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Longtan HPP, located in Tian’e County of Guangxi Zhuang Autonomous Region, has a 216.5m-high RCC gravity dam, ranking first in the world in terms of height of RCC gravity dam, scale of underground headrace power system, lifting height of vertical ship lift, and unit capacity of fully air-cooled turbo-generator units at the time. Its installed capacity is 6300MW. Longtan Dam won the International Milestone RCC Project Award.
The project development is mainly for power generation and concurrently for flood control and navigation. The project is developed in two phases. At the first phase, the installed capacity is 4900 MW (700MW7), and the reservoir has a NPL of 375m, a total storage of 18.35 billion m3 and a flood control storage of 5.0 billion m3. At the second phase, the installed capacity will be 6300 MW (700MW9), and the reservoir will have a NPL of 400m, a total storage of 29.83 billion m3 and a flood control storage of 7.0 billion m3. For the first phase, the construction period was 9 years, the construction of its main structures was officially commenced on July 1, 2001, the first unit was put into service on July 1, 2007, and all the 7 units were put into operation on December 7, 2009.
Main Technical Features and Key Technical Issues:
The height of RCC gravity dam, the scale of underground powerhouse and the lifting height of ship lift of Longtan project hit the world record, and its anti-dip combined high slope at the left-bank intake was up to 420m. The details are as follows:
Longtan Dam is 192.0m high at the first phase with a concrete volume up to 3.90 million m3 and will be 216.5 m at the second phase, much higher than the available dam-building references in China and other countries. Therefore, the building of Longtan high RCC concrete dam has been a key scientific and technological project. It was listed as a key national scientific research project during the Eighth- and Ninth-Five Year Plan Period and a key one of State Power Corporation during the Tenth-Five Year Plan Period. HydroChina ZhongNan organized and coordinated a lot of scientific research institutes to carry out studies on high RCC dam design, seepage control technology, rapid construction technology in hot and rainy season, dam building materials and so on and got fruitful achievements. Many of the achievements were of advanced level in China or even in the world, and some were of international leading level.
Longtan underground powerhouse was designed as being completed in one time. The huge underground powerhouse system consists of headrace tunnels, a powerhouse, a main transformer cavern, tailrace surge shafts, tailrace tunnels and other auxiliary caverns, with caverns and tunnels being arranged in a crisscross pattern. As far as the scale of single underground powerhouse is concerned, the project ranked largest among the existing power stations and those under construction and about to be constructed, so the technical requirements on its design and construction were extraordinary, and it was listed as a key scientific research project of State Power Corporation during the Tenth-Five Year Plan Period. Many achievements of the studies met the requirements of project construction.
A scheme of two-stage counterweight-type vertical ship lift with an open channel in the middle was adopted as the navigation structure for Longtan project. The whole structure extends 1800m and includes five parts, i.e., upper approach channel, first-stage vertical ship lift, open channel as passing track, second-stage vertical ship lift, and lower approach channel. The maximum lifting height of the vertical ship lift is up to 179m, so the technical requirements on design were extraordinary.
The anti-dip combined high slope at the left-bank intake was up to 420m high. The excavated slope and the upstream side were in the scope of rock mass, thus the slope was very difficult for design and construction and was one of the key technical problems to be tackled. During the Seventh- and Eighth-Five Year Plan Period, the intake anti-dip high slope for Longtan project was listed as a key national scientific research project, and the results of the studies achieved leading level of China and solved major basic theoretical and technical problems in slope design and provided bases for the design. During the construction, further studies and analyses were conducted based on the geological conditions revealed and the monitored conditions so as to guide the adjustment of design and construction measures and ensure the smooth construction of the slope and project safety.
In addition to the above mentioned, major technical problems in Longtan project development also include the technologies for flood-releasing and energy-dissipation and large-capacity turbo-generator units, and the corresponding studies have achieved effective results and ensured the smooth progress of design and construction.