Investigations of strength and fracturing characteristics of flawed sandstone by true triaxial compression: Sensitivity to the flaw orientation

Abstract

True triaxial experiment with a synchronous acoustic emission (AE) monitoring system is a popular measure for the assessment of strength and cracking behaviors of brittle flawed rocks under anisotropic stress circumstances. This measure is employed to invest the dependency of the strength and fracturing characteristics of flawed sandstone under true triaxial stress on the flaw orientation. Observations first quantitatively reveal the three types of failure mechanisms including structure-control, stress-structure collaborative control and stress-control, dependent on the flaw orientation with respect to the 3D (three-dimensional) stress. Second, the elastoplastic strain increment ratio (EPSIR) method is creatively introduced to identify the stress thresholds in flawed sandstone under true triaxial stress. Third, a significant increase in the true triaxial strength of flawed sandstone among the tested flaw configurations is correlated with the intensification of the shear mechanism. The 3D stress-driven progressive failure of flawed sandstone is also investigated experimentally, as well as the AE (acoustic emission) characteristics and the strength prediction. Current experiments provide insights into the brittle failure mechanisms of flawed rocks and help interpret the excavation instability in deep underground engineering.