A novel FEM–DEM coupling methodology for hydro-mechanical modeling in fractured geological media

This study presents the development, verification, and validation of a novel coupling methodology for simulating coupled hydro-mechanical (HM) processes in fractured geological media. The proposed numerical approach, OGS–3DEC, integrates the finite element method-based OpenGeoSys (OGS) for fluid flow and the discrete element code 3DEC for mechanical deformation. These two simulators are linked through a hierarchical sequential coupling scheme that enables two-way data exchange. This approach modifies the effective stress in the fractured medium through evolving pore pressure while updating permeability and porosity based on stress and deformation. The methodology was verified through benchmark tests including one-dimensional consolidation in a porous matrix, radial fluid flow along a fracture plane, and fluid injection-induced fracture opening and slip. The results demonstrated excellent agreement with analytical solutions. Additionally, the model was validated against field-scale data from a fault reactivation experiment at the Mont Terri Rock Laboratory, with simulated pressures, flow rates, and displacements closely matching observed values. The OGS-3DEC simulator provides a reliable and efficient tool for modeling the HM behavior of fractured rock masses, with applications in geotechnical and subsurface engineering. • Developed FEM-DEM methodology coupling OGS and 3DEC for HM analysis. • Implemented sequential data exchange for accurate OGS-3DEC coupling. • Verified via benchmark tests on matrix consolidation, fracture flow, opening, and slip. • Validated against Mont Terri field data, confirming model reliability. • Simulated fluid injection-induced fracture propagation and fault reactivation.