The presented work documents the influence of Voronoi block size and shape as well as internal mesh size on the calibrated fracture toughness KIC. It is documented that Voronoi based procedures have an inevitable error of up to ± 30%. On the other hand, this approach is able to reproduce complex fracture pattern in a realistic manner with reasonable computational power. The work propose a KIC calibration procedure and documents based on the comparison with lab tests, that crack propagation, fracture pattern as well as stress-strain behavior of brittle solids can be duplicated by calibrated Voronoi based DEM simulations. The thesis also documents a swelling law for the DEM code UDEC including parameter determination and validation on lab tests with swelling cement. Finally, calibrated concrete models with one or two holes under different boundary conditions are used to predict swelling induced cracking. Numerical predictions were compared with corresponding lab tests and showed satisfying results.