THE ACOUSTIC-EMISSION FROM ROCK UNDER STRESS AND HYDRAULIC PRESSURE

The essential conditions for effective and ecologically safe exploitation of underground waste storage are maintenance, prevention, and monitoring of tightness of rock masses covering and surrounding the reservoir rock complex. This monitoring can be realized by a especially designed acoustic measurement system. The reservoir rock complexes - without leakage - are supposed to be in physical equilibrium; without changes of rock dynamic properties the acoustic emission vanishes. In contrast, as is shown, the results of the field tests carried out in coal mines proved that there was a correlation between the stresses and the acoustic emission ratio. The laboratory experiments also showed correlation between changes of permeability of coal samples and acoustic emission. The explanation of the observed results is based on the development of inelastic deformation of a rock skeleton. The plastic strains in the porous rock appear after overcoming the yield point. The yield point value can be extended by increase of shear stresses, effective stresses and interstitial pressure. In particular, there are three kinds of dynamic phases which may appear preceding the failure of leak tightness: (1) breaking of the rock masses due to stress (Griffith criterion of stability may be expressed in terms of the acoustic emission parameters), (2) the dilatant corrosion of pressure plasticity resulting from chemical, physical and thermal activities, and (3) the destructive increase of pressure in rock pores. This paper presents the statistical parameters describing the acoustic emission from the rock mass and the dynamic processes mentioned above are described in terms of seismoacoustic activity.