On May 20, after 14 hours of continuous work, tube sections E4 and E3 of the Dalian Bay Subsea Tunnel project, built by the Second Company of CCCC First Harbor Engineering Co., Ltd., a Qingdao-based central SOE, "sweetly joined hands" for the first time in 30-meter-deep seawater, achieving millimeter-level precise mating.

Measurements showed that the mating deviation of the tube sections and the leveling accuracy both met the design requirements, demonstrating the domestically leading technical strength of the Dalian Bay Subsea Tunnel's core vessels — the leveling vessel "Jinping 1", the installation vessels "Jin'an 2" and "Jin'an 3" — and the participating personnel, while further improving the collaborative capability among the participating units.

The E4 tube section installed this time is a standard section, 180 meters long, 33.4 meters wide and 9.7 meters high, weighing about 60,000 tonnes. Its immersion position is at a water depth of more than 30 meters, which imposed new requirements on diver safety assurance and the installation quality of the end bulkheads. In addition, the construction waters are close to a temporary navigation channel, posing high navigation safety risks, and both vessel maneuvering and traffic control faced challenges. To effectively avoid the risk of cables scraping the slope, the distance between the mating ends of the immersed tube during the immersion stage was optimized, placing higher demands on the immersed tube installation construction.

To ensure the smooth progress of the immersed tube installation, the Second Company of CCCC First Harbor Engineering Co., Ltd. actively seized effective work windows and optimized the immersion process. Just 25 days after the successful installation of tube section E3, it scored another success, further shortening the immersed tube installation cycle and providing valuable experience for further improving the efficiency of immersed tube installation in the future. At 6:00 a.m. on the 20th, tugboat formation began. After successively completing processes such as channel turning, mooring, and immersion and mating, tube section E4 was successfully mated with tube section E3, with the entire floating transport and installation taking 14 hours.

The Dalian Bay Subsea Tunnel is about 5.1 kilometers long in total and includes a newly built subsea immersed tube tunnel project, land-section tunnel works, and road works. The immersed tube subsea tunnel is 3,035 meters long and consists of 18 prefabricated tube sections. It is the first large-scale cross-sea immersed tube tunnel project in northern China, and the progress of immersed tube installation is crucial to whether the entire line can open to traffic on schedule.