There are Hong Kong, Zhuhai and Macao in the south and Dalian Bay in the north.
The construction of major engineering projects leads to effective investment and stable economic growth, which is an important support for achieving high-quality economic development.
From Lingdingyang at the southern tip of the motherland to Dalian Bay 2,000 kilometers northward, China's technology, equipment, and experience in the construction of cross-sea immersed tube tunnels are becoming more mature.
In the cross-regional practice of the super project, what difficulties did the builders overcome?
What are the technological innovations?
Economic Daily reporters recently went to the construction site of the Dalian Bay Subsea Tunnel to conduct interviews and investigations.
At sea, equipment such as grab boats and excavators are working together, and the machines roar; on land, workers are busy with concrete pouring and other processes.
In the autumn season, the reporter saw a hot construction scene on the site of the Dalian Bay Subsea Tunnel Project.
In 2017, Dalian, Liaoning Province, launched a major livelihood project-Dalian Bay Subsea Tunnel and Guangming Road extension project, which is expected to be completed and opened to traffic in 2023.
Among them, the Dalian Bay Subsea Tunnel is the first large-scale sea-crossing immersed tube tunnel project in northern China, and it is also another cross-sea traffic project with high technical difficulty, complicated construction conditions and high environmental protection requirements after the Hong Kong-Zhuhai-Macao Bridge.
On May 6, 2013, the first immersed tube installation of the Hong Kong-Zhuhai-Macao Bridge Island Tunnel Project opened a new era of cross-sea immersed tube tunnel construction in China.
In 2021, at the construction site of the Dalian Bay Subsea Tunnel, China has completed the installation of more than 50 "carrier-grade" immersed pipes.
From the exploration of installing a pipe joint in 96 hours to more than 10 hours, the construction technology of cross-sea immersed tube tunnels in our country has continued to be used in super projects such as the Hong Kong-Zhuhai-Macao Bridge, Dalian Bay Subsea Tunnel, and Deep-Medium Passage for 8 years. Exploration and innovation.
In just a few years, how has China achieved rapid progress in the field of cross-sea immersed tube tunnels?
What are the technological innovations and breakthroughs?
What unexpected difficulties have you encountered?
What does it mean for the next undersea tunnel project?
Record precision docking
Located at the junction of the Yellow Sea and the Bohai Sea, the old city of Dalian has a "C"-shaped bay structure. The north-south traffic arterial road has only two passages, Donglian Road and Northeast Road, and the traffic volume has already far exceeded the designed traffic volume.
Dalian urgently needs to alleviate the bottleneck problem of north-south traffic in the main urban area and expand the space for urban development.
The Dalian Bay Subsea Tunnel and Guangming Road Extension Project are major projects in Liaoning Province constructed in the PPP mode to solve this problem.
"After the completion of the submarine tunnel, Dalian will add a new fast track running through the north and south. In the past, it took more than an hour to bypass Dalian Bay, and it would be possible to cross it in the next 10 minutes. This will help ease the traffic congestion in the central city of Dalian and expand the space for urban development. It is of great significance to promote the integration of the two sides of the Dalian Bay." Li Jin, Secretary of the Party Working Committee and General Manager of Dalian Bay Subsea Tunnel Co., Ltd. said that the project will not only facilitate citizens' travel, but will also optimize the city's functions and promote the integration of Dalian Bay.
Immersed pipe installation is the core control project of the Dalian Bay Subsea Tunnel, which is extremely difficult.
First, the prefabricated immersed pipe weighing tens of thousands of tons must be sealed on the land, and then transported to the sea section by section by buoyancy, and then sunk into the seabed to form a tunnel.
In this process, in the face of complex seabed topography and hydrological conditions, the construction needs to find an accurate window period with the help of marine weather forecasts.
On September 15, the two cross-sea immersed tube tunnels between the north and south of China, which were constructed by China Communications First Navigation Engineering Bureau Co., Ltd., once again ushered in a historic moment of dual "pipes"-the world's longest and widest steel shell immersed tube The E12 pipe section and E11 pipe section of the deep and medium passage of the tunnel were smoothly connected, and the length of the completed tunnel exceeded the 2,000-meter mark. On the same day, the E9 pipe section of the Dalian Bay Subsea Tunnel, the first large-scale immersed tube tunnel in northern China, was successfully installed, and the immersed pipe installation task was halfway through.
The E9 pipe joint installed this time is the eighth immersed pipe installed in the Dalian Bay Subsea Tunnel this year, and the fourth pipe joint completed in the third quarter of this year, which ran the "new speed" of domestic immersed pipe installation.
