Hybrid precast tunnel segments in fiber reinforced concrete with glass fiber reinforced bars

The interest in using fiber reinforced concrete (FRC) for the production of precast segments in mechanical excavated tunnel lining is continuously growing, as witnessed by the studies available in literature and by the actual applications. The possibility of adopting a hybrid solution of FRC tunnel segments with Glass Fiber Reinforced Polymer (GFRP) reinforcement is investigated herein. The proposed solution can cover the situations in terms of requirements that cannot be satisfied with the FRC solution only. On the same way the use of GFRP bars can avoid the problems related to the use of traditional steel rebars. A typical metro tunnel geometry is considered, and full-scale segments are designed, cast and experimentally validated. In particular, one flexural and one point load full-scale tests are carried out, for the evaluation of the structural performances (both in terms of structural capacity and crack pattern evolution) of tunnel segments with hybrid solution, under bending, and under the TBM thrust. The experimental behaviors are compared with the ones obtained on fiber reinforced only segments, with the same geometry and concrete material. Finally, the obtained results are discussed, and the effectiveness of the proposed technical solution, in increasing the bending resistance and, mainly in reducing the crack width under flexural and TBM thrust, is highlighted.