"Navigating the main channel of the Yangtze River presents the Chongqing Yangtze River Tunnel with significant challenges," said Kong Yuqing, the project manager for the shield machine at China Railway 14th Bureau Group Corporation Limited.

Further, Kong elaborated, "The tunnel descends to a maximum water depth of 42 meters, with a mere overburden thickness of 10 meters at its minimum. The water pressure can escalate up to 0.9 megapascals, equivalent to a pressure of 9 kilograms per square centimeter on an area as small as a fingernail."

The Chongqing Yangtze River Tunnel is a single-bore, dual-track tunnel. It's a highly challenging and risk-intensive engineering project, classified as a Grade I high-risk tunnel.

Unlike traditional drill and blast methods, the excavation of the tunnel beneath the Yangtze River and adjacent land sections adopted large-diameter slurry balance shield tunneling to ensure construction safety. This is the first underwater tunnel in China that blends drill and blast, shield tunneling, and cut-and-cover excavation techniques.

The shield tunneling method is an entirely mechanized construction approach employed in tunneling projects. A shield machine resembling a cylindrical body with a cutter head propels forward under thrust.

"This technique guarantees both construction and operational safety, warding off river water from flooding the tunnel," explained Chen Yang, a Senior Engineer in tunnel construction at China Railway Eryuan Engineering Group Co. Ltd (Chongqing). "This method not only safeguards the river's navigability but also ensures the safety of the construction project."

Chen added, "We have employed innovative techniques, such as in-tunnel assembly and disassembly of the large-diameter shield machine, in the design. This approach overcomes the limitations posed by the bottleneck of the launching and receiving sites, ensuring the smooth implementation of the project."

Upon completion, the Yangtze River Tunnel will facilitate swift and effortless connectivity between Chongqing Railway Station and Chongqing East Railway Station, transforming the former from a terminal station into a through station.

This development promises to establish seamless connections among the Chongqing-Changsha High-speed Railway, Chongqing-Wanzhou High-Speed Railway, and the Chengdu-Chongqing High-Speed Railway within the central urban area of Chongqing.

The Chongqing-Qianjiang section of the Chongqing-Hunan high-speed railway forms a significant part of the Xiamen-Chongqing high-speed railway. According to China Daily, this is a component of the "eight north-south lines and eight west-east lines" high-speed railway network, citing the nation's medium- and long-term railway network development plan.

While primarily catering to long-distance travelers, the Chongqing-Qianjiang section also aims to serve intercity passengers.

Upon completion, this railway section will play a pivotal role in intensifying poverty relief efforts in the neighboring mountainous region and fostering tourism development along the railway line. Moreover, it will empower Chongqing to spearhead and stimulate development in the surrounding areas while driving urbanization in the localities along its route.