The main line of the Dalian Bay Subsea Tunnel and Guangming Road Extension Project is 12.1 kilometers in length. The construction standard is an urban expressway with a design speed of 60 kilometers per hour and 6 lanes in both directions.
Among them, the Dalian Bay Subsea Tunnel is about 5.1 kilometers long, and the submarine immersed pipe section is 3,035 meters long. A total of 18 large immersed pipes need to be installed.
The single-section standard immersed pipe is 180 meters long, 33.4 meters wide, 9.7 meters high, and weighs about 60,000 tons, which is equivalent to the displacement of an aircraft carrier.
Unfavorable weather conditions such as sea wind, wave and flow velocity have a great impact on sea conditions, which brings great challenges to the construction of immersed pipes.
On September 15th, the installation of the E9 pipe section of the Dalian Bay Subsea Tunnel started at 6 am. After the tugboat formation, floating, mooring, and installation procedures were completed successively, the installation was successfully completed at 20:08 in the evening of the same day.
"Climate conditions have a great impact on the installation of immersed pipes. The installation of E9 pipe joints was done in advance by arranging multi-beam scanning of water depth, real-time measurement of sea water density, and eliminating various hidden dangers to ensure the smooth docking of immersed pipes." Dalian Bay Pan Liwen, Chief Engineer of Undersea Tunnel Co., Ltd. said.
For the submarine immersed pipe project, the climate impact is only an "episode", and the real challenges can be described as "one by one".
At the end of last year, Dalian Bay Subsea Tunnel Co., Ltd., after 17 hours of continuous operation, successfully sunk the first section (E1) immersed pipe weighing about 41,000 tons on the seabed, and realized precise docking with the buried section of the north shore, realizing the first seabed in cold regions of China. Zero breakthrough in the construction of immersed tube tunnels.
"The construction area of the E1 pipe joint is based on rock, and the geological conditions are poor, so it is impossible to use a full-lift conventional leveler to insert piles." Pan Liwen said.
In order to ensure the precise docking of immersed pipes, the R&D team spent 3 years tackling key problems, overcoming the technical problem of inability to insert piles under rock foundation conditions, and adopted the nation’s first full-floating gravel bed leveling process for levelling ships.
Everything was difficult at the beginning, and the first step was taken, and the later immersed pipe operations became more and more proficient and smoother.
So far, the construction party, China Communications First Navigation Bureau, has successfully completed the precise subsea docking of 54 aircraft carrier-class immersed tubes, which has also created an unprecedented new record in the history of the construction of cross-sea immersed tube tunnels in the world.
Solve difficulties according to local conditions
"The Dalian Bay Subsea Tunnel project has many new tests such as complex geological conditions, small tunnel curve radius, cold seas to test the durability of concrete, and complicated navigation conditions. The construction is difficult and the quality requirements are high." Pan Liwen said.
The first problem to be solved is low temperature.
The construction of immersed tube tunnels in cold areas is a construction experience that China has never had before.
Dalian is located in the northeastern region of China, and the cold winter weather will bring a lot of inconvenience to the construction, which is a great challenge for both the ship's machinery and the construction personnel.
The sea breeze blows outdoors for half an hour in winter, and no matter how thick the clothes are, no one can guarantee whether the equipment will malfunction in the low temperature state.
The installation of the first section of immersed pipe in Dalian Bay was carried out in winter. However, China’s first set of special equipment for immersed pipe installation "Jin'an 2" and "Jin'an 3" did not consider the effect of low temperature at the beginning of the design.
Therefore, in accordance with the construction characteristics in winter, the construction party carried out a series of adaptive transformations on the main ships such as the immersed tube bed leveling vessel "Jinping 1", the immersed tube installation vessel "Jin'an 2" and "Jin'an 3": the installation of boilers Heat preservation equipment such as heating and heating equipment, replace low-temperature grade gear oil and hydraulic oil, wrap the exposed oil pipes and water pipes with insulation cotton, move the winch hydraulic station to the engine room, and customize cold-proof tarps for deck equipment... All this is to ensure that the ship will not be constructed in winter. Affected.
The fourth work area of the Dalian Bay Subsea Tunnel is responsible for the installation of immersed pipes.
