Daily Science | "Submarine Embroidery" provides Chinese solutions for the world's tunnel projects

At the bottom of the vast Lingding Ocean, a 6.8-kilometre-long undersea tunnel is like a hidden dragon entering the sea, connecting the east and west artificial islands of the Shenzhong Passage, becoming an important link in the connection between the two sides of the Pearl River Estuary.

Shenzhong Tunnel, the world's first two-way eight-lane steel-shell concrete immersed tunnel. In the construction of the whole project, the technical content is high and difficult, and a number of innovative measures are adopted, which enriches the "Chinese standard" of the world's cross-sea immersed tunnel and contributes the "Chinese plan" to the world's cross-sea channel project.

What technical problems did the engineering team overcome to make the immersed tube complete the "first kiss on the sea"? And what innovative way was used to place the immersed tube "silently" on the seabed? Recently, the reporter interviewed the builders of the submarine immersed tunnel of the Shenzhong Passage and listened to them talk about the "Chinese wisdom" behind the immersed tunnel.

"Yihang Jin'an 1" came into being

The Shenzhong Tunnel is a two-way eight-lane steel-shelled concrete immersed tunnel connected by 32 "aircraft carrier-like" immersed tubes. A single standard section is 165 meters long, 46 meters wide, 10.6 meters high, and weighs about 80,000 tons. The difficulty of installing these behemoths at an underwater level 40 meters is comparable to the docking of the "Heavenly Palace".

From the beginning of the construction project, it has faced one after another world problems that need to be solved urgently: new form of steel shell structure, ultra-wide size, ultra-long floating distance, and long waterway closure time...... If you want to do a good job, you must first sharpen your tools, and the existing equipment cannot meet the construction requirements, and it has become the only way to develop new programs and equipment.

The world's first immersed tube floating installation integrated ship "Yihang Jin'an 1". Photo courtesy of CCCC First Harbor Bureau

Recalling the construction process of overcoming difficulties, Ning Jinjin, executive deputy chief engineer of the Shenzhen-Zhongshan Passage Project Department of CCCC First Harbor Bureau, remembers vividly: "After the immersed tube was built, it was towed from Guishan Island, 50 kilometers away, and if you drive on the highway, 50 kilometers will pass with one foot of the accelerator." However, dragging 80,000 tons of immersed tubes, these 50 kilometers are very laborious, so we built a new ship called 'Yihang Jin'an 1'. ”

The "Yihang Jin'an 1", which has been independently developed and built by scientific researchers for three years, is a special ship for the construction of immersed tubes in submarine tunnels with the largest installation capacity, the highest sinking accuracy, the most efficient construction operations and the most advanced performance, integrating the functions of immersed tube floating, positioning, sinking and installation. With a length of 190.4 meters and a width of 75 meters, the deck area is equivalent to two football fields, and it is another epoch-making technological innovation in the field of undersea tunnel construction.

"Yihang Jin'an 1" needs to safely transport about 80,000 tons of immersed pipes from Guishan Island to the construction area of the Shenzhong Passage 50 kilometers away, which is not an easy task. How to keep the integrated ship moving forward safely at all times?

Kou Xiaoqiang, chief engineer of the Shenzhen-Zhongshan Channel Project Department of the Hong Kong Research Institute of CCCC First Harbor Bureau, said: "We have developed a dynamic monitoring technology specifically for immersed tube floating, and the main core point of this technology is to focus on the attitude and force of the immersed tube in the process of floating, and feed it back to the float commander in real time. ”

The "Deep Sea Wisdom Eye" escorts the construction of the seabed

The giant "Yihang Jin'an 1" tows a giant immersed tube the size of an "aircraft carrier", and if it loses its positioning signal in the vast sea, it is tantamount to losing its "eyes", and the risk is unimaginable.

