On August 28, the pilot section of the Tongjing Road North Extension Project in Suzhou, surveyed and designed by the China Railway Fifth Survey and Design Institute Group, officially broke ground. The project is China's largest-diameter tunnel passing beneath a high-speed railway and adopts the independently developed “low-clearance full-casing cast-in-place pile rig technology,” the first application of its kind in China.

Tongjing Road is an important component of the “seven vertical, five horizontal” trunk roads in Suzhou's overall urban plan, the main framework of the city's road network, an important north-south corridor crossing the Shanghai-Nanjing High-Speed Railway, the Beijing-Shanghai Railway and the North Ring Expressway, and one of the key roads Suzhou plans to open up during the 13th Five-Year Plan period.

Passing beneath the Shanghai-Nanjing High-Speed Railway bridge is one of the most important control points of the project. In response to difficulties including the project's location in the center of the old city, the many protected buildings on both sides of the Shantang River scenic area, complex traffic organization, and numerous controlling factors for the tunnel alignment, the designers, after multiple site surveys and full collection and analysis of data, reviewed the scheme with sister organizations, carried out technical research, and optimized the scheme. They adopted a 13.25 m diameter large-section slurry shield to pass beneath the Shanghai-Nanjing High-Speed Railway bridge—a feat akin to “holding a ceremony in a snail's shell.”

At the same time, addressing the technical difficulty of a working height of only 2.5 m, they summarized the design, construction and operation experience of similar projects, combined the requirements of the client with specific engineering conditions, and through thorough analysis, verification and comprehensive comparison of multiple schemes, joined with several organizations on special research topics to innovatively develop a “low-clearance full-casing cast-in-place pile rig” and related technologies that can meet low-clearance construction conditions. Its main indicators meet the technical requirements of conventional full-casing cast-in-place pile rigs, and it received high praise from review experts while filling a domestic gap.

It is understood that the Tongjing Road North Extension Project is an important component of Tongjing Road, with a route length of about 2.49 km, and is scheduled to be completed and opened to traffic in 2021. Once completed, the project will be of great significance for improving the road network in the Suzhou area, enhancing north-south traffic capacity, and promoting social and economic development along the route.