Work area manager Wang Dianwen said: “We have taken countermeasures based on the actual conditions of the northern cold regions, and carried out independent upgrades and innovations to the system software of special ships. Many technologies have not been considered before, and it can be said that they have filled part of the installation of immersed tunnels. Technology gaps in the field.” Taking the underwater cable socket installation process as an example, the characteristics of the bulk prefabrication of the Dalian Bay Subsea Tunnel’s dry-docking method determine the increase in the number of sockets. Affected by the epidemic, the long period of procurement of complete sets of equipment from abroad will inevitably affect the overall process. After several months of research, the technical team has adjusted the installation process of underwater cable sockets from primary outfitting to secondary outfitting. This not only overcomes the impact of the epidemic, but also realizes the localization of this technology.
Nowadays, the project is proceeding in an orderly manner according to the time node, and the busiest construction on land is undoubtedly the immersed pipe prefabrication.
The reporter saw at the scene that workers tied steel bars into steel cages one after another.
After the concrete is poured, these giant matchbox-shaped pipe sections will be connected into a standard immersed pipe weighing tens of thousands of tons.
It is the first time in the country to pour the pipe festival in winter.
“It only took two years to study the anti-freezing and anti-seepage of high-strength concrete to ensure a hundred-year service life under seawater environment.” Pan Liwen said, “Finally, the Dalian Bay Subsea Tunnel innovatively adopted dry-dock immersed pipe prefabrication and realized multiple The work surface is carried out at the same time.” According to reports, this set of prefabricated immersed pipe methods tailored for the Dalian Bay Subsea Tunnel has reached the international advanced level after industry assessment.
In addition to the cold climate, complex sea geological conditions also pose challenges for construction.
Different from the single geology dominated by more silt, the geology of the Dalian Bay Subsea Tunnel in the north is complex and changeable. The geological pipe joints are full of karst trenches, karst troughs, boulders, stalagmites, and rich red clay in the middle.
Pan Liwen introduced, “There are many submarine caves and karst trenches in the construction sea area, and the rock foundation is cracked. Five of the 18 immersed pipes are located on the clay layer. This part of the construction requires the clay to be excavated, refilled with gravel, and vibrated and leveled. The immersed tube can be installed later.”
Leveling is an important part of the installation of immersed pipes.
Ma Zonghao, deputy general manager of Dalian Bay Subsea Tunnel Co., Ltd., introduced that before leveling construction, the foundation trench needs to be excavated, and the rock foundation blasting and slag removal processes are added to the foundation trench. “We adopted underwater high-precision blasting, Advanced techniques such as underwater precision excavation are all domestic leading technologies."
After the leveling conditions are met, the leveling vessel, known as the "undersea 3D printer", enters the site to lay a "bed" for the immersed pipe to sleep peacefully.
However, there will be a lot of cracks in the slope of the foundation trench in the Dalian Bay waters after reef explosion.
This also means that the full-lift leveling process used in the past will not be suitable for Dalian Bay.
In order to solve this difficulty, the research and development team of China Communications First Shipping Bureau organized the backbone of the research to concentrate on the semi-floating leveling, half-width leveling, lowering the platform height, widening the leveling vessel, and setting up positioning piles for the leveling vessel... Experienced numerous technical demonstrations and deductions.
During the three-year preparation period, more than a hundred special technical seminars have finally determined the leveling process of the full-floating gravel bed.
"In order to ensure the precise control of leveling in the floating state, GPS and sonar are used. The leveling process of full floating is the first in the country." said Tian Aizhe, deputy secretary of the Party Working Committee of Dalian Bay Subsea Tunnel Co., Ltd.
It is the solution and breakthrough of such problems that have allowed the continuous development and progress of cross-sea tunnel engineering technology.
Rich experience is not something that you can have overnight, but continuous innovation and accumulation in difficult practice.
In addition, in consideration of the final joint, the Dalian Bay Subsea Tunnel innovatively adopts the "jacking segment method" process. All work is completed in a dry operation environment, with simple structure production, guaranteed construction quality, and short construction period. , The advantages of low construction cost and strong safety.
"On the one hand, this process avoids the lifting of large ships and is more economical; on the other hand, it is not affected by wind and waves and has higher safety. The most important thing is that the accuracy of quality is higher. This process is the first in China. We also applied for a patent." Pan Liwen said.
It is worth mentioning that the Dalian Bay Subsea Tunnel will also realize the handover of "physical engineering" + "digital engineering" in the future.
"The so-called digital engineering is the deep application of BIM technology, Internet collaboration technology, and Internet of Things technology to the entire life cycle of engineering design, construction, operation and maintenance. Simply put, all entities in the tunnel will form a database through computer modeling." Pan Liwen said, “For example, where the steel bars used for prefabricated immersed pipes are produced, what is the furnace number, what is the batch number, which team does it... These contents will all be digitalized.”
