China to build world's fastest underwater high-speed rail after record-breaking river tunnel

China has completed excavating a tunnel beneath the Yangtze River, the country's largest waterway, marking a major milestone for a project that will connect Shanghai's Chongming Island with neighboring Jiangsu Province and expand the national high-speed rail network. China's largest-diameter tunnel boring machine finished its crossing beneath the river on Thursday, clearing the route for high-speed rail construction.The achievement set a world record for the longest single-heading underwater shield drive. It also marked the first-ever underground connection between a large horizontal shield machine and a vertical shaft, according to the China Global Television Network.The Chongtai Yangtze River Tunnel is a 14-km-long high-speed rail tunnel lying 89 m below the Yangtze River. A view of Chongqing's skyline with Yangtze River in China. Photo by Pexels Due for completion by the end of this year, the project will provide Chongming, China's third-largest island, with its first high-speed rail link.Designed for trains traveling at 350 kilometers per hour, the tunnel is expected to become the world's fastest underwater high-speed rail tunnel when it opens.The journey beneath the river will take approximately two minutes, the South China Morning Post reported, citing the China Railway Tunnel Group.The tunnel is engineered to withstand intense water pressure while minimizing ground settlement. Engineers said the project required millimeter-level precision to ensure the safety and comfort of trains operating at such high speeds.The Chongtai tunnel is expected to cost more than 7.1 billion yuan (US$1.05 billion). It forms a key part of the Shanghai–Chongqing–Chengdu High-Speed Railway, one of China's flagship transport corridors linking the country's eastern coast with its interior.