What is the design plan for risk elimination and reinforcement of small and medium-sized hazardous reservoirs?

The risk elimination and reinforcement design of small and medium-sized dangerous reservoirs is a necessary technical measure to ensure that the project can exert its potential comprehensive benefits. This article takes the small (1) type Sanhekou Reservoir on the Shaqu River tributary of the Sushui River Basin in Yuncheng City as an example to analyze the content of the project construction, summarize the risk elimination and reinforcement design plan of the dam project, and design the specific construction organization The plan was discussed.

1 Project Overview

The Sanhekou Reservoir is located 30km southwest of Wenxi County. It was built in November 1973 and completed in May 1975 to store water. It is mainly used for flood control and irrigation. The small (1) type reservoir has a total storage capacity of 3.257 million m3, a controlled drainage area of ??41.5km2, a designed irrigation area of ??15,000 acres, and a downstream protection area of ??13 villages with a population of more than 12,000, 10,000 acres of cultivated land and 25 enterprises.

After years of operation, the Sanhekou Reservoir dam area has become seriously silted up, with a siltation thickness of 14m and a sedimentation volume of 380,000 m3. The soil of the dam body partially contains calcareous nodules and gravel, and the dry density of the fill soil is low, resulting in poor filling quality. During the construction of the dam, the dam foundation covering layer and strongly weathered layer were not completely removed, forming leakage channels and affecting the normal operation of the reservoir. .

The irrigation hole is located in the middle of the dam. It is a semi-circular arch pressureless hole. The entrance is controlled by a conical ball gate, and the hoist is opened and closed by a wire rope. The culvert is 80m long, 1.2m wide and 1.7m high. The entrance floor elevation is 720m, the longitudinal slope is 1/200, and the maximum discharge is 1.0m3/s. In the early stage of water storage after the dam was built, due to poor fill quality, the dam body on the left side suffered significant subsidence, with the maximum subsidence being 70cm. The subsidence of the dam caused the concrete body at the entrance of the irrigation tunnel to break, causing water leakage; the masonry part of the side wall of the irrigation tunnel The mortar fell off, and there were many longitudinal and transverse cracks in the culvert. There were two longitudinal cracks 1m away from the entrance, 1cm to 4cm wide and about 15m long. The tapered ball gate and the winch were seriously damaged and aged due to years of operation, and the water-stop function failed. Severe water leakage.

The spillway is located on the right side of the dam. It is an open spillway. The bottom elevation of the entrance is 733.2m. There is a four-hole masonry arch working bridge with a net cross-section width of 26m and a total length of 90m. The energy dissipation form is steep slope towing. Energy dissipation, the steep slope section is 20m long and the slope ratio is 1:3. The designed maximum discharge capacity is 630m3/s.

There is obvious leakage on the bank slope where the spillway connects with the dam. The entire bank slope is wet and the amount of leakage is large. The foundation cleaning at the bottom of the spillway is not complete. There is a layer of sand and pebbles. There is seepage along the bottom of the spillway. The entrance of the spillway is The protective masonry was too short, and there was obvious collapse of the right bank slope. The reservoir management room is seriously damaged; the reservoir does not have necessary observation facilities.

2 Engineering Construction Tasks

Due to historical reasons, there have been many hidden dangers since the dam was built. Therefore, the reservoir has been a "disease reservoir" since its completion. After 35 years of diseased operation, the current dam height of the reservoir has been reviewed to meet the design flood standard of 30 years and the calibrated flood standard of 300 years. However, the spillway foundation leaks seriously; the stability safety factor of the downstream dam slope is less than the allowable value. , the dam body has obvious subsidence, posing a threat to the safety of the dam; the weathered layer of the dam foundation was not cleaned during the construction of the dam foundation, resulting in large leakage and the possibility of piping. The dam lacks safety monitoring facilities, seepage observation facilities, backward communication facilities, no water situation reporting system, blocked flood control and rescue roads, weak management facilities and many other problems, which seriously affect the normal and safe operation of the dam.

Therefore, in June 2008, the dam was identified as a Category III dam and a dangerous reservoir. If the dam is not reinforced in time, the stability of the dam structure and engineering safety will inevitably be affected. The reservoir flood control protection scope includes 13 villages including Fencun and Xiayuan with a population of more than 12,000, 10,000 acres of cultivated land, 25 enterprises and Wenyuan Highway. The area is densely populated, has developed agriculture, and has prosperous industry.

If the reservoir fails, it will cause huge losses. Downstream roads, farmland, industrial and mining enterprises and 13 villages along the coast will be submerged, and the economy will be seriously affected. Therefore, it is very necessary to strengthen the Sanhekou Reservoir Dam.

The main contents of the Sanhekou Reservoir risk relief reinforcement are: anti-seepage reinforcement of the dam; thickening the collapsed part of the upstream dam surface and the downstream dam surface; anti-seepage treatment of the spillway entrance foundation , repair the side walls of the spillway; repair and strengthen the entrance and body of the irrigation tunnel; replace the tapered ball gate and hoist at the water inlet; harden the road on the top of the dam, repair the wave wall; increase the number of dams Seepage and deformation observation facilities; renovation of the reservoir management station.

