Interface Stress Analysis and Failure Mechanism of Rock–Concrete Composite Structures Under Multi-directional Stress Waves

The rock–concrete interface serves as the weak point of concrete structures based on rocks; the initial failure of the interface under stress waves can easily cause instability and failure of rock concrete composite structures. This study conducted a range of numerical investigations using MAT-COHESIVE-MIXED-MODE cohesive element to describe the failure properties of rock–shotcrete’s interface transition zone (ITZ). The research results can reveal ITZ’s failure mechanism and mechanical property under different stress wave incidence orientations and confining pressures. It can be concluded that under multi-directional dynamic stress waves, the failure mode of the ITZ is represented as a complete failure with the angle from 0° to 45°, the local penetration failure of the ITZ with the angle from 60° to 90°, and the highest failure rate of only 4.89%. Under different confining pressure, the 40 MPa as a threshold can reduce the failure rate of the ITZ from 100% to 41.74%. The confining pressure delayed the stable stage initial angle of tensile and shear displacement from 60° to 75° under the coupling effect of the multi-directional stress wave and confining pressure. For interface displacement control, the incidence angle should be better than 75° under confining pressure, and the angle can be controlled above 60° without confining pressure. Therefore, for tunnel surrounding rock support, attention should be paid to displacement and deformation control at positions where the angle between the excavation blasting direction and the primary lining surrounding rock bonding surface is less than 75°.