"The Bureau of Mines investigated acoustic emission (ae) and the Kaiser effect in six types of rock: St. Cloud gray granodiorite, Barre granite, Dresser basalt, Salem limestone, Berea sandstone, and a volcanic tuff. Ae signatures were used for interpreting the rock deformation stage and for indicating mechanisms of failure in uniaxial compression. The research demonstrated the advantages of using the volumetric stress-strain curve, as opposed to the more conventional uniaxial curve, for correlating ae response signatures with deformation stages and fracture processes in the rock. Standardized experimental procedures were used for the ae monitoring. The Kaiser effect was shown to be capable of determining prestress levels to within a few percentage points in uniaxial compression tests. Also, prestress memory was shown to be retained in the rock for periods of up to at least 5 months, the maximum period of testing. The Kaiser effect ae technology holds promise for providing a comparatively inexpensive and less complex method for examining stress history in rock. However, since the confining stress has a pronounced influence on the Kaiser effect, it must be considered in developing technology for determining peak field stresses based on the Kaiser effect." - NIOSHTIC-2 NIOSH no. 10007404

National Institute for Occupational Safety and Health