At 7 p.m. on December 29, after 25 hours of arduous effort, the domestically leading and province-first deepwater "∞"-shaped double-wall steel cofferdam was successfully sealed at the bottom at the Nanyang Xiangjiang Grand Bridge on the Pingyi Expressway, marking another new breakthrough by Hunan Road & Bridge in the field of deepwater cofferdam technology.

The Nanyang Xiangjiang Grand Bridge is located in Nanyang Village, Helonghu Town, and Xinquan Town, Xiangyin County, crossing the west branch of the Xiangjiang River. With a total length of 2,807.6 meters, it is a controlling project of the Pingyi Expressway. The maximum designed pile length of the main piers is 100 meters, and the maximum drilling depth reaches 130 meters. Deepwater foundation construction is the key and difficult part of the bridge construction. The maximum water depth at the main piers from No. 30 to No. 33 is nearly 30 meters, and the cofferdam height is more than 30 meters.

In response to the difficulties of deepwater foundation construction, the project technical team of Hunan Road & Bridge Yangtze River Branch optimized the cap structure, reducing the pile foundation of a single cap from 9 to 7 piles, and for the first time boldly adopted a new "∞"-shaped double-wall steel cofferdam structure without an internal bracing system. Combined with the single-section integral assembly process and various measures such as excavator-based foundation cleaning and air-driven mud suction, rapid sinking was achieved, producing excellent results of low cost, high quality, and a short construction period, and realizing technological innovation, technology-driven efficiency, and rapid construction.

The successful bottom sealing of the "∞"-shaped double-wall steel cofferdam without an internal bracing system at main pier No. 33 smoothly solved the construction problems of long duration and high safety risk in the deepwater foundation construction of the Nanyang Xiangjiang Grand Bridge, providing valuable experience for advancing the project's "rapid construction."