China installs world's longest undersea steel-casing concrete pipe tunnel

China installed the final section of a 6,845-meter-long undersea tunnel in the Greater Bay Area, Guangdong Province, on June 11 .

The June 11 event marked the completion of the tunnel's two-way, cross-sea installation, according to Guangdong Communications Group. It is the world's longest and widest undersea steel-hulled concrete tube tunnel , allowing eight lanes of traffic in both directions, and is part of the 24km Shenzhen-Zhongshan cross-sea connection project, according to CGTN.

The project's tunnel consists of 32 tubes, each 165 meters long and weighing 80,000 tons. They are transported along the Lingdingyang Canal by the Yihangjinan-1, a specially designed ship.

Yihangjinan-1 is currently the world's largest and most advanced ship for subsea pipe transportation and installation, with the highest installation capacity, highest positioning accuracy and most efficient operation. The ship helps to more than double the efficiency of pipe transportation and installation compared with traditional technology. In addition to pipe transportation and jointing, some other important steps in the construction of a subsea tunnel are foundation treatment, including trenching, treatment and leveling.

Standard underwater tubes are dropped from the ship's bilge into place, aligned with the others. The final tube module, E23, requires complex pre-fabrication and mechanical coupling. Once the E23 tube is in place, a hydraulic jack pushes the coupling attached to the E23 outward, connecting it to the end of the E24 tube.

A specially designed ship was used to transport the final section of the underground pipeline on June 8. (Photo: CFP).

"The Shenzhen-Zhongshan Corridor's undersea tunnel uses prefabricated pipes and is shaped like a giant drawer. In this way, we can fully utilize the advantages of the equipment, reduce construction risks, and ensure the reliability of the project upon completion," said Zhong Huihong, deputy director of the Shenzhen-Zhongshan Link Management Center.

The Shenzhen-Zhongshan route will play a key role in the development of the Guangdong-Hong Kong-Macau Greater Bay Area. The project's bridges, artificial islands, and tunnels form an above-and-below water transportation system that is considered one of the world's most difficult cross-sea projects. The route is expected to open to traffic in 2024, reducing travel time between the two cities from about two hours to 30 minutes.