Nanjing, next to Baguazhou, under the main channel of the Yangtze River where hundreds of rivers compete, a "great dragon" is connecting the two sides of the strait with fiery momentum. The A3 standard (hereinafter referred to as "Heyan Road Crossing River Tunnel") of the southern section of the Nanjing Heyan Road Crossing River Tunnel Project undertaken by the Tunnel Bureau of Yigongju Group uses the "Zhenxing" super-large diameter shield machine manufactured by China Jiaotong Tianhe Successfully crossed the Yangtze River again.

The Heyan Road Crossing River Tunnel is a major country project that CCCC has implemented to implement the long-term integration strategy proposed by General Secretary Jin Ping. It also implements the "transportation power" strategy and is a large-scale river crossing channel for the upcoming middle and lower reaches of the Yangtze River. A model project implemented for construction. An expert group composed of 5 academicians of the Chinese Academy of Engineering including Qian Qihu evaluated the Heyan Road Crossing River Tunnel as "the most difficult shield tunnel in China at present". The Heyan Road Crossing River Tunnel with a total length of 2,976 meters has an excavation diameter of 15.03 meters and complex geological conditions. It is the country's first super-large-diameter shield tunnel to cross faults and lava formations. The maximum construction water pressure is 0.79 MPa. During the four-year construction period, the builders of CCCC continued to improve themselves and tailor-made the domestically-made super-large-diameter shield machine "Zhengxing", which overcomes the global tunnel construction problem of segment floating, creating a shield construction of 100,000 square meters. The precedent of "no seepage and no leakage".

A dripping construction legend

In April 2021, as the super-large-diameter shield machine "Zhenxing" steadily crossed the deepest part of the river bottom, the shield tunneling construction immediately broke through the thousand-ring barrier. The project manager Wang Yisheng said with emotion, “The Heyan Road Crossing River Tunnel is difficult to construct with the shield. The operation of the shield machine is “the difference is only a few thousand miles away”. We have successfully overcome the problem of water leakage in the tunnel. Now the tunnel project has entered. It has reached a new stage." Water seepage is a technical problem that plagues the construction of shield tunnels, and it is also a hurdle that the Heyan Road Crossing River Tunnel cannot bypass. Water leakage not only affects the normal construction of the tunnel, but also increases the construction cost. If improperly handled, it will also increase the safety risk during the tunnel operation period.

As early as before the construction of the Heyan Road project shield, the project department held several seminars on the problem of water leakage, not only not letting go of every detail that caused the water leakage, but also "catching the thief first" to solve the problem. Key technical difficulties. The problem of segment floating directly affects the quality of segment splicing and can easily lead to leakage. It has become the consensus of everyone to focus on breaking through this key technical point. The project technical team formulated a series of countermeasures against the problem of segment floating, including reinforcement of the first 20 meters of ground. At the beginning, the condition was good, but as the segment assembly gradually passed through the 20-meter reinforcement treatment area, the segments assembled thereafter showed a clear upward trend. The technical team quickly carried out countermeasures and continuously adjusted the construction plan and machine parameters, but the effect was not satisfactory. That was the most tormenting period in the career of Xu Wenli, chief engineer of the project's electromechanical industry. "The joy of shield launching has long been forgotten, and all I have in my mind are how to solve the problem of tube floating as soon as possible." He said, on the one hand, the super-large diameter shield machine "Zhenxing" weighs 4,000 tons. The construction machine cannot be shut down, otherwise it will easily cause risks such as unstable tunnel face, ground subsidence, settlement and cracking of residential buildings. On the other hand, if the problem of segment floating is not resolved as soon as possible, the further forward the shield machine is, the greater the risk of water leakage in the tunnel.

Faced with the tremendous pressure of rising pipes, the project party branch secretary and chief engineer Zhao Xiaopeng and Xu Wenli kept cheering up their young colleagues while secretly gritting their teeth and struggling with problems. One day, the scene of a diver wearing a lead block while diving came to Xu Wenli's mind, giving him inspiration, "Can we increase the counterweight to offset the buoyancy of the tube?" Xu Wenli's proposal received everyone's support. The technical team immediately carried out theoretical calculations and came to the conclusion that a load of 200 tons needs to be applied. Will such a heavy load have an adverse effect on the tunnel and shield machine? Xu Wenli frowned. In order to verify the feasibility of the counterweight load, the project team welded scrap steel plates together and carried out a counterweight load test. “We pay attention to the floating amount of the segments 24 hours a day, and observe the construction effect one by one, while constantly optimizing the parameters and synchronizing the grouting mix ratio.” Xu Wenli recalled. Finally, the project team used grouting to maintain a dynamic balance between the buoyancy of the segment and the gravity generated by the 200-ton load. When the shield machine advances to the 100th ring, the maximum floating amount of the segment is always controlled within 3 cm. The project team successfully controlled the floating of the segment, which means that the Heyan Road Super Large Diameter Shield Scientific Research Team has created a domestic super large diameter shield The highest level of construction. Subsequently, the project department successively solved a series of technical problems that would affect the quality of the project, such as segment measurement and segment assembly, and finally created the construction legend of "dripping water" in the construction of super large-diameter shield tunnels in China.

