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Hong Kong Special Administrative Region of the People’s Republic of China
Three major cities in China – Hong Kong, Macau and Zhuhai – are connected by a series of bridges, tunnels, link roads, and boundary crossing facilities, providing a new direct link between the east and west banks of the Pearl River Delta for passenger and freight land transportation. At the expected cost of approximately $10.6 billion US dollars, the construction of the massive Hong Kong-Zhuhai-Macau Bridge project began in December 2009.
A major project component is the Hong Kong Boundary Crossing Facilities (HKBCF) that will serve as a transportation hub and provide clearance facilities for goods and passengers using the bridge. The HKBCF is located on a 150-hectare artificial island that was reclaimed from open waters just northeast of the Hong Kong International Airport. The landing points for the link roads and tunnels will utilize 20 hectares of the island. The remaining 130 hectares will be used for the HKBCF cargo, passenger, and vehicle inspection facilities; offices for the immigration, customs, and excise departments; road networks; and a public transport interchange and traffic control surveillance system.
The artificial island’s sea wall was built using a new, non-dredge approach. Large 30-meter-diameter steel caissons were dropped into the sea a few meters apart and joined by a flexible steel wall. As the mud was dug out from the middle, each 450-ton caisson drove itself down towards the hard strata. This new reclamation technique was used instead of the conventional approach of dredging out the soft mud down to the bedrock and replacing it with marine sand. Additional ground strengthening measures were also needed to help stabilize the island’s soft marine mud before constructing boundary crossing facilities and tunnel landing points. Trevi Hong Kong joined these stabilization efforts by installing jet grout columns in a key area of the island.
Stabilizing with Jet Grouting
Trevi Hong Kong installed 450 jet grout columns with diameters ranging from 1.2 meters to 3.0 meters to a depth up to 35 meters. The jet grouting was performed by drilling a hole to the required depth, followed by rotating and extracting the drill rod while simultaneously pumping high pressure fluid through nozzles at the foot of the drill string. A combination of air and cement grout slurry was injected as the breaking-up and consolidation agents, using the TREVIJET T1/S bi-fluid system.
The artificial island’s geological conditions challenged the stabilization efforts. The top ground layer of about 8.5 meters of sand fill is followed by approximately 18.5 meters of very soft marine mud. Trevi Hong Kong needed to penetrate through the soft sand fill and marine mud into at least 1 meter of the alluvium material that rests below.
