Recently, Dalian Metro Line 5, the first undersea subway line in Northeast China, was officially opened to traffic in Dalian, Liaoning Province. The successful landing of Dalian’s Super Undersea Engineering Project represents one more global technological challenge that has been tackled by the Chinese people.
The undersea tunnel section of Dalian Metro Line 5 spans a total length of 2,882 meters, with the undersea section accounting for 2,310 meters. It is noteworthy that this is the world’s first large-diameter shield tunnel in the karst strata of sea area. The construction of the tunnel employs a 12.26-meter-diameter slurry shield TBM (Tunnel Boring Machine) for submarine excavation, recognized by industry experts as an unprecedented global technological challenge because of the following four key features:
Long excavation distance: the shield machine is able to continuously excavate 2,882 meters of hard rock stratum with high strength.
High safety risks: the large-diameter shield machine underpasses important buildings, structures and transportation facilities such as waterways and piers, posing high environmental and safety hazards.
High water pressure: the tunnel is buried at a considerable depth and thus subject to high water pressure, equivalent to the pressure of three people standing on an area the size of an egg.
Complex geological conditions: the tunnel passes through a 1,538-meter karst development zone characterized by intense rock dissolution. More than 1,000 karst caves of various sizes were discovered during the exploration phase, requiring the shield excavation process to be conducted with extreme caution, akin to mine clearance operations.
On January 18, 2019, the large-diameter slurry shield TBM “Haihong”, specially designed for the project, was put into operation after in-depth research and meticulous investigation. On January 10, 2021, the Super Undersea Engineering Project achieved a successful breakthrough, completing the tunnel excavation through marine karst geology ahead of schedule by over 240 days. This accomplishment sets a new domestic record in the field and represents a milestone achievement in tackling the global technical challenge of tunnelling through such formations with large-diameter shield machines. Consequently, the project was awarded the most prestigious international prize in the tunnelling industry for the year 2021 – the ITA Tunnelling Award.
On June 20, 2022, Dalian Metro Line 5 achieved full tunnelling breakthrough. In September of the same year, all 18 stations along the line were capped. On October 8, the track laying of the line was completed. On November 28, the line passed the comprehensive acceptance testing. On December 1, the line underwent an unload trial run. Finally, on March 17, 2023, Dalian Metro Line 5 was officially opened for commercial operation.