China, August 2026 – Construction workers have completed the inspection and replacement of 104 shield cutting tools over 21 days at the Jintang undersea tunnel, working under high water and soil pressure. The operation represents a significant construction milestone for the 16.18-kilometre tunnel, which is being developed as part of the Ningbo-Zhoushan railway and is expected to become the world's longest undersea high-speed rail tunnel.
The Jintang tunnel includes an 11.21-kilometre shield-bored section and will connect Ningbo with the Zhoushan islands. The project is being constructed by two large-diameter shield machines operating from opposite shores. On the Ningbo side, the Yongzhou machine is required to pass through 4,940 metres of alternating soft and hard rock, with rock strength reaching up to 191 MPa. At the tunnel's deepest point, approximately 92 metres below sea level, water and soil pressure reaches 8.5 bar, while a 2,000-metre section experiences pressure above 6 bar.
These conditions make routine cutter inspection and replacement considerably more difficult than conventional shield tunnelling. Traditional compressed-air working methods provide limited effective working time and are generally constrained by depth. To address the challenge, the project team spent three years adapting deep-sea saturation-diving technology for tunnel construction and developed a domestically manufactured saturation hyperbaric system known as the “Deep-Sea Space Station.”
The system combines living, transfer and control modules and can accommodate up to nine workers for extended periods. Workers can reach the tunnel face through a transfer chamber and remain there for shifts of up to eight hours, supporting continuous multi-shift operations for as long as 28 days before controlled decompression. The approach is intended to reduce the health and operational risks associated with repeated pressure changes during high-pressure maintenance work.
The latest achievement highlights how advances in tunnelling equipment, pressure-management systems and specialised workforce protection are becoming increasingly important as rail networks extend through difficult marine and geological environments. With the Yongzhou shield machine having advanced 3,936 metres—nearly 80 percent of its planned section—the project provides a significant engineering case study for future high-speed rail schemes involving long underwater tunnels and high-pressure construction conditions.
Source: Global Times
High-Pressure Cutter Replacement Advances Ningbo-Zhoushan Rail Tunnel
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Undersea railway construction is pushing tunnelling technology into increasingly demanding operating environments, particularly where high water pressure and complex geology constrain conventional maintenance methods. In eastern China, engineers have completed a major shield-machine cutter replacement operation on the Ningbo-Zhoushan high-speed railway, demonstrating a new approach to sustained work at extreme depths.
