Cracking behavior and fracture mechanism of rock-concrete composite interface under different stress conditions: Experimental and numerical approaches

The cracking behavior and mechanical characteristics of rock-concrete (R-C) composite under different stress conditions are crucial for ensuring engineering safety and stability. In this study, a numerical model of R-C composite was established employing Particle Flow Code (PFC), and systematic numerical tests on uniaxial compression, splitting tension, and variable-angle shear were conducted, with the rationality of the model validated through laboratory tests. The effects of interface dip angle, interface roughness, interface strength, and concrete strength on the fracture characteristics were explored. The results show that the compressive strength of composite exhibits a ''V''-shaped trend with rising interface dip angle β, while tensile and shear strength decrease as β increases. Enhancing concrete strength effectively inhibits crack propagation in composite and improves its crack resistance. Under compression and tension, the cracking behavior of composite is governed by β, interfacial strength coefficient (ISC), interface roughness, and concrete strength ratio. The crack can penetrate and merge across the interface at low β, whereas at high β, interfacial crack tend to form, inhibiting crack merging between material layers. For a given β, there are two critical thresholds for ISC and strength ratio that determine crack propagation paths. Moreover, increased interface roughness weakens interfacial crack propagation. The cracking modes can be summarized as interfacial cracking, through bi-material cracking, and single-material cracking. Under variable-angle shear conditions, increasing interface dip angle, ISC, and interface roughness all lead to weakened interfacial cracking. Finally, a strength prediction model for the fracture behavior of R-C composite under different stress conditions was developed.