China’s First "Ternary Mixed Gas" Shield Underwater Pressurized Operation Equipment Put into Use

On May 8, China’s first set of "ternary mixed gas" shield pressurized operation equipment, independently developed by China Railway 11th Bureau Group under China Railway Construction Corporation Limited, was officially applied to the Jintang Undersea Tunnel of the Yongzhou-Zhoushan Railway, marking a major breakthrough in China’s shield ultra-high pressure pressurized operation field.

China News Network reported that the Jintang Undersea Tunnel is a key control project of the Yongzhou-Zhoushan Railway, spanning the Jintang Waterway between Ningbo and Zhoushan in Zhejiang Province. With a total length of 16.18 kilometers and a shield section of 11.21 kilometers, it is the longest undersea high-speed railway tunnel in the world. The project construction adopts two super-large diameter shield machines, which start simultaneously from both sides of Ningbo and Zhoushan and tunnel towards each other, aiming to achieve high-precision docking underwater after passing through high water pressure and various complex strata.

The maximum depth of the Jintang Undersea Tunnel is 78 meters below sea level, with the highest water and soil pressure reaching 0.85 MPa, equivalent to a pressure of nearly 30 kilograms on the area of a one-yuan coin. To cope with such extreme working conditions, the research team drew on deep-sea diving technology and successfully developed the helium-nitrogen-oxygen "ternary mixed gas" shield pressurized operation equipment suitable for shield construction.

People’s Network stated that this equipment covers two key modules: gas distribution and gas supply, integrating 113 sub-modules including gas distribution hub, gas supply hub, human breathing apparatus, deck decompression chamber, and pressure monitoring and flow control. It operates with a combination of automatic and manual control, scientifically proportioning helium, nitrogen and oxygen for human breathing in different high-pressure environments to meet the ultra-high pressure pressurized operation needs of world-class projects.

Compared with the traditional saturated pressurized operation method, the equipment does not require the construction of a large-scale pre-posed residential cabin system, which greatly shortens the maintenance operation cycle. During operation, personnel entering the cabin wear special mixed gas breathing apparatus, supplied with gas through external pipelines, and the exhaled gas is actively recovered in the cabin. After completing the task, the personnel exit the cabin through scientific decompression and enter the deck decompression chamber for secondary decompression and recuperation.

The equipment can support 3 people to enter the cabin at the same time for 60 minutes each time, and 24-hour continuous operation can be realized through the cooperation of two groups of cabins. Xinhua News Agency noted that the application of this equipment not only solves the technical bottleneck of ultra-high pressure pressurized operation in undersea shield tunnels but also provides technical support for the construction of similar projects at home and abroad.

In the future, China Railway 11th Bureau Group will continue to optimize the performance of the "ternary mixed gas" shield pressurized operation equipment, promote technological upgrading and innovation, and further improve the efficiency and safety of shield construction. This will help accelerate the construction progress of the Jintang Undersea Tunnel and lay a solid foundation for the smooth opening of the Yongzhou-Zhoushan Railway, which will enhance regional transportation connectivity and promote economic and social development in the Yangtze River Delta region.