The world's largest sea-crossing project, the Hong Kong-Zhuhai-Macao Bridge connecting Hong Kong, Zhuhai, and Macao, is under intensive construction.
　　The Hong Kong-Zhuhai-Macao Bridge starts from San Shek Wan on Lantau Island, Hong Kong, passes through Hong Kong waters, and runs westward along the north side of the 23DY anchorage, crossing the Tonggu Channel, Lingding West Channel, Qingzhou Channel, and Jiuzhou Channel of the Pearl River Estuary, ending at the artificial islands of the Zhuhai and Macao ports, with a total length of about 35.6 kilometers. The CB05 contract's non-navigable span has 62 piers, and the substructure construction bridge length is 5,440 meters. The Hong Kong-Zhuhai-Macao Bridge can be said to be a new milestone in China's bridge-building history. The design service life of ordinary bridges is 100 years, but this bridge is 120 years, an increase of one-fifth in lifespan, built entirely according to the highest international standards. Once completed, it will become the sea-crossing bridge with the longest design service life in China.
　　To increase the bridge's service life by 20 years is by no means an easy task for the builders of the Hong Kong-Zhuhai-Macao Bridge.
　　Because the bridge area crosses the Lingdingyang area of the Pearl River Estuary, construction is greatly affected by environmental factors such as ocean winds, waves, currents, tides, fog, and rain. The available effective construction time is short, and construction efficiency is very low. At the same time, the structural construction of the Hong Kong-Zhuhai-Macao Bridge is also full of technical difficulties. In the substructure construction of the CB05 contract, the builders need to lift components weighing over 1,000 tons 199 times and over 200 tons 299 times, with the largest single component weighing more than 2,500 tons. Under such circumstances, the installation accuracy of the bridge's pile caps and pier shafts requires that the horizontal position deviation must not exceed 10 millimeters, and the verticality must be controlled within 1/3000. Such precision on the turbulent sea is self-evidently technically difficult.
　　Since the impact of waves is an important factor affecting construction accuracy, the builders have also taken great pains to develop a new type of double-wall locking steel cofferdam without internal bracing, used as a water-stop structure for the installation of precast pile caps and pier shafts. For shallow-buried pile cap installation, the cofferdam can not only stop water but also greatly reduce dredging workload and minimize environmental pollution; the concrete for the reserved holes in the pile cap is constructed in a water-free environment, free from wind and wave disturbances, which better ensures concrete construction quality; at the same time, the bottom-sealing concrete increases the stiffness of the main bridge substructure, reduces the free length, and effectively ensures the durability and service life of the bridge. At slack tide, the water outside and inside the cofferdam is at the same level, but after the tide rises, the builders fill the cofferdam with water, and using the head difference generated during one ebb tide cycle, the cofferdam can be expanded and removed. This is the essence of cleverly utilizing the sea's rise and fall tides to quickly dismantle the double-wall locking cofferdam.
　　On the other hand, to achieve a 120-year design life, the Hong Kong-Zhuhai-Macao Bridge must also overcome the erosion of seawater itself. In the ocean, chloride ions are highly corrosive to concrete and steel reinforcement, so the corrosion resistance of durable concrete must be greatly improved. Other bridges only protect the steel reinforcement, but we not only used stainless steel reinforcement for the first time but also sprayed a layer of silane impregnation on the concrete surface.
　　It is understood that in the construction of the Hong Kong-Zhuhai-Macao Bridge, high-tech methods to extend the bridge's life, such as sacrificial anode cathodic protection, anti-corrosion coating for steel pipes, controlling the chloride ion diffusion coefficient of concrete, increasing the thickness of the concrete cover, stainless steel reinforcement, and silane impregnation, have been widely used.
　　According to reports, the pile caps and pier shafts of the non-navigable span substructure of the Hong Kong-Zhuhai-Macao Bridge were prefabricated as a whole in one go for the first time nationwide. The integral prefabrication of pile caps and pier shafts achieved automated opening and closing of large integrated formwork; realized the integral lifting of pile cap and pier shaft, pier cap reinforcement, and inner formwork; and one-time pouring of the pile cap and bottom pier shaft section, with a small age difference, avoiding shrinkage cracks at the junction of the pile cap and pier shaft due to age differences.
　　The reason for adopting such a process is that there are too many uncontrollable factors on site, and the impact of waves and wind climate is relatively large. In terms of quality, safety, and schedule, factory operations are more controllable and have greater advantages than on-site operations. The builders made two sets of integral opening and closing formwork, so that both the pile cap and pier shaft can be prefabricated as a whole at one time. With the push of a button, the formwork automatically opens, and with another push, it moves away. After the pile cap component is moved out, the reinforcement cage is installed as a whole, and with another push of the button, the formwork closes. There is no need to remove the formwork piece by piece, and it also avoids the problem of cracks that easily occur when the pile cap and pier shaft are prefabricated separately.
　　In the construction of the Hong Kong-Zhuhai-Macao Bridge, the bridge builders have been brave in innovation, continuously optimizing construction plans, improving work efficiency, summarizing much quality management experience, and achieving a series of technological innovation results. The topics "Research on Precision Control of Composite Pile Steel Pipe Insertion" and "Research on Installation Precision Control of Embedded Pier Foundations" published by the project department's QC group have successively won national first prizes; "Double-Wall Locking Steel Boxed Cofferdam without Internal Bracing" and "Construction Method for Quickly Dismantling Locking Steel Cofferdam in the Sea by Cleverly Utilizing Head Difference" have applied for national patents; and many papers have been published in national-level journals.