Fluid Flow Analysis On Sheared Rock Masses Using The Discrete Fracture Network Method

While shear flow behavior through fractured media has so far been studied at the scale of single fractures,we propose a numerical analysis on the effect of shearing deformation on the permeability and fluid flow patterns at the scale of fractured rock masses,using a twodimensional distinct element program based on a realistic discrete fracture network realization.With the assumption that the rock matrix is impermeable,linearly elastic and fluid flows only in fractures,we carried out several numerical experiments on three fracture network models.Having varying fracture densities(1.4,1.45 and 1.5),we calculated the changes in permeability of the stimulated shearing fractured rock mass under different criteria,and the influence of shear on the mechanical properties of the fracture networks.They included normal fracture stiffness variation,fracture densities,normal stress loading conditions,and permeability flow in both horizontal and vertical directions.The numerical experiments show that upon initiation of shear,the permeability increases or decreases,with contact asperities overriding each other,thereby leading to an increase in shear stress with the increasing shear displacement,which causes the change in the mechanical properties of the network and the reorientation of the fluid flow direction.The existence of different orientations of fractures and their connectivity in different stress states defines the possible behavior of fluid.The change in permeability with maximum minimum flow rate of 1E-8 and 1E-9 respectively,are plotted against the shearing rate displacement of 0.5m.The simulation results showed that,for flow in the horizontal direction,the shearing aperture during shearing greatly influenced the flow no matter the densities of the cracks present;and for flow in the vertical direction,the rate of shearing displacement and degree of dilation influenced the fluid flow.On the other hand,the varying fracture stiffness values changes in accordance to the surrounding in situ stresses of the rock masses and has direct effect on the rate of displacement of the fracture network.The results can give a fundamental understanding of fluid flow via fractured rock masses experiencing shear and assist in decision-making analysis of engineering applications.