Abstract
Hydro-mechanical properties of a single fracture are governed by several parameters such as contact area, roughness, tortuosity, aperture, channeling, matedness, sample sizes, normal stress, flow regime, and flow boundary conditions. In this study, photogrammetry with numerical modeling and laboratory measurements were used to investigate the influences of roughness, normal stress, aperture, water pressure, and different flow boundary conditions on fluid flow in an artificial granite fracture. A Finnish Kuru grey granite block was mechanically split, and a 250 mm × 250 mm × 100 mm slab pair sample with a tensile crack in the middle was extracted. A photogrammetry-based method was used to reconstruct a 3D model of the fracture geometry. The resulting model was numerically simulated with COMSOL using the Navier-Stokes equations. Fluid flow experiments were computed with the Forchheimer equation. Comparison between the numerical modeling results and the analytical solution confirms that the 3D roughness geometry has a crucial role in defining the transmissivity, especially for nonlinear flow. On the other hand, normal stress increases fracture closure and increases contact areas, decreasing the hydraulic aperture and changing the flow paths. The presented method can be used in the contactless estimation of fluid flow properties of rock joints.
Highlights
The flow of ground water in fractured bedrock is an essential problem when considering the usage of rock mass as a barrier to prevent radionuclides escaping from a geological spent nuclear fuel repository
In this study, 20 flow tests were performed on 250 mm × 250 mm artificial tensile crack with two normal stress conditions of 0 MPa and 0.5 MPa
Photogrammetry can be used to obtain the physical aperture with high precision
Summary
The flow of ground water in fractured bedrock is an essential problem when considering the usage of rock mass as a barrier to prevent radionuclides escaping from a geological spent nuclear fuel repository. The stress state of the bedrock will change during time, and the excavations and filling of the tunnels will cause changes in the stress state of the bedrock. These are aspects that should be considered with applications such as tunnel construction, deep underground repository system, or groundwater management. The numerical modelling was solved by the Navier-Stokes equations (NSE) for water as incompressible and single Newtonian fluid flow in the COMSOL software.
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