China deploys advanced gas system for world’s longest undersea high-speed rail tunnel

China has introduced its first domestically developed "ternary mixed gas" pressurised operation system, now officially in use at the 16.18-kilometre Jintang undersea tunnel, which is recognised as the world’s longest undersea high-speed rail tunnel. As reported by Global Times, a partner of TV BRICS.

The newly implemented system enables the precise mixing of helium, nitrogen, and oxygen for pressurised working conditions during cutter inspection and replacement on shield tunnelling machinery. It is designed to support construction activities under extreme underwater pressure while maintaining stable operational conditions.

Ultra-high-pressure environments present one of the most complex technical challenges in modern tunnelling. Conventional compressed-air methods are typically limited to a safety threshold of 0.5 megapascals, whereas the deepest section of the Jintang tunnel reaches approximately 0.85 megapascals due to its 78-metre depth beneath sea level.

To address these conditions, the construction team responsible for the 6,270-metre shield tunnelling section on the Zhoushan side developed a specialised solution inspired by technologies used in deep-sea diving. The resulting ternary gas mixture integrates helium’s low density and high diffusion properties, reducing physiological risks associated with high-pressure work environments and supporting safer breathing conditions for operators.

The system incorporates gas mixing and supply modules alongside more than 100 integrated submodules, including distribution hubs and breathing apparatus components. It is capable of supporting operations across a pressure range of 0.5 to 1 megapascals, enabling sustained performance in demanding undersea construction environments.