Estimation of reinforcing effects of FRP-PCM method on degraded tunnel linings

Fiber-reinforced plastic (FRP) is a practical alternative construction material that has been extensively adopted in the reinforcement of concrete structures. The reinforcing effect of FRP grids needs to be quantitatively estimated when the grids are applied to degraded tunnel linings to assist with the maintenance design. In the present study, the reinforcing effect of FRP grids embedded in Polymer Cement Mortar (PCM) shotcrete (the FRP-PCM method) on degraded tunnels was estimated. Laboratory direct shear tests and bending tests were carried out on specimens reinforced with various grades of FRP grids to obtain the mechanical properties of the bonding surfaces between the PCM and the concrete reinforced by FRP grids. The bending test results showed that the bearing capacity of beams reinforced by FRP grids subjected to bending loads improved by around 40%. A numerical modeling of the reinforced tunnels by the FRP-PCM method was performed using the properties obtained from these laboratory tests to investigate the reinforcing performance of the FRP-PCM method on degraded tunnel linings. Numerical models with different loosening pressures acting on the tunnel lining, ground classes, degrees of lining deterioration, and degrees of tunnel health were considered, and the suitable conditions under which the application of the FRP-PCM method could effectively reinforce tunnel linings were proposed.