THE ACOUSTIC EMISSION AND ITS FREQUENCY CHARACTERISTICS IN ROCKS UNDER DIFFERENT TYPES OF UNIAXIAL COMPRESSION

The acoustic emission in granite and limestone samples during different types of uniaxial compression were simutaneously monitored through two different frequency windows, the variation of the rate of acoustic emission and the frequency characteristics of acoustic emission throughout the whole process from application of loading to the failure of the rock sample were studied. When the applied stress was less than 90% of the strength of rock samples, the variations of the rate of acoustic emission and its characteristics were different for diiferent rocks. There were also some differences between the variations of the rate of acoustic emission under different types of uniaxial compression. When the applied stress was higher than about 95% of the strength of rock samples, the rate of acoustic emision through different frequency windows all increased supraexponentially. But the rate of acoustic emission through the higher frequency window increased more rapidly than that through the lower frequency window immediately before and during failure of the rocks. These two features could be used to predict the burst of rocks.The variation of the emission rate with time depended upon the path of the loading. Loading with constant rate of increase; keeping the loading constant or decreasing the loading for a period of time during the loading process all brought to different kinds of variation of the rate of acoustic emission respectively. So it might be possible that the stress state could be deduced from the variation of the emission rate.