Macmahon and Herrenknecht have collaborated to design the largest raise drill in the world. It allows larger, deeper shafts to be drilled in a single pass and is currently deployed to BHPB’s Olympic Dam in South Australia. The RBR900VF, or the ‘big rig’ as Macmahon calls it, “offers clients raise drilling options previously beyond the operational capacities of any machine in the world,” Rob Barker, Macmahon’s Group General Manager – Market Development, told the audience at the Mining Indaba in Cape Town last month. “The ability to drill longer holes in a single pass will avoid costly mid-level development that is currently required with existing machines.”
The big rig can drill up to 2,000 m depth, with diameters between 3 and 8 m. It has been designed and manufactured with proven technology and componentry from Herrenknecht tunnel boring machines (TBMs). “This provides certainty of reliability, as already demonstrated at Olympic Dam whereby the inaugural hole was completed ahead of schedule.”
The rig is relatively compact and is track mounted for easy mobility and fast setup. It has also been designed to fit underground in order to drill level to level. The rods have also been specifically designed to reduce the size of the chamber required when working underground.
The rig is highly automated, being transported to the work site by a diesel hydraulic, self propelled transporter. Jacking legs lift the machine clear of the transporter and lower it onto the surface. The automated procedure means that no manual handling is required to complete the task, lowering the risk of injury during installation of the rig. Once the rig is in position, the transport frame is removed and power packs and rod feeder are moved into place.
The rig features one of “the most significant development in raise drilling practices, and that is the fully automated loading and unloading of drill rods,” Barker said. “Prior to the big rig, on most other raise drills, rods are manually rolled down the rod rack and into place for a ‘rod loader’ to feed the drill head. Rolling of rods is typically an area where safety hazard are present, due to the weight of the rods, and the pinch points surrounding them.
“The drill rods on the big rig are made from vanadium modified steel, heat treated for increased strength of up to 15% over other rods. This is required to reduce breakages and increase safety when drilling with such heavy gear, to such great depths.
“Once the pilot hole is drilled, the reamer head is attached underground inside the drive, and is raised toward the surface. The reamer is pulled back through the rock at between 6 and 10m advance per day.
“The reamer head is pulled all the way to the surface until it breaks through the concrete foundation. When it reaches the top, it is secured by slings so the rods can be disconnected, while the reamer is suspended at the top of the hole. The reamer then needs to be lifted out of the hole.”