Barangaroo South harbourside basement, Australia, challenges and solutions

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Barangaroo South is a major mixed use development located at the southern end of the Barangaroo development project in Sydney, Australia (Wong et al., 2013). It is located on Sydney’s Central Business District waterfront on the foreshore of Darling

Harbour as shown in Figure 1, and has a site area of over 7.5 ha. The vision of the developer for the project, Lend Lease, is that Barangaroo South will enhance Sydney’s position as an inter- nationally appealing, globally competitive and environmentally sustainable city. The development will be Australia’s first large- scale carbon dioxide neutral precinct.

Located on the southern third of the 22 ha Barangaroo site, stage 1A of Barangaroo South will feature three commercial towers ranging in height from 39 to 49 storeys, sharing a common, two- level basement to be retained around its perimeter by an approximately 770 m long diaphragm wall, socketed into Sydney sandstone. As the basement excavation will be below sea level, it is essential that the site retention wall for the basement also acts as a cut-off against groundwater ingress. This had to be consid- ered when designing the reinforcement and the temporary ground anchor support required prior to construction of the permanent floor slabs.

A number of challenges had to be overcome during the design and construction of the diaphragm wall, including difficulties associated with old harbour walls and buried wharf structures, steeply dipping rock levels and buried cliff lines, accommodating the proposed future Sydney Metro tunnels, the close proximity of existing building basements, as well as complex bulk excavation staging. Stringent wall deflection and settlement criteria needed to be met, as well as the need to consider seismic events and sea level rise due to climate change.

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