Closure site of the main bridge of the Hong Kong-Zhuhai-Macao Bridge
Yesterday morning, at the closure gap of the Jianghai Direct Ship Channel Bridge of the Hong Kong-Zhuhai-Macao Bridge, the last steel box girder had been lifted into place the previous night, and workers began welding operations, marking the successful closure of the main bridge. After the closure of the main bridge, subsequent construction such as bridge deck paving and traffic engineering will be fully carried out. At present, the part under the responsibility of the mainland is progressing smoothly, while the Hong Kong and Macao sections are relatively lagging behind. It is expected that the bridge will be ready for traffic by the end of next year.
Four years of offshore construction, yet dare not claim mastery
The Hong Kong-Zhuhai-Macao Bridge, with a total length of 55 kilometers, is a super-large sea-crossing link connecting Hong Kong, Zhuhai, and Macao, including the main sea bridge and tunnel project, as well as the ports and connecting lines of Hong Kong, Zhuhai, and Macao. The main project consists of a 6.7-kilometer undersea immersed tube tunnel and a 22.9-kilometer bridge project, with two artificial islands at the east and west ends of the tunnel.
The closure this time was for the main bridge project. The previous night, under the lifting of two bridge deck cranes, the last middle-span steel box girder of the CB04 section of the bridge project was slowly positioned and successfully lifted by the early morning of yesterday. After the successful lifting of the last steel box girder, Yu Lizhi, deputy general manager of the Second Branch of Guangdong Changda Company, still stated that although various lifting technologies are gradually maturing, the risks and consequences of each construction have not changed. After more than four years of offshore construction, he still holds awe for the sea and dares not say he has "mastered the craft."
"This steel box girder, about 8.6 meters long, is just one of the most inconspicuous segments among more than 200 steel box girders for the 22.9-kilometer main bridge, but it means that the civil engineering of the main bridge, which started on June 28, 2012, is officially coming to an end," said Jing Qiang, deputy director of the Engineering Management Department of the Hong Kong-Zhuhai-Macao Bridge. From pile foundations, caps, to bridges, steel towers, and stay cables, every seemingly ordinary construction step is a process of challenging new difficulties and innovation.
All steel box girders prefabricated and assembled in factories
According to the relevant person in charge of the Hong Kong-Zhuhai-Macao Bridge Authority, the Hong Kong-Zhuhai-Macao Bridge is the first to use steel structures on a large scale in the superstructure of bridge projects, making it the bridge with the largest steel consumption in the world. Most of the 22.9-kilometer bridge over the sea uses steel box structures, and the box girder part alone requires 425,000 tons of steel, enough to build 60 Eiffel Towers. The bridge is divided into three sections for construction, of which CB01 and CB02 sections, with a total length of about 16 kilometers, are entirely steel box girder structures, and CB05 section, about 6 kilometers, uses a mixed structure of reinforced concrete and steel box girders.
"All steel box girders are assembled, welded, and coated in factories on land, reducing the impact of environmental factors on manufacturing quality, improving the working environment for operators, accelerating manufacturing progress, and making product quality more stable," said the person in charge of the construction unit. In the manufacturing of steel box girders, intelligent plate unit assembly and welding robot systems, advanced ultrasonic phased array testing equipment, and factory-based "long-line" assembly methods were adopted, replacing the previous production mode mainly based on manual operation, greatly improving the quality and stability of finished products, enabling the overall steel structure manufacturing technology of the Hong Kong-Zhuhai-Macao Bridge to reach the world's advanced level, and further promoting technological progress in the entire industry.
In the erection of each steel box girder, several thousand-ton jacks are needed for positioning to achieve millimeter-level precision, which requires several jacks on the same plane to act in unison. This precision adjustment system is used for the first time in domestic bridge construction. To complete the installation of steel box girders, a total of 16 research institutions (universities) and manufacturers, including CCCC Highway Consultants Co., Ltd., Zhejiang University, and OVM, participated in scientific research, representing a convergence of domestic "top wisdom" in bridge construction.
Undersea tunnel progress exceeds 80%
Another important part of the main project of the Hong Kong-Zhuhai-Macao Bridge, and also the most difficult part of the entire bridge, is the 5,000-meter-long undersea tunnel, which will be connected by 33 immersed tube segments of reinforced concrete structure. Each immersed tube has a displacement larger than an aircraft carrier, making it the world's largest undersea immersed tube tunnel.
On June 12 this year, the undersea tunnel of the Hong Kong-Zhuhai-Macao Bridge completed the docking of the 27th immersed tube, with a built tunnel length of 4,702.5 meters, exceeding 80% of the total length. Su Quanke, chief engineer of the Hong Kong-Zhuhai-Macao Bridge Authority, introduced that efforts will be made to complete the immersion of all immersed tubes by the end of this year, and the final joint will be made in the first quarter of next year, so that the tunnel and bridge will be connected.
