Existence analysis of hydraulic conductivity representative elementary volume in fractured rocks based on three-dimensional discrete fracture network method

The complexity of fractures in rocks results in heterogeneity and anisotropy of their hydraulic properties. The existence of hydraulic conductivity representative elementary volume (KREV) is a fundamental question in comprehending the hydraulic behavior of fractured rock masses. This article introduces an analytical procedure for determining the existence of KREV in fractured rock masses, which considers the distribution of underground apertures using a discrete fracture network (DFN) model. The procedure follows four basic steps: inverse modeling to generate a 3D DFN; calibration of the effective aperture by combining the results of packer tests and flow simulation using finite difference methods; calculation of the equivalent conductivities in 10 domains and 31 different flow directions; analysis of the fit error between the conductivity ellipsoid to determine the existence of KREV. The proposed approach is applied to the fractured rocks surrounding the 3013 exploration adit near the underground powerhouse of the Three Gorges Project as a case study. The results show that most fractures in the study area have apertures ranging from 0.06 to 0.25 mm and follow a lognormal distribution. The KREV size is 14-16 times the fracture spacing. Investigation of this model has significant implications for understanding flow through fracture networks in related fields.