| Abstrakt: |
Abstract: a1_The evaluation of stress-deformation stage of rocks, mainly time prediction of the origin of extensive brittle fracturing, belongs to the present important tasks of geomechanics. Laboratory results obtained are very important for the assessment of the origin of natural earthquakes as well as induced seismic events. Laboratory experiments were oriented to the evaluation of the possibility to predict the time of the total fracturing of the rock samples subjected to the uniaxial loading. The sandstone samples were studied. In all experiments the ultrasonic emission was recorded. Time series of ultrasonic emission were analyzed by autocorrelation method. It was found that during the fast rock sample loading the ultrasonic emission could be observed when 65% of total strength of the material is exceeded. Following parameters of the course of autocorrelation function were used: - the first value of autocorrelation coefficient R(1) - the number of positive autocorrelation coefficients (correlation radius) - the trend of autocorrelation function according to linear time dependence. For the short term rock sample loading, after the crossing of the 90% of the total strength of the material, the significant increase the value of correlation coefficient of linear approximation are observed. The dependence of the autocorrelation function is nearly linear. It means that the value of the first autocorrelation coefficient R(1) increase as well. The correlation radius at different values of acting load (starting from the 90% of strength limit) however is nearly the same. For the cyclic loading, in the case of second cycle, the autocorrelation methods can be applied, due to the Kaiser effect, after the maximum acting stress of the first loading cycle is exceeded. The nature of the ultrasonic emission originating during short-term test is influenced mainly by the response of the sample to acting force. |
