Construction World April 2019

COVER STORY

Installation of permanent liner into augered hole.

Working at the water's edge on the Eastern Tower to a depth of 52,6 m.

A magnificent bridge over the Okavango River in the Mohembo Village area which is being piled by Keller’s Franki Africa for main contractor Itinera/Cimolai JV, is a shining example of Franki’s diverse strengths. Here we focus on Franki’s renowned ability to deliver in remote and challenging environments. BRIDGING COMMUNITIES – FRANKI AFRICA’S EXPERTISE ON SHOW

T he bridge, which connects villages on the east of the river with the rest of the country, straddles the Mohembo East (Kauxwi) Ferry landing site with the Mohembo West (Shakawe) Ferry landing site. According to Devendra Lalbasanth, Franki senior Contracts Manager, the 1,2 km bridge, which consists of two towers for the Cable Stayed portion and 18 piers, requires 189 no. 1 200 diameter, permanently cased auger piles at an average of 35 m below platform level. Some of the piles required are being installed to a depth of 50 m. In terms of the ground conditions, the top 12 m consists of alluvial deposits underlain by soft rock, schists and gneisses – metamorphic rock developed from basement granites – and there were no surprises in this regard as the Botswana Roads Authority’s geotechnical investigation, prior to and post the award of the contract, was thorough. “More than thorough,” Lalbasanth says. “In excess of 100 boreholes were drilled and more than 700 rock-strength tests were completed. This was one of the most detailed geotechnical investigations we’ve ever seen.” Lalbasanth says that, on the face of it, the scope of works may sound like a fairly straightforward task in geotechnical terms but the nature of the site and the surrounding area, including roads and general access, were extremely challenging especially for

bringing in the specialised equipment that was required for the job. And it was no ordinary equipment that had to be transported to the site. It included a Liebherr 355 – one of the largest augering machines in Africa – two Casagrande B180s, a Bauer BG 18 and two Liebherr 845 service cranes. “Getting this equipment to site was certainly the greatest challenge facing the Franki team. For example, before this job the Liebherr 355 was doing rigid inclusions at Clairwood Logistics Park in Durban and we converted it to an auger configuration before transporting it to Mohembo, 1 500 km away,” Lalbasanth says. He adds that a huge debt is owed to abnormal load transport specialists Transcor Transportation for their efficiency and perhaps, above all, patience in the delivery of the equipment. “The trip from Durban to the site took 14 days!” As the geotechnical work takes place on both sides of the river, it was also challenging getting the plant across the river. “For this we must thank our clients, the main contractor, who provided us with a 150 t pontoon for the job.” To date Franki has completed 50% of its work. “We look forward to seeing this bridge completed. The design shows that it will be a magnificent structure with both towers literally towering over the landscape in the shape of elephant tusks. I thank all our team, the local residents in the Kauxwi and Shakawe areas, Transcor Transporters and our clients, Itinera/Cimolai JV, for their continued efforts in ensuring a successful contract,” Lalbasanth concluded.

Okavango River bridge, Botswana

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CONSTRUCTION WORLD APRIL 2019