ABSTRACT
Crack-sensitivity of ultrasonic wave velocities is used to monitor the development of the micro-structure and to identify the onset of dilatancy. Changes of wave velocities and permeability, which are characteristically related to the generation of micro-cracks, allow the determination of the dilatancy boundary. The equation given by Cristescu & Hunsche (1998) is confirmed. During loading in the dilatant stress domain the patterns of micro-cracks develop anisotropically, depending on the geometry of loading. Cracks are found to propagate predominantly parallel to the direction of the maximum principal stress. Therefore, measurable changes in permeability and the permeation of fluids affecting strength are directly coupled with both crack density and orientation of the micro-cracks. The results are used to assess loading conditions as expected in situ. We conclude that pore pressure effects on strength and integrity due to permeation are of concern only in the dilatant stress domain where dilatancy and permeability develop with strain.
