ABSTRACT
Abstract We present and analyze results from suites of experiments performed on sandstone cubes in which the bulk acoustic emission and the ultrasonic compressional and shear wave velocities in the three principal directions were monitored and measured simultaneously with the stress and strain as samples were deformed in three orthogonal directions independently. This combination of measurements has enabled us directly to link the acoustic emissions to the formation of new crack damage. The results from cyclic uniaxial loading tests confirmed the existence of the Kaiser stress-memory effect. Furthermore, the effect was found to occur in each principal direction independently, regardless of whether or not stresses had been applied along orthogonal axes. This suggests that the crack damage formed during stressing is highly anisotropic, with new microcracks formed during each stress cycle having their crack normals oriented parallel to the minimum principal stress direction. The observed effects have been modelled in terms of the elastic closure of pre-existing cracks, and the formation of new highly-oriented dilatant cracks that produce acoustic emission activity. Keywords: Rocks, Cracking, Acoustic Emissions, Wave Velocities, Triaxial Loading, Anisotropy.
