The Dalian Bay Undersea Tunnel, the first immersed tube undersea tunnel in northeastern China was completed and opened to traffic this month. Reporter Guan Yang drove there and has this story.

For many of us, when talking about an undersea tunnel, the image of a long tube suspended in the water might come into mind. But that's not the case, an immersed tube undersea tunnel actually sits on the seabed.

After 4 years of construction, the undersea tunnel in Dalian which consists of 18 tubes, each weighing nearly 60,000 tonnes, is now in service.  

SUN ZHU Deputy Chief Engineer, Dalian Bay Undersea Tunnel "We've drawn lessons from the installation of immersed tubes of the Hongkong-Zhuhai-Macau Bridge. But due to the differences in oceanic climates and seabed geology, this project was more complex. The core achievement was solving durability issue for offshore concrete structures under cold seawater."

With a lifespan of 100 years, the tunnel accommodates a two-way six-lane urban expressway. The 5.1 kilometre-long passage reduces travel time from one hour to just five minutes, and connects the industrial zone in the north to the prosperous business area in the south.

GUAN YANG Dalian, Liaoning Province "Not only can an underground transport project like this help ease traffic in congested city zones, but it also can help cut down on pollution when green technologies are employed and improve a city's living conditions."

SUN ZHU, DEPUTY CHIEF ENGINEER, Dalian Bay Undersea Tunnel "We know that sand mining is a major environmental threat to rivers. Not even one unit of river sand was used in the production of concrete and mortar mix for the project. We've set an example of how to get the job done with 400,000 tonnes of artificial sand."

During the construction, the builders have set a series of records such as installing one immersed tube in 12 hours and precision underwater blasting. These helped enhance China's leading position in the field of immersed tube tunnel construction.

LIU JIAN Deputy Operaing Manager,  Dalian Bay Undersea Tunnel "The tunnel is equipped with 15 intelligent sensing units which can detect earthquake, fire, carbon monoxide concentration and so on. Nearly 40,000 sensors have been installed to ensure safety."

Experts say that with independent intellectual property rights, this mega-project in Dalian will further promote the development of China's cross-sea immersed tube tunnel construction, and for the world's tunnelling industry. 

Guan Yang, CGTN, Dalian.