Uniaxial compression failure and energy dissipation of marble specimens with flaws at the end surface

It is a fact that a large number of defects such as cracks, voids, inclusions, weak planes, and joint sets are generated within the rock mass during the process of rock formation because of geological-tectonic evolution. The existence of these preexisting natural defects poses potential threats to the stability and safety of structures built on the rock mass. Therefore, it is highly significant to better understand the effects of the preexisting defects on the rock mechanical and fracture behaviors for the stability and safety assessment of rock structures. Uniaxial compression tests were carried out by using ϕ50 mm × 50 mm cylindrical marble specimens with double parallel flaws at end surfaces. When tests were performed, a high speed camera was used to capture the failure processes of the marble specimens. The effects of the flaw length and inclination angle on the mechanical properties and crack propagation of marble specimens were investigated. Further, the experimental results indicate that the uniaxial compressive strength, elastic modulus, and peak strain of the specimen decrease slightly before the flaw length reaches the threshold value. Compared to flaws at vertical angle 90°, flaws at inclined angles (0°<α<90°) of the same length have larger effect on the mechanical properties of marble. It is found from both the experimental and theoretical analysis that cracks usually do not start from the tip of vertical end flaws and most of initiation cracks are developed into dominant cracks. In addition, there are few branches and bifurcations in the crack propagation process, and further, local spalling also occurs at the surface of the specimen. The specimens with inclined flaws exhibit shear failure or combined shear and tensile failure and the ones with vertical end flaws show axial splitting tensile failure. The variation trend of energy consumption parameters is consistent with that of uniaxial compressive strength. It is found that total strain energy of the specimen is positively correlated with its uniaxial compressive strength. Finally, the difference between mechanical and crack propagation processes of marble specimens with end flaws under dynamic and static loads were compared.