Crack path at bedding planes of cracked layered rocks

Abstract

The evolution of cracks in layered rocks is a basic issue in stability analyses of underground openings in layered rocks. This study presents the crack penetration/deflection behaviour of bedding planes in layered rocks with a designed three-layer system that consists of two pre-existing cracks. The effects of crack spacing (S, between two pre-existing cracks), layer thickness (T), and their ratio (S/T) on the cracking paths of a propagating crack are investigated. A semi-artificial (SA) method is suggested to prepare the test specimens, which includes a natural rock layer and artificial bedding planes. The SA specimens offer advantages over natural rocks and pure artificial materials. Numerical simulations of the crack penetration/deflection behaviours are also conducted based on a two-dimensional particle flow code. The results indicate that the crack path is determined by a critical S/T ratio. The propagating crack can deflect along the bedding planes and coalesce with pre-existing cracks if the S/T ratio is lower than the critical value. If the S/T ratio is greater than the critical value, the propagating crack will penetrate the bedding planes and rock layers without experiencing any crack coalescences. The critical S/T ratio decreases as the plane strength increases. Load-displacement responses and acoustic emission activities are also discussed to improve the understanding of crack/bedding plane interaction in layered rocks.