Rocks to receive tomographic attention

A Virginia Tech researcher is attempting to give engineers the ability to scan rock for stresses with the same technology that physicians use to scan patients for medical problems.

With a $375,000 award from the National Science Foundation (NSF), a Virginia Tech researcher is attempting to give engineers the ability to scan rock for stresses and failures with the same technology that physicians use to scan the human body for medical problems.

Erik Westman, assistant professor of mining and minerals engineering (MinE) at Virginia Tech, has won a five-year NSF Faculty Early Career Development Program (CAREER) Award to develop a practical method for predicting failures in rock masses.

Westman is said to be adapting tomographic imaging – the same technology used in medical CAT scans – so that it can be used by engineers in the field to monitor redistribution of stresses within rock masses.

Tomographic imaging ‘looks inside’ a mass by transferring energy in the form of acoustic or seismic waves from one boundary to another. ‘In the case of rock mechanics,’ Westman explained, ‘the waves are transferred from one side of a rock mass to another or from a borehole to the interior of a mine.’

Tomographic imaging is a non-destructive testing method, similar to those already used on a limited scale by engineers to find stresses and predict failures in large structures such as aeroplane bodies, Westman said. ‘It’s more difficult to obtain useful images in rock, which is more massive and where changes in stress and material type occur naturally and frequently,’ he notes.

Scientists have done some testing of tomographic imaging on rocks in laboratory settings. Westman plans to advance the technology from the lab to the field, so that images of large rock masses can be successfully scanned.

‘NSF is interested in several applications for this technology, such as monitoring hazardous and nuclear waste repositories, dam and bridge abutments, and tunnels,’ Westman said. Tomographic imaging also could be used by mining engineers to detect potential rock bursts, which occur when pressure causes rock in underground mines to spontaneously explode. Another potential use is the periodic imaging of fault lines associated with earthquakes, to help geologists predict fault failure.

Westman’s CAREER project also has an educational component. ‘Right now,’ he said, ‘we can simulate the loading of a rock mass on a computer. This research will make it real. Our undergraduate and graduate students will be able to use images of real rock masses to study stresses and failures.’ In addition to employing the tomographic imaging in MinE courses in the future, Westman and colleagues at the University of Colorado at Boulder will create a website so that students at both schools can use the technology.

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