Fracture evolution and failure behaviour of marble specimens containing rectangular cavities under uniaxial loading

To analyse the fracture coalescence behaviour around hole-like flaws in rock, rectangular cuboid marble specimens containing a single rectangular cavity or two rectangular cavities with different layouts were tested under uniaxial compression. Failure characteristics of specimens and strain concentration regime (SCR) evolution on specimen surfaces were measured by means of acoustic emission (AE) and digital image correlation (DIC) techniques respectively. Numerical simulations were further conducted on specimens with the same specimen and cavity dimensions using the discrete element method (DEM), and the inclination angle between centroids of two cavities with respect to the horizontal direction was varied to investigate its influence on failure modes and mechanical properties of specimens. Results showed that both cavity number and layout have a significant influence on mechanical behaviour of marble specimens. The existence of two cavities leads to more degradation of mechanical properties than a single cavity. For specimens with two cavities, the strength first decreases and subsequently increases with increasing inclination angle, and the specimen with two vertically aligned cavities has the maximum strength. Four failure modes were observed in specimens, namely splitting failure, shear failure, mixed tensile/shear failure, and surface spalling. In addition, absorbed energy per unit volume e was introduced to characterise the fragmentation of different groups of specimens. Specimens containing cavities absorbed less energy per unit volume, and thus were less fragmented after failure.