Innovative Blasting to Improve Mining Processes at Middlemount Coal

By T. Goswami(1), D. Gumbleton(2), C. Rosales(3)

Abstract

Middlemount Coal (MCPL) embarked on a ‘process improvement’ project earlier this year. The objective was to holistically approach all aspects of the mining operation and to systematically improve each underperforming activity to increase overall efficiency. These aspects included, among others, highwall stability, improving percentage cast, lifting machine productivity and coal recovery. Once improvements were realised, further innovative blasting techniques, such as Double Cast blasting, or through-seam blasting or even a combination of both could then be trialled in order to further reduce costs at the operation.

Many factors influence highwall stability.  These include the local geology, highwall geometry and the water saturation level.  However, these factors are in the realm of geology and geotechnical expertise that is generally outside the purview of a blasting engineer while an important secondary influence is the cumulative damage inflicted on the highwalls due to ongoing blasting events. To address this phenomenon, high resolution accelerometers (typically 0.5 Hz to > 10,000 Hz) were used to measure near field vibration on the highwall including the directionality of the vibration. Following this, any necessary changes were made to the blast delay sequence, primer locations and the maximum instantaneous charge (MIC) resulting in a marked improvement in the quality of the highwall.

Multi-point initiation techniques using electronic initiators combined with optimal excavation procedures have been successfully used to address an ongoing hard dig issue at the mine. It is well known that higher dig rates can be achieved by simply ensuring that the excavator bucket bite proceeds in the same direction as the blast initiation sequence e.g. as could be seen from the timing contours of an initiation design. Through application of these innovative multi-point initiation and timing designs we have increased the percentage cast, which has improved the dozer push and excavator dig rates.

A trial Double Cast blast has since been implemented at the site with mixed success. In this regard, the concept has proven to be sound and has the potential for providing additional cost savings. This requires thorough assessment of rock properties, coal seam mapping, 3D modelling and scheduling to make Double Cast and through-seam blasting a successful blasting practice at MCPL. In practice it is not possible to carry out sufficient full-scale blasting experiments to guarantee a statistically significant analysis of the results. However, by monitoring each blast and the effect on subsequent mining operations, enough measured data will eventually become available to provide solid evidence for the benefits and cost savings of implementing Double Cast and through seam blasting.

This work could not have been achieved in such a short timeframe without the high-level support of MCPL management and the cooperative working arrangements with the team of technically capable people.

1.     Tapan Goswami, Mining Consultant, Blast Outcome Services, 2 Glenridding Grove, Lakelands, NSW 2282, Australia.

2.     Daniel Gumbleton, Technical Services Superintendent, Middlemount Coal, PO Box 24 Middlemount QLD 4746, Australia.

3.     Cesar Rosales, D&B Engineer, Middlemount Coal, PO Box 24 Middlemount QLD 4746, Australia.