Influence of freeze-thaw cycles and shear rate on sandstone-concrete interfacial bond strength: Experiment and degradation model

In the construction of tunnel engineering in cold regions, the good bonding between shotcrete and surrounding rock is the premise to ensure the stability of engineering support. However, the interface bonding between shotcrete and surrounding rock will be degraded by the freeze-thaw (F-T) cycles and the blasting vibration generated in the construction process of drilling and blasting method. Therefore, Firstly, the interfacial shear mechanical properties tests with different F-T cycles (i.e., 0, 5, 10, 15, and 20) and different shear rates (i.e., 0.25, 1.0, 2.0 and 4.0 mm/min) were carried out. Secondly, the effects of F-T cycles and shear rate on the variation of stress-displacement curve, the peak strength and interfacial failure mode of sandstone-concrete interface were analyzed. Finally, an interface degradation model for evaluating the effects of the above two factors was proposed. The primary conclusions are as follows: (1) With the increase of F-T cycles, the interfacial peak strength decreases gradually, while the adhesion area of sandstone on the concrete side increases gradually. The interfacial shear failure caused by F-T actions mostly occurs on the sandstone side. (2) With the increase of shear rate, the peak strength and the shear stiffness of sandstone-concrete interface increase gradually. The shear deformation of the interface is mainly reflected in the damage form of "abrasion, extrusion and shearing" between particles. (3) The greater the strength difference of rock materials on both sides, the side with weaker rock strength is the key area for interfacial F-T deterioration and debonding. (4) A new interface degradation model of rock-concrete interface shear strength considering F-T actions and shear rate was established, and the reliability of the theoretical model was verified. The study provides experimental and theoretical reference for exploring the interfacial debonding evolution mechanism of shotcrete in tunnels in cold regions.