Crack Initiation Evolution Under Triaxial Loading Conditions

Abstract

In response to high demands for minerals and in the light of rapid advancement in instrumentation and testing facilities, mines, tunnels, and infrastructures are getting deeper at an annual increasing rate. For instance, Australia’s deepest Gwalia gold mine near Leonora is extending beyond 2 km depth in the hunt for more ore. In Europe, the Gotthard sub-alpine base tunnels exceeding 10 m wide are excavated at depths greater than 2 km. At depth, explosion-like fractures occur which are known as stress spalling, slabbing, or rock bursting due to high-pressure environment, high temperature, and low porosity. Although rockburst and spalling failures have both been observed in the past 50 years and investigated by numerous researchers, this phenomenon is yet mysterious and the physics behind is still not fully understood. Recent researches have suggested that the spalling strength can be related to the crack initiation point. Various methods have therefore been proposed to identify the crack initiation at laboratory scales based on stress-strain response. Limited models are also available based on applied stresses, but only under triaxial conditions. This study aims to compare the volumetric strain method (as a strain-based technique) with the improved Griffith and Hoek-Brown criterion (G-HB) (as a stress-based method) to determine the crack initiation stress threshold under triaxial loading conditions.