At sea, grab dredgers, long-reach excavators, telescopic-boom excavators and other equipment operate in coordinated fashion, rumbling merrily;

On land, more than 200 workers skillfully complete processes such as rebar tying and concrete pouring inside insulated sheds. The slogan on the steel plate reading “The North's First Subsea Tunnel as a Gift to the People of Dalian” is bright and eye-catching.

On January 12, at the construction site of the Dalian Bay Subsea Tunnel Project——a key project in Liaoning Province——the cold winter wind could not dampen the builders' enthusiasm. Amid the roar of machinery, a scene of bustling construction activity unfolded before the reporter's eyes.

In the south, there is the Hong Kong-Zhuhai-Macao Bridge; in the north, there is Dalian Bay.

The Dalian Bay Subsea Tunnel draws on the mature immersed-tube construction technology of the Hong Kong-Zhuhai-Macao Bridge. It is the first immersed-tube subsea tunnel to be built in northern China, and its construction team basically comprises the original crew from the Hong Kong-Zhuhai-Macao Bridge project. The entire project is expected to be completed and opened to traffic in 2023.

“The whole project is progressing smoothly. More than a month ago, the first immersed tube was successfully laid on the seabed, achieving a breakthrough from zero in the construction of China's first immersed-tube subsea tunnel in a cold region. We are now laying the groundwork for the installation of the second batch of immersed tubes,” said Zhang Haiying, chief engineer of the General Project Management Department of the Dalian Bay Subsea Tunnel Project.

The immersed-tube works are the core controlling component of the Dalian Bay Subsea Tunnel and are extremely difficult. First, the immersed tubes prefabricated on land, weighing tens of thousands of tons, must have their ends sealed and be transported one by one to the sea by buoyancy, then sunk to the seabed and joined to form the tunnel. In this process, construction must contend with complex seabed topography and hydrological conditions, and use marine weather forecasts to find precise window periods. The Dalian Bay Subsea Tunnel has a total length of 5.1 kilometers and consists of 18 immersed tubes. The heaviest single immersed tube weighs about 60,000 tons, equivalent to the displacement of an aircraft carrier.

To ensure the flawless installation of the immersed tubes, the R&D team spent three years on research, established 25 research projects, and completed 140 specialized construction plans, overcoming numerous technical challenges such as the narrow waters at the docking end, cumbersome cable-handling methods, the large longitudinal slope of the immersed tubes, and high installation precision requirements.

On the day the first immersed tube was installed, after 17 hours of continuous operation, the immersed tube——135 meters long, 33.4 meters wide, 9.7 meters high and weighing about 41,000 tons——was successfully laid on the seabed and precisely docked with the buried section on the north bank.

Zhang Haiying said with full confidence that the first step is always the hardest; having taken it, the later immersed-tube operations will certainly become increasingly proficient and smooth. This year, 9 immersed tubes are expected to be installed, accounting for about 50% of the total workload.

With a good first step comes a new atmosphere. Entering 2021, the project is advancing in an orderly manner according to schedule, and the busiest onshore work is undoubtedly the prefabrication of immersed tubes.

The reporter saw at the site that workers wearing cotton hats and padded coats tied rebar one by one into reinforcement cages. After concrete pouring, these giant matchbox-shaped tube sections will be connected into a standard immersed tube weighing tens of thousands of tons.

Pouring tube sections in winter is the first of its kind in China. Affected by severe cold weather, how to ensure the quality of concrete pouring has become the biggest difficulty. To this end, the contractor redeveloped the concrete mix ratio, customized a special water-reducing agent, and carried out proper concrete temperature control and subsequent steam curing to ensure normal winter construction.

“The task is arduous and hard work, but it is very glorious!” Zhang Chao, chief engineer of the Third Work Area of the General Project Management Department, told the reporter that the project is of great significance, the workers have no complaints about not stopping work in winter, and everyone is going all out to do their utmost to resolutely complete the construction task and contribute to the revitalization and development of Liaoning.

According to reports, once the Dalian Bay Subsea Tunnel Project is completed, Dalian will gain a new north-south express corridor, thereby alleviating the bottleneck in north-south traffic in Dalian's main urban area and expanding the city's development space.