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The cofferdam is a temporary water retaining structure built to protect the foundation pit in the construction of hydraulic engineering. Its layout has great influence to the flood safety, project progress and cost. Relying on the diversion tunnel project of a hydropower station, this paper firstly optimized the design of the cofferdam type at the outlet of the diversion tunnel, and then compares various construction schemes such as earth rock cofferdams, concrete cofferdams, stoplogs gate, and concrete cutoff walls. The cofferdam scheme was designed, and the construction technology and construction scheme of the cofferdam were systematically expounded. The analysis results show that the cofferdam at the exit of the diversion tunnel uses the stoplogs gate type to control the flood season, which meets the requirements of the project safety flood control, significantly reduces the amount of cofferdam engineering and the project cost, and has strong technical feasibility. [ABSTRACT FROM AUTHOR]

Shaanxi Hanjiang River to Weihe River diversion tunnel water inrush problem is one of the key technical problems that restrict the smooth development of the project. In this paper, aiming at the problem of water inrush in the typical section of acrossing Jiaoxi River, the ADINA software was used to establish the hydrogeological conceptual model, and the variation law of the groundwater table, the velocity vector and the water inflow were calculated under different conditions. The results show that the fault location is greatly affected by the excavation disturbance, and there is concentrated leakage. Therefore, it is very easy to form the leakage channel and occur the water inrush in the fault location. [ABSTRACT FROM AUTHOR]