Demonstration and application of NMM-based fractured porous medium flow model

In natural rock masses, the shapes of three-dimensional (3-D) blocks cut by arbitrary fracture networks may be very complex. Owing to the geometric complexity and difficulty of mesh discretization of 3-D blocks and fracture facets, explicit consideration of fracture networks in flow analysis of fractured porous medium (FPM) is very challenging. Using the numerical manifold method based on independent covers (NMMIC), an FPM flow model was proposed that can deal with very complex 3-D fracture networks. In this paper, the convergence of NMMIC was first demonstrated. The theoretical basis of the arbitrary refinement of computational meshes was proven. Moreover, three peculiarities of NMMIC meshes, that is, arbitrary shape, arbitrary connection, and arbitrary refinement of independent covers, were concluded. Finally, some two-dimensional (2-D) tunnel flow examples were analyzed and the numerical results were compared with the analytical results. 3-D examples with complex fracture distributions were also analyzed. In addition, the computational scale of the developed program was tested by increasing the number of computational elements. The results show that our model can accurately analyze the groundwater flow of rocks surrounding tunnels with complex fracture distributions.

Automated summary

In this study, an FPM flow model based on NMMIC method was proposed to handle complex 3-D fracture networks. The convergence of NMMIC, theoretical basis of arbitrary mesh refinement, and peculiarities of NMMIC meshes were demonstrated. By analyzing 2-D and 3-D tunnel flow examples and testing the computational scale, it was confirmed that the model can accurately analyze groundwater flow in rocks with complex fracture distributions.