Piling at Harbour Arch

Developed by the Amdec Group, Cape Town’s Harbour Arch project – comprising six individual towers – is one of the largest mixed-use precincts delivered to date in the city. The towers’ establishment required an intricate geotechnical design, with the works executed by Keller, formerly known as Franki Africa.

The project comprised lateral support and foundation piles. The lateral support was essentially an 11 m deep triple basement, constructed by means of soldier piles, jet grout columns, anchors and gunite arches, with dewatering included in the scope of works.

“The foundation piles comprised largediameter, temporarily cased augered piles, which were socketed into hard rock,” explains Daryn Cloete, contracts engineer, Keller. The excavation consisted of loose sandy soils, stiff clays and hard rock material. In total, some 66 000 m³ of material was removed to spoil sites. Concrete obstructions and old foundation footings, as well as the relocation of services, presented major challenges and the resequencing of the works. This included the building of a cable tray capping beam on top of the lateral support piles to house the relocated services.

Additionally, on one section of the project site, the rock level was much deeper than envisaged and Keller had to install largediameter temporarily cased auger piles for the foundations.

“The jet grouting proved to be a winner with regard to sealing the basement against largescale water ingress. It was an important factor in the design of the project,” adds Cloete.

Apart from the basement's final level being below mean sea level, the Keller site team also had to contend with substantial groundwater in the excavations, which required dewatering. This water was pumped and filtered prior to removing it from site

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