Workers exit the pressurized module after undersea shield machine maintenance. [Photo/Yongpai app]

Construction is advancing on the Jintang undersea tunnel of Ningbo-Zhoushan Railway as China's first high-pressure, saturated-entry system enables continuous cutter replacement 75 meters below the seabed.

The Yongzhou shield machine completed its first underwater cutter replacement in the Ningbo section of the Jintang undersea tunnel on Feb 6, marking the first use of a domestically developed high-pressure system that allows workers to live and operate under sea-floor pressures, enabling long-term maintenance in conditions that would otherwise be too dangerous.

The Jintang undersea tunnel stretches 16.18 kilometers, including 11.21 km underwater, and is buried up to 78 meters deep. In the Ningbo section, the shield machine must navigate 24 alternating hard and soft ground layers.

"Replacing worn cutters underwater is extremely challenging," said Hu Hao, project manager for the Ningbo section. "Unlike on land, workers face immense water and soil pressure."

The high-pressure system features pressurized living, shuttle, and control modules that simulate deep-sea conditions. Workers live in the pressurized module and travel by shuttle to the shield machine face to perform maintenance, eliminating repeated decompressions and significantly improving safety and efficiency.

Nine workers rotated in three shifts, maintaining 24-hour operations for 22 days. Under traditional methods, underwater work was limited to 40 minutes per person per day with long decompression periods.

The Ningbo section is now over 60 percent complete, with precise sea-floor alignment expected by the end of the year.