At 10:18 a.m. on May 16, with the cutterheads of two super-large-diameter shield machines, "Dinghai" and "Yongzhou," rotating simultaneously, the Jintang Subsea Tunnel of the Ningbo-Zhoushan Railway officially entered the shield tunneling construction phase.

The "Dinghai" shield machine ready to launch

Tunnel sets multiple records

The Jintang Subsea Tunnel is a controlling project of the entire Ningbo-Zhoushan Railway line. Connecting the cities of Ningbo and Zhoushan, the tunnel is about 16.18 km long and is currently the world's longest, largest-diameter subsea high-speed railway tunnel with the most complex geology and the greatest construction difficulty.

"Four highs, three larges, two complexities" succinctly sums up the difficulty of the project: the "four highs" mean that tunnel construction will overcome nearly 200 MPa of highly strong, weakly weathered tuff, challenge construction under 0.85 MPa of high water pressure, achieve high-precision subsea shield docking with radial misalignment of less than 20 mm, and face the high risk of dismantling the shield machine inside the tunnel at a water depth of 21.2 m at the section;

The "three larges" refer to the large excavation diameter of the shield machine, the great difficulty of subsea docking operations, and the large variation in rock properties as the tunnel passes through changing strata;

The "two complexities" are complex adverse geology and complex underwater topography. Within the tunnel alignment there are a total of 9 faults, 6 densely jointed zones, and 1 tectonic influence zone. The underwater terrain is covered with complex features such as tidal sand ridges and channels subject to alternating scour and siltation, as well as underwater shoals, sharply increasing construction hazards.

The shield machine incorporates 12 cutting-edge technologies

The shield-driven section of the subsea tunnel is about 11.21 km long, and we have undertaken 6.27 km of construction on the Zhoushan Jintang side. The cutterhead excavation diameter of the "Dinghai" shield machine reaches 14.57 m, the whole machine is about 135 m long, and its total weight is about 4,350 t.

To cope with the complex subsea working conditions, the shield machine is equipped with the internationally advanced, independently developed sixth-generation intelligent shield system, innovatively applies new intelligent and green tunnel construction technologies, and is the first to introduce 12 cutting-edge technologies, including advanced geological forecasting, saturated hyperbaric cutter replacement, simultaneous two-component grout injection at the shield tail, double-layer shield shell, segment floating monitoring, and backfill grouting scanning.

To ensure the safe, high-quality, and efficient advancement of subsea tunnel construction, during the earlier shield machine selection, assembly, and commissioning process, the builders repeatedly invited internal and external shield experts to review and validate the construction plan. Relying on its own Laboratory of Intelligent Construction of Large Shield Tunnels under the National Center of Technology Innovation for Digital Construction, they made every effort to advance the research, development, and application of key technologies and equipment for intelligent construction of large shield tunnels, simulated various risks and challenges that the shield machine may encounter during subsea construction, and can ensure that the shield machine completes subsea tunneling in optimal condition.

Adopting the "industrialization of shield construction workers" model

According to reports, in subsequent construction, eight technical challenges will be overcome, including long-distance, high-water-pressure shield tunneling in complex marine environments and the subsea docking and dismantling of a super-large-diameter shield. To address the tunneling challenges of large shields in strata with uneven hardness and softness and in long-distance, large-burial-depth, high-water-head strata, the builders will also start with shield slurry parameters and shield machine attitude, among other aspects, to continuously strengthen process control.

In addition, in construction management, the construction team relies on the "industrialization of shield construction workers" model, which is unique in the domestic market, to refine and implement the management mechanism of "integration of people and machines, fixed personnel for fixed machines, professional maintenance, and unified responsibilities, rights, and interests." Combined with "6S management," whose main indicators are six core essentials including safety, organization, and cleaning, the development goals of "refined project management and factory-style site management" have now been preliminarily achieved.

Will end the history of no train service in the Zhoushan Archipelago

The newly built Ningbo-Zhoushan Railway project is needed to achieve the goal of building a one-hour high-speed rail transportation circle in Zhejiang Province, and is also needed to accelerate the integration of Zhoushan and Ningbo into the national economic development strategies of the "Belt and Road" and the Yangtze River Economic Belt.

The project is about 76.4 km long in total. The line starts at Ningbo East Station in the west and extends eastward to Jintang Island, Cezi Island, and Zhoushan Main Island in Zhoushan City. It is one of the ten landmark projects in Zhejiang Province's major corridor construction. After the line opens to traffic, it will end the history of no train service in the Zhoushan Archipelago and is of far-reaching significance for Zhoushan City to proactively integrate into national strategies such as the joint pursuit of the "Belt and Road," the development of the Yangtze River Economic Belt, and the integrated development of the Yangtze River Delta, effectively promote the integrated development of Ningbo and Zhoushan, and build Zhejiang Province's "one-hour transportation circle."