Synergies between Heat- and Stress-Induced Spalling Theory Applied to Rock and Concrete in Tunnel Applications

Fire-induced and stress-driven catastrophic failures in rock and concrete are commonly known as spalling (or rockburst in its severe form) that have jeopardised the safety of personnel, seriously damaged rock structures, and shut down operations for months or even permanently in certain circumstances. Particularly in Australia, spalling and rockburst in deep excavations results in a heavy toll on mine safety and have become a constraint to the economic viability of several Australian deep mines since the early 1950s. The prevailing industry approach is to treat such unwanted failures and associated microseismic events as a result of insufficient energy absorption by the spalling-prone rock/concrete at the post-peak stage. However, this approach does not allow efficient handling of heat- or stress-induced failures as it requires an in-depth understanding of their mechanics. Prediction of these events based on the available failure criteria does not help either due to the numerous criteria involved and the difficulty in determining their parameters at the excavation scale. A proper understanding of the fracture growth in such failures is needed to understand the behaviour of rock or concrete structures resulting in a sudden release of energy at deep excavations. This paper investigates the similarities and differences between heat-induced concrete spalling and stress-driven rockburst and further examines the effect(s) of material, geometrical, geological properties, and the applied deviatoric stresses on these failure modes.