Ultrasonics and RACOS®
Evaluating the propagation properties of seismic waves in rocks is a powerful tool for the determination of rock deformation characteristics. If suitable frequencies are used, the sound waves react in a very sensitive manner to loosening, hollow spaces and cracks in the tested material and are thus used for crack detection or for the depiction of the development of micro-cracks under changing stress conditions. At Gesteinslabor Dr. Eberhard Jahns, the velocities of both compression and shear waves (transversal waves) can be determined in a laboratory experiment. Based on these experiments, moduli such as the dynamic Young’s modulus or dynamic bulk modulus can be calculated – a useful measure to calibrate static vs. dynamic moduli.
RACOS® (Rock Anisotropy Characterization On Samples) is a set of procedures for determining the 3D in situ stress on core samples (Braun 2006, Braun 2008; for further information please visit the homepage of Dr. Roland Braun Consultancy in Rock Mechanics). Measurements of the directional propagation velocities of P- and S-waves under hydrostatic loading allow for the determination of the strain elasticity and seismic anisotropy ellipsoids. These data enable some conclusions to be drawn about the fabric and the structural inventory of the rock body. In this respect most important is the determination of the recent 3D in situ stress field from which the drill core was taken at depth.