Related research on diversion and closure technology in water conservancy and hydropower project construction?

With the continuous development of China's social economy, there are more and more water conservancy and hydropower projects, and diversion and closure is one of the key links in the construction process. Therefore, it is necessary to solve the related problems of diversion and closure technology in the construction process, take corresponding solutions according to the actual situation of the dam, and consider the safety of dam staff to ensure the smooth completion of the project.

1, project overview

The power station adopts the development mode of low dam riverbed long tail canal, and the dam and the left and right bank flood levees are used as auxiliary dams to form the reservoir. The dam is located on soft foundation, the cofferdam and foundation adopt suspended cutoff wall, the main building is Grade III, the corresponding diversion building is Grade V, the corresponding design flood standard is 10 ~ 5 years, and the diversion design flood standard is 10 years.

2, water conservancy and hydropower engineering construction diversion method

2. 1 Construction diversion structure. The diversion method adopts the completed 4-hole sand sluice and 4-hole flood sluice for diversion. In the first stage, cofferdam is used to retain water, and the diversion standard is 10 once a year. The 4-hole sand sluice and 4-hole flood sluice built on the left side are used for overflow. During this period, the flood gate on the right side of the riverbed 12 hole, the dam section of the right bank gate and the flood dike near the upstream right bank dam section will be constructed. In the second stage, the gate blocks water, and the diversion standard is 10 flood.

2.2 Longkou design. Longkou is on the left. According to the characteristics of pre-occupied filling slag and the narrow degree of riverbed, the width of the longkou is determined to be 60.0m, and the longkou occupation is divided into three areas: the width of the longkou in area I is 60 m ~ 30 m, and the average velocity of the longkou is 3.333m/s ~ 3.730m/s； m/s; The width of the longkou in Zone II is 30m ~ 10m, and the average velocity of the longkou is 3.765m/s ~ 3.805m/s; The closure width of Zone III is10m ~ 0m ~ 0m, and the average closure speed is 3.726m/s ~ 0m/s. When the closure of Longkou, the upstream backwater level is 399.0 1m, the downstream level of Longkou is 397.00m, and the maximum instantaneous drop is1.88m. At the top of the dike,

According to the Gizba formula.

Where: V-flow; K- stability coefficient (0.90); γ s refers to the bulk density of the block stone (take 2.72); γ refers to the bulk density of water (take1.00); D refers to the equivalent diameter of the sphere.

2.3 upstream and downstream cofferdam construction

After the diversion tunnel meets the flow conditions, temporary roads will be built from the construction road on the left bank to the upstream cofferdam, and the upstream cofferdam will be filled. According to the difference of upstream cofferdam of impervious body, the construction is divided into two stages. In the first stage, the weir body is filled to an elevation of 464m, and the construction of C 15 concrete core wall is started. The second expectation is that after the completion of concrete, the weir body and concrete impervious body above 464m elevation will be filled at the same time. Main construction methods and measures: cofferdam filling material source, weir body filling material source, earthwork excavation; Digging out clay materials from the stockyard; Centralized mixing of concrete. Construction roads and cofferdam filling construction roads are the same as river closure construction roads. The temporary construction access road is built from the left bank construction access road to the cofferdam foundation, and the cofferdam is filled by the temporary construction access road, and the cofferdam is filled layer by layer.

3. River closure technology for water conservancy and hydropower construction

3. 1 Interception materials

Interception materials are mainly filling materials, clay sealing materials and large stones. Embankment filling materials are mainly temporary dam excavation materials, supplemented by yard; The clay sealing material mainly adopts the excavation material of the covering layer of the yard; Large stones are selected as blasting materials for the left and right banks to meet the needs of intercepting and throwing materials. The filler excavated from the dam is temporarily stored downstream of the dam. At the same time, in order to improve the feeding strength, 5000m3 excavated materials will be prepared in mid-August to meet the needs of embankment filling strength. Clay sealing materials are directly loaded and filled with overburden excavation materials; The selected large stones are temporarily stacked on the left bank dike construction platform for easy throwing, and the stones are about 500m3. The dike front is designed according to the average monthly flow of 3. 1.9m3/s in August. The pre-occupied area is distributed on the left bank. The length occupied in front of the dike is 35m, and the maximum average flow velocity of closure with a width of 5m is 5 m/s. Combined with the excavation of the left bank end of the dike, a large-scale backflow field is formed. Small stones, medium stones and common stone residues are used for roads, and external traffic roads are closed before river closure.

3.2 River closure process

3.2. 1 Blasting closure construction. If the dam site is located in the canyon area, and the rock is hard, the traffic is inconvenient, the bank slope is steep and there is no transportation equipment, directional blasting can be used for river closure. In order to throw a lot of materials into the river closure at the critical moment, in addition to directional blasting of rocks, a huge concrete block support can be blown up by blasting when the river bed is closed in advance, so that the block falls into the water and the river closure is realized. However, it should be pointed out that although the water flow can be cut off by using the instantaneous huge throwing intensity, due to the great instantaneous throwing intensity, when the material enters the water, a huge squeezing wave will be generated, which may destroy the repaired dike and cause the downstream river to stop flowing instantaneously. In addition, when directional blasting rocks, it is also necessary to check the distance of individual flying stones, air shock waves and the safety influence distance of earthquakes.

3.2.2 Sluice closure construction method. For the interception of artificial drainage channels, piers are often built in advance, and finally the sluice is used for interception. In natural rivers, if conditions permit, a sluice can also be set up, and finally the sluice can be used for river closure. This method was adopted in the drainage channel of Guimen River in Sanmenxia, and the maximum drop during sluice discharge was 7.08m, which lasted more than 30 hours. The sluice closure of Shenmen Island spillway was also considered, but the pier was washed away during the flood season, and later it was changed to tubular stone barrier closure.

3.2.3 Construction method of intercepting throwing blocks. Throwing block is the most commonly used river closure method at home and abroad, which is suitable for all kinds of situations, especially for river closure with large flow and large drop. This method is to throw stones or artificial blocks (concrete blocks, concrete tetrahedrons, lead wire cages, bamboo cages, willow pillows, string stones, etc.). ) intercept the water flow at Longkou, forcing the river to be discharged through the diversion building. Throwing blocks are used for river closure. According to the different ways of throwing and throwing, river closure can be divided into three ways: plane closure, vertical closure and mixed closure. First, build a pontoon bridge or trestle bridge in Longkou, transport the blocks by dump trucks or other means of transport, throw them along the front of Longkou, throw small materials first, and gradually throw large blocks with the increase of flow velocity, so that the piled dams will rise evenly under water until they are exposed to the water. Generally speaking, the discharge per unit width is less than that of vertical plugging method, and the maximum velocity is also smaller, and the water flow condition is better, which can reduce the scour of Longkou foundation bed. Therefore, it is especially suitable for river closure on easy-to-scour foundation.

Concluding remarks

To sum up, due to many factors affecting the construction of water conservancy projects, and the complex conditions of water conservancy projects in China, the specific construction is relatively difficult, and the effective control of diversion and interception technology directly affects the quality and progress of engineering construction. Therefore, the diversion and interception project is the key to the construction of the whole water control project, and the difficulty of the interception project depends on the flow and discharge conditions of the river. The drop, velocity and topographic and geological conditions of Longkou; Material supply and construction methods, construction equipment and other factors. Therefore, it is necessary to fully analyze and study in advance and take corresponding measures to ensure the smooth completion of diversion and closure tasks in the closure construction.

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