ABSTRACT:

An intact rock specimen when subjected to uniaxial compression experiences multiple stages of deformation. This begins with the formation of micro-fractures at low stresses and subsequent transition into the development of a macroscopic failure plane at its ultimate strength. These fractures, when monitored through active ultrasonic signals, tend to act as low-pass filters that attenuate the waveforms. In present study, active seismic monitoring was conducted on Lyon’s Sandstone specimens while they were subjected to uniaxial compression. A Lab-view controlled seismic system with sampling frequency of 100 MHz was used to acquire seismic waveforms in real time. In the experiments, the effect of ultrasonic transducers on the seismic measurements was investigated using two different P-wave transducers. The transducers were coupled to the rock specimen at different locations along its axial length so that the wave transmission is normal to the major principal stress direction. Under the application of load, changes in seismic velocities and amplitude of the active signals with respect to the stress magnitudes were processed for characterization of crack initiation (CI) and crack damage (CD) stress thresholds. The possible mechanisms for seismic attenuation based on the friction dissipation model and displacement discontinuity model have also been put forward.

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