Truck and loader productivity is a significant part of all large open cut mining operations. It typically accounts for 60% of the total mining costs. When rock is blasted, the resulting fragmentation size distribution produced has a significant effect on all further downstream processes, especially loader and truck productivity in the loading and hauling phases of the mining operation.
Typically optimum drill and blast designs have considered only getting the rock to a manageable size for the trucks and loaders. Provided this objective was fulfilled, the aim was then to minimise both drilling and explosives costs. There is becoming an increasing awareness that blast designs now need to take into account the subsequent downstream effect on loading and hauling productivity, as well as the effect on the crushing, grinding and refining processes.
The objective of this thesis project was to determine the impact of fragmentation on truck and loader productivity at the Porgera mine. This was achieved by collecting field data on blast fragmentation, loader productivity and truck productivity from site and then analysing for trends. Scale model testing was also carried out at the JKRMC to further understand the relationship between fill factor and fragmentation size distribution characteristics.
The resulting size distribution of a muck-pile after blasting affects loader and truck productivity in two main aspects:
2. Fill Factor
Digability is the ease at which at a loader bucket is filled. Digability can be increased by a number of factors, such as loader type, operator skill and loading strategy, however the most significant factor contributing to digability is the size of the fragments being dug. Increasing fragmentation leads to increased digability. Fill factor refers to how well a container such as a loader bucket or truck tray is filled. Fill factor is directly related to the size distribution of the rock being loaded.
It was found that increasing the fragmentation at the Porgera mine through blast design and properties of explosives used, had a significantly positive effect on truck and loader productivity. Through increasing fragmentation over a series of 3 trial blasts, truck payload was increased by 10% and loader dig time was decreased by 36%. Both of these positive production increases led to an overall productivity increase in the loading and hauling phases of mining of 12%.
Scale model testing carried out at the JKRMC found that the uniformity coefficient characteristic of the Rosin Rammler size distribution curve, has much more effect on fill factor than the X50. A decrease of the uniformity coefficient from 1.5 to 0.5 increased fill factor by 15%. This result was further supported by the field results in which the uniformity coefficient was decrease from 0.91 to 0.78 for a 10 % increase in the truck payload.