Hydromechanical rock mass characterization using discrete fracture network models – a case study based on terrestrial laser scanning and rock mechanical testing

Understanding the anisotropic hydraulic and mechanical properties of fractured rock masses is of great importance for a safe and optimal utilisation of the subsurface. Two sandstone quarries are utilized to obtain fracture network characteristics by Terrestrial Laser Scanning (TLS) producing 3d point cloud data. Semiautomatic analysis of the point clouds provides the probability density functions for each of the fracture parameters used as stochastic input for a Discrete Fracture Network (DFN) model. Rock mechanical laboratory tests are carried out to determine the mechanical properties of the intact rock and fractures. These parameters are then combined in the DFN model to calculate spatially variable tensors for permeability, Young's modulus and Poisson's ratio. Thereby, the spatial resolution of the tensor description is adapted to the grid size which can be used in further hydromechanical models. The approach allows to populate these models with more realistic parameters which incorporate also the effect of fractures on the rock mass behaviour. Obtained results are subsequently compared with conventional engineering rock mass classifications. The applied workflow allows for upscaling of rock properties determined in the laboratory to the anisotropic rock mass properties required for further hydromechanical modelling on larger scales, e.g., the reservoir scale.