At 10:00 on January 23, at the Jintang Subsea Tunnel construction site in Beilun District, Ningbo, as the last batch of concrete was poured into the formwork, the Ningbo-side shield working shaft of the Jintang Subsea Tunnel of the Ningbo-Zhoushan Railway—the deepest extra-large-diameter shield working shaft in China at 58.13 meters—was completed. The project has achieved important progress, laying a solid foundation for the entry, assembly and launch of the shield machine.

The Jintang Subsea Tunnel is located beneath the Jintang Waterway between Ningbo and Zhoushan, starting from Yinzhou District of Ningbo in the west and ending at Jintang Town of Zhoushan in the east, crossing the Jintang Waterway with a total length of 16.18 kilometers. The shield tunnel section is 11,210 meters long, with a maximum burial depth of 78 meters and a maximum water depth of 39 meters. It is the world's longest subsea high-speed railway tunnel and a key controlling project of the entire Ningbo-Zhoushan Railway. In the construction of this world-class extra-large-diameter shield tunnel, for the first time two 14.57-meter extra-large-diameter shield machines were launched from the Ningbo and Zhoushan ends respectively to bore toward each other, achieving precise undersea breakthrough with an error of no more than 20 millimeters, and completing the disassembly of the shield machines inside the tunnel—a new construction method.

The Ningbo-side shield working shaft of the Jintang Subsea Tunnel is 22.6 meters long, 21.1 meters wide and 58.13 meters deep, with a nine-level underground structure equivalent to the height of nearly 20 stories. The area around the working shaft is densely packed with pipelines, including 23 petroleum pipelines, 1 water supply pipeline and 37 strong- and weak-current electrical lines, presenting difficulties such as an ultra-deep foundation pit, alternating soft and hard rock, and a complex surrounding environment. The nearest petroleum pipeline is only 5.5 meters from the working shaft, making the construction extremely difficult—like "performing a ceremony inside a snail's shell."

According to reports, the Ningbo-side shield working shaft was constructed top-down layer by layer using the open-cut top-down method. The strength of the slightly weathered dacite increases with excavation depth, reaching up to 227 MPa. Because the surrounding environment is "sensitive," blasting was not permitted, so only mechanical excavation could be used, and the lifting and transport of reinforced concrete and materials carried high safety risks.

Excavation of the Ningbo shield shaft of the Jintang Subsea Tunnel began in May 2023. During construction, the construction management unit, the Shanghai-Hangzhou Passenger Dedicated Line Company, together with the project department of China Railway 14th Bureau Group, optimized and improved the construction plan, adopting monitoring technologies such as advanced geological forecasting and automatic warning of surrounding rock monitoring and measurement to promptly and accurately grasp changes in the surrounding rock of the shield shaft and effectively guard against safety risks. Based on the characteristics of the rock strata, the project team used various equipment such as rotary drilling rigs, small drilling rigs and hydraulic breakers for foundation pit excavation, and customized automatic opening-and-closing hoppers and a 71-meter-long concrete pump truck for muck lifting and concrete pouring. They innovatively developed a standardized, modular and reusable new truss formwork system, and adopted integrated formwork support for constructing the concrete walls of the main structure, doubling work efficiency.

In terms of construction methods, the innovative "tofu-cutting" approach was used, employing a method of dividing into blocks before excavation to improve excavation efficiency. Through the efforts of all participating personnel, the ultra-deep foundation pit excavation and concrete structure sealing were successfully completed in eight months, creating an ultra-deep working shaft that is "solid inside and beautiful outside, with no seepage or leakage," providing the necessary conditions for the subsequent assembly and launch of the shield machine.

The Ningbo-Zhoushan Railway starts from Ningbo East Station in the west, passes through Yinzhou District and Beilun District of Ningbo, Jintang Island, Cezi Island and Zhoushan Main Island of Zhoushan, and ends at Baiquan Town of Dinghai District in the east. It has seven stations—Ningbo East, Yunlong, Qiu'ai, Beilun West, Jintang, Ma'ao and Zhoushan—with a total length of about 77 kilometers and a design speed of 250 kilometers per hour. It is intended to build Zhejiang Province's "one-hour transportation circle" and form a convenient passenger transport corridor between the mainland and Zhoushan Island. Once completed, the project will fill the gap of the last prefecture-level city in Zhejiang Province without railway access, and is of great significance for improving the railway network layout, promoting tourism development along the line, realizing the integrated and co-urbanized development of Ningbo and Zhoushan, and accelerating the integration of Zhoushan and Ningbo into the "Belt and Road" and the Yangtze River Economic Belt.