Shear Specific Stiffness of Fractures and Fracture Intersections

Fractures in rock masses influence strongly the mechanical and hydraulic properties of a rock mass. Thus, the detection and characterization of fractures using geophysical methods is of critical importance for maintaining the integrity of sub-surface infrastructure and subsurface waste or storage repositories. While the effects of single fractures or sets of parallel fractures on seismic wave propagation have been studied by many scientists and engineers, little research has been performed to determine the role of fracture intersections on seismic wave attenuation and velocity. A fundamental question is whether the specific stiffness or compliance of an intersection is the same or differs from the stiffness of any of the individual fractures within two intersecting sets of fractures. In this paper, we show from experimental and numerical studies that the stiffness of fracture intersections can be less than, equal to, or greater than the stiffness of the individual fractures depending on the applied bi-axial loading conditions.