On January 10, the domestically produced super-large-diameter shield tunneling machine "Dinghai" rolled off the production line in Changsha. It will be used in the construction of the Jintang Subsea Tunnel of the Ningbo-Zhoushan Railway, the world's longest and largest-diameter subsea high-speed rail tunnel.

"Dinghai" was jointly built by China Railway 11th Bureau Group and CRCC Heavy Industry. It has a maximum excavation diameter of 14.57 meters and a total weight of 4,350 tons, eight times the weight of an ordinary shield tunneling machine. Its cutterhead, about five stories high, is painted with a pattern of the "Dragon King of the East Sea," conveying an imposing presence, the traditional cultural implication of "suppressing the sea," and the builders' determination to overcome the challenges of the subsea high-speed rail tunnel.

The Jintang Subsea Tunnel is a controlling project on the entire Ningbo-Zhoushan Railway (from Ningbo to Zhoushan in Zhejiang Province). Its shield-driven section is about 11.21 kilometers long with an excavation diameter of 14.57 meters. The tunnel is being built using the bidirectional shield method, with two shield machines tunneling toward each other from Ningbo and Zhoushan respectively. China Railway 11th Bureau Group is undertaking the construction of the 6.27-kilometer section on the Zhoushan side.

"This time we are facing a '***' engineering challenge," said Wang Shuang, project manager of the Ningbo-Zhoushan Railway project of China Railway 11th Bureau Group. The geological structure and underwater topography around the tunnel are complex. Construction must pass through high-strength, weakly weathered tuff with a strength of nearly 200 MPa and cope with high water pressure of 0.85 MPa, placing high demands on the cutterhead design and shield body sealing performance. To this end, "Dinghai" innovatively adopts six core technologies: integrated advanced geological forecasting, cutter replacement under saturated compressed air, simultaneous two-component grouting at the shield tail, a double-layer shield body, segment floating monitoring, and backfill grouting scanning.

In subsea tunnel construction, having two shield machines bore toward each other can reduce construction risks and shorten the schedule, but the breakthrough is difficult. Wang Shuang said "Dinghai" has an advanced guidance system and tunnels forward according to coordinate information input by technicians. During tunneling, it transmits position information back in real time and continuously corrects and adjusts its posture, ultimately achieving high-precision breakthrough with a radial deviation of less than 2 centimeters.

In a subsea tunnel with a burial depth of 85 meters, lifting equipment cannot be used to dismantle and hoist the shield machine. The project team innovatively developed a series of tooling devices that can dismantle and transport components such as the cutterhead, shield body, and drive units within the narrow tunnel space. Among them, a new hydraulic device can "jack up" the main drive weighing more than 300 tons. "The innovative research and development results of this project have accumulated rich technical experience for subsea tunnel construction in China," Wang Shuang said.