Using wave attenuation techniques for monitoring of stress levels

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Virginia Tech

Stress can have a significant effect on the stability of pillars. To get an accurate picture of pillar stability, information is needed not only on the initial stress magnitude and distribution but also on all subsequent stress changes.

Sonic methods have the potential to be among the fastest, most economical and least destructive means of stress measurement. Wave propagation velocity has long been applied to the investigation of the upper mantle and crust stress. Recently, it has also been applied to rock burst prediction and mine site investigations. Another parameter for investigating stress in rocks is the attenuation coefficient. Attenuation has been observed to be more sensitive to stress changes than wave velocity; however, the measurement of attenuation is more difficult than that of wave velocity.

In this study, the mechanism of sonic attenuation in rock is reviewed. Both the velocity and the attenuation of sound waves in five different rock types under various stress levels were examined in the laboratory. It was found that the relationship between the velocity ratio and stress and that between the attenuation ratio and stress, for a specific rock type, can be expressed by simplified second order polynomial equations.