January 10 news: The Tongjing Road North Extension Project in Suzhou, surveyed and designed by China Railway Fifth Survey and Design Institute, completed the toughest 'journey through' in urban tunnel history on the 9th—a large-diameter shield successfully crossing the 350 km/h Shanghai-Nanjing Intercity High-Speed Railway.

Process monitoring data shows that the cumulative settlement did not exceed 1 millimeter. This is the world's first 'toughest case' of a large shield crossing an operational high-speed railway in construction history, and also a successful case stimulated by urban development needs that encompasses a 'package' solution covering design, construction, and equipment manufacturing.

The project is located about 2.1 kilometers west of Suzhou Station, with a total length of 2,490 meters. It is a north-south 'dead-end road' in the central urban area that Suzhou planned to focus on connecting during the '13th Five-Year Plan' period.

This was originally the longest north-south main road crossing the city, but it has become a 'pain point' for Suzhou's decade-long difficulty in north-south connectivity. The main reason is that connecting this road faces major risk points such as crossing the Wanshun Building, Bao'en Temple and other ancient structures, as well as the Shantang River and the operating Shanghai-Nanjing Intercity High-Speed Railway, Beijing-Shanghai Railway, and North Ring Expressway, all concentrated within a short distance of just over 400 meters—during shield tunneling, 30 meters away is the side crossing of Wanshun Building and other cultural heritage buildings, and 118 meters is the underpass of the Shantang River. These are all top-level difficulties in construction history.

More importantly, 305 meters ahead of the project is one of China's busiest high-speed rail lines, the Shanghai-Nanjing Intercity High-Speed Railway, with high-speed trains passing every 3 minutes. Any deviation would lead to unimaginable consequences.

Since February 2017, China Railway Fifth Survey and Design Institute has been overall planning and fully promoting the Tongjing Road North Extension Project, joining forces with multiple units to carry out technical research. The Tongjing Road North Extension Project uses a 13.25-meter diameter large-section slurry shield to underpass the Shanghai-Nanjing High-Speed Railway bridge, while currently in China, underpassing high-speed railway bridges all use shield tunnels with a diameter of about 6 meters. To use a large diameter to underpass a high-speed railway bridge, the first step is to determine the optimal underpass location. Tongjing Road is located in the center of Suzhou's old city, with many controlled and protected buildings on both sides of the Shantang River scenic area, complex traffic organization, difficult connections, and many controlling factors for the tunnel route plan. It can be said to be 'doing a ritual in a snail shell' (making the most of a tight space).

At the same time, the working space under the high-speed railway bridge is only 4 meters. It is necessary to embed 30-meter-long isolation piles within a 4-meter clear height to ensure the passage of the large shield. There were no similar construction technology cases at home or abroad before. The Fifth Railway Survey and Design Institute set up a research group to carry out theoretical model research, new structure design, precise construction control, and whole-process risk prevention and control research. It innovatively developed a 'low-headroom full-casing cast-in-place pile machine' and related technologies, filling the gap in construction technology at home and abroad.

Finally, after more than ten rounds of coordination with railway, planning, road, environmental protection, cultural relics, electric power, river channel and other management units, and after optimizing and comparing multiple schemes, the project team decided to adopt a shallow-buried shield tunnel scheme to open a 'crossing path' with short distance and shallow depth.

On January 9, at the construction site of the Tongjing Road North Extension Project crossing the Shanghai-Nanjing Intercity, many domestic industry experts and scholars witnessed the last isolation pile being drilled under the Shanghai-Nanjing Intercity bridge. The left-line large-diameter shield tunnel has successfully crossed under the Shanghai-Nanjing Intercity. Process monitoring data shows that the cumulative settlement is less than 1 millimeter, marking that the toughest node of the 'dead-end road' that has blocked Suzhou for ten years has been cleared.

The project is planned to be completed and open to traffic in 2022, which will greatly improve the regional traffic conditions of the thousand-year-old city of Suzhou.