The Gongbei Tunnel of the Hong Kong-Zhuhai-Macao (HZM) Bridge Zhuhai link line reached the key sprint stage on April 3 toward opening the span by the end of this year.

The record-breaking 2,741-m tunnel with six dual lanes is the only passage linking the bridge main body with Zhuhai. It encompasses three distinct tunnel sections connecting the Gongbei Checkpoint region with land and two engineered islands.

Innovative technologies have been applied to construction of what may be the most difficult tunnel to build in the world. 

One of the technologies is the creation of hard frozen soil for digging a 255-m underground section to prevent it from sinking into a water-rich layer of sandy soil, reported CCTV Plus.

Gongbei Tunnel [Photo courtesy CCTV 13]

Before excavation, the underground structure was reinforced with 36 special steel pipes that have freezing function within a length of 255 m and diameter of 1.63 m.

By hard-freezing moist sandy soil around the pipes, engineers could safely carry out excavation.

The landmark structure on the Pearl River Estuary took shape when the first floor of the three-story West Artificial Island's main body was capped on March 31.

With floor space of 20,000 sq m, the structure is of fabricated construction and fair-faced concrete finishes. The first floor incorporates fair-faced concrete columns, beams, and cantilever slabs.

According to the design, architectures on the two islands share resemblance in the shape, both including a main structure, square and ring road. Nonetheless, different functions are formulated for buildings on each island.

First floor of main body of West Island capped on March 31 [Photo courtesy southcn.com]

An integrated operation center for transportation, management, service, rescue, and sightseeing is planned on East Island. On the other hand, the main structure of West Island will mainly encompass offices, monitoring room, and living quarters featuring administration of the immersed tubes, office facilities, and sightseeing services.