The impact of broken rock behaviour on shovel dipper capacity, truck body design and tire life


Dr Tim Grain Joseph (President & Principal Engineer - JPi mine equipment), Mr Steven Duncan (Mining Engineer - PCS Potash), Mr Mark Curley (Research Associate - JPi mine equipment)

This paper outlines an alternative means of evaluating the behaviour of broken rock and soils relative to the capacity of truck bodies, shovel dippers and excavator buckets. Existing on-board haul truck suspension monitoring systems permit an evaluation of both incremental loading of a truck body and by association, the bucket payload achieved by load pass. An evaluation of material angle of repose permits the truck body payload capacity to be determined through a double integration process using a polar co-ordinate system, which then identifies the broken material or soil density and swell factor through knowing the bank density of the material. This knowledge in relation to a known bucket struck capacity, identifies the bucket fill factor. For a given truck body geometry, broken rock angle of repose and density; the load distribution affecting tire performance, measured as tonne-kilometre per hour (tkph) is evaluated and compared to the tire manufacturer recommended tkph limit. The results of the analysis performed here show that the truck body designs investigated indicate the design angle of repose and broken rock material density assumptions used do not permit the target load distribution, directly impacting tire performance, to be easily achieved. The analysis procedure developed then provides a means of refining truck body design to meet performance expectations specific for a broken rock or soil behaviour. A codicil to this work is that in the field, running surface conditions also have a compounding impact on tkph response, such that up to three times the anticipated tkph, due to a truck body payload centroid, may be experienced accelerating the loss of tire life. It is thus critical that mining operations associate such impacts to the level of diligence in haul road design and maintenance; thus reinforcing the parallel efforts made by truck body designers in accounting for such angle of repose and material density parameters as investigated here.