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World’s Longest Undersea High-Speed Rail Tunnel TBM Rolls Off the Production Line
Ningbo, February 26 (China National Radio) — According to reporter Yu Ye and correspondents Ma Jingbo and Li Denghui, on February 26 a super-large-diameter tunnel boring machine named “Yongzhou,” with its cutterhead adorned with the “Ruilong” motif, rolled off the production line in Changsha, Hunan Province. With a cutterhead excavation diameter of 14.57 meters, the machine will be deployed in the construction of the Ningbo portal section of the Jintang Subsea Tunnel on the Yongzhou Railway, which is set to become the world’s longest undersea high-speed railway tunnel.
The “Yongzhou” tunnel boring machine was 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 4,350 tons, and is equipped with 308 custom-designed cutter tools, achieving world-class assembly standards. The TBM’s cutterhead is adorned with motifs of “Rui Long” (Auspicious Dragon) and “Xiangyun” (Auspicious Clouds), symbolizing the builders’ aspiration to embark on the undersea tunneling journey aboard the auspicious energy of the dragon and with the courageous spirit to overcome all obstacles.
The Jintang Subsea Tunnel is one of the key, control-level projects along the entire Ningbo–Zhoushan Railway. Stretching 16.18 kilometers from Yinzhou District in Ningbo City in the west to Jintang Town in Zhoushan City in the east, the tunnel includes a 11.2-kilometer shield-tunneling section with a maximum burial depth of 78 meters. It passes beneath the 100,000-ton-class Jintang Main Navigation Channel. Two shield machines were launched simultaneously from Ningbo and Zhoushan, advancing in opposite directions, and ultimately achieved underwater splicing with an accuracy tolerance of no more than 20 millimeters—less than the diameter of a five-cent coin. This will mark the world’s first successful underwater splicing and subsequent dismantling of ultra-large-diameter shield machines.
According to reports, the “Yongzhou” tunnel boring machine, departing from the working shaft at the Ningbo end, will undertake a single-heading advance of 4,940 meters. During this journey, it must pass beneath 23 oil pipelines, various surface structures, seawalls, docks, and the main navigation channel—totaling 42 potential risk sources—and contend with highly complex geological formations and marine conditions. Nearly 70% of the ground consists of hard rock and unevenly mixed soft–hard strata, with maximum rock strength reaching 200 MPa. The tunnel section will experience 14 alternating transitions between soft and hard strata, requiring frequent high-pressure cutterhead replacement operations by personnel at a depth of 70 meters below sea level. The sheer complexity, difficulty, and risk of this long-distance crossing are unparalleled worldwide.
According to Hu Hao, Project Manager of the Yongzhou Railway project at China Railway 14th Bureau, in response to the complex construction challenges posed by the undersea tunnel, the project team implemented six innovative design modifications to the tunnel boring machine. These included a heavy-duty pressurized cutterhead featuring 70 additional disc cutters compared with conventional designs—adding more than 100 tonnes of weight—and a reduced cutter spacing with an increased number of cutters. Moreover, the team pioneered the world’s first intelligent monitoring system for disc cutter wear, significantly enhancing the cutterhead’s wear resistance and rock-breaking capability and thereby ensuring high tunneling efficiency.
“The tunnel boring machine is equipped with the most precise and technologically advanced guidance system currently available, serving as the ‘eyes’ of the equipment during excavation. It is also fitted with specialized systems for ahead-of-face geological forecasting and ahead-of-face grouting reinforcement, enabling proactive detection and preemptive stabilization of adverse geological conditions ahead of the TBM face, thereby ensuring the precision and safety of the underwater jointing operation,” said Zhao Dabin, Deputy Project Manager of the Ningbo–Zhoushan Railway Project at China Railway 14th Bureau Group. In addition, the TBM features a double-shell design: upon completion of tunneling, the inner shell is carefully dismantled from within—reminiscent of a cicada shedding its exoskeleton—while simultaneously providing support to the surrounding strata, thus facilitating in-situ dismantling in the high-pressure, confined environment beneath the sea.
According to reports, in connection with the construction of the Jintang Subsea Tunnel, the project team established a dedicated task force to systematically identify and address key technical challenges. This effort has resulted in the formulation of more than ten research projects, including “Research on a Comprehensive Set of Construction Techniques for the Full-Process In-Situ Docking of Ultra-Large-Diameter Shield Tunnels Under the Seabed.” The team is comprehensively advancing technical research in multiple areas—such as equipment configuration, breakthroughs in complex and challenging technologies, and the development of high-quality tunneling methods—to build a robust technological foundation for the future construction of additional strait-crossing tunnels in China.
The Yongzhou Railway has a total length of approximately 77 kilometers and is designed for a maximum speed of 250 kilometers per hour, making it a dedicated passenger railway. Upon completion and opening to traffic, it will fill the final gap in Zhejiang Province’s “one-hour high-speed rail network across the province” and “high-speed rail connectivity among all prefecture-level cities,” thereby playing a vital role in optimizing the railway network layout, boosting tourism along the route, advancing the integrated and metropolitan development of Ningbo and Zhoushan, and accelerating the integration of Zhoushan and Ningbo into the Belt and Road Initiative and the Yangtze River Economic Belt.
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