Research on mechanical performance of longitudinal joints in segmental tunnel linings strengthened by fiber-reinforced plastic grid with polymer-cement-mortar method

In this study, we propose the use of a fiber-reinforced plastic grid with polymer-cement-mortar (FRP Grid-PCM) to reinforce segment joints in tunnel shield linings. These joints play a crucial role in determining bearing capacity but are vulnerable to deterioration during operation. To investigate how to enhance the flexural performance of longitudinal shield lining joints, we built eccentric short column specimens by bolting two half-corbel columns together and tested them in the laboratory. The test program comprised two control specimens and three strengthened specimens with FRP grid applied on one side, away from the axial load. The tests varied two main parameters: loading eccentricity and the number of FRP grid layers. We conducted a detailed analysis of the failure process, bearing capacity, and bending stiffness of longitudinal joints under different conditions. Furthermore, we developed an analytical model to predict the flexural bearing capacity of longitudinal joints upgraded with the FRP Grid-PCM method and validated it through experimental results. The research demonstrates that the FRP grid effectively reduces joint opening and rotation angles while enhancing the bearing capacity of the short column, particularly with concurrent increases in loading eccentricity and the number of FRP grid layers. Overall, our findings offer a novel alternative for improving the flexural performance of longitudinal joints in shield tunnels.