Ground- and surface water management and utility provisions throughout an open pit mine require attention and thorough planning in order not to coincide with the mining activities themselves. Trenches, ditches, and sloped surfaces are used to direct ground- and or surface water over sometimes long distances to sumps from where the water is pumped out of the mining and or hauling areas. The mixed usage (e.g. combination of haul road and drainage function) of some of these sloped surfaces require constant attention and regular maintenance.
Surface exposed Utilities are in most cases either overhead on poles or laying on the surface and are occasionally buried at area’s where the utilities are crossing haul roads and or other obstructions.
Expanding the mine in many cases implicate the need to re-position the water management provisions and the routing of utilities requiring planning, time, labor, and impacting the mining operation and productivity.
Utility installations for common civil use have transformed from overhead to underground installations. And open-trench installation methods have changed into trenchless installation where the utility is installed underground by usage of Horizontal Directional Drills and Augerbore machines. This not only applies for electrical power supply cables but also for telecommunications (optical fibre) and larger utilities like gas, water, drainage and sewer pipes.
Subsurface mechanical boring techniques for installation of utilities were developed multiple decades ago with different techniques for different applications in both soil and rock, and even in hard rock conditions. The flexibility and capabilities of these drilling techniques makes them specifically suited for some of the challenges in open pit mining.
One of these techniques is Horizontal Directional Drilling or HDD. With this technology a hole can be drilled from an entry pit at any location in the mine towards an exit pit with three-dimensional control of the drilling path. The hole diameter can be enlarged to any size to fit cables, conduits and pipes for fluid transport or perforated pipes for drainage purposes, with pipe materials ranging from high pressure polyethylene (HDPE) all the way up to steel and cast iron. The drill fluids used in HDD are lubricating the drilling tools, stabilizing the boreholes, and are transporting the cuttings out of the borehole.
Image: VERMEER Horizontal Directional Drill
A variety of HDD machines, cutting tools and drilling methods are available to cope with specific underground conditions and challenges. For softer rock conditions Dual Rod drilling machines or single rod units with a mud-motor (a drill-fluid driven motor driving a tri-cone bit) are available in various capacity ranges. Air pressure powered HDD percussion hammers can be deployed in very hard rock conditions. Installation capabilities of the equipment are depending on the size of machine and the underground conditions and can go up to 2 kilometers in distance, and 1.5 meters in diameter.
Image: VERMEER Auger Boring Machine.
For short distances of large diameter holes where a high accuracy on-grade installation is required, auger boring could be used. This drilling technique uses dirt bits, rock roller cones or polycrystalline bits to drill through the formations. The rock chips are being removed by means of an auger moving inside a steel casing pipe. Cuttings are transported back towards the Auger boring machine from where it is excavated out of the entry pit.
The use and flexibility of abovementioned underground drilling techniques can help in addressing the challenges related to utility installation and water management in open pit mines without disturbing the mining activities during and upon the installation.
For more information:
Vermeer Equipment Suppliers (PTY) Ltd
T: +27 (11) 6080893