Experimental and numerical investigations on crack development in 3D printed rock-like specimens with pre-existing flaws

Rock masses contain various discontinuities such as flaws, cracks, join sets and more, each significantly affect the crack initiation, propagation and coalescence patterns of new cracks which dominates the ultimate failure of geostructures. The interaction of the pre-existing flaws with each other and with the newly formed cracks is complicated which demands a comprehensive look into the phenomenon. This paper focuses on the applicability of the 3D printing technology coupled with the digital image correlation (DIC) and the bonded particle model (BPM) in replicating real behaviour of natural rocks containing pre-existing flaws. Systematic flaws configurations are considered including single, coplanar, partially overlapped and fully overlapped arrangements to enable a comprehensive coalescence analysis. The results show that the BPM is capable of precisely modelling the crack initiation location, type (tensile, shear or mixed-mode) and coalescence type detected by the DIC. Moreover, it is shown that the 3D printed specimens can reproduce the previously identified cracks and coalescence types. By the analysis of the displacement fields, a new coalescence type is detected and introduced and named as type X, which is a mix of wing crack and quasi coplanar secondary shear crack. The analysis of the displacement vectors revealed five types of cracks: shear opposite slip crack, tensile opposite crack, tensile compliant crack, shear compliant crack, and mixed tensile-shear crack. Furthermore, the comparisons made between the peak loads of the experiments and the simulations show a god agreement in terms of peak load magnitude and flaws inclination angle dependency.