Possibilities of forecasting of rock sample total fracture by application of correlation analysis of acoustic emission events series

The series of acoustic emission events from loaded rock samples were studied by means of correlation analysis. As characteristic parameters of the correlation functions were chosen: the first values of the autocorrelation coefficients, the number of positive autocorrelation coefficients and the linearity of the autocorrelation function. The increase in the values of the autocorrelation coefficients and the trend to their linear decrease is evidence of increased mutual effect of the individual events on one another, i.e. of the redistribution of stress in the sample. The predictive character of correlation parameters is absolute and they need not be relatively judged in the course of the whole loading process. It was found that the rock is being stressed close to its critical state if the correlation coefficient of the approximation line increases above 0.9, the correlation radius is longer then 20 s, and the value of the first autocorrelation coefficient reaches 0.6 (it is twice more than at the beginning of loading). The experiments were carried out on the various types of rock samples with different structure sandstone and migmatite. The loading was carried out in a broad range of loading rates and different loading patterns. The nature of the ultrasonic emission originating during short-term test is influenced mainly by the response of the sample to acting force. During long-term test the parameters of ultrasonic emission reflect rheological properties of rocks sample. Results obtained under laboratory conditions could be applied to seismoacoustic investigation of rock burst occurrence. Introduction One of the present significant tasks of geomechanics is the assessment of the stress-strain state of rocks, and especially forecasting the occurrence of their extensive brittle fracture. A number of methods and procedures are used to study deformation processes in rock massif and in forecasting sudden releases of seismic energy (Anifrani et al. 1995, Newman et al. 1995, Sornette and Sammis 1995, Voight 1989). In this contribution, we deal with a laboratory method of assessing the instability of rock samples based ultrasonic emissions from loaded rock samples. Deformation processes, taking place in-situ, can be modeled by laboratory methods under simplified conditions. To be specific, the system of loading can be chosen, and the reaction of various types of rocks to the loading can be studied. Although a considerable simplification of