Technologies used to build an ultra-deep foundation pit in the coastal soft soil of Zhuhai are being viewed as a model for construction in the Guangdong-Hong Kong-Macao Greater Bay Area.

The foundation pit for the Shizimen Tunnel is the deepest and most challenging of its kind to be constructed in Zhuhai, the China Construction Third Engineering Bureau reported to peers at the construction site June 29. The Housing & Urban-Rural Planning & Construction Bureau concurred that methods used improve the technical level of construction of ultra-deep foundation pits in coastal soft soil and provide excellent references for later projects in the region.

The base plate of the 2,687-sq-m (3,214-sq-yd) shaft, which is 36 m (39 yd) deep underground, was cast June 23. The contractor had to overcome sludge with a thickness of 20 m (22 yd), a short distance of 10 m (11 yd) between the site and coastline, and abundant underground water that imposed high risks for construction.

Shizimen Tunnel shaft [Photo by Yu Pengfei & Liang Maoxing to Zhuhai Daily]

More than 40 steel reinforcement cages, which weigh up to 150 tons, depth of 58.8 m (64.3 yd), breadth of 6 m (6.6 yd), and thickness of 1.5 m (1.6 yd), were forged; and 530 cubic m of concrete was poured in the soft soil to ensure engineering quality, according to project manager Liu Shijie.

Spanning 2.8 km (1.7 miles) from north to south, the S-shaped dual four-lane tunnel will connect Hengqin Financial Island and the Zhuhai International Convention & Exhibition Center in Shizimen across the Maliuzhou Waterway. Currently, construction of the major structure is well underway, clearing the way for submarine tunneling shields to be used in October. A tunneling shield is box-like with shutters open for digging as it moves forward.

Upon completion by 2023, the project will alleviate traffic pressure on the Hengqin Bridge to the west and help to balance development between the north and south parts of the Shizimen Central Business District. It is also considered essential to the integration of Hengqin, Hongwan, Zhuhai Free Trade Zone, Wanzai, and Shizimen as a new urban center and Hong Kong-Zhuhai-Macao Bridge Economic Zone.