leading to the reversed seepage problem of the groundwater through concrete slab under drawdown condition. Based on the establishment and calculation of the three-dimentional finite element seepage model, the analysis and comparison was made between the overall seepage prevention composed of concrete slab + composite geomembrane and the partial seepage prevention composed of concrete slab + composite geomembrane + vertical grouting curtain [1,2]. The result was found that the seepage gradient requirement was met up by both forms, but due to the prevention of supply from the groundwater in the left bank and reservoir tail, the uplift pressure was formed locally in the overall seepage prevention, whereas such problem did not exist in the partial form. With the extra water supply from the groundwater, the partial seepage prevention works better in terms of leakage. Besides, the design of coarse sand drainage layer is well-served in reducing the water pressure beneath the composite geomembrane on the bottom of the reservoir [3]. It is suggested that the high groundwater should be fully utilized for security and economic benefit. The achievement and experience of this partial seepage prevention design should be taken into consideration for other similar projects.