The riverbed tunnel of the Sutong GIL Utility Tunnel on the Huainan—Nanjing—Shanghai 1,000 kV AC UHV power transmission project began shield tunneling on the 28th. This is currently China's deepest and highest-water-pressure ultra-long-distance tunnel, and it is also key to the construction of the world's first UHV GIL utility tunnel project.
The Huainan—Nanjing—Shanghai UHV project crosses the Yangtze River about 1 kilometer upstream of the Sutong Bridge in Jiangsu, using two 1,000 kV GIL (gas-insulated rigid transmission line) circuits laid in a utility tunnel (tunnel) to cross the Yangtze.
The bottom elevation of the riverbed tunnel structure of the Sutong GIL Utility Tunnel project is -74.83 meters, and the water and soil pressure exceeds 0.9 MPa, making it currently the deepest and highest-water-pressure tunnel in China. At the same time, the geological conditions in the Yangtze River are complex, featuring high permeability, high density, and high quartz content, posing major technical difficulties and construction challenges.
It is reported that the "Zhuoyue" slurry balance shield machine, tailor-made for this project, has a diameter of 12.07 meters, a total length of 139 meters, and a total weight of 2,467 tons, equivalent to four stories high and the weight of 500 elephants. Its total installed power is 615 kilowatts, and its maximum tunneling speed is 60 millimeters per minute.
According to the plan, the shield machine will launch from the working shaft on the south bank and tunnel northward, passing beneath the Yangtze River levee on the south bank to enter the river channel, then successively passing beneath the Changshu Port dedicated waterway, the Yangtze main channel, and the Yingchuangang dedicated waterway, before passing beneath the north bank levee to reach the working shaft on the north bank. The total length of the shield section is 5,468.5 meters.
The north ring project of the Huainan-Shanghai line is one of the 12 key power transmission channels in the National Action Plan for Air Pollution Prevention and Control, and it is also Jiangsu Province's first UHV AC project. The project starts at the Huainan Substation in Anhui and ends at the Huxi Substation in Shanghai, passing through Anhui, Jiangsu, and Shanghai, crossing the Huai River and the Yangtze River. The total line length is 759.414 kilometers, with a Jiangsu section of 519 kilometers, and a construction substation capacity of 12 million kilovolt-amperes. 
       After the Sutong GIL Utility Tunnel project is completed, the north ring project of the Huainan-Shanghai line will operate in a closed loop with the already-commissioned Anhui-to-East power transmission Huainan—North Zhejiang—Shanghai UHV AC transmission demonstration project, forming an East China UHV ring network running through the load centers of Anhui, Jiangsu, Zhejiang, and Shanghai. It will also constitute the world's first UHV AC double-ring network.