Tailor-made shield weapon

To build a world-class project, we must have a "sharp tool" at hand. For the construction team of the Heyan Road Crossing River Tunnel Project, the domestically produced shield machine "Zhenxing" manufactured by CCCC Tianhe is a weapon for them to challenge the Heyan Road Crossing River Tunnel Project. The "Zhenxing" shield machine cutter head is 15.03 meters in diameter, 135 meters in length, 4,000 tons in weight, and 246,400 kilonewtons in maximum thrust, specially designed to open up the Heyan Road Crossing River Tunnel. For the first time, it used a variety of technologies such as a fully intelligent segment assembly system and an intelligent remote security monitoring and management system, and achieved many world firsts. It can meet the construction requirements under a variety of complex geological conditions, especially the localization of core components, which not only reduces the cost, but more importantly, firmly grasps the core technology in its own hands.

The Heyan Road Crossing River Tunnel has complex geology and the highest construction water pressure of 0.79 MPa. It is also the tunnel project with the highest water pressure in the country. The tunnel's excavation distance in soil-rock composite strata is about 1865 meters. During construction, the thickness of the overburden at the bottom of the Yangtze River with high water pressure is only 10.25 meters, and 5 fault zones have to be crossed. According to its geological conditions, China Communications Tianhe has carried out a "tailor-made" design and manufacturing, and prepared a "tool kit" to deal with all risks, including atmospheric pressure tool change device, muddy water tank layered backwash system, cutter head telescopic swing device, A number of key technologies such as ultra-long-distance non-tool-changing technology for super large diameter shield machines, and three-way ball valve extension devices. When driving in the upper soft and lower hard formations, increase the speed of the cutter head, reduce the driving speed, and strengthen the settlement monitoring to control the construction; when crossing the fracture zone, use the methods of grouting and reinforcement of the fracture zone in advance and optimization of the tunneling parameters to control the risk source ; In the karst section, it is equipped with advanced detection and advanced grouting systems, which have the functions of advanced detection and treatment of karst caves. Unlike imported shield machines, the "Zhenxing" independently developed by CCCC has made independent innovations in terms of functional design and transportation methods. "Our domestically-made super-large diameter shield machine has stronger flushing capacity for cutter heads, newer segment transportation methods, and higher transport efficiency than imported shield machines. More than that, in the heart of the shield machine's main drive, the "Zhenxing" 'Innovation through the ball hinge bearing to ensure that the main drive in a complex construction environment, in addition to the telescopic function, it can also swing, enhance the shield machine's adaptability to the complex construction environment of the river bottom. "CCCC Tianhe Design and Research Institute" Shujun, the chief designer of the "Zhengxing" shield machine, is very confident in the performance of the shield machine.

Craftsmanship of excellence

To complete the construction of the Heyan Road Crossing River Tunnel well and quickly, it is inseparable from high-tech equipment and support means, and it is also inseparable from the support of "soft power". The spirit of craftsmanship comes out. This feeling has blossomed in the hearts of every builder of the project.

"In the past, there were no relevant industry standards for the construction of super large diameter shield machines. We crossed the river all the way by feeling the stones. The reason why the project can be done to the extreme is the meticulous craftsmanship. If you can't do something Achievements, I feel ashamed of my family, ashamed of the people of Nanjing, and ashamed of such a good engineering project opportunity." Zhao Xiaopeng said. "Soft power" is embodied in the pursuit of excellence in engineering quality. The builders measure the accuracy of each segment and the accuracy between each segment in each ring, creating a standard operation procedure like a tunnel construction pipeline. The project is about 400 meters away from the Yangtze River embankment in a straight line, and the groundwater is directly connected to the river water. When the shield is launched, in order to ensure that its launching posture is perfectly matched with the position of the wire brush used for sealing and sealing, so as not to leave a trace of leaking water, the technician must climb to it when welding each piece of wire brush. The spot was precisely determined on a shelf more than ten meters high at the scene. In this state, they don't know how many times they go back and forth every day, so cautiously, just to ensure "zero leakage."

Keywords: engineering construction, engineering news

The young team with an average age of 32 has created the industry's highest level of box culvert assembly accuracy within 3 mm, and the control of the staggered number of tubes within 4 mm has amazed the owners. Since the start of construction in 2018, the project has won 12 awards such as the 2018 May 1st Labor Certificate of Jiangsu Province, and obtained a number of national utility model patents. Not only has it built a good social reputation and corporate brand in the industry, but also the project department It has also become a training center and scientific research center for China Communications Construction's large-diameter shield construction talents.Editor/Xing Wentao