On December 15, 2009, the Hong Kong-Zhuhai-Macao Bridge officially started construction, and it has been under construction for 7 years. According to the latest progress, it is expected to be ready for traffic by the end of 2017.
Many technologies are firsts, creating new standards
The main bridge project closed this time includes three navigation channel bridges (Jiuzhou Channel Bridge, Jianghai Direct Ship Channel Bridge, and Qingzhou Channel Bridge) and non-navigation channel bridges in deep and shallow water areas. The non-navigation channel bridge in the deep water area uses a 110-meter span full-width full-pier steel box continuous girder bridge, and the non-navigation channel bridge in the shallow water area uses an 85-meter span steel-concrete composite girder.
According to the person in charge of the construction unit, Lingdingyang is a typical weak ocean current sea area, and every year a large amount of sediment flows in from the Pearl River Estuary. If the bridge piers are too dense and block the sediment, Lingdingyang may gradually become a mudflat or even an alluvial plain. To reduce the water-blocking rate of the bridge foundation and ensure flood discharge and tidal flow at the Pearl River Estuary and smooth navigation, the non-navigation channel bridges of the Hong Kong-Zhuhai-Macao Bridge use embedded caps, burying 188 bridge caps 8-15 meters below the seabed. The scale is huge, and it is the first of its kind in China and even worldwide.
The foundations of the non-navigation channel bridges of the main project of the Hong Kong-Zhuhai-Macao Bridge all use large-diameter steel pipe composite piles. The bridge piers, composite girders, steel box girders, and steel towers are all prefabricated on land and transported by sea for integral lifting. The three navigation channel bridges are also not built in the traditional way, especially the integral lifting technology of thousand-ton steel towers, which is a major innovation in China's bridge industry.
The design service life of this bridge is 120 years, with extremely high precision requirements. Taking the steel pipe driven piles of the main bridge as an example, the national standard requires a precision of 1/100, while the Hong Kong-Zhuhai-Macao Bridge requires 1/250. Assuming a pile foundation length of 100 meters, after insertion into the seabed, the plane error required for ordinary bridges is 1 meter, while the error for the Hong Kong-Zhuhai-Macao Bridge is 0.4 meters.
Hong Kong and Macao connecting lines will determine the opening time
In addition to the main project, the Hong Kong-Zhuhai-Macao Bridge also has connecting lines for Hong Kong, Zhuhai, and Macao. The three connecting lines will connect with the main project, linking the three places from their respective port artificial islands.
The Zhuhai connecting line, with a total length of about 3.3 kilometers, started construction in September 2013. At the end of January this year, the section from Hengqin North Interchange to Hongwan Interchange of the Zhuhai connecting line was successfully completed and opened to traffic ahead of schedule. According to the "Key Work Tasks for Implementing the Pearl River Delta Planning Outline in 2016" issued by the Guangdong Provincial Government this year, the Zhuhai connecting line of the Hong Kong-Zhuhai-Macao Bridge will be fully completed and opened to traffic next year.
The project under the responsibility of the mainland is progressing smoothly, while the Hong Kong and Macao sections are lagging behind considerably
The day before the closure of the main bridge, the Finance Committee of the Hong Kong Legislative Council approved 11 funding applications, including HK$169 million for the Immigration Department to install computer systems at the Hong Kong Port Control Point of the Hong Kong-Zhuhai-Macao Bridge, which will be completed by the end of next year, or other control points. Li Ka-chiu, Deputy Secretary for Security of Hong Kong, stated that the Hong Kong Port project of the bridge is expected to be completed by the end of next year, and it is expected that 73 "e-Channels" and 96 traditional immigration counters will be set up within the first 10 years after the port opens.
According to the plan of the Macao government, between the Macao Peninsula and the Zhuhai-Macao Port Artificial Island, there is also a reclamation new town Area A. The Macao Port will be connected to Macao New Town Area A by a bridge from the southwest side of the artificial island, and then enter the Macao Peninsula through New Town Area A. Affected by the lagging progress of Macao's reclamation project, the Macao section of the Hong Kong-Zhuhai-Macao Bridge has also been lagging behind.
The Macao government stated that in order to achieve the goal of opening to traffic simultaneously with the Hong Kong-Zhuhai-Macao Bridge, in the construction of the connecting line in the new town area, consideration will be given to building a temporary trestle bridge as an emergency plan for connecting the Zhuhai-Macao Port Artificial Island and the Macao Peninsula.