Underground drilling and blasting can be costly when it goes wrong.
However, mines can optimise the performance of drill and blast patterns by using the latest surveying and in-hole data capture technology along with a formal quality control procedure.
Underground drilling and blasting equipment is getting more sophisticated in the underground environment, with remote monitoring and automated technology.
However, human error in underground drilling and blasting patterns is still a factor that can increase costs dramatically, according to AVKO Mining operations manager Steve Durkin.
Durkin says understanding mistakes in underground drilling and blasting operations can optimise productivity and reduce costs.
“Accuracy with top hammer drills is dependent on geology and operator skill, and when things do not go to plan, and strict quality control procedures are not in place, it is difficult to define what caused the poor result,” Durkin told Australian Mining.
“Mistakes in underground drilling and blasting patterns mean poor blast results, poor fragmentation, and loss of resource,” he said.
“Mines can chieve more with long term planning in contract negotiations.”
Durkin says the end result of an underground drilling and blasting operation is dependant on quality control.
“Mining companies are constantly pushing the boundaries of stope size at their operations to reduce the cost per tonne impact of access and ore drive development. This means stope drilling holes are getting longer,” Durkin said.
“Accuracy with top hammer drills is dependent on geology and operator skill,” Durkin said.
“Drilling performance is dependent on ground conditions, hole dimensions, and rig capacity. However, there can be up to 20% difference in metres at the end of shift,” he said.
“More importantly, experienced and skilled operators can reduce maintenance costs by orders of magnitude over inexperienced or ‘rough’ operators.”
Durkin said benefits could be gained by a change in mining practice in underground drilling and blasting.
“The most common practice now is for a geologist to provide a mining engineer with a stope block in three dimensions,” Durkin said.
“The mining engineer then designs the drilling and firing pattern based on straight holes. The drill operator then drills the required holes, which are charged to the design and fired,” he said.
“There are no questions asked when everything goes to plan and break out goes to design. But when t he pattern bridges, or worse, it is often too late to investigate the true reason for the bridge,” he said.
Operators are left to make assumptions about the cause of failed blasts.
“The end result of such an investigation will invariably be that holes were not drilled straight or charging was not done to plan. These assumptions may well be right, in any case the blame is not placed on the design, so the same design will be used again and the shift bosses and foremen will be asked to keep a closer eye on the drilling and charging process,” Durkin said.
If the same thing happens again, the tendency will be to re-design the drilling pattern to give more contingency, according to Durkin.
“This may be the right thing if the design was a bit optimistic,” he said.
“However, if the problem is with drilling or charging accuracy, changes will only increase the cost per tonne.”
“If the process involves a high-level of quality control, the drilling, for example, should be in-hole surveyed, especially for long-hole rises and the initial slot-opening rings.”
“By conducting in-hole surveying, the mining engineer will have an accurate 3D plan of blast-hole location in relation to any relief void.”
The charging planner can take the information gained from this stage and show charge-up personnel why holes are being charged in a certain pattern.
“The quality control process should then carry on to the charging process with regular assessments, as charged plans should take into account problems encountered while charging. This may include wet holes, voids, and over-charged or under-charged holes,” Durkin said.
Mining is not always an exact science and sometimes problems will be encountered.
“The investigation into why an adverse event occurred will provide much more useful information on how to stop it from happening again with this high level of quality control,” Durkin said.