Bachy Soletanche Group Limited (BSGL) was awarded the major part of the foundation contract works of the new iconic project – New Central Harbourfront Site 3 by Vibro (H.K.) Ltd with Henderson Land Development Company Limited, one of the prime listed property developers in Hong Kong, being the Client.
The project proposal is based on an idea of “a bridge” and aims to present to the world a new world-class iconic landmark of Hong Kong. The development comprises three buildings with panoramic views and a huge Public Open Space with much greenery as an urban forest. The building closest to the Victoria Harbour will be multi-functional while the other two will be prime A offices.
The contract works awarded to BSGL includes over 853 m diaphragm wall in 1.2 m long and 1.5 m thickness, 31 numbers of large diameter bored piles, low headroom interlocking pipe pile wall and grouting works, all by the end of 2023. Under the tight schedule, other activities to be carried out in parallel by two other contractors and site constraints encountered, it will be a challenging project for BSGL to race against time.
There are a few site constraints in the project including sensitive ground settlement control due to the presence of live MTR (Mass Transit Railway) railway structure, Central Wanchai Bypass tunnels, footbridge with high pedestrian flow and existing seawall structure in the vicinity, congested working environment, concurrent foundation construction activities with other contractors, utilities obstructions and restricted low headroom working conditions.
Meanwhile on site, teams are busy with slurry wall construction and grouting pretreatment to former existing seawall layer and high permeability zone to avoid bentonite slurry leakage during diaphragm wall construction. At this stage, over 80% of casing grout works have been completed in stage 1 of the project.
Apart from that, to construct diaphragm wall under existing footbridge (6 m height), two low headroom clamshells and one low headroom hydrofraise HC-05 are deployed. The height restriction increase the difficulties by lengthening rebar cages lapping time than the usual 12m cage length. It involves the connection of over 12 cage elements for a typical 45 m deep panel. There are two low head room panels completed so far at this moment.
Working near either MTRC structure or Highway structures will require close monitoring on settlement and vibration, with stringent limit set within 4mm and 7.5mm/s respectively. This strict requirement imposes close control on the amount and magnitude of chiseling works allowed in diaphragm wall construction. After a chiseling trial demonstration, the client’s supervision team and MTRC’s representatives are both satisfied with the proposed chiseling method and associated controls and thus approve and allow chiseling to be conducted within the MTRC railway protection zone together with close monitoring alongside.