Anisotropic features of geometry and permeability in fractured rock masses

A geometric anisotropy factor (A f) of two-dimensional, natural fracture systems has been defined according to fracture spacing and orientation in a given direction. Geometric anisotropy of fracture systems has a major effect on the percolation threshold (the critical fracture density) of fracture systems below which the overall permeability is zero.A two-dimensional distinct element code (UDEC) has been used to calculate directional flow-rates of fracture systems. Simulated and natural fracture patterns, sampled on outcrops in the Lake District (England), have been tested to examine the relation between geometric anisotropy and permeability anisotropy, which is demonstrated to have a power-law form. Also, the differential anisotropy factor (A f) results in different universal exponents which govern the relation between fracture density and flow rates.