On October 31, a super-large diameter shield tunnel boring machine with a maximum excavation diameter of 16.64 meters was unveiled in Changsha, Hunan. This machine will be used for the construction of the Haitai Yangtze River Tunnel, currently the world's longest underwater highway tunnel. It is the largest diameter shield machine independently developed in China to date, marking a new breakthrough in the industrialization of domestically produced super-large diameter shield machines.

The “Jiang Hai” will be applied in the construction of the Haitai Yangtze River Tunnel

This shield machine is named “Jiang Hai” and was jointly created by China Railway Construction Heavy Industry Group and China Railway 14th Bureau Group. The machine is approximately 145 meters long and weighs about 5,000 tons. At the site, reporters learned that the name “Jiang Hai” symbolizes its function, bridging the Yangtze River and the sea; its cutting wheel is painted in deep blue waves, representing the machine’s capability to navigate fluidly through both rivers and seas.

The Haitai Yangtze River Tunnel is located in the Yangtze River estuary area of Jiangsu Province, stretching from Haimen District in Nantong to Taicang City in Suzhou. The total length of the project is 39.07 kilometers, with an 11.185-kilometer underwater tunnel designed to accommodate six lanes of traffic, at a design speed of 100 kilometers per hour. The shield tunnel section measures 9,315 meters long, with a maximum excavation diameter of 16.64 meters, traversing through complex geological strata including silty and clayey layers with sediment, and reaching a maximum depth of about 75 meters; the highest water pressure reaches 7.5 bar. It is characterized by extremely long distances, large diameters, high water pressures, considerable burial depths, and complex working conditions.

The “Jiang Hai” will face multiple challenges

Song Huan, a senior engineer for the Haitai Yangtze River Tunnel project under China Railway 14th Bureau, explained that the shield machine will perform ultra-long-distance single-sided excavation underwater in the Yangtze River, especially when crossing the river and the adjoining embankments, where the settlement must be controlled within 1 centimeter. This presents significant construction challenges, as geological surveys of the riverbed are limited and many unknown areas remain uncontrollable, akin to “crossing a river by feeling for stones.” The diameter exceeding 16.6 meters implies that the torque required for the excavation is substantial, leading to high loads on the main drive bearings. The exceedingly high water pressure of 7.5 bar demands exceptional pressure-resistance capabilities from integral components such as the main drive seals and shield tail seals. Ensuring the machine’s continuous operation for 9,315 meters in the complex riverbed environment while maintaining high-performance loads is the primary challenge and dilemma for the research and development team.

Fan Ruiqiang, a senior engineer from the Tunneling Machine Research and Design Institute under China Railway Construction Heavy Industry Group, mentioned that the research team has innovatively addressed the project’s construction risks and difficulties. They implemented targeted designs for critical components like the cutting wheel and main drive. The team also equipped the machine with a soft soil cutting wheel featuring the capability for regular pressure tool change, as well as cutting tools that are large, highly durable, and resistant to wear. The main drive has a telescoping feature that can sense the overall stress on the cutting wheel, preventing overload on the main bearing due to abnormal stress in special situations, facilitating tool change operations, and aiding in cutting wheel rescue. Additionally, a monitoring system has been configured to continuously track the operating conditions of the main drive. The shape dimensions and structural thickness of the shield were tailored to local conditions, larger hydraulic cylinder specifications were adopted, and optimization of the mud circulation system and grouting system was implemented to enhance overall performance. An intelligent assembly system for segment connection components was also established to meet construction requirements.

Furthermore, the research team leveraged years of underwater and large-diameter shield tunnel construction experience, increasing the opening rate of the shield machine's cutting wheel and introducing a high-pressure, high-flow center flushing system and a cutting wheel filter mud cake warning system. They have also implemented a telescoping camera system that allows observation of the cutting wheel’s working area without personnel needing to enter the pressured chamber, effectively assessing and reducing the risk of mud cake formation while improving bottom dredging efficiency. Additionally, they applied a self-developed fourth-generation synchronous injection dual-liquid slurry technology to achieve millimeter-level precision control of settlement in the shield tunnel, ensuring construction safety and efficiency.

A new leap in the development of super-large diameter shield machines in China

Generally, shield machines with diameters of 14 meters and above are referred to as super-large diameter shield machines. The “Jiang Hai” is another super-large diameter shield machine independently developed by Chinese enterprises, following the successful launch and application of the 16.07-meter diameter “Jing Hua.” The successful unveiling of the “Jiang Hai” signifies a new leap for Chinese enterprises in the development and application of 16-meter-class super-large diameter shield machines, establishing a comprehensive industrial chain for the industrialization of super-large diameter shield machines.

The Haitai Yangtze River Tunnel is a key project promoted in the "Yangtze River Mainline Cross-River Channel Layout Plan (2020-2035)" and the "Comprehensive and Three-dimensional Transportation Corridor Planning for the Yangtze Economic Belt in Jiangsu Province." It is also a significant cross-river channel project for Jiangsu's 14th Five-Year Plan, with completion expected by 2028. Once constructed, it will effectively divert traffic from the Su-Tong Yangtze River Bridge, significantly contributing to the integrated development of the Yangtze River Delta region and the nation’s strategy for the development of the Yangtze River Economic Belt, optimizing the layout of cross-river channels along the Yangtze, and promoting the integrated development of city clusters along the river.