Stefanutti Stocks Geotechnical is applying its wealth of experience in the construction of deep piled foundations in Namibia, where it is installing 76 permanently cased, raked oscillator piles for river bridges.
The bridges are on the outskirts of Swakopmund and form part of the upgrade of the old salt road to a new highway between Swakopmund and Walvis Bay.
The required plant and equipment were mobilised from South Africa. This road trip took about a week, followed by a set up period of about two days when Stefanutti Stocks Geotechnical’s Bauer BG28 (with a BV1500 HD oscillator) and Kobelco Crawler Crane were set up and commissioned. These weigh in at just under 120 and 55 tons respectively!
The geology in the Namibian desert consists of sand, calcite, granite and boulders. All the deep pile foundations will have their sockets founded into the calcite and granite. However, to get to this rock, it was required in some cases to drill over thirty metres into the sand and through boulders, which tend to move when drilled, making drilling very difficult. “Permanently cased oscillator piling is only chosen in challenging geological conditions,” says Marcin Szatkowski, Stefanutti Stocks Geotechnical site agent. Drilling deep and through boulders poses various challenges – and the experience of the site team, most recently at the rail-over-road bridge in Saldanha and river bridges at Soweto Bridge and Bushbuckridge, means they are aware and prepared to deal with conditions in terms of the methodology required to complete the piles. “The majority of the piles are not vertical – they are at 9.5 degrees due to moments imposed on the bridge. This means that on a 35-metre pile, the distance from the original pegged platform position down to the toe of the pile, is almost six metres away from the horizontal.”
The bridge will cross the Swakop river, which may look dry on the surface, however, water is encountered about two metres below the dry river bed. This is also an environmentally sensitive area, thus great care needs to be taken to protect the environment.
“Materials for the project are mainly sourced from local manufacturers, and the quality of the concrete ready-mix suppliers here are on par with South African suppliers – if not better,” says Szatkowski, who has been pleasantly surprised by the level of management involvement by suppliers, who constantly visit the site to make sure their product conforms to standards.
Stefanutti Stocks Geotechnical is currently working day and night on this project, to optimise the utilisation of its equipment and as at May 2018 the contract that commenced in October 2017, is at 50 per cent completion.
Source: Marcin Szatkowski, Stefanutti Stocks Geotechnical site agent