Stress threshold identification of progressive fracturing in Bukit Timah granite under uniaxial and triaxial stress conditions

Abstract

This paper reports the results of an extensive study of the deformation and fracturing of Bukit Timah granite in Singapore under uniaxial and triaxial loading conditions. In the investigation, the stress fracturing thresholds (crack initiation, crack coalescence and crack damage) were determined using stress–strain and stiffness curves and the acoustic emission (AE) detection technique. Crack initiation was found to be best determined by the volumetric strain curve in both uniaxial and triaxial compression tests. The subjectivity of determining the crack closure region and these stress thresholds can be overcome and the results validated by the AE technique by simply observing the cumulative curve of the AE count plotted against deviator stress, which showed four distinctive zones of fracturing. Furthermore, AE detection in the loading stage was found to be a powerful method for determining the phenomena of stable and unstable crack propagation, which are helpful in predicting the rockburst phenomenon. Finally, a comprehensive petrographical analysis using a petrological microscope and a scanning electron microscope was performed to identify the mode of cracking and the characterisation of the cracking pattern.