"Immersed tunnel measurement is one of the big difficulties, because we can't see or touch it on the bottom of the sea, and we need to locate it accurately, which is a problem in our surveying community." According to Suo Xuhong, director of the measurement and management center of the Shenzhen-Zhongshan Channel Project of CCCC First Harbor Bureau, in order to install a pair of bright eyes for the "Yihang Jin'an 1", the project team spent 18 months to develop a set of intelligent measurement and control system. "The whole chain is guided by a pair of 'eyes' to guide the installation, so that we can know its three-dimensional position at all times during the construction process, which facilitates the execution of the overall task."

The innovation team has achieved penetration between systems on the self-developed new measurement and control software, which can collect GPS and Beidou signals. Which signal is more stable and more accurate? Then opened a long road to tackle key problems.

"We did hundreds, if not thousands, of experiments, from day to night, from land to sea, covering all areas." Suo Xuhong said that although the process was arduous, the team was overjoyed by the results of the final test, as they found that the data provided by the Beidou system was very stable. The team effectively integrated the Beidou satellite system with the self-developed intelligent TT&C system, and iteratively upgraded the model.

Everything was progressing step by step, but as the installation window for the deepest section of the entire line E9 approached, the innovation team began to think about a new topic. The installation of immersed tube sinking mainly relies on the installation of a 9-storey survey tower on the top of the immersed tube to receive Beidou signals and obtain positioning data, while the E9 will be installed in a deeper sea area of nearly 40 meters underwater, beyond the height of the survey tower. At the same time, the final joint of the immersed tunnel of the Shenzhong Passage is like a "drawer" inside the E23 immersed tube, and it is impossible to erect a measuring tower, and the traditional process has nothing to do.

Under the test of reality, the innovation team marched into the difficulties and developed an underwater binocular camera positioning system. This system is embedded in the final joint like a human eye, known as the "deep sea wisdom eye", which can provide real-time 3D attitude data in the final joint launch process, and display a 3D visual interface, providing more reliable and high-precision positioning data for the installation and docking of immersed tubes on the seabed.

Creating "Deep Speed" and "Deep Precision"

At 11:45 on June 17, 2020, the first section of the immersed tube E1 of the Shenzhong Tunnel was successfully docked, completing the "first kiss on the seabed", and the debut of the integrated ship was declared successful. Subsequently, the innovation team successively completed the perfect placement of immersed tubes E1 to E22, and also accumulated construction experience of 22 immersed tubes, but the E23 pipe section has a built-in final joint and a special structure, so everyone dare not take it lightly.

The docking of the final joint is like "embroidery on the bottom of the sea", and the error should be controlled at the "millimeter level". In order to achieve this difficult goal, after two years of technical demonstration and one year of joint design, the builders pioneered a new process of integral prefabricated underwater push-out final joint of immersed tube in the world.

"In the end, the joint is very simple, like a drawer, you can easily pull the drawer out at home, but my 'drawer' is about 1,600 tons, and it is very difficult to pull it out in a very deep place under water." Ning Jinjin said, "So we made a joint design in advance, using the method of balanced water pressure and jack pushing, so that only 8 jacks can push out the central shaft." If you don't have this water pressure balance, it will take about fifty or sixty jacks to push it out, which is an optimized design. ”

On June 10, 2023, the integrated ship "Yihang Jin'an 1" towed the last section of the immersed tube E23 and the final joint to complete the last "Shenzhong Journey", and the immersed tunnel of the Shenzhong Channel was officially closed. The innovation team has created a deep-to-medium speed of "9 knots a year" and a deep-to-medium accuracy of "7 consecutive immersed tubes for millimeter-level docking".

During the construction of the Shenzhen-Zhongshan Tunnel, the innovation team faced problems and overcame difficulties with the fighting spirit of "daring to teach the sun and the moon to change the sky", filled a number of industry gaps, and truly realized the intelligent construction of the cross-sea channel. It is like a giant dragon sneaking under the Lingding Ocean, with its majestic posture of 6,845 meters, it has created a glorious chapter in the history of world engineering.