Effect of the Minor Principal Stress on Crack Initiation Stress Threshold

Abstract

The rapid expansion of urban and mining infrastructures worldwide over the last two decades has seen an escalation of development in hard rock, including urban tunnels, deep open pits, and underground mines. However, despite many success stories, the pervasiveness of rock burst and spalling remains yet a major unresolved ground control problem in many deep mines and tunnels. Spalling is characterised as a sudden explosion-like rock failure that occurs spontaneously and could affect both the short-term and long-term viability of mining operations. Previous studies strongly show that the spalling strength in low-porosity rocks can be associated with the initiation of internal cracks in the sample. However, very limited studies are available that looks at the effect of all the principal stresses on rock crack initiation stress threshold. This paper investigates the previously ignored effect of the minor principal stress on the crack initiation stress level of sandstone cubes tested under true triaxial loading conditions. The results reveal that the minor principal stress has a profound effect on the crack initiation point. As a result of this study, a new crack mode-changing stress (CMCS) concept is also introduced which is defined as the corresponding minimum principal stress required to change rock fracturing from splitting to a sliding failure mode.