Experimental and DEM-based investigation of crack growth in rocks with pre-existing flaws

The presence of flaws in naturally occurring rock masses is one of the major factors contributing to its strength and failure behaviour. The present study focuses on analysing the failure mechanisms associated with different types of flaws (open and closed) and their orientations. In this paper, the behaviour of open and closed flaws in artificial rock specimens (gypsum) of different strengths under uniaxial loading is investigated. Experimentally, the critical flaw angle corresponding to the minimum peak strength is identified, and the final failure crack patterns emerging from the pre-existing flaws are examined. Numerically, the Particle Flow Code (PFC) is employed to study microcrack development using a calibrated flat-jointed bonded-particle model. The calibrated models for the various gypsum strengths successfully reproduce the maximum and minimum peak strengths, as well as the final failure patterns, for most cases. Experimental stress analysis indicates that a 45° closed flaw for high‑strength gypsum is more critical than a 45° open flaw. This behaviour is further investigated numerically by analysing the sliding behaviour along the closed flaw through tracking the displacement of rigid particles surrounding the flaw.