Theoretical and experimental study on the local head loss effect of complex rock fracture networks

Research on the seepage characteristics of rock fracture networks remains a challenge in hydraulic engineering design and construction. In order to establish a theoretical model that can describe the seepage characteristics of complex fracture network, based on the equivalent seepage resistance model, considering the local pressure drop loss effect at the intersection of fractures, and the equivalent local loss resistance model (E-loss model) is established. To verify the applicability of the theoretical model, two kinds of quadrilateral and hexagonal columnar jointed rock mass fracture networks are established with transparent polymethyl methacrylate (PMMA) plates as test objects. Through physical model tests, the influence of the water pressure drop conditions on fracture flow is explored. The results indicate that the theoretical model suitably reflects the experimental results under laminar flow conditions at a low Reynolds number. General-purpose computational fluid dynamics (CFD) code FLUENT is applied to analyze the mesoscale flow state in the fracture network, and the internal streamline and velocity vector characteristics are obtained. The results show that with the sudden decrease of fracture width in the fracture network, there is an obvious eddy current blocking effect, which is consistent with the analysis results of the theoretical model.