In February 2013 UEA Civil & Mining completed a successful trial for Alcoa using terrain levelling technology to construct a new haul road at their Bauxite mine in Western Australia.
The environmentally sensitive area of Dwellingup State Forest in Western Australia is home to the only remaining Jarrah forest in the world which has been under threat from the dieback pathogen, Phytophthora cinnamomi, for more than 80 years. It has become widespread due to the transportation of infested soil to uninfected areas.
Large areas of the forest remain free of dieback, including areas within Alcoa’s mining lease. Therefore it is one of Alcoa’s key environmental objectives to minimise the spread of dieback and construct all haul roads dieback free.
Top Soil, Overburden and Secondary Overburden Removal (SOBR)
After clearing the area where mining is planned the topsoil, overburden and secondary overburden are removed leaving the caprock exposed. The caprock is a solid concrete-like layer averaging about 1m thick with deep peaks and troughs. The cratered finish cannot be traversed by heavy equipment as it is too rugged even for track driven machines.
Once the SOBR is complete the area must be backfilled creating an even surface to allow the drill and blast team to easily travel over the area. Prior to the trial the standard process was to transport ore from another area of the mine which is then spread over the uneven caprock layer. Bauxite is used so that all of the remaining rock material can be mined after blasting.
Unfortunately this process requires the bauxite being used as backfill to be sourced from another section of the mine and hauled to the area under construction, requiring additional ancillary gear, as opposed to it being transported to the crusher for processing.
The purpose of the trial undertaken by UEA Civil & Mining was to make suitable dieback free material in situ to backfill the treacherously uneven caprock creating an area over which a drill rig could tram for the purposes of drill and blast; as well as preconditioning of the cap stone for later rehabilitation purposes once mining in the area has been completed.
Two machines were used – the Vermeer T1255 Terrain Leveller to cut the caprock and create the backfill; and the Cat 980G Wheel Loader to push the material into SOBR areas.
On the initial pass, the T1255 started on an area of dieback free “green material” cutting the backfill material in situ and creating a stable platform for the operator and the two machines to work on as it progressed. Once the first lot of material has been produced and side cast the process became simpler on subsequent passes.
Working in tandem the two machines worked from the outside to the centre line. The T1255 terrain levelling attachment is a rotating ground engagement tool that uses an array of picks to break rock into 150mm down aggregate which the Cat 980G pushes forward along the SOBR area. The wheels on the loader assist in compacting the material in situ, which is followed by the sheer weight of the T1255 further compacting the backfill into place. This greatly assists the drilling process once complete.
This terrain levelling method proved ideal for both site preparation and haul road construction. No backfill material was brought into area, with all of the material created in situ and dieback free. The finished product which was likened to a “dance floor” created a smooth, level surface suitable for drill and blast operations.
The process using terrain levelling technology, and only two personnel, took a little longer than conventional methods, but this being the initial trial gains in productivity can easily be achieved on future projects.
Visit the photo gallery to view more images and see the haul road construction process step by step.
For more information about this project or UEA Civil & Mining,please send enquiries to Dominic Hallam.