Estimation of Effective Hydraulic Conductivity in Fractured Rock: Integrating Transmissivity Derived by the Landau–Lifshitz–Matheron Formula and Discrete Fracture Networking Model

Fractures are the main pathways for groundwater flow and solute transport in rock. Modeling flow through hydraulically connected fractures is crucial for evaluating fractured rock environments. The Discrete Fracture Network (DFN) model is one approach to assess mass transport in fractured media. Recent advancements in DFN modeling allow flow simulation considering not only fracture connectivity but also heterogeneity within fractures. Continuous modeling using effective hydraulic conductivity is another approach to assess mass transport in fractured media. Estimating effective hydraulic conductivity also requires the evaluation of fracture connectivity and intra-fracture flow. Among them, fracture connectivity can be evaluated using conventional DFN modeling. However, the evaluation of intra-fracture flow remains challenging due to computational costs and uncertainties during modeling. To address this, this study utilized the fracture effective transmissivity derived by Landau–Lifshitz–Matheron formula, which accounts for both transmissivity heterogeneity and flow patterns within fractures without explicit modeling of intra-fracture flow. Combining effective transmissivity with a conventional DFN model enabled effective hydraulic conductivity estimation, considering both fracture connectivity and intra-fracture flow. The proposed approach was applied around the Horonobe Underground Research Laboratory. The resulting effective hydraulic conductivity was compared with that by conventional approach and the value directly derived from long-term inflow and hydraulic pressure data. Our approach estimated the directly derived effective hydraulic conductivity better than conventional approach.