At the southernmost tip of Dadeng Island, the sea wind carries the salty, damp air, and the waves lap day after day against the bridge piers “growing” out of the water. Supported by an innovative support structure developed by the project team of the Xiamen New Airport Area Huandeng Road Phase II Project under The Sixth Engineering (Xiamen) Co., Ltd. of CCCC Third Harbor Engineering Co., Ltd., a bridge spanning the sloping revetment, with most of its structure located over the sea, is steadily taking shape amidst the symphony of spray and steel components.
The bearing platform, acting as the “foundation” supporting the entire bridge, needs to be buried about 80 centimeters below the low-tide level. However, seawater erosion, a daily tidal range of 3.95 meters, and unpredictable winds and waves have turned this sea area into a constantly shifting “underwater maze,” posing significant challenges for the installation of the steel cofferdam. Moreover, traditional steel cofferdam construction relies on large floating cranes and ample working space, but this area’s large tidal range and confined site make it nearly impossible for large equipment to operate. Using traditional methods would not only be inefficient but could also lead to installation precision issues due to tidal changes, creating potential safety hazards.
“Looking at the waves crashing against the steel casing pipes back then, we knew clearly we had to adopt a different ‘divide and conquer’ construction approach,” recalled Wu Zhaofeng, the project’s chief engineer.
The project team’s breakthrough lay in the wisdom of “splitting and reassembling.” They abandoned the traditional “integral hoisting” mode for steel cofferdams and developed a support structure of “suspended steel brackets + modular removable steel cofferdam.” It’s like “playing with Lego” at sea, disassembling the massive steel cofferdam into smaller, prefabricated layers, and then precisely assembling them using the support structure.
The core of this structure is two pairs of suspended steel brackets installed longitudinally along the bridge direction on the steel casing pipes, paired with two pairs of disc-type supports composed of a support base plate, adjustment wedges, and connecting screws. This combination’s anti-interference capability allows it to adapt well to the various changes in the marine environment.
The suspended steel brackets allow the cofferdam to “stand” on the steel casing pipes, avoiding direct impact from water level fluctuations, while the adjustment wedges of the disc-type supports can compensate in real-time for minor displacements caused by tides, ensuring each component fits together seamlessly. Combined with the disc-type supports, they form a support device enabling precise positioning of the steel cofferdam, while also simplifying the separation process of the bottom formwork and the sealing concrete, significantly enhancing construction flexibility and solving traditional dismantling difficulties. The system within the device also integrates dynamic sensing and intelligent adjustment functions. On-site personnel can monitor tidal-induced displacements and stress changes in real-time through sensors and use the micro-motion mechanism of the adjustment wedges for automatic compensation, achieving a “perception-feedback-adjustment” closed-loop control of the construction process. Additionally, the project team applied new anti-corrosion coatings and sealing designs to the device’s connection nodes, significantly improving the structure’s durability in harsh marine environments.
The benefits brought by this innovative construction method resulted in a visibly improved construction efficiency. The project construction period was shortened by 30% compared to using traditional techniques, and reliance on large marine equipment was eliminated, greatly reducing equipment costs. Furthermore, all steel components can be recycled and reused, preventing marine waste generation, which earned high recognition from maritime authorities. The standardized production mode on land also allows for component prefabrication precision to be controlled at the millimeter level, eliminating uncertainties associated with offshore operations. This construction method, through its modular, recyclable, and intelligent technological approach, provides a brand-new solution for bridge foundation construction under similar complex sea conditions.
When the last steel cofferdam component was dismantled and recycled, project manager Liang Yuexin stood on the shore, watching the tide flood the former construction area, and remarked with emotion, “The completion of a bridge is not merely a combination of steel and concrete; it is the crystallization of wisdom and responsibility.”
Today, the main structure of Bridge No. 9 has been successfully completed, and this independently developed “Construction Method for Installation and Dismantling of Steel Cofferdams for High-pile Bearing Platform Foundations of Offshore Bridges” has been submitted for a national invention patent. It stands like a “technological anchor,” firmly rooted in the ebb and flow of the sea.
Content provided by Lin Yangyang, Zheng Xuechao
