Multiplex Zhuhai Link under Gongbei Port ready to go

The sometimes two-level Gongbei Tunnel from the Hong Kong-Zhuhai-Macao Bridge West Island to the Maoshengwei Zhuhai-Macao Cross Border Industrial Zone was completed on Feb 24.

A challenge arguably even more daunting than the Bay Bridge islands-tunnel-spans project itself, the submerged and subterranean passage was accomplished using a five-story boring machine. But the loose soil and silt under water, roads, and building foundations had to be frozen first to keep things from collapsing. Large-diameter steel pipes were placed in a circle around the tunnel opening in advance and freezing tubes inserted to harden the unstable soil.

To ensure no interruptions to customs clearance at Gongbei Port, an innovative long-distance curved pipe roof with soil-freezing method was adopted to safely construct the double-deck six-lane tunnel under the port.

Above/below sea Gongbei Tunnel

The area of excavation cross-section is up to 337 sq m (403 sq yd), which is around the size of a basketball court. The pipe roof around the tunnel is composed of 36 steel pipes with a length of 257 m (281 yds) and diameter of 1,620 mm (64 inches) at intervals of about 356 mm (14 inches). 

Technical challenges included controlling the jacking precision of the long pipe roof group, guaranteeing precise thickness of long horizontal soil freezing, and controlling ground surface deformation of the underground excavation section.

So, today the Gongbei Tunnel forms the Zhuhai HZMB link line and the world's longest bi-section/level highway tunnel, according to its operator, China Railway Construction Corp Ltd.

With a length of 2,741 m (1.7 miles), it is a record-breaking engineering feat. The below-ground and underwater segments run parallel at first and then overlap before diverting again due to topographical and environmental constraints.

Starting point of Gongbei Tunnel

The largest cross-section is more than 20 m (22 yd) in height -- equivalent to a seven- or eight-story building, said Pan Jianli, project head of China Railway 18 Bureau Group.

Construction began five years ago on the only passage connecting the bridge's main body with Zhuhai. Its completion marks a breakthrough in key construction technologies.

Located in an urban area, the tunnel is situated close to Macao. Preserving waterside scenery, preventing noise, and dealing with sensitive soil imposed higher requirements regarding landscape design and construction than that of an ordinary highway.

The Zhuhai Link, as the sole connection to the HZMB from the Chinese mainland (excepting Macao), is a major impetus for the harmony and connectivity of the Guangdong-Hong Kong-Macao Greater Bay Area.

Multifaceted Gongbei Tunnel [Photos courtesy nanfangplus]