On January 10, the subsea tunnel between the Train Station stop of Dalian Subway Line 5 and the Suoyvwan South Station was completed successfully. Invested and managed by CREC North Investment Group, surveyed by China Railway Major Bridge Reconnaissance & Design Institute, and constructed by China Railway First Group, the tunnel is the world’s first large shield tunnel in karst stratum, the longest large shield tunnel in hard rock stratum in China, and a subway subsea tunnel with the longest diameter in China. Its completion marks that China has overcome the global challenge of using shield machines to penetrate the karst formation under the sea. Construction of the tunnel provides experience for shield tunneling in subsea karst formations and long-distance hard rocks in the construction of sea-crossing tunnels.

The length of the tunnel-shielding section from the Train Station to the Suoyvwan South Station is 2,882 meters, of which 2,310 meters travel through the waters of the Suoyvwan Bay. In high-strength hard rock formations, the excavation distance is quite long, which means the shielding needs to continuously cross the whole distance of 2,882 meters. Construction was extremely difficult and risky. The shield machine needed to pass through various structures such as navigation channels and wharfs, and it had to cross the 1,538-meter-long strongly-developed karst area with more than 1,000 karst caves along the line. The construction team had to overcome problems that are considered global challenges by experts of the construction industry, such as crossing high compressive strength of seabed rocks (a maximum of 118 MPa), tunneling under large buried depth, and resisting high water pressure.

CREC adapts a new construction management model that integrates design, general contracting, construction, equipment, and manufacturing, and strives to overcome the daunting challenge of building long tunnels under deep water. China Railway First Group and China Railway Hi-Tech Industry Corporation Limited jointly develop the air-cushioned mud-water balance shield machine “Haihong” for the sea-crossing operations. With a diameter of 12.26 meters, the machine is equipped with high-end technologies to perform comprehensive functions. The shield machine is installed with an intelligent information management system and a special tool-change system with analysis functions.

The construction department set up an innovation team named after Liang Xijun, a worker of CREC with the title of National Model Worker, to carry out research activities in technical operations. The team gained a lot of achievements, including digging tunnels with large shield machines in karst development area under the sea, guaranteeing the complete sealing of large shield machines, enabling operations in large shield machines under high water pressure, tool management of long-distance large shield machines in lard rock, and deposition control of buildings and structures with large shield machines. These technological breakthroughs enabled shield machines to steadily and continuously cross under the sea, making a record of shield tunneling as long as 212 meters in a month in long-distance hard rock formations under the sea. (By Xue Liang, Niu Rongjian, Tang Jiajia, Tang Jianjun)