Study on Bearing Capacities and Failure Stages of Tunnel-Type Anchorage Considering Different Failure Modes

The existing studies mostly take the occurrence of plastic zones or stress peak point transfer on the contact surface of anchor rock as the criterion for the limit state. However, due to different engineering geological conditions, there are significant differences in the fracture surface alignments of tunnel anchors, and the ultimate bearing capacity of the tunnel-type anchorage (TTA) cannot be accurately derived. To further explore the working process of the TTA under pull-out loading, the power exponential form was used to characterize the shape of the inverse cone damage rupture surface, based on Mindlin's stress solution and the peak shear stress control theory. The interface failure stress distribution was obtained, the equations for the bearing capacities under 2 damage forms were given. Five domestic TTA suspension bridges were taken for example and verification in both damage forms, and the effects of different parameters on the TTA load-bearing capacity were analyzed. The results show that, the main source for the bearing capacity is the cohesive force on the fracture surface, which is more than 50% of the total. The bearing capacity increases linearly with the length and the cohesion force, and grows with the inclination angle at a slowing rate. The bearing capacity would first increase and then decrease with the inclination angle under the interface failure form. These derived results are basically in agreement with those previous experimental and numerical results. The analysis of the proposed analytical displacement curves indicates that, the working process of the TTA has 3 visible stages, and the final failure mode is a combination of the interfacial failure and the inverse cone failure.