In-situ fracture stiffness determination

In-situ experiments to determine the hydrologic and mechanical characteristics of large naturally occurring fractures were conducted at the NAGRA test site in Grimsel, Switzerland. In addition to seismic measurements across a fracture zone in the FRI test area and flow measurements into the zone, deformation of the fracture resulting from pressurization of the zone was also measured. The deformation is modeled in three different ways: as a mathematical crack employing linear elastic fracture mechanics; as a mathematical crack with an additional restraining stiffness between the faces of the crack, and as a row of coplanar two-dimensional cracks.