Using the new PRA-Sline rock augering system, provided by Stratum Drilling Solutions, Keller UK is drilling through hard sandstone to install piling to support the mining head gear at the £3.2bn Woodsmith Mine, near Whitby, North Yorkshire.
A new Hutte 207 rig is installing six 750mm diameter cased and bored piles to 20m depth below the piling platform, all this working at 46m below ground level.
“We wouldn’t have been able to carry out this job without these augers and the Hutte 207,” says Shaun Davison, Keller’s general manager for piling and rail.
“The rock augering system is being used rather than down the hole hammer (DTHH) techniques. This has allowed us to get the job done, along with a combination of good planning, plant, equipment and personnel.”
“We knew the rock strata was quite hard due to previously working within the mine shaft. Coupled with the fact that DTHH compressed air drilling wasn’t allowed in the shaft, we knew our rock augering systems would struggle and we needed to source an alternative. After months of researching the latest rock auguring technique the PRA-Sline stood out as the most efficient and reliable augers to use and this proved the case,” adds Davison.
“Working with two drilling crews on 12-hour shifts 24/7, drilling the bores took an average 20 hours to auger to depth. We were able to install all the piles to program.”
As well as working with Stratum Drilling Solutions, for the last six months, Keller has worked closely with engineers Arup, main contractor Careys Civil Engineering and mine owners Sirius Minerals to come up with the solution.
Woodsmith Mine is being developed by Sirius to extract Polyhalite for use as an agricultural fertilizer.
Sirius is in the process of sinking production and service shafts down to the potash deposits, which are located 1.5km below the earth’s surface. The production shaft is one of the deepest in Europe at 1,530m.
Diaphragm walls have been installed at the service shaft to ensure the passages are stable and waterproof and Keller has installed the piling. This will be bolted to the mining head gear which must be constructed underground for environmental reasons.
The mine also features a 37km (23-mile) tunnel which is currently under construction 360m below ground level which will transport the mined Polyhalite on conveyor belts to Sirius’ Wilton processing plant near the North Sea coast and onto the company’s Teesside harbor facility for export.