Using the Vermeer T1255 Terrain Leveller UEA Civil & Mining has completed a successful trial for Alcoa, constructing a new “dieback free” haul road at their Bauxite mine site in the environmentally sensitive area of Dwellingup State Forest in Western Australia.
The dieback pathogen, Phytophthora cinnamomi, has been threatening the world’s last remaining jarrah forest for more than 80 years. 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.
After clearing an 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 secondary overburden removal (SOBR) is complete the area must be backfilled to create an even surface. 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. 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 as opposed to it being transported to the crusher for processing.
The purpose of the trial was to produce suitable dieback free material in situ to backfill the uneven caprock to create a new haul road over which a drill rig could tram for the purposes of drill and blast.
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.
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, which is followed by the sheer weight of the T1255 further compacting the backfill into place.
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.