DAMAGE MECHANISMS IN STRESSED ROCK FROM ACOUSTIC-EMISSION

To better understand the phenomena leading to the failure of rock, unc onfined compression experiments on Charcoal granite specimens were per formed with the monitoring of acoustic emission (AE). Localization in the form of spalling near the free surface was detected by the concent ration of hypocenters. The AE locations, which look random in space an d time before localization, actually were clustered and have fractal s tructure in either space or time. After localization, the fractal dime nsions reduced significantly in a certain range of distance and time. The analysis of interaction between spatial and temporal clustering re vealed the size of clusters in both space and time. The cluster sizes may be related to the intrinsic properties of the rock. The seismic mo ment tenser was evaluated through a deconvolution technique to obtain the source mechanism and orientation of each AE event. The dominant mo de of failure from AE was sliding on inclined planes, although a signi ficant number of source planes were parallel to the loading axis, whil e the growth of cracks perpendicular to the loading axis was inhibited . This preferential growth of microcracks is related to a tensorial me asure of damage and is used to study stress-induced anisotropy.