Blast off with a better image

BLAST specialists are now in a position to define what they want in 3D image analysis software. Sarah Belfield writes

BEING able to quickly, safely and accurately acquire 3D spatial data is leading to the power to improve blast design and blast assessment.

But, according to CSIRO’s George Poropat, the successful adoption of 3D imaging for these sorts of productivity improvements now depended on practicalities such as what features software should carry to allow mining operations put their captured data to work.

The rapid evolution of 3D imaging in recent years meant the ability to produce 3D images containing embedded spatial data was no longer the question, Poropat said.

“We can create 3D images from a few square metres up to thousands of square metres,” he told delegates at a recent conference on drilling and blasting productivity.

“We’ve created 3D images of people’s faces, we’ve created images of six square kilometres from an aircraft. That’s the sort of scales we can work over. So the process of creating them is not really the issue.”

Spurring on advances in 3D imaging capabilities were the drawbacks of traditional, manual methods of characterising rockmass, which were quite slow and costly.

It was now possible to map rockmass structures “a hell of a lot faster” than manual methods, he said.

Poropot described a case where two mappers sent to Malaysia were able to map around 1700 structures in five days using 3D imaging. Previously, it had taken about six man-weeks to manually map some 1400 similar structures. Not only had the manual process taken longer to complete — and therefore had been more costly — but it also led to a major set of structures being under-represented.

But while 3D imaging was rapidly becoming a simple point-and-click exercise, “the applications then depend on the ability to deliver robust software that uses the 3D image data to add value to an operation”, Poropat said.

“Once you’ve created the 3D image you then have to have some tools to get data out of there, otherwise it’s just a curiosity, something you can turn around on a computer screen and say ‘Look, gee whiz, it’s three dimensional.’

“You’ve also got to be able to take that data into your [mine planning] systems.”

One area of planning that would benefit from smart use of 3D imaging was blast design.

If rockmass structure could be better characterised, blast simulations would improve because models of how the rock will behave during blasting will be more accurate.

Exercises becoming possible included the mapping of planes on rockmass surfaces, and the mapping of linear traces to planes. The fitting of planes to traces was on the cards, as was being able to identify dominant joint sets in a statistically reliable way.

The interaction of joint planes was a promising application, where structures mapped at the surface via a 3D image were ‘grown’ back into the rockmass to see whether the presence of a wedge was likely.

“What we’ve done now is developed software which will automatically identify when a wedge is free to move, meets certain criteria and thus becomes [classifiable as] a hazard,” Poropat said.

This was possible because software could now handle the geological reality that joint planes stopped short when encountering other joint planes. Older packages didn’t honour that rule and allowed joints to pass through each other.

That simple development allowed the modelling of very complex rockmass structures.

“The software’s now been developed to the stage where it will now identify the existence of blocks right through the whole rockmass. That’s the first stage to giving you in situ block-size distribution [which is] potentially a really important parameter in terms of feeding it into blast modelling.”

Poropat showed an example: a model of a stack of five hypothetical benches. The benches contained rockmass shapes derived from joint measurements obtained via 3D imaging.

He said it was now possible to map the residual jointing in each block to see what might happen if the benches were under stress. Referring to a colour-coded display of the modelled benches, he said: “The blocks that it shows there, the red ones, they’re all free to move out of the face. The green blocks behind are all blocks that may come loose when the front ones move out. So it’s a very powerful technique.”

Blast assessment was also in line for improvement leaps thanks to 3D images. The measurement of swell, heave, fragmentation and ore dilution was similarly light years ahead of manual methods. According to Poropat, the most important thing about using 3D images to assess how blasts perform was being able to feed those results back into blast design processes.

The impression Poropat left delegates with was that the ball was now in the blast specialist’s court. The question he posed was ‘What are the software tools that need to back up 3D imaging to make the practice of blasting better?’

George Poropat

CSIRO Exploration and Mining

07 3327 4425 or

07 3327 4444

George.Poropat@csiro.au

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