The study presents the first step of a research project that aims at investigating and modeling the geomechanical characteristics and failure mechanism of rock mass containing non-persistent rock joints using laboratory tests carried out on 3D printed sandstones. This paper focuses on modeling the behavior of intact sandstone analogues under compression and indirect tension tests using a 2D hybrid finite-discrete element method (FDEM) implemented in Irazu software. The advantage of FDEM approach is its ability to model the transition from continuum to discontinuum domain during intact rock fracturing. The models were calibrated against data sets of uniaxial/triaxial compression and Brazilian tests. Stress-Strain curves and failure mechanisms of models were compared to the experimental results, it was shown that the calibrated models could capture the strength and the brittle failure aspect of the sandstone analogues through crack initiation, propagation, and coalescence and are in good agreement with the laboratory results.
The failure of a rock mass often occurs as a result of sliding along pre-existing discontinuities and defects and/or the breaking of intact rock bridges. This process can be described as a transition from a continuum to a discontinuum, as the failure begins with initiation and growth before merging into larger fractures. The Finite/Discrete Element Method (FDEM) pioneered by Munjiza (2004) is a hybrid method that combines both continuum and discontinuum approaches and has been widely used to model the behavior of brittle rocks, including interactions along pre-existing discontinuities and the formation of new fractures (Mahabadi and Lisjak 2014; Hamdi et al. 2015). FDEM also applies fracture mechanics principles to predict the initiation and development of fractures. When the failure criterion within the intact rock is met, a crack is initiated, and the model evolves from FEM into DEM.
The combination of FDEM with Discrete Fracture Network (DFN) can simulate the behavior of a rock mass with pre-existing fractures. DFN is a process of randomly generating a 3D representation of rock fractures that considers their primary characteristics including orientation, persistence, intensity, and spatial distribution to produce a realistic model of a rock mass (Hamdi et al. 2014, 2018). The rock mass consists of a complex interplay of two components: the intact rock and spatially distributed rock joints of various orientation and persistence. The first step towards modeling the behavior of a rock mass is the understanding of the behavior of the intact rock material. Upon that, the effect of different DFN characteristics on the overall behavior of the rock mass can then be examined distinctly. In this study, the FDEM method is used to model the behavior of 3D printed intact sandstone analogues using the Irazu software. Laboratory tests including uniaxial/triaxial compression and indirect tension tests were performed on the sandstone analogues prior the numerical modeling. The analogues exhibited a brittle behavior and had a uniaxial compressive strength UCS and tensile strength of 32.5 MPa and 5.5 MPa, respectively. The 2D models are then calibrated against the laboratory data sets and the results are discussed.
