The 55-kilometer-long Hong Kong-Zhuhai-Macao Bridge, hailed as the “Everest” of the bridge industry, is one of the world's most challenging mega-projects and the longest sea-crossing bridge. As a super-large sea-crossing link connecting Hong Kong, Zhuhai, and Macao, the Hong Kong-Zhuhai-Macao Bridge integrates bridges, islands, and tunnels into one, resembling a giant dragon lying across the waves and piercing the sea. Once open to traffic, the travel time between the three places will be shortened from 3 hours to half an hour.
　　Since 2003, more than 200 research institutions and over a thousand scientists and engineers across the country have carried out more than 300 scientific research projects for this project, with a cumulative investment of nearly 500 million yuan, creating more than 40 construction methods, obtaining over a hundred invention patents, and publishing more than 500 papers. “The support of national key scientific research forces has provided strong backing for the smooth completion of the Hong Kong-Zhuhai-Macao Bridge.” Su Quanke, chief engineer of the Hong Kong-Zhuhai-Macao Bridge Authority, said that compared with the sea-crossing bridge-tunnel transportation cluster projects already built internationally, the Hong Kong-Zhuhai-Macao Bridge has the largest project scale and construction difficulty.
　　Since construction began in December 2009, the main project of the Hong Kong-Zhuhai-Macao Bridge has been fully connected, and it will be ready for traffic before the end of the year. In this final sprint stage, an Economic Daily reporter explored on site the high-tech codes behind this mega-project.
　　Erecting Steel Girders across the Sea
　　As the bridge with the world's largest steel consumption, the Hong Kong-Zhuhai-Macao Bridge uses up to 420,000 tons of steel plates for its main girders alone. The builders turned all the steel into steel components and then transported them to the site for assembly.
　　The main project of the Hong Kong-Zhuhai-Macao Bridge includes a 22.9-kilometer main sea-crossing bridge and a 6.7-kilometer immersed tube tunnel. When the reporter got into a car and drove onto the bridge from the Hongwan end in Zhuhai, what was felt was the smoothness of a dual six-lane road. On this bridge, which stretches out of sight in both directions, there are three cable-stayed bridges with the shapes of “sail,” “dolphin,” and “Chinese knot,” carrying profound meanings.
　　As the bridge with the world's largest steel consumption, the bridge uses up to 420,000 tons of steel plates for its main girders alone. “This is equivalent to the weight of 10 Bird's Nests or 60 Eiffel Towers.” Su Quanke said that the builders turned all these 420,000 tons of steel into steel components and then transported them one by one to the site for assembly, just like children building with blocks.
　　Building with blocks reflects the “four modernizations” concept of the bridge construction: through “large-scale, factory-based, standardized, and assembly-based” construction, rough civil engineering is transformed into precision manufacturing and precision installation, meeting the needs of project quality, schedule, and safety.
　　To build with blocks, the block components must first be made. Many of the giant components of the Hong Kong-Zhuhai-Macao Bridge are built using large equipment designed and produced by China itself. The giant factory buildings built for the bridge are located near the bridge. Components weighing thousands or even tens of thousands of tons—including piers, towers, and immersed tubes—are produced on large automated production lines in the factory buildings, then transported by giant ships to the site and installed using large lifting or immersion equipment.
　　Yu Lie, deputy director of the Hong Kong-Zhuhai-Macao Bridge Authority, told reporters that the technical difficulty of “building with blocks” in the open air is great, involving the main structure, artificial island construction, large-scale industrialized manufacturing, underwater structure water-stop technology, and offshore assembly-based embedded pile cap construction, among many other aspects. For this reason, the National Science and Technology Support Program launched the project “Research and Demonstration of Key Technologies for the Construction of the Hong Kong-Zhuhai-Macao Bridge Sea-Crossing Cluster Project” in 2010, addressing various difficulties in bridge construction and playing a supporting role in science and technology.
　　The Hong Kong-Zhuhai-Macao Bridge is also the first steel bridge in China to use robotic welding. Chai Rui, deputy chief engineer of the Hong Kong-Zhuhai-Macao Bridge Authority, introduced that during steel bridge welding, the steel material generates great internal stress after uneven heating and cooling contraction. “So we use multi-head welding robots to achieve uniform welding. Multiple welding heads weld simultaneously, avoiding uneven heating and cooling and eliminating internal stress caused by the welding process.”
　　In the “building with blocks” bridge construction, there was once a spectacular scene of a steel tower 106 meters tall and weighing more than 3,000 tons “rotating 90 degrees in the air” at sea and then being installed with high precision, an unprecedented feat in the history of bridge construction at home and abroad. “If the country's overall scientific research and equipment strength had not progressed to the current level, such an overall design could not have been completed.” Su Quanke said.
　　Immersed Tubes Connect the Long Tunnel
　　Building a deeply buried immersed tube tunnel nearly 50 meters underwater is regarded internationally as a “technical forbidden zone.” In response, the builders carried out 15 major categories and 136 special studies, breaking through many worldwide difficulties.
　　After the car passes over the main sea-crossing bridge, it reaches the west artificial island. On the island, the car goes from above ground into the ground, passes through the 6.7-kilometer undersea tunnel, and then emerges from the east artificial island onto the Hong Kong section of the bridge.
