EVALUATION OF THE 2-D PERMEABILITY TENSOR FOR FRACTURED ROCK MASSES

An approach is established to evaluate the 2-D permeability tensor of naturally fractured rock masses by using modified UDEC . Based on the superposition principle, directional flow-rates through a unit square of fractured rock under head gradients in two orthogonal directions ca n be calculated with UDEC. Then the flow-rates are transformed into fl ow-rates through a field rock mass for evaluating the permeability ten sor. Two kinds of fractured rock models, fixed hydraulic fracture aper ture and variable hydraulic fracture aperture under stress, were studi ed by using this approach. For the first model, the permeability tenso r of a fractured rock mass only depends upon the statistical features of fracture pattern geometry, including orientation, trace length, den sity of fractures. For the second model, the permeability tensor stron gly depends upon both the geometry of the fracture pattern and the app lied stress, such as the direction and magnitude of principal stress a s well as the ratio of major principal stress to minor principal stres s.