f Frequency analysis of acoustic wavefield in rocks under stress

In this work we present the results of frequency analysis of acoustic wavefield excited in rock blocks under uniaxial compression. This work leads up to the important problem of massif stability control during mining, for example. The problem of localizing the zones of extreme mining stresses where the fracture process is more intensive is very actual for damage prediction in mines. In order to interpret the results of observations under mining conditions correctly one should study the relation between seismic signal parameters and physical process characteristics in detail. This work is aimed to investigate the acoustic wavefield frequency changes due to the changes of rock material properties under stress. We present two results of laboratory experiments: 1. Spectrum analysis of natural radiation induced by cracks during fracture process in rock samples (acoustic emission (AE) process). 2. Spectrum analysis of ultrasonic test signals (ultrasonic test was produced for attenuation measurements during the loading of the sample ). The experimental study of the crack-forming process in rocks was carried out in High Pressure Physics Institute of Russian Academy of Science. The blocks of marble and limestone with dimensions of 500 · 500 · 1000 mm were compressed along the longest axis by the unique 50 000-ton press [1]. We mounted the piezo-transducers on the sample surfaces to register the AE signals and the ultrasonic test signals. It is well known fact that the brittle fracture process in rocks is accompanied by elastic wave radiation (AE process). So the AE process is the analogy to seismic activity in mines. Then we applied cross-spectrum and coherence function analysis, and median frequency analysis to the full waveforms of recorded signals.