Original title: Combined construction, construction of ultra-long undersea tunnel (craftsman's unique skill)
A three-arm drilling rig is laying holes. Photo by Han Wenming
Workers are checking the segment splicing. Photo by Ding Xiang
Aerial view of the construction site of the shield section. Photo by Yu Yongqun
Core Reading
With a total length of 17.48 kilometers, of which 14.37 kilometers are long (9.95 kilometers in the sea area), this nearly 10,000-meter undersea tunnel will become the world's longest undersea road tunnel after completion. In the face of complex geological conditions and difficult working environment, the construction team carried forward the spirit of craftsmanship, borehole survey, innovative design, precise construction, and intelligent management, and fully invested in the tunnel construction, contributing to the smooth development of the project construction.
The shore of Huangdao is rippling with blue waves; Deep under the sea, equipment roars...... Here, the Jiaozhou Bay Second Tunnel Project (hereinafter referred to as the "Second Tunnel") in Qingdao City, Shandong Province is under intense construction, which will become the world's longest submarine road tunnel after completion.
In the face of complex geological conditions, the construction team of the second tunnel project carried forward the spirit of craftsmanship and promoted the smooth development of the project construction from survey planning to implementation. Since the full start of the main line project in September 2022, the construction of the main line tunnel has exceeded 8.6 kilometers.
Recently, the reporter walked into the project site to see how the tunnel crossed the seabed for nearly 10,000 meters.
Formulate a construction plan——
After 9 years of exploration, the total length of cores taken on the seabed reached 28,000 meters
The first question encountered in the construction of the undersea tunnel is: how to take the route?
There is an active fault within Jiaozhou Bay, called the Cangkou Fault Zone, which is located exactly on the planned route of the Second Tunnel. From which position to wear it? How to wear it? What engineering method is used to wear it? Only by solving this series of problems can the construction of the undersea tunnel be possible.
As a result, figuring out the geological composition of this part of the seabed has become the first problem to be overcome in this project. In 2013, Guo Yongjian, senior engineer of the Chief Engineering Office of Qingdao Guoxin Jiaozhou Bay Second Submarine Tunnel Co., Ltd., left the postdoctoral workstation of civil engineering of Tongji University and became the first postdoctoral fellow of the second tunnel team, and also began a nine-year survey plan.
"Only by understanding the real situation of the seabed can we have confidence in engineering planning and scheme design." Guo Yongjian said. On the one hand, he traveled all over the major scientific research institutes, and on the other hand, he jointly organized marine surveys with the survey unit China Railway Bridge Survey and Design Institute.
Surveys require drilling to detect the geology and drive a drill ship at sea. In two years, Guo Yongjian led the survey team to drill 237 holes and take cores with a total length of 28,000 meters on the seabed, laying a solid foundation for the future seabed project across Jiaozhou Bay.
The survey results show that there is a large area of granite on the bottom of the second tunnel, among which a large number of diabase are interspersed, there are many fractures, and some of them have good water conductivity, the geological conditions are extremely complex, and the engineering difficulty is multiplied.
After repeated investigation by the expert group, combined with the results of geological survey, the engineering scheme found the optimal solution between safety and economy: the Qingdao end on the east bank of the second tunnel is dominated by tuff and the shield method is adopted, and the Huangdao end on the west bank is dominated by granite, which adopts the drilling and blasting method, supplemented by the open cut method in the land area, and carries out combined construction, and excavates from the east and west banks of Jiaozhou Bay to the bay at the same time, and finally the super-large diameter shield and the large-section drilling and blasting tunnel will be docked on the seabed.
Design of fresh air channel——
Numerical simulation analysis was carried out, and a 2.5-section ventilation technology was proposed
In addition to route design, there is also the challenge of tunnel ventilation. As the person in charge of the design of the second tunnel project of the Fourth Survey and Design Institute of China Railway (hereinafter referred to as the "Fourth Railway Institute"), Sun Wenhao has been engaged in engineering design for 25 years, but when facing the second tunnel project, "we cannot find a reference sample, and we need to find a new way by ourselves".
According to the traditional design idea, the ventilation during the construction of the submarine tunnel is realized by using vertical shafts, usually one at each end and in the middle of the sea, with a distance of five or six kilometers, which is called three-stage ventilation. However, this method does not work in the second tunnel: according to the regulations on the protection of Jiaozhou Bay in Qingdao, in order to protect the ecological balance of the sea area, it is not allowed to build ventilation shafts in the sea area.
"Keep exploring and innovating, and you will definitely find a solution." Sun Wenhao said that some ultra-long tunnels have compartments at the top, but they are only used for smoke exhaust in the event of a fire, and can these exhaust ducts be used for daily ventilation. If feasible, can service tunnels used as evacuation rescues also be used for ventilation?
This idea opened the design team's idea: use the intermediate service tunnel as a fresh air channel to send fresh air in, and separate the exhaust flue at the top of the main line tunnel to exhaust the dirty air to form a closed loop of air supply and exhaust.
But is such a design feasible? To this end, on the basis of numerical simulation analysis, the Tiesi Institute built a physical model dozens of meters long in Wuhan for verification, and the data met the requirements. Because this ventilation method is set up with two supply and exhaust fan rooms on the seabed, which is generally between the two-stage and three-stage ventilation, it is called the 2.5-stage ventilation technology, which provides a new solution for the ventilation of the world's ultra-long submarine tunnels, which is also the patented technology of the Iron Fourth Academy.
