Relations between fracture tensor parameters and jointed rock hydraulics

The fracture tensor is a combined measure of joint geometry parameters. The possible relations between the properties of the fracture tensor and the h ydraulic properties of jointed rock including the equivalent continuum beha vior are investigated in this paper through numerical experiments performed at the two-dimensional level incorporating joint networks with two joint s ets. The possibility of a nonzero average block permeability and the equiva lent continuum behavior of a joint system can be expressed with the help of the first invariant of fracture tensor (F-o). A threshold value of F-o (to achieve nonzero block permeability) between 3 and 6 and a cutoff value of F-o (to achieve equivalent continuum behavior) between 10 and 30 were obtai ned for the joint geometry configurations studied in the investigation. Bot h the threshold value and the cutoff value of F-o were found to depend on t he relative orientation of joint sets. Joint systems with low relative orie ntation angles (for systems with only two joint sets) and low densities do not show hydraulically equivalent continuum behavior. A nonlinear relation seems to exist between the directional permeability and the fracture tensor component for the connected joint configuration when rock blocks contain o nly minor discontinuities. For rock blocks containing major discontinuities , this relation becomes linear.