The First Corridor of the Yangtze River
World's First UHV Yangtze River Crossing Utility Tunnel Completed
On August 21, 2018, the Su-Tong GIL Utility Tunnel Project (hereinafter referred to as the "Su-Tong GIL Utility Tunnel Project") of the Huainan-Nanjing-Shanghai 1000 kV AC UHV Power Transmission and Transformation Project was officially completed, marking a breakthrough in the critical passage and key node for the closed-loop operation of the East China UHV AC ring network.
Upon completion, the Huainan-Nanjing-Shanghai Project, together with the already operational Anhui Power Transmission to East China Huainan-Wannan-Shanghai Project, will form the East China UHV AC ring network running through the load centers of Anhui, Jiangsu, Zhejiang, and Shanghai. This is the world's first UHV AC double-ring network, which will significantly enhance the East China power grid's capacity to accommodate external power, improve the level of safe operation of the grid, and is of great significance for promoting the sustainable economic and social development of East China and Jiangsu Province, and further enhancing China's power technology level.
The tunnel was invested in and constructed by State Grid, designed by China Railway Fourth Survey and Design Institute, and constructed by China Railway 14th Bureau Group. Ultra-long Distance GIL Innovation Project
The Su-Tong GIL Utility Tunnel Project currently has the highest voltage level, largest transmission capacity, and most advanced technology in the world. Gas-insulated metal-enclosed transmission lines (GIL) are laid in the tunnel, using metal conductive rods for power transmission, enclosed in a grounded metal shell and insulated by pressurized gas.
Compared with conventional cables, GIL has significant advantages such as large transmission capacity, low loss, high personal safety, extremely low electromagnetic fields, immunity to environmental impact, high operational reliability, land saving, and no electrical (thermal) aging. It is particularly suitable as a supplementary transmission technology when overhead transmission or cable transmission is limited. Its investment is lower than that of cables, and maintenance costs are lower than those of cables.
The project starts at the south bank (Suzhou) connection station and ends at the north bank (Nantong) connection station, crossing the Yangtze River 1 kilometer upstream of the Su-Tong Bridge. It uses two 1000 kV GIL circuits laid in the tunnel, with reserved space for two 500 kV cables and municipal utility pipelines for communications, cable TV, etc. The project is scheduled to be completed and put into operation in 2019. World's First Application of Large-diameter Shield Tunnel to Power Utility Corridor
The Huainan-Nanjing-Shanghai 1000 kV AC UHV Power Transmission and Transformation Project is one of the twelve key channels for air pollution control of the State Council.
The Yangtze River here is wide, with the narrowest point close to 5000 meters. The traditional method is to build towers over the river, with two towers in the water, each designed to be 450 meters high. The foundation pit of one tower is equivalent to 27 standard basketball courts and requires more than 200,000 cubic meters of reinforced concrete. This limits low-altitude space, affects shipping, and the tower foundations in the river are subject to long-term scouring by the river, requiring annual filling with stones, which impacts port construction and infrastructure development in Jiangsu.
"The main channel of the Yangtze River has more than 3,000 large ships every day. The technical and economic advantages of the overhead crossing scheme are not obvious, and the construction risk is high. The tunnel has the advantages of small impact on the surrounding environment and low operation and maintenance costs." State Grid Corporation decided to adopt the tunnel method to cross the river.
"There is no such long-distance transmission technology and facility in the world today. This is a pioneering feat," experts praised. Jointly Building the World's Highest Pressure-resistant Shield Machine
The tunnel has a total length of 5468.5 meters, with the deepest point at 78.4 meters and a maximum water and soil pressure of 9.8 bar, equivalent to an adult elephant standing on a single seat of an ordinary car. It is currently the deepest and highest water pressure power tunnel crossing a river in China.
The geological conditions in the river are complex, characterized by high permeability, high density, and high quartz content. The tunnel will cross the Yangtze River levee, long-distance strata rich in harmful gases, and the river scour channel section. The technical difficulty is high and the construction risk is high. It is currently the longest single-head excavation power utility tunnel in China, with an additional 1780 meters of methane-rich strata, making it the power utility tunnel with the highest construction risk among large-diameter river-crossing tunnels.
To overcome this world-class challenge, the project department established an expert group led by Academician Qian Qihu of the Chinese Academy of Engineering to jointly carry out scientific and technological research. They developed the world's most advanced slurry balance shield machine, with an excavation diameter of 12.07 meters, a total equipment length of 140 meters, and a main drive seal design pressure of 10 bar. It is currently the large-diameter slurry balance shield machine with the highest working pressure in the world.
Drawing on the Swiss SUVA mining safety regulations, the shield machine is specially equipped with dedicated equipment to actively respond to harmful gases, enabling methane detection, early warning, and explosion-proof functions. The tunnel lighting and exhaust systems have been designed and modified for explosion-proofing, ensuring construction safety. Shield Machine Manufacturing and Construction Set Multiple World Records
China Railway 14th Bureau Group and shield machine manufacturer Herrenknecht have had a good cooperative relationship in the field of large-diameter shields for more than a decade, with their core technologies supporting each other. From signing the order to site acceptance, the shield machine took less than 8 months. Using the method of transporting the entire single-section trolley, on-site assembly and debugging took only 45 days, creating a world record for the manufacturing and assembly time of large-diameter shield machines.
