The Middlemount Coal Mine, 90km northeast of Emerald in Queensland, is an open cut operation owned by Middlemount Coal Pty Ltd – a 50-50 joint venture between Peabody Energy and Yancoal.
The mine produces mid-volatile PCI and low-phosphorous semi-hard coking coal for export markets via a truck and excavator strip mining process augmented by cast blasting and dozing.
Improving cast blast outcomes
In January 2014, Action Drill & Blast, which has been contracted at Middlemount since 2011, in conjunction with the client and engineering consultants, investigated means to improve the mine’s production cost efficiencies, particularly the cast-doze-dig process.
The improvement program focused on implementing tools and methods that would deliver reliable and efficient results for the best value, rather than simply using more explosives.
A key opportunity identified was the introduction of electronic initiation systems. The technology is particularly well suited to cast blasting projects where creating the muck pile profile to suit the digging fleet or eliminating the need to dig it all together, is just as important as the primary objective of fragmenting the rock.
One of the key advantages of electronics is their advanced timing capability making it possible to change the height of the pile and where the pile sits, by changing the timing between the holes. In turn, this gives much greater control over the blast energies and movement.
Electronics also get the most out of the explosive column, compared to older technology. By making the holes work together, rather than on their own, the same energy is used more effectively, without the need for extra explosives or holes.
Before launching the initiative, cast blasting at Middlemount was achieving cast to the final position of under 20 percent, versus an optimum outcome of over one-third of material to the final position.
Since the trial period in 2014, cast percentage has increased significantly.
While electronics were mainly introduced to improve cast blasting results at Middlemount, they have also been used for vibration control as the pit moved towards a major water pipeline serving a regional town.
With precise control over blast timing and vibration prediction functionality, the vibration levels can be predicted at various points, particularly sensitive ones. The blast timing can then be modified to protect those points, and the vibrations can be eliminated, mitigated or at least aimed in a direction where nothing of value needs protecting.
Because of the accuracy of the timing, the explosive energy releases at the exact time it was set to, with no unplanned spikes.
With this capability, the ADB team successfully fired within 100m of the pipeline with no damage caused.
Reducing the risk of misfires is another advantage the technology offers when operated by a skilled blast team. Because communication with the detonator is possible well before firing day, the Davey Electronic system can identify where a possible failure may occur allowing it to be corrected before the blast fires. One issue with traditional ‘one-way communication’ detonators is that a misfired explosive surrounded by fired explosives gives little visual indication from the surface that something has gone wrong. A misfired hole is often only discovered when unexpected large lumps of hard material or even the explosive itself is found.
The ADB Middlemount team celebrated another performance result in July when it hit a safety milestone after reaching 2,000 days LTI-free – a testament to the success of ADB’s best practice safety system, ActionSAFE.
As a result of the collaborative initiative to improve cast blasting, ADB’s ability to meet targets consistently, its commitment to continuous improvement and exceptional safety record, the team freed up a whole digger fleet for more productive work, contributing to increased mine production and cost efficiencies.
Action Drill & Blast has been providing an integrated drill and blast service at Middlemount since 2011. The company is responsible for managing all production drilling and blasting activities, equipment, labour, and associated maintenance, technical and HSET services. It works hand-in-hand with Middlemount’s management, operations and planning teams at all levels, from strategic planning, scheduling and optimisation initiatives down to blast-by-blast advice.