Pre- and post-failure characterisation of low-strength rocks by generalised crack initiation and crack damage

For the past 50 years, characterizing and generalizing rock behaviour has been of great interest for researchers in rock mechanics and rock engineering. Advanced loading and measurement techniques have improved the accuracy and the resolution of stress–strain curves as well as the precision of defining dilatancy, lateral or volumetric strains, and tangential modulus. Several techniques and procedures are being used to identify particular stress levels, such as those associated with crack initiation (CI) and crack damage (CD). This study examines these variables for weak rocks subjected to uniaxial compression, which is rarely investigated in the literature. The behaviour of the rock under unconfined conditions is important since the confinement is limited within a distance close to an excavation. Along with the CI and CD levels, post-failure modulus and dilatancy angle are correlated with the uniaxial compressive strength for convenience. The intriguing idea of characterizing rocks of different origins and variable strength resulted in generic relationships. Additionally, a modulus-dilatancy relationship is presented depending on the modulus of elasticity and post-failure modulus.