EFFECT OF FRACTURE DENSITY ON BLOCK HYDRAULIC CONDUCTIVITY OF 2-D DISCRETE FRACTURE NETWORK SYSTEM

Fracture geometry parameters such as orientation, density and size play an important role in the hydraulic behavior of fractured rock masses. The two dimensional steady-state fluid flow through DFN(discrete fracture network) at various fracture density condition is addressed to examine the effect of fracture density on the hydraulic characteristics of fractured rock masses based on numerical experiments. Total of 378 2-D DFN systems are generate using two fracture sets with fixed input parameters of fracture orientation and gamma distributed fracture size, and various fracture density condition. DFN systems were divided into three groups in which the intersection angles between the two strikes of the two fracture sets are 30, 60 and 90 degrees, respectively. Each group has two sub-groups having different size distributions. Two different cases are considered in this study for the variation of fracture density for the fracture sets. In the first case, density for the fracture sets are increased simultaneously. In the second case, the fracture density for second fracture set is changed while the density of first fracture set is remained constant. The directional block conductivity including the theoretical block conductivity, principal conductivity tensor and average block conductivity were estimated for the generated DFN blocks. The results obtained from this study show that the higher the fracture density, the greater the directional block conductivity. The degree of fracture connectivity seems to increase with the increase of flow path. The chance for equivalent continuum behavior increase with the increase in fracture density in the first case. In the second case, however, the anisotropy of block hydraulic conductivity increases with the increase in fracture density, and the chance for the equivalent continuum behavior of the 2-D DFN system were found to decrease. The directional block hydraulic conductivity is more prominent for discrete fracture systems with higher fracture density.