On the morning of the 3rd, as the "Xinyue" shield machine slowly arrived at the dismantling position of the Jiangnan receiving shaft, the shield tunnel of the Nanjing Jiangxinzhou Sewage Collection System Phase II Construction Project (Jiajiang River Crossing Section), undertaken by China Railway 14th Bureau Group, was successfully completed, marking the smooth breakthrough of the largest-diameter sewage river-crossing shield tunnel currently under construction in China, and the successful application of the new socket-type segment technology in underwater shield tunnels.

The Nanjing Jiangxinzhou Sewage Collection System Phase II Construction Project (Jiajiang River Crossing Section) starts on the west side of the Jiangxinzhou Citizens' Square in Jianye District, Nanjing, crosses the Jiajiang River and enters Binjiang Park, and ends at the Jiangnan working shaft, connecting with the existing sewage channel. The project route has a total length of 755.6 meters, of which the shield tunnel is 693 meters long, with a segment outer diameter of 8.8 meters and a segment ring width of 1.5 meters. The tunnel passes through the "Jiajiang River Drinking Water Source Protection Zone," and its location is special. Along the route, it mainly crosses the embankments on both banks of the Jiajiang River, the Jiajiang River, existing bridge abutments, and various municipal underground pipe networks. Moreover, limited by the structural dimensions of the launching shaft, the shield machine had to be launched in split mode, involving numerous construction procedures. During the split launching period, a long-term shutdown under pressure for nearly a month beneath the embankment was required, with many risk factors and great construction difficulty.

According to Shan Xiaobo, technical director of the project of China Railway 14th Bureau Group, the shield tunnel adopted a straight-discharge slurry balance shield machine with an excavation diameter of 9.15 meters, launched from the Jiangxinzhou working shaft and received at the Jiangnan working shaft. Based on the previous construction experience of crossing the same type of geological strata in the Jiajiang River Tunnel of the Nanjing Yangtze River Fifth Bridge, the project team conducted a comprehensive analysis combined with the later segment assembly and grouting technology application, formed the optimal shield machine selection scheme, and redesigned and modified the shield machine's erector, achieving an assembly precision of 1 millimeter.

In order to ensure the safe and smooth tunneling of the shield tunnel, the project team invited internal and external experts for consultation and diagnosis on multiple occasions, especially formulating targeted construction schemes for split launching of the shield, long-term shutdown under pressure, advancement in the river section, and shield reception, strengthening the application of new technologies. At the same time, relying on the Dunzhiyun and big data systems, the team strengthened remote monitoring of the surrounding environment and ground surface, strictly controlled the shield tunneling attitude and corrected deviations in a timely manner during construction, and adjusted the tunneling parameters of the shield machine in real time, ensuring that settlement was controlled at the millimeter level.

To ensure the forming quality of the tunnel and reduce later operational risks, the project adopted a complete set of construction technologies of "new socket-type segments + dual-fluid simultaneous grouting + double water-stop sealing gaskets," which is the first of its kind in China. This technology places extremely high requirements on segment prefabrication and assembly precision, shield equipment adaptability, and shield machine tunneling attitude adjustment, with no experience to draw on. To ensure the successful application of the new socket-type segments, the construction team cooperated with renowned universities such as Tongji University to strengthen research cooperation, invited design masters and industry experts on multiple occasions to jointly study and demonstrate the scheme on site, refined construction details, and jointly carried out scientific research topics. They jointly studied the scheme, and it took half a year from segment design to trial production and finally to production and use, forming a set of mature assembly techniques. This not only saved half the labor and improved the high-precision assembly level, but also greatly improved the intelligent assembly level of shield tunneling using the new segment technology.

The successful application of the new technology enabled the 3,712 segments in the tunnel to be assembled in an orderly manner, solid inside and beautiful outside, with the formed tunnel lines clean and smooth, no leakage in the tunnel, segment upward displacement controlled within 5 millimeters, and segment misalignment controlled within 2 millimeters, far exceeding design and specification requirements. According to expert review, the successful application of this technology not only greatly reduces project cost, but will also supplement new solutions for the construction of large-diameter and underwater shield tunnels in China, with broad application prospects.

It is reported that after the tunnel breakthrough, subsequent internal and external sewage pipeline construction will be carried out, and the project is scheduled for completion acceptance in December. After the project is put into use, it will serve as a backup for the existing sewage river-crossing pipeline, and can directly transport about 400,000 cubic meters of sewage per day from the main urban area of Nanjing to the Jiangxinzhou Sewage Treatment Plant, greatly improving the economic efficiency of water conveyance through the river-crossing channel and the safety and reliability of the existing main channel operation. It will benefit 1.74 million residents in the Neiqinhuai River Basin, the Waiqinhuai River Shuangqiaomen to Sancha River interception system, and the Hexi New Town area of Nanjing, further meeting the people's needs for a better life.