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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]

In high latitude region of western China, the environment is in harsh condition that it is cold and dry in winter and has long ice period, which causes many water resource problems. In order to relieve the serious water shortage condition in cold and dry region, a large number of long distance water diversion projects were established to improve the water resource condition, such as increasing farm irrigation, human and animal drinking. While the ice damage occurs frequently under severe ice conditions in cold and dry region, especially in ice period in winter and thawing period in spring, it is easy to form drift ice with different velocities, different plan sizes and different thicknesses, which produces different extrusion forces or impact forces to damage tunnel lining, causing project failure. The failure project could not realize the original planning and construction goal, giving rise to the water allocation pressure. The water allocation would cause water shortage which influences diversion irrigation and farming production in spring. Based on the intense researches on the collision simulation problem of the interaction between drift ice and diversion tunnel, this paper used the symmetric penalty function in the finite element contact-impact algorithm to conduct the theoretical study on collision simulation problem between drift ice and water diversion tunnel. ANSYS/LS-DYNA was adopted as the platform to establish tunnel model and drift ice model. LS-DYNA SOLVER was used as the solver to solve and analyze the damage degrees of drift ice on tunnel. The physical model tests were conducted to verify and reveal the impact damage mechanism of drift ice on diversion tunnel. The physical model was constructed by the geometric scale of 28, which is the ratio of the experiment facility to the prototype in the test. The results show that tunnel lining surface will form varying degrees of deformation and failure when the tunnel lining is impacted by the drift ice with different velocities, different plane sizes and different thicknesses. It is also discovered that the impact stress increases with the flow velocity and their relationship presents linear variation. The impact stress also increases with the drift ice’s plane size and their relationship presents nonlinear variation. The impact stress increases with the drift ice thickness when the drift ice thickness is less than 0.5 m. While the drift ice thickness is greater than 0.5 m, the maximum stress value shows little change. The relationship between drift ice’s plane size and maximum stress shows approximately linear variation. Meanwhile, the software simulation and test observation results are almost the same. The impact of drift ice on the tunnel lining would cause the deformation of lining, but the deformation has little influence on the tunnel stability. The drift ice’s long time erosion would cause the tunnel lining surface to fall off, and further break the strength and stability of the tunnel structures. The study supplies theoretical support and technical guarantee for water diversion project security in cold and dry region of western China. [ABSTRACT FROM AUTHOR]