Study on mechanical properties and fracture behaviours of rock-mortar specimens with an interface crack under radial compression

Abstract

Rock-mortar (R-M) structures are commonly used in underground mines to ensure safe mining production. However, the imperfect bonding between rock and mortar leads to initial cracks at the R-M interface, posing a significant challenge to mining operations. To better understand the fracture properties of R-M composite structures containing an interface crack, this study developed numerical models of R-M disc specimens using the particle flow code (PFC2D) and validated them through laboratory tests. Subsequently, Brazilian splitting tests at a rate of 0.15 mm/min were conducted to study the effects that the length-to-diameter ratio (a/R) and crack inclination angle (θ) have on the fracture properties of R-M structure. The results reveal that the peak load of R-M specimens decreased with the increasing a/R and increased with the increasing θ. As a/R increases, the difference between the peak loads of R-M specimens with larger θ and those with smaller θ increases. For a/R = 0.2 and 0.4, the cracks in the R-M specimens with θ = 0°, 15°, 30°, 45° and 60° primarily initiated from the interface crack tips, while those with θ = 75° and 90° initiated away from the interface crack tips. The larger the θ, the closer the initiation location was to the center of interface crack. For a/R = 0.6 and 0.8, the cracks no longer initiated from the interface crack tips at θ = 60°. Additionally, cracks were more likely to initiate and propagate in mortar with lower strength. Moreover, a fracture criterion was established and validated. This criterion provides a quantitative method to predict the failure of R-M structures.