Cracking behaviour of tunnel lining under bias pressure strengthened using FRP Grid-PCM method

Abstract

During operational stage, lining cracking is a common anomaly for road tunnels, which seriously affects the integrity and service-life of tunnels. Bias pressure is one of the most important factors that cause lining cracking. In order to provide a novel and effective control method for lining cracking, a series of scale tests regarding the strengthening of tunnel lining using fiber reinforced plastic grid with polymer-cement-mortar (FRP grid - PCM) were carried out, and the effects of various parameters on the control of lining cracking, such as the acting range of bias pressure, the layout range of the FRP grid layer and the number of FRP grid layers were studied. The scale tests were composed of seven specimens, including two reference specimens under different acting ranges of the bias pressure and five strengthened specimens with different strengthening parameters. The inhibitory mechanism of FRP grid layer for lining cracking was also discussed. The results show that the FRP grid layer could effectively bear tensile stress, so that the propagation of the tensile crack was effectively suppressed, and the bearing capacity of the lining was significantly improved. When the acting range of the bias pressure was small, that is, the internal force of the lining section was dominated by the bending moment, the FRP grid layer could improve the rigidity of the lining. More specifically, the gain increased with a concurrent increase in both the number and the layout range of FRP grid layers, whereas it worsened with an increase in the acting range of the bias pressure. The results showed that the FRP grid - PCM method is a potential control method for the tensile crack of the lining.