Brief Introduction of China Guodian Wan 'an Hydropower Station

Wan 'an Hydropower Station is located in the middle reaches of Ganjiang River, 2 kilometers away from wanan county, 90 kilometers away from Ganzhou and 320 kilometers away from Nanchang. The dam site controls the drainage area of 36900km2, accounting for 44% of the total drainage area of Ganjiang River. According to the planning of Ganjiang River basin, the development task of this project is mainly to generate electricity, and at the same time, it undertakes flood control tasks in the middle and lower reaches of Ganjiang River, as well as shipping, irrigation, reservoir breeding and other tasks. It is a large-scale water conservancy and hydropower project with remarkable comprehensive benefits. It is the largest hydropower station in Jiangxi Province at present. From left to right, the hub consists of non-overflow dam section on the left bank, surface overflow dam section, bottom outlet dam section, riverbed powerhouse dam section, non-overflow dam section on the right bank, ship lock, earth dam and irrigation canal heads on the left and right banks. The final design water level of Wan 'an Hydropower Station is 100m, the total reservoir capacity is 22160,000m3, and the initial operating water level is 96 m. The hub project is completed at one time according to the final scale.

Since the first unit of Wan 'an Hydropower Station 1990 was put into operation, the comprehensive benefits of the project have been fully exerted. In terms of power generation, five units have been installed in the power station, with a single unit capacity of1000 MW. By 2003, the cumulative power generation was1600 million kW·h, which not only improved the power efficiency, but also played the role of peak shaving, frequency modulation and emergency standby in the system. In terms of shipping, the shoal from Wan 'an to Ganzhou 18 was flooded, which completely improved the 90-kilometer navigation channel in the reservoir area and increased the downstream navigation depth by 0.2m in the dry season. The ship lock is a 2×500-ton first-class ship lock, with the effective size of175×14× 2.5m. By the end of 200 1 year, the lock has been opened 206 times12 times, passing through ships144,000, with a total freight volume of 8. In terms of flood control, 1994, 1995 and 1997 caused major floods, and the maximum inflow and discharge of the reservoir after water storage were 14300 m3/s and1500m3/respectively.

The total investment of Wan 'an Hydropower Station is 210.80 billion yuan. Main quantities of main works: earthwork excavation of 2.53 million m3, earthwork backfilling of 2.07 million m3, concrete pouring 1.5 1.000 m3, curtain grouting of 23000m, consolidation grouting of 23300m, and metal structure installation of1.2840t.

Main engineering features

The dam site of Wan 'an Hydropower Station is located at the outlet of the canyon, and the river surface is about 450 meters wide in dry season. Although the geological conditions are not very complicated, faults, weak interlayer and deep weathering trough are the main engineering geological problems of dam foundation. The main feature of this project is the large peak flow, with the check flood once every ten thousand years reaching 33,900 m3/s, and the requirements for comprehensive utilization are high. Because Ganjiang River is the north-south water transport artery that runs through Jiangxi Province, it is required to keep navigation during the construction period. According to the above characteristics, the overall layout of the hub is as follows: the flood discharge structures and main powerhouse are arranged in the main river bed, and the ship lock is arranged on the right bank, so that the main buildings are coordinated with each other, which well conforms to the river regime and meets the requirements of comprehensive utilization of the hub. The design makes full use of technological innovation, mainly including:

1. Wan 'an lock is the single-stage lock with the highest design head in China at present. According to the design code of shiplock at that time, a complex decentralized water conveyance system should be selected. The water conveyance system of single-stage lock with high head (more than 30m) abroad is very complicated. In contrast, Wan 'an Shiplock only adopts a simple decentralized water conveyance system, which successfully solves the hydraulic problems and berthing conditions of high-head shiplocks, greatly simplifies the structural layout and saves engineering investment. At the same time, it is the first time in China to use the permanent lock to solve the problem of temporary navigation during construction, so that the permanent lock can be used for temporary navigation after the main river bed is closed.

2. The dam height of Wanan RCC overflow dam is 44m, and the dam axis length is 164m. Some leading and advanced new technologies were adopted in dam design at that time, such as the research results of the national key project "Application of RCC dam construction technology in large-scale water conservancy and hydropower projects". In terms of construction technology, the belt conveyor is used to transport concrete for the first time in China, which successfully solves the technical problems such as aggregate separation of high-throw concrete. Due to the long-term intermittent construction of overflow cofferdam and roller compacted concrete in flood season, technical difficulties such as temperature control and crack prevention of concrete, flood season protection and combination of new and old concrete have been added, which have been overcome in construction. The RCC overflow dam of Wan 'an Hydropower Station, as an example of RCC dam built earlier in China, has been included in the Design Guide for RCC Dam issued by the Ministry of Energy and the Ministry of Water Resources 1992.

3. The powerhouse of Wan 'an Hydropower Station is another large riverbed powerhouse after Gezhouba Hydropower Station in China, which is at the leading level in the design of similar powerhouse in the same period. The factory building is complex in structure and unplanned in shape, which is prone to cracks. By optimizing the structural shape, using reasonable layers and blocks in the concrete mixture ratio, the hydration heat of cement is reduced as much as possible, and only a few surface cracks appear in the factory building concrete, which is rare in the built projects at home and abroad.

4. The dam section of the bottom hole adopts closed pumping apron, and a closed impervious curtain is set around the apron to block seepage from all sides into the foundation of stilling basin, and vertical and horizontal drainage ditches are set to form a unified drainage network, which comprehensively reduces uplift pressure, reduces the apron thickness from 4m to 2.5m, and reduces concrete by about 20,000m3. At the same time, the block size should be adopted reasonably, and the side length should be less than 10m. During the construction and operation, no cracks were found in the apron block, which ensured the pumping effect. After prototype monitoring, the uplift pressure at the bottom of apron is lower than the design value, and the total displacement is only 50 ~ 60L/min, which shows a downward trend year by year, and good results have been achieved.