Mechanical Behaviors of Anchorage Interfaces in Layered Rocks with Fractures under Axial Loads

Rock bolts are widely employed as an effective and efficient reinforcement method in geotechnical engineering.Sandwich composite structures formed by hard rock and weak rock are often encountered in practical projects.Furthermore,the spatial structure of the rock mass has a direct influence on the effect of the anchorage support.To investigate the impact of rock mass structure on the mechanical characteristics of anchorage interfaces,pull-out tests on reinforced specimens with different mudstone thicknesses and fracture dip angles are conducted.The experimental results indicate that the percentage of mudstone content and fracture dip angle have a significant influence on the pullout load of the samples.A weaker surrounding rock results in a lower peak load and a longer critical anchorage length,and vice versa.The results also show that 70%mudstone content can be considered a critical condition for impacting the peak load.Specifically,the percentage of mudstone content has a limited influence on the variation in the peak load when it exceeds 70%.Optical fiber deformation results show that compared to the rock mass with fracture dip angles of 0°and 60°,the rock mass with a fracture dip angle of 30°has a more uniformly distributed force at the anchorage interface.When the fracture dip angle exceeds 60°,the dip angle is no longer a key indicator of peak load.The accuracy of the experimentally obtained load-displacement curves is further verified although numerical simulation using the discrete element method.