Another milestone reached in HZMB construction

The 12-m final closure joint between the E29 and E30 immersed tubes was precisely docked by Zhenhua 30, the world's largest floating crane, on the 30-m-deep bed of the Lingding Sea on May 2.

The island-tunnel project comprises 33 immersed tubes and a final joint with total length of 5,664 m and design lifespan of 120 years. Each standard tube weighs almost 80,000 tons, is 180-m long, 37.95-m wide, and 11.40-m high. This is China's first immersed tunnel in the open sea, and the world's longest immersed road tunnel as well as the only deeply buried one of its kind, hailed as the "Mount Everest in transportation engineering."

Final closure joint docking site 

The E1 immersed tube connects the western and E33 with the eastern engineered islands of the bridge. The 5.6-km east-west tube is 40-m deep and began to be installed in May 2013.

The final closure joint is placed between the E29 and E30 tubes in a wedged shape forming by two symmetrical inverted right-trapezoid units. It adopts an elastic steel structure with an upper base of 12 m and lower of 9.6 m. The steelwork weighs 2,400 tons originally and becomes about 6,000 tons after concrete is poured. The entire precast installation construction technology is the first used in the field globally, and the steel-concrete-steel (SCS) sandwich immersed tunnel initiated a new construction method domestically.

The 12,000-ton floating crane hoists the last segment to dock underwater. [Photos by Li Jianshu / Zhuhai Daily]

"To lift a 6,000-ton jumbo segment touches on a new area of engineering that we've never delved in the past. A buoyancy weighing thousands of tons might affect the installation process. We added all the deviations to make it pass a tight margin of error of just 15 centimeters and send it to the ideal position," Lin Ming, the chief engineer of the management department for the island and tunnel project of the HKZM Bridge, was quoted by CCTVPlus as saying on May 2.

Until 6 pm on May 1, preparation work for the final joint docking had been completed. According to the project's general management department deputy general manager, Yin Haiqing, the docking started at 5:53 am, and the joints will be welded together after davit arm rotation, submergence, implantation, precision adjustment, girder pushing, drainage, and holing-through survey in more than a dozen of days.