South African company Franki Africa (a Keller company) is currently involved in constructing the foundations for a further expansion at Olkaria, the largest geothermal power station of its kind in Africa.
Franki were recently appointed to design, install and test the pile foundations for Unit 6, which is the latest addition to the ongoing expansion to the Olkaria I geothermal power station.
This latest expansion project (Unit 6) broke ground in December 2018, and piling commenced in May 2019. Unit 6 will add another 83.3 MW to the output capacity of Olkaria I, bringing the total output capacity of Olkaria I up to 274 MW.
A comprehensive geotechnical investigation was done on the site, and the results of this investigation formed an integral part of the foundation design. The Franki team was commissioned to provide a “design and construct” solution for the foundations. The in-house design team was able to use this valuable information to provide optimal foundation solutions to meet the stringent settlement criteria set down for the various structures.
The design included foundations for the turbine building, cooling tower, hot well, and scrubber areas. Initially a combination of two soil improvement techniques, (dynamic compaction and rigid inclusions) and a piled foundation were considered. After careful analysis and taking differential settlement into account, the team finally concluded piled foundations for all the structures would be the most suitable. The ground conditions were conducive to the CFA (Continuous Flight Auger) piling method.
The 600 mm Ø CFA piles were designed to withstand loads of up to 1 200 kN, installed to depths of up to 15 m.