World's longest undersea high-speed rail tunnel advances in Ningbo

China's domestically developed ultra-large-diameter tunnel boring machine has excavated more than 4,000 meters from the Ningbo side. [Photo provided by China Railway 14th Bureau Group]

Construction of the world's longest undersea high-speed rail tunnel, the Jintang Undersea Tunnel of the Ningbo-Zhoushan Railway, reached a major milestone on Aug 31, as the "Yongzhou", China's domestically developed ultra-large-diameter tunnel boring machine (TBM), surpassed 4,000 meters of excavation from the Ningbo side.

The TBM is boring the Jintang undersea tunnel, a key section of the Ningbo-Zhoushan Railway. Stretching 16.18 kilometers between Ningbo's Beilun district and Jintang Island in Zhoushan, the tunnel includes an 11.21-kilometer shield section. Two TBMs are advancing toward each other from opposite sides to connect beneath the sea.

The Ningbo-side section is 4,940 meters long, with its deepest point reaching 92 meters below the seabed. The project faces 28 alternating soft and hard geological formations, with hard rock and mixed strata accounting for nearly 70 percent of the Yongzhou route.

To address these challenges, engineers developed advanced systems including high-pressure cutting equipment, high-precision guidance technology, and a domestically developed "deep-sea space station" for pressurized maintenance. An AI-powered tunnel boring model also helps analyze real-time data and provide early warnings, enabling more proactive risk management.

Once completed, the railway will end Zhoushan's history of no rail service. Travel from Ningbo to Zhoushan is expected to take as little as 26 minutes by high-speed rail.