When constructing dams for water conservancy and hydropower projects, most projects use diversion tunnels to divert water.
After completing the diversion task, if the diversion tunnel does not need to be converted into a permanent hydraulic structure, it must be sealed to ensure that the project can effectively function. The sealing structure of the diversion tunnel is a permanent structure, and its importance is equivalent to that of the barrage. In order to construct and seal the building, a gate must be installed at the entrance of the diversion tunnel, and the river water can be blocked and stored in the reservoir through the lower gate.
Therefore, the sealing of the diversion tunnel consists of two parts. First, the blocking gate (concrete gate or steel gate) is used to cut off the river water entering the tunnel, and then the appropriate location is selected with concrete (usually called blocking gate). Head) Completely seal the diversion tunnel that has completed its mission to ensure that the water stored in the reservoir does not leak to the downstream.
Extended information:
The construction diversion method in which river water is directed downstream through hydraulic tunnels on the shore. Tunnel diversion is suitable for:
1. The river valley is narrow and the terrain conditions are not conducive to the layout of open diversion channels;
2. The geological conditions of the riverbank mountains are good and tunnels can be excavated;
p>
3. Some projects require blocking the entire river bed at one time and construction throughout the year. Compared with open channel diversion, the flow rate of tunnel diversion is smaller, but with the development of construction technology, the diameter of diversion tunnels has a tendency to increase. As of 1985, the largest diversion tunnel in the world was the diversion tunnel of the Burei Hydropower Station in the Soviet Union, with a width of 17m and a height of 22m.
The characteristics of the tunnel diversion project are:
1. Since the tunnel is built in the mountain on the shore, the hub layout can be simplified; 2. When the diversion flow is large, several tunnels can be built. tunnels;
3. In order to meet the flood discharge requirements at different construction stages and different reservoir water levels, several diversion tunnels can be set up at different elevations;
4. The flow tunnel can be combined with a permanent project or converted into a permanent project;
5. The flow conditions in the tunnel are generally complex and the operation conditions are difficult to observe;
6. The upstream enclosure The weir is high and the water level difference between the upstream and downstream is large during the construction period.
The layout of the diversion tunnel should be adapted to local conditions. When arranging, attention should be paid to the following:
1. Make full use of the terrain conditions and shorten the length of the tunnel line as much as possible. When the dam site is located in a river bend, it should be The tunnel line is arranged on the convex bank;
2. The entrance and exit of the tunnel are arranged to ensure smooth water flow and maintain a necessary distance from the feet of the upstream and downstream cofferdams to prevent erosion;
3 The selection of the entrance and exit elevations must consider interception drop, navigation, wood crossing and blocking conditions;
4. The geological conditions along the tunnel line are required to be good, the rock mass is stable, there are few faults, and there are no cracks. development. In hard and complete rock formations, temporary tunnels may be unlined or partially lined. In order to reduce tunnel roughness, improve water drainage capacity and reduce leakage, smooth blasting and anchor shotcrete support may be used during construction;
5. When the flow or velocity of important projects is large, attention should be paid to taking exit energy dissipation measures.
Reference: Baidu Encyclopedia-Diversion Tunnel