Mechanical behavior of rock-shotcrete interface under static and dynamic tensile loads

The rock-shotcrete interface has become common in underground tunnels following the widespread application of shotcrete as a support element. The static and dynamic tensile properties of the rock-shotcrete interface were measured using Instron 1342 and split Hopkinson pressure bar (SHPB) apparatus. The effect of loading rate and interface geometry on interface tensile behavior was studied using four levels of loading rate and six types of interface geometries. The results demonstrate that the interface has typical loading rate dependency, which means that bearing capacity of the interface increases with an increase in the loading rate. The bearing capacity and failure modes of the interface are sensitive to the interface geometry. The measured peak load exhibits an early increase and later decreasing trend; there is a critical value (1.2 mm and 1.8 mm under static and dynamic load) in geometry parameter “h” as the dominant failure mode changes from adhesion to cohesion. An interface with greater “h” leads to low bearing capacity. Therefore, the rock surface should be a reasonable roughness during rock surface preparation, and an appropriate depth of sawteeth is crucial to obtain reliable support strength in tunneling engineering.