A comparative study on the crack development in rock-like specimens containing unfilled and filled flaws

Rock masses consist of various discontinuities that significantly affect the crack development patterns 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 and demands a comprehensive investigation. This paper couples the 3D printing technology with the digital image correlation (DIC) and the bonded particle model (BPM) to study failure of rock-like specimens with pre-existing flaws. Systematic flaws configurations are considered including single, coplanar, partially overlapped and fully overlapped arrangements. The flaws are considered to be unfilled and filled with a weak material. The DIC strain and BPM displacement vectors analysis indicate the strong effects of the filling material on the deformation behaviour of the 3D printed specimens. The failure pattern of the single filled flaws is transformation from compressive failure (0 degrees) to shear failure (15 degrees-60 degrees) and to tensile failure (75 degrees-90 degrees). However, in the coplanar flaws failure is transformation from compressive (0 degrees) to mixed-mode compressive shear (15 degrees-301, then to shear (451, to mixed-mode tensile-shear (60 degrees-75 degrees) and then to pure tensile (90 degrees). However, the partially coplanar filled flaws all (except 0 degrees which is compressive failure) exhibit mixed-mode failure in the order of compressive-shear (15 degrees-30 degrees) and transformation to the tensile-shear (45 degrees-90 degrees). BPM displacement vectors revealed five crack types in the specimens by the analysis of the relative movement of the vectors in some critical locations such as flaws tips, rock bridge and coalescence zone. Moreover, a new coalescence type was identified in the 15 degrees flaw (either unfilled or filed) which is named Type X and is a mixed-mode shear tensile crack with a coplanar secondary shear crack. Furthermore, it is observed that the peak load of the filled specimens are much higher than that of the unfilled ones because the filling material requires extra energy to fracture and thus the filled specimens can carry larger load before fail.