ANISOTROPIC FEATURES OF GEOMETRY AND PERMEABILITY IN FRACTURED ROCK MASSES

A geometric anisotropy factor (A(f)) of two-dimensional, natural fract ure systems has been defined according to fracture spacing and orienta tion in a given direction. Geometric anisotropy of fracture systems ha s a major effect on the percolation threshold (the critical fracture d ensity) of fracture systems below which the overall permeability is ze ro. A two-dimensional distinct element code (UDEC) has been used to ca lculate directional flow-rates of fracture systems. Simulated and natu ral fracture patterns, sampled on outcrops in the Lake District (Engla nd), have been tested to examine the relation between geometric anisot ropy and permeability anisotropy, which is demonstrated to have a powe r-law form. Also, the differential anisotropy factor (A(f)) results in different universal exponents which govern the relation between fract ure density and flow rates.