'Triple-mix gas' shield equipment sets multiple world records

(ECNS) -- The world's first "triple-mix gas" hyperbaric intervention system for shield tunneling, independently developed by China Railway 11th Bureau Group, completed its first large-scale cutterhead tool replacement operation under ultra-high pressure on Thursday in the Jintang Subsea Tunnel in Zhoushan, east China's Zhejiang Province. The tunnel is the world's longest undersea high-speed railway tunnel.

The operation set multiple world records in shield tunneling, including the greatest operating depth, highest pressure, largest number of tool changes and longest continuous operating period.

The Jintang Subsea Tunnel is a key project of the Ningbo-Zhoushan Railway. It stretches 16.18 kilometers across the Jintang waterway between Ningbo and Zhoushan, including an 11.21-kilometer shield-tunneling section.

The tunnel reaches a maximum depth of 78 meters below sea level, where water and soil pressure can reach 0.85 MPa — equivalent to around 30 kilograms of force exerted on an area the size of a one-yuan coin.

As the shield machine moves from soft soil into hard rock, cutting tools designed for soft ground must be replaced with disc cutters suitable for hard rock. Carrying out such work in a hyperbaric environment has long been a major global challenge in undersea tunnel construction.

To address this challenge, China Railway 11th Bureau Group developed a helium-nitrogen-oxygen "triple-mix gas" system based on deep-sea diving technology. Helium has a low density, disperses rapidly and offers a high level of safety, helping to reduce risks such as nitrogen narcosis and oxygen toxicity while creating a safer breathing environment for workers under extreme pressure.

The equipment allows three workers to enter the hyperbaric chamber at the same time, with each able to work for up to 60 minutes per session. By rotating teams, the operation was able to continue around the clock.

Construction of the Jintang Subsea Tunnel has now advanced 10,005 meters, completing 89.3% of the shield-tunneling section.

The Ningbo-Zhoushan Railway is a key project under China's Medium- and Long-Term Railway Network Plan (2016-2030). The 76.4-kilometer line, designed for speeds of up to 250 km/h, will connect Zhoushan to the national railway network for the first time.

(By Tang Yuxian)