title: Concepts for upscaling hydromechanical properties of fractured rock masses - a comparison of classification schemes, discrete fracture network and synthetic rock mass models
Creators: name: Gottron, Dominik
Publisher: name: UNSPECIFIED
Year: 2022

description: Fractured rock masses are a complex system which demand complex analysis in order to investigate its hydromechanical characteristics. This thesis presents a workflow and opportunities, applying empirical, analytical and numerical upscaling techniques on fractured rock masses for the generation of spatially variable hydraulic and mechanical properties. To test the practical value of the upscaling concepts applied, two sandstone and a granite outcrop were investigated. These outcrops were surveyed using a Terrestrial Laser Scanner (TLS) in order to obtain geometrical properties, i.e., orientation, size and intensity, of the various fracture sets. It is shown that TLS represents an efficient technique for true-to-scale 3D visualization and fracture network analysis. Furthermore, the fracture network statistics derived from outcrop analysis is improved. Mechanical properties of intact rock and fractures were obtained by laboratory tests. Unconfined compressive strength and deformation modulus of the fractured rock mass were determined utilizing empirical relationships based on conventional engineering rock mass classification schemes. Uncertainties were considered by a probabilistic approach, utilizing Monte Carlo simulation techniques, for the various input parameters. Empirical equations, incorporating intact rock properties, consistently produce plausible results considering isotropic conditions. A Discrete Fracture Network (DFN) modeling approach was used to integrate the geometrical properties of the fracture network with the mechanical properties of rock and fractures. Based on analytical DFN-Oda approaches, spatial variable tensors for permeability, deformation modulus and Poisson’s ratio were computed assuming isotropy and vertical-transverse isotropy. Results indicate a substantial spatial scatter in hydromechanical properties and a drastic reduction in deformation modulus of the fractured rock mass in comparison to the intact rock due to the prevailing fracture networks. It is demonstrated that DFN-Oda approaches allow to derive anisotropic and spatially varying hydromechanical properties providing a comprehensive hydromechanical characterization of fractured rock masses. Utilizing a lattice-spring-based synthetic rock mass (LS-SRM) modeling approach, representing a discontinuum method, the complex mechanical behavior during failure of the rock masses including crack initiation, propagation and coalescence was investigated. The analysis demonstrates that the behavior of fractured rock masses including the failure mode is significantly influenced by to the geometry as well as the properties of the prevailing fracture network. The concepts for upscaling and the workflows tested in this thesis are applicable to any rock type. Realistic descriptions capturing the anisotropy and spatial variability of a fractured rock mass with respect to its hydromechanical characteristics are particularly achievable using DFN-Oda as well as LS-SRM modeling approaches. This is demonstrated by the successful application to the case studies.