On February 26, an extra-large-diameter shield tunneling machine named "Yongzhou" with a cutterhead painted in a "Auspicious Dragon" pattern rolled off the production line in Changsha, Hunan. With an excavation diameter of 14.57 meters, it will be used in the construction of the Ningbo end of the Jintang Subsea Tunnel of the Ningbo-Zhoushan Railway, the world's longest subsea high-speed railway tunnel.
The "Yongzhou" shield machine was jointly developed by China Railway 14th Bureau Group and CRCC Heavy Industry Group. With a total length of 135 meters, a total weight of 4,350 tons, and 308 specially made cutters, its assembly has reached a world-class level. The cutterhead is painted with "Auspicious Dragon" and "Auspicious Cloud" patterns, symbolizing the builders' embarkation on the sea-crossing tunneling journey borne on the dragon's auspicious aura and with the heroic spirit to break through all difficulties.
"Yongzhou" shield tunneling machine
The Jintang Subsea Tunnel is one of the key controlling projects of the entire Ningbo-Zhoushan Railway. The tunnel starts from Yinzhou District of Ningbo in the west and ends at Jintang Town of Zhoushan in the east, with a total length of 16.18 kilometers, of which the shield-driven section is 11.2 kilometers long and the maximum burial depth reaches 78 meters. The tunnel crosses beneath the 100,000-ton-class Jintang main navigation channel. Two shield machines will be launched from Ningbo and Zhoushan respectively to bore toward each other and finally achieve a subsea breakthrough, with a precision requirement of no more than 20 millimeters of error—less than the diameter of a five-jiao coin. This will realize the world's first subsea breakthrough and disassembly of extra-large-diameter shield machines.
It is reported that the "Yongzhou" shield machine, departing from the working shaft at the Ningbo end, will bore a single-head drive of 4,940 meters. It will not only pass beneath 23 oil pipelines and 42 risk sources including various surface buildings, seawalls, wharves, and the main navigation channel, but also face complex geological formations and marine environments. Hard rock and uneven soft-hard strata account for nearly 70 percent, with the highest strength reaching 200 MPa. Along the section, it will face 14 alternating transitions between soft and hard strata. The highly variable long-distance crossing requires frequent manual high-pressure cutter replacement operations at a subsea depth of 70 meters. The complexity, difficulty, and risk of construction are unparalleled worldwide.
Interior of the "Yongzhou" shield tunneling machine
According to Hu Hao, project manager of the Ningbo-Zhoushan Railway project of China Railway 14th Bureau, in response to the complex construction characteristics of the subsea tunnel, the project team made six innovative designs to the shield machine, adopting a heavy-duty pressurized cutterhead design that adds 70 more disc cutters than a conventional cutterhead and increases weight by more than 100 tons. By reducing cutter spacing and increasing the number of disc cutters, and by developing and applying an intelligent disc cutter wear monitoring system for the first time worldwide, the cutterhead has stronger wear resistance and rock-breaking capability, ensuring tunneling efficiency.
"The shield machine uses the guidance system with the highest control precision and the most advanced technology available as the 'eyes' for equipment tunneling, and is equipped with special equipment such as advanced geological forecasting and advanced grouting reinforcement, which can carry out advanced detection and advanced reinforcement of unfavorable geology ahead of the shield machine's tunneling, ensuring the precision and safety of the subsea breakthrough," said Zhao Dabin, deputy manager of the Ningbo-Zhoushan Railway project of China Railway 14th Bureau. The shield machine also adopts a double-layer shell; after completion, it will, like a "cicada shedding its shell," disassemble the shield body from the inside while supporting the strata, coping with in-situ disassembly under high pressure and in a narrow space undersea.
Roll-off ceremony of the "Yongzhou" shield tunneling machine
It is understood that, centering on the construction of the Jintang Subsea Tunnel, the construction team specially set up a research task force and identified more than 10 scientific research topics, including "Research on the Complete Set of Processes and Construction Methods for the Entire Subsea Mid-stratum Breakthrough of Extra-large-diameter Shields," comprehensively advancing technical research in aspects such as equipment configuration, tackling key and difficult technologies, and high-quality tunnels, so as to build up technical reserves for more strait tunnel construction in China in the future.
The Ningbo-Zhoushan Railway is about 77 kilometers long, with a design speed of 250 kilometers per hour, and is a dedicated passenger railway line. Once completed and opened to traffic, it will fill the last gap in Zhejiang Province's "one-hour high-speed rail transportation circle within the province" and "high-speed rail access to every city," and is of great significance for improving the railway network layout, promoting tourism development along the line, realizing the integrated and same-city development of Ningbo and Zhoushan, and accelerating the integration of Zhoushan and Ningbo into the "Belt and Road" and the Yangtze River Economic Belt.
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