Cracks and other diseases may occur in the long-term operation of highway tunnels and reduce the structural load-carrying capacity. Strengthening using carbon fiber reinforced polymer (CFRP) sheets and other materials could extend the service time of the tunnels. However, the process of strengthening tunnels is remarkably different from the process of strengthening aboveground structures because of the secondary load. In order to understand the development of stress and deformation of strengthened tunnels under secondary load, a 1 : 10 scaled model was tested to simulate the tunnel strengthened with CFRP under different damage states. The test results show that CFRP strengthening improved the stiffness of the structure and inhibited the propagation of the existing cracks. The peeling of the CFRP sheets made the strengthened structure quickly lose its load-carrying capacity, causing the instability of the structure. The failure loads of the structures strengthened at different damage states were essentially the same, with an average value of 184% of the original failure load. Nevertheless, the early strengthening helped control the structural deformation. The test results also demonstrate that the bonding strength between the CFRP and the lining is essential for strengthening effectiveness. This study provides a theoretical basis for similar engineering reinforcement designs.

Lining crack is a typical disease of highway tunnels in operation, which affects the long-term operation safety of tunnels. The arch surround is suitable for strengthening tunnel projects with serious cracks due to its characteristics of significantly increasing structural bearing capacity and prolonging service life. However, at present, the damage evolution mechanism of arch surround reinforcement structures under loose loads based on the secondary stress mode is not well understood. Aiming at the above problems, in this paper, based on the load structure method, indoor 1:10 model test of arch surround reinforcement for Grade VI surrounding rock and damaged lining structure is carried out and the stress and deformation law, failure mode and ultimate bearing capacity of tunnel after arch surround reinforcement is explored. On this basis, finite element software is used to simulate the whole process of damage evolution of arch surround reinforced the structure, and to explore the mechanism of mechanical damage evolution of arch surround structure after reinforcement. The results show that the arch surround reinforcement can effectively repair the damaged tunnel and greatly improve its bearing capacity. When the residual bearing capacity of lining is 48.4%, the bearing capacity is increased by 164%. The original structure of the second lining and the reinforced structure of the arch surround are both in large eccentric compression failure. The main damaged parts are the vault and the haunch. The failure of the reinforcing structure of the arch surround is caused by the slip cracking of the combined surface between the second lining and the arch surround. Anchor bolts should be added to improve the shear bearing capacity of the combined surface.

Joint characteristics of rock mass are the key factors of tunnel surrounding rock failure. This paper relies on the two-lane mountain tunnel project and takes the IV class surrounding rock as the research object. By means of on-site investigation, numerical simulation and on-site monitoring, the effects of different joint development characteristics under blasting vibration on tunnel surrounding rock deformation, instability mode and force mechanism of rock bolts are studied. It is found that the instability mode of tunnel is obviously affected by the larger joint dip angles. When the dip angle of one group of consecutive joints is kept unchanged and the dip angle of another group of joints is changed, the vault settlement decreases first and then increases with the increase of joint dip angles. The influence of horizontal joint spacing on surrounding rock deformation and vault settlement is much greater than that of vertical joint. Under the most disadvantageous working conditions of the two sets of consecutive joints, the effective range of the axial force of rock bolts depends on joint dip angles and has little correlation with joint spacing. The axial force of rock bolts decreases with the increase of horizontal joint spacing, while the influence of vertical joint spacing on bolt is less.