Good news came again on May 20 for the Tongjing Road North Extension Project in Suzhou: shield tunneling has begun on the right tube, which is expected to achieve breakthrough in August, bringing the full line one step closer to completion and opening to traffic. This is currently China's first large-diameter shield tunnel to pass beneath an operating high-speed railway.

Because the Shanghai-Nanjing Intercity High-Speed Railway and the Beijing-Shanghai Railway divide urban space, Tongjing Road, a major north-south arterial road in downtown Suzhou, had become a "dead-end road." Suzhou had sought for more than a decade to open it through but had been unable to do so.

The Tongjing Road North Extension Project starts at Chengbei Road in Suzhou, connects north to Yongfang Road, crosses Xitang River to the south, and uses a tunnel to pass beneath Qingtang Road, Shantang River, the Shanghai-Nanjing Intercity High-Speed Railway, the Beijing-Shanghai Railway, and the North Ring Expressway, before connecting smoothly with Tongjing North Road. The route length is about 2.49 kilometers. The project is built to the standard of a dual six-lane urban arterial road with a design speed of 60 kilometers per hour. The shield tunnel is 490 meters long in each direction, and the tunnel segment has an outer diameter of 13.25 meters. The tunnel interior is arranged in two levels: the upper level is the carriageway level with three lanes in one direction, and the lower level is an evacuation passage and utility corridor. After completion, Tongjing Road will provide direct access to Yongfang Road, saving 20 minutes compared with detours.

According to Wu Kui, project manager of China Railway 14th Bureau Group, the Shanghai-Nanjing Intercity High-Speed Railway is designed for a speed of 350 kilometers per hour and is one of China's busiest high-speed rail lines, with a minimum headway of 3 minutes. The tunnel is constructed using a slurry balance shield machine and crosses beneath the high-speed railway twice, once for the left tube and once for the right tube. The construction is highly difficult and risky, and there was no previous experience at home or abroad to draw on. With strong support from an expert advisory group including Academician Qian Qihu, the project department formulated a scientific and meticulous construction plan and, with a cautious attitude of "treading on thin ice," strictly controlled tunneling parameters. The left tube crossed safely in a single pass, and monitoring showed that settlement was controlled within 0.4 millimeters, without any impact on high-speed railway operations, providing a solid guarantee for the right tube to cross safely again.

According to Yu Pengchen, shield manager of the project, the shield tunneling work must, within a 490-meter section, continuously pass beneath a dense cluster of protected buildings, the Shantang River, the Shanghai-Nanjing Intercity High-Speed Railway, the Beijing-Shanghai Railway, the North Ring Expressway, and other dense high-risk sources. At the same time, the shield machine has an excavation diameter of 13.67 meters, and along the entire tunnel the cover depth is less than one tunnel diameter, with the shallowest point at 6.47 meters and the deepest at 13.15 meters. The technical requirements are high, construction conditions are complex, implementation is difficult, and public attention is high. After the left tube achieved breakthrough first on February 5, the "Gusu" shield machine underwent disassembly, transport, reassembly, and commissioning over three months before launching again from the launch shaft for the right tube. Because construction of the left tube disturbed the soil of the right tube and the right tube passes beneath more controlled protected buildings, the second shield drive is more difficult. Drawing on the experience of the smooth crossing of the left tube, the project further improved the visual intelligent construction system and intelligent monitoring and sensing warning technology for buildings and structures. Through big data and the Dunzhiyun platform, tunneling parameters of the shield machine are analyzed and controlled in real time, and engineering technicians and the expert team remotely monitor the shield machine's attitude to ensure that tunnel construction is foolproof.

It is reported that the Tongjing Road North Extension Project is planned to be completed and opened to traffic in 2022. By then, Tongjing Road, this north-south arterial road, will be successfully extended northward, connecting the northern and southern areas and being of great significance for improving regional traffic conditions.