Effects of normal stress on shear properties and acoustic emission characteristics of bonded rock-concrete interfaces

Direct laboratory shear tests, accompanied by acoustic emission (AE) monitoring, were performed to examine the influence of normal stress (ranging from 4 to 16 MPa) on the shear behavior and acoustic emission characteristics of bonded granite-concrete interfaces. The findings indicate that an increase in normal stress correlates linearly with enhancements in peak shear strength, residual strength and shear stiffness, while also facilitating a transition from ductile to brittle modes. Furthermore, elevated normal stress induced a 'double peak stress' phenomenon following softening, which intensified the degree of interfacial damage. AE analyses indicate that peak shear stress is responsible for generating high-energy AE signals, while the cumulative AE energy exhibits a slight increase prior to failure. Conversely, the cumulative AE count diminishes under elevated normal stresses. The b value and F-function serves as an effective indicator of crack evolution; The significant decrease in b-value at peak stress and the significant increase in F-value at peak stress are associated with brittle damage. Additionally, the proportion of shear damage signals in specimens, as determined by the joint Gaussian Mixture Model (GMM) and Support Vector Machine (SVM), was found to exceed 75% and to rise with higher normal stress levels. These findings underscore the significant influence of normal stress on the brittle-ductile transition and the degree of interfacial damage, thereby providing theoretical insights for the optimization of tunnel lining design in the context of high geostatic stresses.