Crack analysis of pre-cracked brittle specimens under biaxial compression

Abstract

Crack propagation process in rock like specimens has been studied experimentally and numerically considering both; a single crack and double cracks in the center of specimens. The rock-like specimens are specially prepared from Portland Pozzolana Cement (PPC), fine sands and water. These precracked cylindrical specimens are experimentally tested under compressive loading. Effect of confining pressure on the crack propagation path of specimens with single crack is explained first. In these experiments, it has been observed that the crack propagation path is diverted from its rout due to lateral confinement compared to that of the uniaxially loaded pre-cracked experiments. The same experiments are numerically simulated by an indirect boundary element method using higher order displacement discontinuity elements. Effect of lateral stress on the crack propagation of specimens containing single and double cracks have been studied and compared with the experimental results showing a good agreement between them. Effect of confinement on the cracks coalescence in the specimens containing two cracks is also investigated. It has been observed that wing cracks are produced at the first stage of compression and start their propagation toward the direction of uniaxial compressive loading in the absence of confinement. In the presence of confining pressure the propagating wings are diverted related to the uniaxially loaded cracks and showing a mixed mode crack propagation phenomenon due to both induced tension and shear. It is also observed that the crack coalescence path is affected a little bit (due to confinement) compared to that of wing cracks.