First! The largest river-crossing sewage shield tunnel under construction in China was successfully completed

CCTV news broadcast reported that on the morning of June 3, Nanjing Jiangxinzhou Sewage Collection System Second Channel Construction Project (crossing Jiajiang Section), designed by the Fourth Railway Institute and constructed by the Fourteenth Bureau of China Railway, the "Xinyue" shield machine slowly arrived at the Jiangnan receiving well, marking the completion of the largest diameter sewage river-crossing shield tunnel under construction in China. It also means the successful application of the first underwater shield tunnel "new bell and spigot segment" technology in China. In order to further improve the quality of water environment and ensure the safe and stable operation of Jiangxinzhou sewage treatment system, the "upgraded version" of sewage river-crossing tunnel

was built by the first shield construction technology

in China. The Nanjing Municipal Government has decided to start construction of the second channel project of Jiangxinzhou Sewage Collection System, with a total length of 755.6 meters. The project of crossing the Jiajiang River starts from the west side of Jiangxinzhou Citizen Square in Jianye District. After crossing the Jiajiang River, it enters the Jiangnan working well of Binjiang Park and connects with the current sewage transmission channel.

The shield tunnel is 693 meters long, the outer diameter of the segment is 8.8 meters, the maximum buried depth is 23.4 meters, and the maximum water pressure is 0.34 MPa. It is located in the "Jiajiang Drinking Water Source Protection Zone". It needs to cross the Jiajiang River, the embankment, the abutment and the municipal pipeline network. The minimum thickness of the covering soil at the bottom of the river is only 10.23 meters. Limited by the size of the launching shaft structure, the shield machine must be launched separately, and the construction process is numerous and difficult. Shan Xiaobo, the technical director of the

project, introduced that the project adopted a complete set of construction technology of "new socket and spigot segments + double-liquid synchronous grouting + double-channel sealing gasket", which was the first in China and required high accuracy of segment prefabrication and assembly, adaptability of shield equipment and adjustment of shield posture. The tenon and mortise principle of

new socket and spigot segments

shows the wisdom

of China. At present, the shield tunnel structure in China is basically composed of reinforced concrete segments and bolts, and the segments are assembled and connected by different types of bolts.

The "new socket and spigot segment" adopts a new joint segment structure, that is, the longitudinal joint of the segment adopts the bolt connector, and the circumferential joint adopts the plug-in connector. During the

construction, the segment assembly can be pushed in place at one time, the joints are dense, and manual hand hole plugging and other processes are no longer needed.

In order to ensure the successful application of the new socket and spigot segments, the project team cooperated with Tongji University and other well-known universities, combined with the construction experience of the Jiajiang Tunnel of the Fifth Yangtze River Bridge in Nanjing crossing the same type of geological strata, integrated the later assembly and grouting technology, improved the shield assembly sucker, so that the accuracy reached 1 mm. Wu Wenqing, the

project leader of

forming tunnel, introduced that the complete set of construction technology of bell and spigot segments of shield tunnel has enriched the basic scientific research in the field of shield tunnel, and will establish relevant technical system, control methods and standards in the future. It provides new solutions and theoretical support for the construction of large-diameter and underwater shield tunnels in China, and has great application prospects, which may lead to a new round of technological revolution in the industry.

At the same time, the project invites experts to consult the pulse, rely on the big data system to strengthen monitoring, strictly control the attitude of shield tunneling, and ensure that the settlement is controlled at the millimeter level. "By optimizing the tunneling assembly, the average assembly time of the first ring is not more than 45 minutes." Project shield manager Yao Yinbin introduced. The floating amount of tunnel segments is controlled within 5 mm, and the dislocation of segments is controlled within 2 mm, which is far higher than design and specification requirements.

In addition, combined with the change of the new socket and spigot segment assembly process, the design team of the Fourth Railway Institute innovatively proposed a new sealing and waterproofing system, which truly achieved the goal of "watertight" first-level waterproofing of the tunnel. After the shield tunnel of the second channel

of Jiangxinzhou sewage collection system runs through, the follow-up pipeline construction will be carried out. Two pipes with a diameter of 2.2 meters will be laid inside, and the project is expected to be completed and accepted by the end of the year.

By then, about 400000 cubic meters of domestic sewage in the main urban area of Nanjing will be transported directly to Jiangxinzhou Sewage Treatment Plant through two pipelines to "cross the river side by side". It will benefit 1.74 million residents in the inner Qinhuai River Basin, the Shuangqiaomen to Sancha River interception system of the outer Qinhuai River and the new urban area of Hexi, effectively ensuring the safety of the water environment within the service scope of the Jiangxinzhou sewage collection system.