Expert eye on stress management

A HIGHLY qualified geotechnical engineer with a leading Australian mining consultancy has emphasised the importance of ongoing rock stress modelling and measurement in ensuring the safe and effective operation of underground mines, and says technology and industry know-how in the area have come a long way in the past three decades.
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Installing stress measurement cells in an underground mine.

Staff Reporter

Coffey Mining principal consultant Rob Walton ranks as one of Australia’s – and possibly the world’s – foremost authorities on rock stress measurement, having managed or reviewed the results from stress measurement programs at more than 50 sites and lectured on the subject in many corners of the globe.

He also previously worked for the CSIRO’s geomechanics division, where he was involved with the development and use of equivalent material models and the application of numerical models to study the behaviour of mines and tunnels. He is credited with helping develop a worldwide market for Australian rock stress measurement instruments and other geotechnical instruments.

Changes Walton has seen in rock stress modelling and measurement in Australia have been largely positive, he says, contributing to a mining industry that today is much safer and more efficient overall.

“About 30 years ago, when many Australian mines were rapidly changing with the move from track to trackless mining, the move from cut and fill to long-hole open stoping and the introduction of improved ground support techniques, little measurement was carried out to assist in the design, operation and safety of the mines,” he said.

The wheels were set in motion when the CSIRO, Australian Coal Industry Research Laboratories and some large mining companies began researching and developing techniques for modelling and measurement in an effort to improve mine design and safety.

“After a few years, a general attitude developed that significant measurement of certain rock parameters, including physical rock properties, rock stress and deformation or displacement, ground support performance and acoustic emission rates, could tell mine managers what was required to efficiently and safely operate their mines,” Walton said.

“I’m pleased to say that over the past 25 years there has developed a more sensible attitude to the proper integration of modelling and measurement to assist mine design, operation and safety. This has been largely the result of better education of mine managers, mine planning and geotechnical engineers, and mine geologists.”

Significant advances had also been made with the methods of measurement and the instruments used, he said.

“I’m particularly enthusiastic about global rock mass monitoring techniques such as microseismic monitoring, new rock stress measurement techniques, new methods to measure the early strength of shotcrete and wireless measurement systems,” Walton said.

“Some of the new measurement technology is just fantastic, and we’ve come a long way since the 1970s when measurement in Australian mines was first recognised as critical to good mine design.”

As a modern example of where modelling and measurement was aiding in mine design, Walton highlighted Newcrest Mining’s approach at its Ridgeway gold mine in New South Wales. Ridgeway, a sub-level caving operation, is now about 1km deep, with mining at deeper levels planned.

Since underground production began at the site, three rock stress measurement programs have been undertaken to provide the necessary information for numerical modelling, which is carried out on a continuing basis by the mine’s geotechnical department.

Certain parameters are measured as mining progresses to provide information for back-analysis via the numerical models. These include rock properties, change in rock stress, rock displacement and microseismic event and location monitoring.

Newcrest said the process of modelling and associated measurement would continue for the life of the mine.

Australia’s Mining Monthly

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