From the start of excavation on June 28, 2017, to completion, it took 14 months, with an average daily advance of 14.12 meters and a monthly average of 417 meters, setting a new world record for large-diameter shield tunnel construction.
The entire tunnel has no leakage points and has received more than 6,000 on-site visits from domestic and foreign visitors. Academician Qian Qihu of the Chinese Academy of Engineering praised it as an industry benchmark project with the best on-site management, the best physical quality, and the fastest construction progress in China. The jointly developed "Zhuoyue" shield machine set new world records in both manufacturing and on-site assembly and debugging cycles. The UHV AC double-ring network between Huainan, Nanjing, and Shanghai in East China, crossing the Yangtze River via a tunnel, is hailed as a pioneering feat in the history of power construction.
China Railway 14th Bureau Group's Indissoluble Bond with Nanjing
Since the 1990s, China Railway 14th Bureau Group has undertaken projects such as Nanjing Lukou International Airport and Nanjing's first urban subway, becoming a backbone force in Nanjing's infrastructure construction. In particular, the Nanjing Yangtze River Tunnel, the first tunnel under the Yangtze River, which they constructed, has won all major awards in the construction industry, including the China Science and Technology Progress Award. Not long ago, their Youth Olympic Axis underground project, the first and largest urban underground interchange in China, won the Zhan Tianyou Award.
China Railway 14th Bureau Group regards the Nanjing Yangtze River Tunnel as the "Whampoa Military Academy" for cultivating core talents in large-diameter shields. Starting from a high point in the field of super-large-diameter shield tunnels, more than 30,000 segments are seamlessly integrated, and the entire tunnel has no leakage points over the years. It has become a landmark project for Nanjing's river-oriented development, a masterpiece of China Railway Construction's large-diameter shield tunnels, and a shining名片 of China Railway Construction.
Since then, leveraging their first-mover advantage, they have participated in the construction of a number of large-diameter shield tunnels, including the Nanjing Metro Line 10 river-crossing tunnel, the Yangzhou Slender West Lake Tunnel, the Wuhan Metro Line 8 Yangtze River Tunnel, the Beijing-Shenyang High-speed Railway Wangjing Tunnel, the Beijing-Zhangjiakou High-speed Railway Tsinghua Yuan Tunnel, the Wuhu Yangtze River Tunnel, the Hangzhou Wangjiang Tunnel, the Changde Yuanjiang Tunnel, and the Changsha Metro Xiangjiang River Tunnel. At the same time, they have won bids for a number of subway projects, including the Nanjing Metro North-South Line Phase I, Ningli, Ninghe, Line 7, and Line 2 West Extension. The Nanjing Fifth Bridge Jiajiang Tunnel, the largest diameter shield tunnel in Nanjing with an excavation diameter of 15.46 meters, is about to start excavation, and the Heyan Road river-crossing tunnel is accelerating construction. Currently, of the 5 river-crossing tunnels under construction on the Yangtze River, they are building 4. They are also constructing the first public-rail combined super-large-diameter shield tunnel on the Yellow River, the Jinan Yellow River Tunnel, and the Wuhan Heping Road South Extension Yellow Crane Tower Tunnel with an excavation diameter of 16.01 meters, firmly holding the discourse power in the field of large-diameter shield construction in China.
Nanjing has become a lucky place for the 14th Bureau's large-diameter shield business. In August 2016, they established China's first large-diameter shield specialized company in Pukou, Nanjing. Industry authority Academician Qian Qihu of the Chinese Academy of Engineering praised them as the first construction enterprise in China to master the core technology of large-diameter shield construction, with core competitiveness in the field of large-diameter shield construction under complex geological conditions.
China Railway Construction's No.1 Brand, Dedicated to Being the Leader in Large-diameter Shield Business
In the field of super-large-diameter and underwater shield construction, the 14th Bureau's large-diameter shield has taken the lead in achieving five "full coverages" in China: full coverage of crossing "rivers, lakes, seas, and cities," full coverage of geological conditions, full coverage of industries involved, full coverage of shield diameters, and full coverage of construction techniques. With the advantage of core construction technology and more than 150 invention patents and innovative methods, the 14th Bureau's large-diameter shield brand has become a solid support for technology research and development. At the end of 2017, the 14th Bureau's large-diameter shield brand was rated first among the first ten major brands of China Railway Construction.
At the beginning of 2018, the Nanjing branch of the large-diameter shield technology postdoctoral workstation was established, and a large-diameter shield technology research and development center was jointly founded with Southwest Jiaotong University. A large-diameter shield data monitoring and command center was built, and an annual large-diameter shield technology forum was initiated. A strategic plan of "possessing core talents, mastering core technologies, and formulating core standards" was proposed.