THRILLS AND DRILLS The main purpose of this drilling programme is to obtain sufficient geotechnical data for optimisation of the north and south pits
Chemicals manufacturer Foskor awarded drilling contractor Geomech Africa a contract to conduct geotechnical drilling at the Foskor Mining Division in Limpopo in July, with completion set for October.
The project is meant to obtain sufficient geotechnical data for optimisation of the north and south pits.
The drilling programme is expected to last three months and the team is currently a couple of days ahead of schedule, explains Foskor chief rock engineer Nkosi Nene.
A geotechnical risk assessment of the north and south pyroxenite pits was carried out in 2010. At the time it was concluded that several orientated geotechnical boreholes should be drilled to identify the continuity of the rock.
The ongoing drill programme entails drilling two and five holes in the north and south pit, respectively. The holes, range from 300 m to 500 m deep.
Additionally, downhole surveys are completed at the end of each day to ensure that the direction of the holes does not deviate by more than 2º from the required angle –70º.
Further, structural identifications and their respective orientations, are measured by means of optical and acoustic televiewer.
“There are instances where the upper sections of the rock mass are highly fractured making the drilling and identification of strata more complex.
“The holes had to be grouted in places to allow the drill to pass through larger cracks and specific muds were used to assist in preventing the collapse of unstable strata into the borehole,” says Nene.
He notes that Geomech Africa drilling supervisor Kiewiet Mahlangu tested various scenarios and their impact on the formations as the drill advanced until the correct balance was found. The final solution involved polymers such as Aus plug, CR650 and bentonite.