Coordination and cooperation guarantee project
In the construction process of major projects, in addition to breaking through various technical problems in response to local conditions, there must also be applications and breakthroughs in response to different scenarios and working conditions.
Only continuous innovation can promote the continuous maturity and improvement of the entire technology.
During the construction of the submarine tunnel, how to ensure that the construction and navigation are correct?
This tests the organization, coordination and execution capabilities of the project.
Dalian Bay has narrow waters, complicated navigation conditions, frequent passenger and cargo ships, and more than a hundred ships during the peak period of offshore construction, and the construction period is only 50 months, which brings great challenges to construction safety and maritime navigation capabilities.
China's important shipbuilding and offshore engineering manufacturing bases, such as Dalian Port Passenger Terminal, Dalian Shipbuilding Industry Corporation, and Dalian Shipbuilding Industry Corporation, are all located in the hinterland of Dalian Bay.
A bird’s eye view of the immersed pipe line of the Dalian Bay Subsea Tunnel from the air happens to intersect with many important shipping lines, especially shipping lines.
This means that while the undersea tunnel is being constructed, it is also necessary to ensure the smooth flow of shipping.
"The water construction of the Dalian Bay immersed tube tunnel mainly includes the excavation of the foundation trench, the leveling of the gravel bed, the floating installation of the pipe joints and the backfilling, etc., all of which take a long time to occupy part of the original channel. In order to ensure the construction operations on the water and the society The navigability of ships is safe, and we have specially excavated a temporary channel with the same navigability as the main channel." Li Jin said.
According to reports, in the Xianglujiao Channel and the northern side of the Ganjingzi Channel, a temporary channel with the same navigation capacity as the original channel was specially excavated for the submarine tunnel project to ensure that ships can only pass smoothly.
The temporary channel is more than 10 meters deep and 200 meters wide. This major project is to ensure that the project construction does not affect navigation.
In addition, the project has also developed a maritime ship management platform in cooperation with research institutions for real-time monitoring and early warning.
During the construction period, the channel was changed many times, which not only ensured the normal navigation of Dalian Bay, but also ensured the safety of offshore construction.
The complicated navigation situation in the Dalian Bay waters is far more than simply digging a new channel.
Li Zhutang, deputy manager of the fourth project area, still remembers the thrilling scene.
On the evening of March 9 this year, all preparations for the placement of the E2 immersed tube were ready.
At this moment, "Jin'an 2" suddenly honked its whistle. It turned out that a small fishing boat hit and rammed into the construction sea by mistake.
The cables connecting the installation vessel to the tugboat and the shore are complicated. Once the fishing vessel encounters the cable, the consequences will be disastrous.
Fortunately, at this time, the alert sea cruiser approached the fishing boat and drove away.
"Because of the fog that day, and the poor light conditions in the evening, the fishing boat did not see us. Fortunately, the maritime cruise ship escorted by the Dalian Maritime Safety Administration." Li Zhutang said.
In fact, in order to fully guarantee the submarine tunnel project, many relevant departments in Dalian have closely coordinated and cooperated with the construction unit to ensure the safety of waters, research and formulate navigation protection plans, and determine on-site control, temporary closure of navigation, and regional speed limits.
In order to improve the implementation efficiency of this highly anticipated major livelihood project, Dalian City Administration Co., Ltd. coordinated the problems and difficulties of the project, held project promotion coordination meetings regularly or irregularly, went deep into the field to solve problems, and took everything conducive to the smooth progress of the project. The measures to advance ensure that the engineering project advances at full speed.
The investment scale is large, the spanning area is wide, the relocation is difficult, and the technical difficulty is high. For serving this single PPP project with the largest investment scale in Northeast China, Liang Chunbo, director of the Dalian City Administration Bureau, said: “On the one hand, we must be familiar with the basics of the project. Understand the situation, grasp the progress of the project, clarify the demands of the project company, and put forward specific work suggestions; on the other hand, it is necessary to coordinate with the municipal and district government departments at all levels and related enterprises to create convenient conditions for project construction."
According to reports, only one unit of the Dalian Urban Management Bureau has coordinated more than 30 local government departments and more than 20 companies involved in pipeline relocation and relocation, and resolved issues concerning sea land use, plans, land acquisition, relocation and reform, cultural relics, environment, navigation, and construction. There were nearly 1,000 difficult matters such as procedures.
Our reporter Su Dapeng