In the past three years, the design team has completed more than 60 volumes of tunnel civil design drawings, totaling more than 5,000 sheets, stacked together to be two meters high. "The drawings of the mechanical and electrical system, bridges and houses have not yet been released, and all the drawings have been completed in more than 150 volumes." Sun Wenhao said.
Carry out construction work -
One hole can be punched in two minutes, and the entire face can be punched in more than two hours, with very little deviation
On the west bank of Jiaozhou Bay, entering the tunnel from the entrance of the Huangdao section of the Second Tunnel Project, the cold air lingers, the surrounding rock is wet, and there is occasional flowing water on the ground. The drilling and blasting method, also known as the mining method, is to carry out construction by drilling, discharging and blasting.
Under the leadership of He Jichao, the person in charge of the rock drilling rig of the China Railway Tunnel Bureau, the reporter came to the 1300-meter tunnel face, at this time, the cave has been completely darkened, and an arched stone face is blocked in front.
A roar resounded through the tunnel, dazzling lights hit the face of the tunnel, and the giant rock drilling rig slowly drove in and stopped directly in front of the face of the tunnel. Half an hour later, the parameters of the design drawings were turned into construction data, and the tunnel outline line, center line and the first row of groove lines were drawn on the surface of the tunnel with paint.
With the measurement and lofting, the driller Du Shuai boarded the three-arm drilling rig and skillfully operated the trolley control lever, and the 5.5-meter drill pipe was as flexible as his arm. Du Shuai aimed the drill pipe at a point on the contour line, without identification, only after listening to a deafening "clang" sound, a 45 mm diameter borehole was impartial, just hit the vault contour line lofting point. "It's a very challenging process for drillers." He Jichao said that it takes 3 to 5 years to train a skilled driller.
Du Shuai has been engaged in driller for 10 years, and now, he can find each point by eye observation, punch a hole for two minutes, and complete the entire face of the tunnel in more than two hours, with very little deviation. In the drilling and blasting section of the second tunnel, there are more than 30 drillers like Du Shuai.
Responding to emergencies –
Use digital twins to build a smart platform and prompt early warning information
The bedrock of the second tunnel is mainly granite, and there are tensile fractures with good water conductivity, and the water output far exceeds that of other submarine projects. How to deal with the challenge of water inrush is the key to the risk management and control of the second tunnel project, and it is also a challenge that the project safety management needs to face.
Once, at the drilling and blasting construction site, the advanced horizontal probe showed that the surrounding rock in front of the tunnel was broken, and the water output reached 1,000 liters per minute. The digital construction platform of the second tunnel project displayed water early warning information in a timely manner, and the management team quickly made a disposal plan.
Not only can early warning information be issued in time in disasters such as water surge, rock instability, collapse, and fire, but the digital construction platform of the second tunnel project brings together all the process data of the builder, designer, constructor, supervisor, and operator. As early as 2020, Li Xiang, general manager of the Second Tunnel Company, put forward the goal of building a digital construction platform with all processes, all elements and all data online, using digital and intelligent technology to ensure the quality and safety of the undersea tunnel, making the Second Tunnel the first digital twin undersea tunnel in China.
"Lo and behold, now the information and location of the staff are displayed here." Zhang Le, deputy manager of the safety and risk management department of Qingdao Guoxin Jiaozhou Bay Second Submarine Tunnel Co., Ltd., opened the personnel positioning module, and on the digital simulation tunnel route, the names of people changed in real time with the personnel positioning. It turns out that the project integrates the 5G converged private network and the Beidou positioning system, from small safety helmets to large equipment, vehicles and even tunnels, all of which have been intelligently upgraded, which can realize real-time positioning and monitoring of on-site personnel, vehicles and equipment.
Qu Liqing, Chief Engineer of Guoxin Group and Chairman of the Second Tunnel Company, said: "The Second Tunnel Project is committed to applying new technologies, new processes, new equipment and new materials to break through the technical problems of intelligent construction and construction control of undersea tunnels. ”
■Further reading
Whole-process supervision to ensure the quality of the project
The second tunnel of Jiaozhou Bay in Qingdao City, Shandong Province needs to cross nearly 10 kilometers at the bottom of Jiaozhou Bay, and the deepest point is 115 meters from the sea level, and the geological and hydrological conditions are extremely complex, not only to pass through the active fault zone, but also interspersed with a large number of intrusive rocks in the granite, with many fractures and some good water conductivity, and the difficulty of the project is multiplied.
In terms of construction, the second tunnel adopts the combined construction method of "shield method + drilling and blasting method + open cut method", excavates from the east and west banks of Jiaozhou Bay to the middle, and docks on the seabed; In order to protect the ecology of the sea area, the 2.5-segment ventilation technology is innovatively designed, and in order to solve the problems of long-distance resource allocation, multi-cross collaborative interaction and high-frequency real-time feedback of the submarine tunnel, the digital twin technology is applied to innovate and develop a digital construction platform with the whole process, all elements and all data online, and the whole process supervision is carried out by digital and intelligent technical means to ensure the quality and safety of the submarine tunnel......