An experimental evaluation of pile-anchor strengthening mechanics for existing tunnels in landslide region

The landslides have an important influence on the force and deformation of existing tunnels, which may adversely affect the liner structures and even endanger normal operation. Current scholars have made few efforts to investigate the reinforcement measures for existing tunnels in the landslide region, and even paid less attention to probe into the pile-anchor strengthening mechanics. A new kind of pile-anchor strengthening system for existing tunnels has been proposed in this paper considering the influences of deforming landslides, in which the anti-slide pile, the anchor cable and the tunnel lining were integrated as one force whole. In order to observe the pile-anchor strengthening mechanics, three physical model tests for comparative analyses were established in case of the tunnel axis parallel to the sliding direction of landslide, including the conditions without reinforcements, only with anti-slide pile and full with the pile-anchor strengthening system. Specially for the pile-anchor strengthening model tests, the extra experimental evaluation for the interaction mechanics between existing tunnel and landslide was added, such as, the tunnel diameter of 40 and 50 mm and the pile-anchor of three and six pairs. In addition, three-dimensional numerical models were implemented to analyze the landslide deformation and the internal force of tunnels after installing the pile-anchor strengthening system. Comparing with non-reinforcement, the bending moment of tunnel and contact stress at interface between tunnel and landslide at the position of 200 m away from tunnel entrance with six pairs pile-anchor reinforcement dropped by 97.2% and 50%. The results show that the deformation of landslide, the bending moment of existing tunnel and the contact stress at the interface between tunnel and landslide pronouncedly diminish after taking the pile-anchor strengthening measures. The new combined pile-anchor system has higher bearing capacity and stability, which can further improve the operation safety of existing tunnels in landslide region.