　　This island and tunnel section is the key to the Hong Kong-Zhuhai-Macao Bridge. Because sea and air traffic is busy here, the bridge must be built high to meet the passage needs of 300,000-ton giant ships, and must be built low to meet the height restrictions for nearby airport flights. Therefore, it had to be submerged into the seabed, and building a deeply buried immersed tube tunnel became the best choice for this section.
　　Before the construction of the Hong Kong-Zhuhai-Macao Bridge island and tunnel project, key technologies for undersea immersed tube tunnels were always in the hands of a few developed countries. The cost of technology introduction or cooperation was extremely high, and some technologies were embargoed against China.
　　Building a deeply buried immersed tube tunnel nearly 50 meters underwater is regarded internationally as a “technical forbidden zone.” Technical research on immersed tube tunnel construction became the top priority of scientific research. Xu Guoping, head of the key tunnel technology project, introduced that since the island and tunnel project was established at the end of 2010, a total of 15 major categories and 136 special studies have been carried out, achieving major breakthroughs in rapid island construction in the open sea, immersed tube tunnel design and construction, factory-based immersed tube prefabrication, open-sea immersed tube floating and installation, final joints of deep-water immersed tube tunnels, and the development of special equipment.
　　China pioneered the rapid island construction technology using large-diameter deep-inserted steel cylinders in the open sea. The entrances and exits of the undersea tunnel are the east and west artificial islands, each equivalent in size to three football fields. According to the traditional cofferdam island construction process, it would take 3 years to form an island, which would seriously affect the marine environment. According to the new technical scheme, 120 giant steel cylinders with a diameter of 22 meters were inserted into the seabed at one time, and soil was filled in the middle to form the island at one time. The Chinese created a world engineering record by building two islands in 221 days.
　　The island and tunnel project of the Hong Kong-Zhuhai-Macao Bridge is also the world's first deeply buried immersed tube. Chinese technicians creatively proposed a new “semi-rigid” immersed tube structure. Compared with the “deep burial, shallow construction” scheme proposed by foreign experts, it saved construction time, saved about 1 billion yuan in investment, and achieved no water leakage at the immersed tube joints.
　　The underwater immersed tube tunnel consists of 33 reinforced concrete immersed tube sections and 1 steel-shell concrete final joint. A standard single immersed tube section weighs up to 76,000 tons. These immersed tubes are docked and placed in the undersea environment, with a difficulty comparable to the rendezvous and docking of spacecraft.
　　“Deep burial falls within the forbidden zone of the immersed tube method, and there are no standards to refer to.” Xu Guoping said that to build the world's longest open-sea deeply buried immersed tube tunnel, the contractor equipped the country's first installation vessel using a deep-water unmanned immersion system, using information and remote control technology to achieve tube section posture adjustment, axis control, and precise docking.
　　Through scientific research, China has mastered a complete set of open-sea immersed tube installation technologies with independent intellectual property rights, creating a “Chinese speed” of installing 10 immersed tubes in one year, far ahead of the international advanced level.
　　A 120-Year Plan
　　The design life of the Hong Kong-Zhuhai-Macao Bridge reaches 120 years, a concentrated display of China's achievements in bridge design, construction, material research and development, and engineering equipment.
　　What is the lifespan of this mega-project? “The Hong Kong-Zhuhai-Macao Bridge can ‘live to 120 years old.’” Su Quanke said: “It can also withstand Category 16 typhoons and magnitude 8 earthquakes.”
　　“This is the first time we have done 120 years. The South China Sea has high salinity and severe corrosion. At the beginning, everyone was worried: can this be done?” Wang Shengnian, head of the durability project of the Hong Kong-Zhuhai-Macao Bridge, said that China's durability technology has developed rapidly, and achievements in new materials and new processes have laid the foundation for the smooth progress of the project.
　　The durability design of the Hong Kong-Zhuhai-Macao Bridge is based on the accumulated results of more than 30 years of observation data from corrosion exposure experiments in the South China Sea, with quantitative analysis and design of all indicators, winning high praise from international peers.
　　Not only is the design life high-standard, but the construction of the Hong Kong-Zhuhai-Macao Bridge also reflects the concept of science and technology leading engineering construction in many aspects.
　　For example, the design and application of disaster prevention and mitigation. The builders specially built a 150-meter-long full-scale immersed tube tunnel experimental platform in Zhangzhou, Fujian, and used 3 years to conduct combustion experiments on large buses, medium buses, and cars. For the first time in the world, first-hand data such as temperature, smoke flow rate, and concentration in the tunnel during a fire were obtained, forming a complete set of key technologies for disaster prevention and mitigation of the Hong Kong-Zhuhai-Macao Bridge immersed tube tunnel.
　　According to experimental tests, the tunnel fire protection facilities can ensure that the immersed tube structure is not damaged within 2 hours at a high temperature of 1200°C. Su Quanke said that the artificial islands have maritime rescue platforms. If an accident occurs in the tunnel, rescue forces can arrive in 3 minutes; if an accident occurs on the bridge deck, they can arrive within 5 to 7 minutes.
　　Yu Lie said that the Hong Kong-Zhuhai-Macao Bridge project is a concentrated display of China's achievements in bridge design, construction, material research and development, and engineering equipment over the past decades, and its construction has also driven the upgrading and technological progress of China's transportation industry.