Construction World December 2017
Category B: Specialist Contractors or Suppliers
THE YACHT CLUB The Yacht club entails the construction of a multi-storeyed double basement development with multi-use space. This site is located in the reclaimed Foreshore area in Roggebaai and is situated on the Malmesbury Group formation. Due to Franki Africa’s experience in this complex area and good work relations with Amdec, Franki was their preferred contractor.
the laterally supported basement excavation to the building contractor and therefore the simplest and most cost-effective solution was installed. The environmental aspects are highly respected and adhered to as when working at extreme depths subterranean water courses are encountered. The water has to be controlled via pumping methods and it is therefore imperative that no contamination of the water is permitted. The ground conditions on site were highly and unpredictably variable with old rock filled docks and piers, and a shallow watertable. The complex nature of the material made the operations on site slightly harder than normal and required a meticulous and all-encompassing design approach. A north to south running sub-surface culvert was situated in the eastern portion of the site within the footprint of the lateral support and piling foundation works, so the designs had to be amended with the aim of accommodating this feature and maintaining its structural integrity while providing the necessary support system. The very demanding work schedule with limited time availability and the phased handover approach where a portion of the site was to be handed over to the building contractor so that the critical-path tower cores and basement sections could be started while Franki was still on site implied that the works had to be carefully planned and executed to perfection. To have successfully completed this project timeously, all operations were to run like clockwork. This was facilitated by the commendable professional companies who did all that was necessary to ensure that this could be done. • Company entering: Franki Afrika • Client: Amdec Property Developments • Contract value: R43-million • Start date: September 2016 • End date: March 2017 • Main contractor: Franki Afrika • Principal agent: Amdec Property Developments • Project manager: Amdec Property Developments • Quantity surveyor: De Leeuw CT • Consulting engineer: De Villiers Consulting PROJECT INFORMATION
The varying bedrock depth and quality resulted in an optimised piled foundation design selection comprising Driven Cast In-Situ (DCIS) Franki enlarged base piles, Oscillator and cased Auger Cast In-Situ piles from east to west respectively. The shallower bedrock region, along the western portion of the site, resulted in the lateral support design amendment to an anchored Rotapile system. The existing concrete culvert situated approximately 500 mm below FEL intersected the site, restricting the required toe-in depth of the soldier piles therefore altering the lateral support geometry and requiring additional restraint to nullify the confinement in that region. The foundation pile design was optimised by straddling the piles along the culvert with transfer beams designed to span across the culvert and effectively transmit the column loads to the foundation. The existing services in the south- eastern resulted in the alteration of lateral support design to anchored soldier piles with additional sacrificial CFA piles installed for a temporary raised working platform without interrupting the foundation piling works. Franki’s scope of work entailed design and installation of lateral support and foundation piles, and the excavation and disposal of approximately 65 000 m 3 of earthworks. The lateral support soldier piles were 400 mm diameter Continuous Flight Augers (CFAs) and 325 mm diameter Rotapiles tied back with a single row of
anchors and gunite arches. The anchors were carefully positioned and inclined to not intersect the canal. Considering the complex ground conditions, the site’s proximity to live canals, railway lines, existing services and neighbours’ sensitivity to noise; CFA and Rotapiles offered the most economical and least disruptive solution for the lateral support; with western portion with shallow bedrock amended to anchored Rotapiles. An optimum foundation piling design comprising Driven Cast In-Situ (DCIS) Franki enlarged base piles, Oscillator and cased Augered Cast In-Situ (ACIS) piles; from east to west respectively, was selected due to the change in bedrock depth and quality. The existing culvert restricted the toe-in depth of the soldier piles, altering the lateral support geometry and requiring additional restraint to nullify toe confinement. The foundation pile design was optimised by straddling the piles along the culvert and using beams to transfer the column loads to the foundations. The lateral support structure installed had to provide a safe environment during the earthworks and lateral support contract as well as for the duration that the building contractor would take to construct the basement structure. The fine balance between time, cost and safety was respected to ensure that the client benefited from the optimum solution. Speed during the construction phase would result in the earlier handover of
2 17 BEST PR O JECTS
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