Laboratory Observation of Spalling Process Induced by Tangential Stress Concentration in Hard Rock Tunnel

Abstract

A series of laboratory experiments were carried out to study the tangential stress concentration–induced spalling failure process of rock in an arch-shaped tunnel model under plane-strain loading condition by considering different geological conditions, i.e., a tunnel with and without a fracture nearby. Different fracture properties, i.e., open fracture and fracture with different infilling materials around the tunnel, were designed to study their influence on the spalling behavior. Digital image correlation (DIC) and acoustic emission (AE) were combined to track the spalling initiation and formation, which is characterized by the deformation field and energy release rate evolution. Spalling at two sidewalls of the tunnel without a fracture under concentrated tangential stress, and formation of various thin slabs and detachment from the free boundary due to the initiation and propagation of dilatant cracks were well reflected. Asymmetrical spalling failure was observed due to the existence of the fracture around the tunnel. It was found that the open fracture makes the spalling more concentrated and leads to larger failure extent and more intensity than the tunnel with a filled fracture.