The first immersed tube of the Shenzhen-Zhongshan Corridor sea channel was moved from shallow to deep basin areas by the Niutou Island Immersed-Tube Prefabrication Factory on April 12.

Next, the 60,000-ton undersea tunnel section will undergo a second fitting-out as the last step before permanent placement in June. Niutou produced the tube using concrete inside a steel shell because a reinforced concrete structure could not carry the load of dual 100-kmph (62-mph) eight-lane roadways. The semi-finished steel shell -- 123.5 m (135 yd) long, 46 m (50 yd) wide, and 10.6 m (12 yd) high -- was manufactured by Guangzhou Shipyard International.

Workers move tube from shallow to deep basin area [Photo by Zhong Fan / Guanhai App]

The Niutou Island plant in Guishan Town on northeast Guishan Island of Zhuhai was also upgraded with "smart" systems. The facility previously prefabricated immersed tubes for dual six-lane roadways of the Hong Kong-Zhuhai-Macao Bridge (HZMB), according to Huang Wenhui, chief engineer of the Shenzhen-Zhongshan link project from CCCC Fourth Harbor Engineering.

Moreover, the project team conducted more than 400 experiments to make the self-flow concrete self-compact to remove air bubbles without vibration. It was the first high-liquidity concrete pouring on such a scale in the country.

Due to a limited construction period, the team designed 200 intelligent trolleys that cut the time required for the tubes to be moved 223 m (244 yd) from the concrete pouring site to shallow basin area. With the new technology, the task will take only three hours in the future.

Spanning 24 km (15 miles), the Shenzhen-Zhongshan link is another world-level complex after the HZMB that integrates bridge, island, and a 6,845-m (7,486-yd) tunnel consisting of 32 steel-shelled immersed tubes. Upon completion in 2024, it will be an important passage between eastern and western cities of the Pearl River Delta.