SUBAUDIBLE NOISE DURING COMPRESSION OF ROCKS

Acoustical monitoring of rock specimens during cyclic compression tests has allowed recognition of similar patterns of behavior for dissimilar types of rock. During first loading of sandstone and quartz diorite cylinders, oscillations in the audio-frequency range emanate from the specimens throughout the test. Upon repetition of loading, the number of sonic disturbances decreases. However up to 60 per cent of the initial high rate of sonic activity during compression is recovered by the rock after a period of rest. After several cycles of loading, the attainment of particular levels of stress is consistently accompanied by sonic disturbances.