First high-speed rail tunnel under Yangtze completed

CHINA: The country’s first high-speed rail tunnel beneath the Yangtze River has been completed in central Chongqing, allowing ballastless track construction and rail installation to begin.

The 11,942 m Caiyuanba Yangtze River Railway Tunnel forms part of the Chongqing–Xiamen high-speed rail corridor. The single-bore, double-track tunnel runs between Chongqing’s Yuzhong and Nan’an districts, threading beneath dense urban development as well as the river.

Xinhua reported that the final excavation was completed on July 24. China Railway Eryuan Engineering Group designed the tunnel, while China Railway 14th Bureau Group carried out the construction.

Final excavation starts the track phase

The alignment passes beneath municipal roads, viaducts, operating urban rail lines, residential buildings, the Yangtze’s main shipping channel and Nanshan mountain. Contractors combined open-cut, conventional mined and shield-tunnelling methods to complete the route.

The shield-driven section extends for 3,845 m, including 1,282 m beneath the Yangtze. Crews used the customised Changjiang slurry-balance tunnel boring machine, which had an excavation diameter of 12.66 m. The machine worked through alternating mudstone and sandstone under water pressure reaching 9 bar, with minimum cover of about 10 m below the river channel.

The TBM completed its drive in September 2025, but other excavation work continued. The July 24 milestone therefore marks completion of tunnelling across the full alignment, rather than the opening of the railway. A Chongqing government update says the project will now move into ballastless track construction and rail installation.

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Caiyuanba link will connect two Chongqing hubs

Once the remaining works are finished, the tunnel will provide an underground rail connection between Chongqing Station and Chongqing East Station. No opening date for this link was stated in the official completion notice.

The wider Chongqing–Xiamen route extends for about 1,600 km and forms one of China’s eight east–west high-speed rail axes. Much of the corridor is designed for 350 km/h operation. The 242 km Chongqing–Qianjiang section opened in July 2025, while the 421 km Ganzhou–Changsha section is scheduled for completion by 2030.

China Railway Group said in March that the national “eight vertical and eight horizontal” high-speed network was around 84% complete. The government plans for all 16 axes to be substantially finished by 2030 and envisages adding another 10,000 km of high-speed line over the next five years, taking the national total to about 60,000 km.

Underwater tunnelling expands on China’s network

The Caiyuanba project joins several underwater tunnels built for high-speed rail. These include the 9.6 km Zhanjiang Bay undersea tunnel on the 350 km/h Guangzhou–Zhanjiang line, an 11.8 km Yangtze crossing at Taicang near Shanghai, and the Shenzhen–Jiangmen tunnel beneath the Pearl River, which is expected to reach a depth of 116 m.