Knowledge of mechanical and strength parameters and also post-peak behavior of rock masses are of considerable importance in designing and analyzing different rock engineering structures. Determination of these parameters with the lowest degree of uncertainty is imperative in economic and safety of rock engineering projects. In this thesis, the effects of fracture intensity and stress on deformability, elastic strength and post peak behavior of fractured rock masses are investigated. The concepts applied in this research work are the fundamental principles of the general theory of elasticity, Representative Elementary Volume (REV), the compliance tensor and the strength criteria of fractured rocks. With inadequate and small scales of rock sample, such investigations may not be possible to conduct in laboratory scale, which necessitates the development of new approaches. There exist different methods for calculating the mentioned parameters of rock masses: Experimental, analytical and numerical approaches. One of the most effective methods is utilizing a hybrid numerical Discrete Fracture Network-Distinct Element Method (DFN-DEM) to study the effects of geometrical parameters and stress on deformation modulus, Poisson’s ratio, strength and post-peak behavior of fractured rock masses. Numerous DFN models with variable fracture intensities and sizes were generated by means of Monte Carlo simulation method. In order to determine the deformability parameters, elastic strength and post-peak behavior, using the DFN-DEM method and UDEC code, the compliance tensors for DEM models with variable geometrical patterns were calculated and the stress-strain curves for these models were studied. Accordingly, considering the scale and stress effects, the REVs related to mechanical and stress parameters for DEM models with particular fracture intensities were determined. The results highlight a negative correlation between the fracture intensity and the values of strength and deformability parameters of the DEM models. An increase in the applied stress yields to the increase of deformation modulus and strength. Compared with the Hoek-Brown criterion, the Mohr-Coulomb strength stress envelope provides a better fit to the results of numerical tests. The work-hardening behavior occurs in most of the stress-strain curves.
