On February 26, 2024, the domestically produced ultra large diameter shield tunneling machine "Yongzhou" was taken offline in Changsha and will be applied to the construction of the world's longest underwater high-speed railway tunnel - the Jintang Submarine Tunnel of the Ningbo Zhoushan Railway, helping Zhejiang build a "1-hour transportation circle".

The "Yongzhou" shield tunneling machine is jointly developed by China Railway 14th Bureau Group and China Railway Construction Heavy Industry Group. It has a total length of 135 meters, a total weight of 4350 tons, a cutter head excavation diameter of 14.57 meters, and is equipped with 308 special cutting tools. The total assembly has reached the world-class level.

The Jintang Subsea Tunnel is a key control project of the Yongzhou Railway, starting from Yinzhou District in Ningbo City in the west and ending at Jintang Town in Zhoushan City in the east, with a total length of 16.18 kilometers. The tunnel construction adopts a bidirectional shield tunneling method, with two shield tunneling machines starting from Ningbo and Zhoushan and heading towards each other, and finally docking at the seabed.

This is also the first time that ultra large diameter shield tunneling machines have achieved underwater docking worldwide. In this project, China Railway 14th Bureau undertook the construction of a 11.2 kilometer tunnel on the Ningbo side, with a maximum burial depth of 78 meters in the construction section.

Hu Hao, the commander of the Yongzhou Railway project of China Railway 14th Bureau, introduced that the geological and marine environment of the Jintang Subsea Tunnel is complex, with nearly 70% of the hard rock and uneven soft and hard strata, with a maximum strength of 200 megapascals. The shield tunneling machine needs to frequently change its cutting tools in the deep sea.

For this purpose, the project team adopted six innovative designs, such as using a heavy-duty pressurized cutterhead design, reducing the distance between the knives, increasing the number of rolling cutters, and increasing the number of rolling cutters by 70 compared to conventional cutterheads, improving the rock breaking ability and excavation efficiency of the cutterhead. It is reported that the "Yongzhou" is also equipped with the world's first intelligent monitoring system for cutter wear, effectively improving the wear resistance of the cutterhead.

The difficulty of underwater docking for shield tunneling machines is high, and the construction accuracy error is required to not exceed 20 millimeters. The Yongzhou vessel is equipped with a high-precision guidance system and advanced geological prediction and grouting reinforcement equipment to detect and reinforce unfavorable geology in advance, ensuring the accuracy and safety of docking in the sea. To cope with the high-pressure and narrow working environment in the sea, the shield machine adopts a double-layer shell, which can disassemble the shield body from the inside and provide support for the formation.

It is reported that the project has achieved multiple innovative results, adding technical reserves for the construction of the China Strait Tunnel. Editor/Zhao E