Seepage behavior and its control performance assessment for a high concrete faced rockfill dam in karst areas

The Jiangpinghe concrete faced rockfill dam is a tall dam of 200 m height located in a karst valley. During construction and reservoir impoundment, cracking of concrete face slabs occurred and an abnormal pressure rise was observed in the dam foundation downstream of the grout curtains, leading to an urgent need to reevaluate the safety of the seepage control system. Inspection borehole packer tests, inverse modelling and cross-correlation analysis were used to investigate the seepage characteristics through the dam and its foundation. On this basis, the performance of the concrete face slabs and the grout curtains was systematically assessed, and the mechanisms causing the local pressure rise in the dam foundation were clarified. The results show that the face slabs, though having a permeability 3.6 times higher than the design value after cracking and seepage treatment, perform well for long-term safety operation. The quality of the seepage control treatment at the karst foundation satisfies the design requirements, which limits the amount of leakage at a sufficiently low level. The local pressure rise in the dam foundation can be attributed to the hydraulic connection through a fault(at the left bank) and depositional contact zones(at the right bank), both of which have enhanced permeability due to groundwater erosion and provide channels for quickly transmitting the reservoir pressure towards downstream across the grout curtains. Although the grout curtains effectively reduce the leakage through the dam foundation, they are not able to completely inhibit the pressure transmission, hence making the abnormal pressure rise occur around the eroded channels. The results are of great significance for completion acceptance and safety evaluation of the Jiangpinghe Hydropower Project. © 2024 Academia Sinica. All rights reserved.