Underpinning method enables a memorable feat of engineering for upmarket Cape Town mixed-use building
“The Docklands development marks a significant paradigm shift in what is possible and achievable in terms of structural engineering in South Africa,”Jaco de Villiers, Aurecon Technical Director.
Situated in the scenic De Waterkant in Cape Town’s sought-after Prestwich Street and located less than 200 m from the V&A Waterfront Marina, The Docklands is a nine-level, mixed-use building that consists of 200 m² retail space, 134 apartments and 160 parking bays.
Aurecon was appointed as the structural engineer to help realise the client’s vision for an affordable, yet upmarket apartment building within walking distance of the prestigious Cape Town V&A Waterfront.
The site housed an existing office building with one level of semi-basement parking, ground floor parking and three levels of offices above that. The proposed new development required three levels of parking and six levels of apartments over the full footprint of the property.
Tight budget and time constraints meant a fast-track construction programme, which negated the option to build from scratch. To overcome this challenge, the project team came up with an innovative conceptual design that incorporated the existing building. Such a solution required an additional two basement levels to be constructed below the existing four-storey structure, while simultaneously constructing four levels above.
The project team’s technical prowess enabled them to design an innovative engineering solution that would enable the centre of the building to be kept in place, while excavating and constructing new basements below and adding new floors on top. It was achieved by implementing a novel ‘underpinning’ method, which included constructing new steel micropiles through existing foundations in a four-pile group arrangement per column and connecting the piles to the existing columns with transfer steel pods. The existing structure was then strengthened with steel additions to existing columns to enable new floors to be continuously added on top.
The next step involved carefully excavating additional basements around the newly installed piles. The pile groups had to be braced against slenderness effects during the restricted excavation work. Upon reaching the final excavation level, the team installed new pad foundations and columns under the existing columns. The steel bracing and piles then had to be removed while the topmost floor of the new building was completed.
The innovative underpinning solution, meticulous planning and collaboration of the project team, as well as finishing on time and within budget, were all contributing factors to the project being considered an immense success.
Construction commenced in September 2017 and was completed in March 2019, with the building ready for occupation by April 2019.
“The implementation of the underpinning method to enable the simultaneous construction of four levels above and two levels below the existing office building is one of those memorable feats of engineering. The luxury development is destined to become an iconic feature in De Waterkant with its cutting-edge architecture and hi-tech interior finishes – a modern new addition to Cape Town’s city skyline,” says Jaco de Villiers.
The project won a Consulting Engineers South Africa (CESA) AON Engineering Excellence Award in the category 'Projects with a value between R50 million and R250 million' in 2019.
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