A parameter study of how initial roughness and normal stress affect the flow and transport properties in granitic-like sheared synthetic fractures

Flow and transport properties of fractured crystalline rock are of great interest for different geotechnical applications, such as storage of carbon dioxide, extraction of geothermal energy, or geologic storage of hazardous waste. For the long-term safety assessment of geological storage of hazardous waste, the understanding of flow and transport properties through the network of fractures is essential. The flow and transport behaviour can be explored using numerical models to investigate what parameters that affect the results. In this work a pilot study is carried out for multiple realizations of single realistic fractures, using fractal theories, which then are numerically sheared using a semi-analytical algorithm. The aperture field is calculated using the average distance of the volume integral of the void that a 1 mm lateral displacement of the sheared surfaces generates. The flow field through the aperture field is solved using Reynolds lubrication equation in linear triangular finite elements. The transport properties, travel length, travel time, transport resistance and specific flow wetted surface, are calculated in a Lagrangian framework using 10,000 particles for each of the 128 flow fields. Evaluating these four metrics, varying initial roughness, 4 < JRC < 10 and normal stress between 0.2 and 20 MPa during shearing, it is concluded that an increase in normal stress generally results in longer travel paths, longer travel times, higher transport resistance and larger specific flow wetted surface while an increase of initial roughness will generally result in longer travel paths, shorter travel times, lower transport resistance and smaller specific flow wetted surface. • Fractal theories are used to generate fractures and a fast semi-analytical scheme to shear them. • The local aperture is calculated based on the integration of aperture of each computational element. • A Lagrangian framework is used to investigate how transport properties are affected by initial roughness and normal stress. • The widespread usage of parallel plate simplification is shown to be slightly to severely non-conservative from a safety assessment perspective for nuclear waste repositories.