On the Evaluation of Crack Initiation Stress Threshold

The rapid expansion of urban and mining infrastructure over the last two decades has seen an escalation of development in hard rocks, including urban tunnels, large open pits, and deep underground mines. However, despite many success stories, explosion-like fractures at depth (commonly known as spalling and rock bursts) still happens. This highly contentious rock failure is found closely related to the initiation of internal cracks in rock where the sample deformation could still beis within beyond the elastic zone. The crack initiation threshold, defined as the onset of stress-induced rock damage, has been therefore widely used as a predictor for in-situ rock spalling strength. The aim of this study is to investigate the effect of material elasticity, porosity, and tensile strength on the crack initiation stress level based on the results of over 3,000 experiments collected from the literature on a wide range of igneous, metamorphic, and sedimentary rocks. The results of suggest that there is a linear relationship between the crack initiation stress level and the porosity material elasticity and tensile strength of rocks of rock. The outcome also deduced that relying on the crack initiation stress rather than the more informative crack initiation ratio can provide misleading guidance in some cases. That is, while the two indicators might seem similar, they can show contradictory trends and conclusions under the same conditions.