By ashleykaren
Bachy Soletanche has been granted a prominent part of the foundations’ contract for a new development site by Hong Kong’s harbor.
The Central Harbourfront Site 3 project includes a multi-functional structure nearest to Victoria Harbor and two office buildings that will be linked by a platform at the roof level, as well as public open space.
The contract contains building over 853m of diaphragm wall, which is 1.2m in length and 1.5m in thickness. Also, it comprises the installation of 31 large-diameter bored piles, a low headroom interlocking pipe pile wall installation, and grouting works.
As predicted, the work should be complete by the end of 2023. Two other contractors will carry out simultaneous foundation construction activities.
Bachy Soletanche stated that the compressed program caused a problem for the project team, which will have to “race against time” to complete the works.
Another challenge for the team will be the diverse site conditions on the project. This contains sensitive ground settlement control because of the presence of live Mass Transit Railway (MTR) structures, the Central Wanchai Bypass tunnels, a footbridge with a high pedestrian flow and an existing seawall structure in the vicinity.
Other site restrictions are a crowded working environment, utility obstructions, and limited low-headroom working conditions.
Already, teams have begun construction on the slurry wall on site and are executing grouting pretreatment to the ex-existing seawall layer and high permeability zone to prevent bentonite slurry leakage during diaphragm wall construction. In stage one of the project, over 80% of the casing grout works have been accomplished.
For building the diaphragm wall beneath the current 6m high footbridge, two low-headroom clamshells and one low-headroom Hydrofraise HC-05 will be utilized. The height constraint boosts the difficulties as it means that the rebar cages have to be longer than the usual 12m length. The wall’s construction will include the connection of more than 12 cage elements for a typical 45m deep panel. Also, two low headroom panels have so far been completed.
Working around either highway structures or MTR structures will need close monitoring of settlement and vibrations, with a strict limit set within 4mm and 7.5mm/s respectively. This stringent requirement imposes close control on the amount and magnitude of chiseling works authorized in diaphragm wall construction.
After a chiseling trial demonstration, the client’s supervision team and MTR’s representatives were pleased with the proposed chiseling method and relative controls. intrinsically, they agreed the chiseling to be executed within the MTR railway protection zone, with close monitoring alongside.
