On the morning of September 21, 2026, the Yangtze River estuary was flooded with boats. 75 meters below the water surface is another tense scene. At the construction site of the left line of the Haitai Yangtze River Tunnel constructed by CCCC Tunnel Bureau, technicians closely watched a series of jumping data on the screen: mud water pressure, cutterhead torque, and propulsion speed. When the excavation mileage jumped to 5334 meters, someone in front of the control console breathed a sigh of relief - the domestically produced largest diameter slurry balance shield machine Cangyuan safely passed through the lowest point of the river.

At this moment, it has been four months since the right tunnel reached the same high point. The two lines have successively passed the most dangerous hurdle, which means that the world's longest shield tunnel crossing the river has finally left behind the most high-risk section.

Diving 75 meters into the bottom of the river

The lowest point of the river is located 75 meters below the mouth of the Yangtze River estuary. The tunnel structure has to withstand an ultra-high water pressure of 0.75 megapascals, which is equivalent to 7.5 kilograms of weight pressing on an area the size of a fingernail. The excavation area is mainly composed of composite soft soil layers such as gravel and coarse sand, with high quartz sand content. The cutterhead rubs against natural sandpaper every time it rotates; The formation has strong permeability and weak overall stability, and even a slight deviation may cause hidden dangers such as settlement, sealing loss, and pressure imbalance.

For this purpose, the builders equipped the Cangyuan with a dragon tooth matrix composed of gradient alloy cutting tools. In a formation with a quartz sand content of about 65%, the tool was not changed during a single excavation of 2220 meters. This steel giant dragon with an excavation diameter of 16.66 meters, a total length of 176 meters, and a total weight of over 5650 tons has maintained a stable speed of about 16 meters per day since its launch in August 2025, diving all the way to the center of the river.

The dragon's intelligence breaks through dangerous obstacles

There is no reference point at the bottom of the river, and the guidance is almost blind. The project team focuses on data: the tool wear monitoring system provides 24/7 monitoring, with an error controlled within 1 millimeter, and can provide early warning before tooth breakage occurs; The main drive monitoring system conducts bidirectional analysis of oil and vibration to capture subtle abnormalities in the equipment; The intelligent excavation control system reduces the average posture deviation to 1.02 millimeters and stabilizes the single loop deviation at plus or minus 3 millimeters. Core parameters such as excavation speed, shield posture, and mud water pressure are dynamically adjusted in real time, forming a construction closed loop with real-time data monitoring, intelligent analysis and judgment, and dynamic parameter optimization. The fourth generation synchronous dual liquid grouting technology and intelligent assembly system enable parallel pipe segment assembly and excavation, increasing construction efficiency by about 50%.

After conquering the extremely deep point, the Cangyuan vessel will adjust its posture, shifting from diving downwards to climbing uphill with its head held high. The water and soil pressure will decrease accordingly, and the construction difficulty will steadily decrease. Why do two lines move in front of each other instead of parallel? The answer lies in safety: the excavation of the first tunnel has already disturbed the surrounding soil, and if the later tunnel is closely pushed forward, it is equivalent to another disturbance in an unstable formation. Maintaining a reasonable time difference and spatial spacing is the basic condition for the safety of the double line structure.

Cross river integration acceleration

The Haitai Yangtze River Tunnel starts from Nantong Haimen in the north and ends at Taicang in Suzhou in the south, with a total length of 39.07 kilometers. The left shield section is approximately 9327 meters long and is constructed according to the standards of a two-way six lane expressway. The design speed is 100 kilometers per hour and it is planned to be completed and opened to traffic in 2028. As a key project in the layout planning of the Yangtze River main line crossing channel and the comprehensive three-dimensional transportation corridor planning of the Yangtze River Economic Belt in Jiangsu Province, it is also a key cross river channel project promoted in Jiangsu's 14th Five Year Plan. After its completion, it will effectively alleviate the traffic pressure of the Sutong Yangtze River Bridge.

On the same day, the project held the Jiaozhu Super Engineering Media Open Day event. More than ten mainstream media outlets, including People's Daily, Xinhua News Agency, China Daily, Science and Technology Daily, People's Political Consultative Conference Daily, and China News Service, entered the construction site to discuss and exchange ideas with the builders, and conducted interviews and reports on the key and difficult points of construction and the application of innovative technologies.keywords:Engineering infrastructure

The Yangtze River surges and the giant dragon lurks. Turning upwards from the deepest section, the significance of this tunnel in implementing the national strategy for the integrated development of the Yangtze River Delta and the Yangtze River Economic Belt, optimizing the layout of the Yangtze River main line crossing the river, and promoting the integrated development of the urban agglomeration along the river is gradually becoming a reality.Editor/Yang Meiling