Study on shear failure characteristics of fiber-reinforced shotcrete-granite interface based on surface scanning

The shear characteristics of the concrete-rock interface play a crucial role in the stability of engineering structures in geotechnical construction. This study utilized a combination of three-dimensional scanning and sculpting techniques to create fiber-reinforced shotcrete-granite combination specimens. Specimens with varying interface roughness were tested in direct shear under different normal stress conditions. A method for analyzing the shear failure characteristics of granite interfaces using the XTOM industrial optical surface scanning system is proposed. Furthermore, an enhanced formula for estimating the peak shear strength of the interface in fiber-reinforced concrete-rock composite specimens is introduced. The research findings suggest the following: (1) The shear strength of the fiber shotcrete-granite interface is significantly increased by normal stress. Specifically, under joint roughness coefficient (JRC) 2.0 conditions, the shear strength at a normal stress of 2.0 MPa is 185.89 % higher than at 0.5 MPa. (2) A method for analyzing the damage characteristics of rough interfaces using surface scanning technology is introduced. Utilizing surface scanning technology, the rough surface is reconstructed both before and after damage, allowing for the extraction of a two-dimensional roughness curve that effectively captures the influence of normal stress and roughness on interface shear failure characteristics. (3) Based on the observed macroscopic and microscopic damage characteristics, as well as the scanning electron microscope (SEM) morphology of the interface after shearing, it is evident that shearing damage predominantly occurs on the side of the fiber-reinforced concrete. Furthermore, it was found that the degree of damage on the concrete side increases with higher roughness and normal stress levels, while the interface shear strength is enhanced by the presence of alkali-resistant glass fiber (ARGF). (4) The calculation formula of concrete-rock interface shear strength was improved, and its accuracy was verified through experiments. The research findings can serve as a data foundation and theoretical support for studying the shear characteristics of fiber-reinforced concrete-rock interfaces and geotechnical engineering construction.