Abstract:

The mechanism which controls violent/non-violent rock failure is studied through an extensive experimental study through uniaxial and triaxial compression loading. The tests were undertaken under quasi-static and post-peak cyclic loading. Axial displacement control system can be employed to measure the post-peak response of the rocks only if the rock demonstrates class I behaviour. Lateral strain control loading system, however, is applicable to measure true post-peak rock behaviour when they exhibit class II behaviour. It was observed that post-peak behaviour of rocks is an intrinsic property and independent of loading condition. In the triaxial compressive testing when the ratio between confining pressure to the unconfined compressive strength increases, rock post-peak behaviour shifts from class II behaviour to class I behaviour. Rock samples with a higher aspect ratio were observed to behave more brittle. The effect of scale on the post-peak response of rock, however, is found to be insignificant.

1 Introduction

Rocks in the deep underground are subjected to high in-situ stresses. Therefore, rock behaviour becomes complicated in response to extraction activities of deep earth resources. Rock behaviour and failure in the deep underground is not well understood, leading to a flaw in engineering designs. Inadvertent violent rock failure at large scales translated into injuries to personnel, loss of lives, production delay, damage to equipment and mine infrastructure, mine closure and lose of the entire mineral reserves exploitation are significant consequences of the lack of proper knowledge in rock failure behaviour. Rock violent failure is a major threat to the future exploitation of deep mining resources all around the world (Akdag et al. 2018).

A Proper characterisation of the total process of rock deformation in pre-peak and post-peak regimes, associated with the decrease of rock load-carrying capacity is critical to many civil engineering applications, mining development projects and mineral exploration operations. Rock brittle fracture damage, detrimental to the stability of surface and underground rock excavations, is amongst major practical applications (Munoz et al. 2016a). In this manner, pioneering studies on the complete stress-strain behavior of rocks undergoing quasi-static compression classify rocks into two categories: class I, characterized by a negative post-peak slope, where fracture propagation is controllable, and class II, showing positive post-peak slope, where fracture propagation is uncontrollable (Hudson et al. 1971, Fairhurst & Hudson 1999).

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