The Ningbo side of the tunnel of Ningbo-Zhoushan railway, the world's longest undersea high-speed railway, had advanced more than 4,000 meters as of Monday using China's domestically-made super-large-diameter shield boring machine "Yongzhou," the Global Times learned. The deepest point of the tunnel lies 92 meters below the seabed.

The achievementmeans that the machine is less than 1,000 meters from the mid-sea docking point, meaning the project has reached a critical milestone of construction, according to a statement the project's constructor, China Railway 14th Bureau Group Co, sent to the Global Times on Tuesday. 

The Jintang undersea tunnel is a key control project of the Ningbo-Zhoushan railway. It runs west from Beilun District in Ningbo to Jintang town in Zhoushan, with a total length of 16.18 kilometers. 

The tunnel includes an 11.21-kilometer shield-driven section, where two shield boring machines are advancing toward each other from the Ningbo and Zhoushan sides for a mid-sea docking, and the drive must pass through 28 alternations of soft and hard strata. It is currently the world's longest undersea high-speed railway shield tunnel, and the one with the most complex geology and the greatest construction difficulty.

To date, the "Yongzhou" shield boring machine has gone through 20 changes in geological strata, safely passed 43 risk sources of various grades, and is now tackling the tunnel's hardest full-face hard-rock section beneath the seabed, the statement said.

The "Yongzhou" super-large-diameter shield boring machine uses a heavy-duty pressurized cutter-head, narrower cutter spacing and more disc cutters, to improve wear resistance and rock-breaking capacity. The machine is also fitted with what is currently the world's most precise and advanced guidance system, as well as special equipment for advance geological forecasting and pre-grouting reinforcement. Its overall assembly meets world-class standards.

The "Yongzhou" shield boring machine is also equipped with "Shenyuan," the first shield-tunneling domain-specific large model in China to receive the national-level certification. By analyzing tunneling data in real time — including tunneling parameters, settlement data and historical cases — the model issues targeted early-warning advice and decision options. Risk management shifts from a passive response to active pre-control, giving the undersea excavation a decision-support tool.

The undersea tunnel project also employs China's first independentlydeveloped shield saturation hyperbaric operation system, the "Deep-Sea Space Station," to overcome the challenge of changing cutters under high pressure beneath the seafloor. It is also equipped with a shield-domain large model known as "Shenyuan," enabling risks to be identified and preempted, the Global Times learned.

The equipment can operate at a maximum depth of 200 meters. Its core systems — pressure control, gas management, life support and emergency support — were all independently developed in China. It has completed cutter-changing operations at depths of between 75 meters and 80 meters below the sea, setting a national record for the highest pressure at which Chinese crews have entered a shield chamber under compressed air.

Once completed, the Ningbo-Zhoushan railway will end Zhoushan Island's history of having no rail service. The high-speed trip from Ningbo to Zhoushan will then take 26 minutes. The line will be of far-reaching importance for integrating Ningbo and Zhoushan into Zhejiang's metropolitan cluster and speeding up the development of Ningbo metropolitan circle.

Global Times