In 2007, WA Surface Mining conducted a trial of a surface miner on location at the Macmahon Mitchell Freeway construction site. The purpose of this trial was to ascertain the viability of using a surface miner in the excavation of limestone required for this important State project.
The surface miner trial was conducted in an area already in the process of being excavated by traditional methods. A rate of between 7000 and 8000 tonnes was being achieved during a 10-hour shift using current operations. The surface miner was set up to mill at a depth of 200mm and 2.2m wide. Six passes were completed at a length of 85m. The trial achieved a production rate of approximately 830 tonnes per hour.
The surface miner was also placed into an area known to contain harder limestone that was difficult for the bulldozers to rip. The surface miner milled through this area at the same depth with no discernable change in production levels.
The limestone produced was of a much smaller and consistent grading than that produced using traditional mining methods. This limestone material could then be used as sub-base for diversion roads constructed during the course of the project. With a small amount of screening it is possible the limestone mined using surface miners can also be used in the actual carriageway construction. Both of these surface mining advantages will help decrease the amount of material that needs to be disposed off site and therefore significantly help reduce transport and base material costs.