3 Project reinforcement design

3.1 Project grade and standard

According to the "Grading and Flood Control Standards for Water Conservancy and Hydropower Projects" (SL252-2000), the The engineering grade is Level IV, the main building level is Level 4, and the secondary building level is Level 5. The flood standards for hub buildings are: designed to occur once in 30 years, and verified to occur once in 300 years. The design flood standard for energy dissipation and anti-scouring of drainage buildings is once in 20 years. According to Article 1.0.6 of the "China Earthquake Peak Acceleration Zoning Map" (GB18306-2001 Figure A1) and "Seismic Design Code for Hydraulic Buildings" (SL203-97), the fortification intensity of dams and buildings is VII degree.

Part 3.2 Project Design

The thickness of the downstream dam slope has been reviewed by the dam stability calculation. The safety factor of the downstream dam slope is less than the value allowed by the specification and needs to be reinforced. The project mainly focuses on thickening the downstream dam slope and building new drainage ditches and downstream dam foot prism drainage. The dam slope upstream of the dam is mainly subject to sinkhole treatment. The collapse pit on the water-facing slope of the dam is located at the top of the irrigation tunnel, with stake numbers 105 to 150, and an elevation between 729m and 732.3m. It is a long strip along the axis of the dam, 45m long, 10m wide, and has a maximum subsidence depth. 0.7m, area 315m2.

There is a pebble layer leakage section about 80m long between the spillway and the right abutment, with an elevation between 726m and 735.5m. The project uses paving for the 80m leakage section between the spillway and the right abutment. The composite geomembrane is used to prevent seepage. When laid, the composite geomembrane is integrated with the geomembrane on the upstream slope of the dam, ranging from 733.2m to 721m.

Due to insufficient protection at the entrance of the spillway, the bank slope has partially collapsed due to flooding. This time, the entrance is protected with a length of 12m, and the total height of the protection is 2m~7.5m; the bottom plate of the entrance section of the spillway is protected with M7.5 cement mortar stone masonry, with a thickness of 0.5m.

The steep slope section of the spillway is located on a gravel foundation. In order to reduce the lifting pressure of the bottom plate, drainage and pressure relief holes are set at the lower part of the steep slope. The hole spacing is 2m and the row spacing is 2m. It is arranged in a plum blossom shape. The drainage hole diameter is φ100mm. The holes are filled with filter geotextile and pisolite materials. According to the "Sanhekou Reservoir Dam Safety Appraisal and Evaluation Report", the subsidence of the dam caused the concrete at the entrance of the irrigation tunnel to break and leak; the mortar on the stone masonry part of the culvert side wall fell off, and there were three longitudinal cracks inside. There was water seepage in the cracks, endangering the dam's safety. Safe operation.

This time, the entrance of the irrigation tunnel was dismantled and rebuilt. It is a cast-in-place C25 reinforced concrete structure. The entrance has two holes. The single hole has a net width of 0.9m, a side wall thickness of 0.3m, a length of 4.2m, and a height of 4.15m; for the culvert The entire section is reinforced with C25 reinforced concrete lining, with a thickness of 0.15m, and the culvert is backfilled with grouting. In addition, it is necessary to improve the observation facilities, increase the dam infiltration line, seepage pressure and displacement observation facilities; repair and transform the dam top road, wave wall, and reservoir management station.

4 Project construction organization and management

The construction sites of the Sanhekou Reservoir hazard removal and reinforcement project are mainly distributed on the main dam. The reservoir is 30km away from the county seat. There is an 8km road connecting the reservoir dam site to Hougong Township. The road condition is good and meets the requirements of construction and transportation. Electricity for construction can be connected from nearby villages. Water for construction can be drawn directly from the reservoir, and domestic water can be drawn from nearby wells through pipelines.

The cement, steel, gasoline (diesel) oil, and wood required for the project are purchased and supplied by Wenxi County, and the transportation distance is 30km. The rough stones, gravel and sand required for the project can be made from stones in the valley downstream of the reservoir and on both sides. The lithology is mainly granite and limestone. After processing, it can be used as coarse aggregate and fine aggregate. It has good quality, large reserves, convenient transportation, good mining conditions, and a transportation distance of 2km. The sand material can be selected from the river bottom material field, 20km away from the dam.

The construction diversion of this project only needs to solve the base flow diversion, and the clean water flow rate is about 0.08m3/s. According to the actual conditions of the dam, the original irrigation holes of the dam are used to divert water, and the reservoir is emptied after the first spring irrigation. After the flood season, the silt in front of the dam is excavated and piled nearby parallel to the dam to form a self-closing cofferdam. , to retain a small amount of clean water for construction use. The excess river water is introduced into the irrigation hole with a 40cm diameter steel pipe and then flows into the river channel.

The main project of the Sanhekou Reservoir danger relief and reinforcement project is the anti-seepage reinforcement treatment of the dam, the treatment of the collapsed part of the upstream slope protection of the dam and the dam slope protection, the anti-seepage treatment of the spillway foundation, and the reinforcement of the irrigation hole. Dam crest wave wall repair, dam seepage deformation and water regime automatic reporting system, management station renovation and other project construction. According to the characteristics of the project, the total construction period of the project is one year, with 365 construction days.

5 Conclusion

In the process of engineering design and construction, we must adhere to the concepts of harmonious management and harmonious construction. The risk relief and reinforcement of the reservoir will not only give full play to its comprehensive benefits, but will also help further enhance the region's ability to withstand natural disasters.

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