Coupled Thermo-Mechanical Study of Crack Initiation Stress Threshold in Porous Sandstone

Abstract

The increasing depth of tunnels and underground mining operations worldwide has resulted in the rise of deep mines at temperatures well above 50°C. Such unwanted thermal gradients not only adversely impact the physical and mechanical behaviours of the rock mass but could also affect the safety of underground mines leading to temporarily and permanently shutting down the operation. The combination of high temperature and high-stress conditions further culminates in explosion-like fractures like rockburst and spalling, which are the main problems in deep mining and tunnel constructions. Spalling is identified as an abrupt explosion-like rock failure that occurs spontaneously and can endanger tunnelling and mining operations, causing injuries and fatalities, and necessitating investigation of the effect of temperature on rock behaviour. It is known that the spalling strength is correlated with the internal crack initiation in low-porosity and brittle crystalline rocks. This paper investigates this phenomenon and examines the influence of coupled thermo-mechanical conditions on the crack initiation stress level of sandstone samples. True triaxial compression tests were carried out on 50 mm sandstone cubes from room temperature (25°C) to 100°C using a high temperature true triaxial testing facility. The results suggest that temperature can have a significant impact on crack initiation and the spalling strength of rock, particularly at low confinement.