Behaviour of FRC segments with GFRP cage under TBM thrust in presence of GAPs

Due to their structural performance and durability, Fibre Reinforced Concrete (FRC) precast segments are now commonly used in major tunnelling applications around the world. The paper investigates the effects of irregular loading on the segments due to poor alignment, which can occur on the tunnel lining during construction as a result of the operation of the Tunnel Boring Machine (TBM). During construction, as the TBM progresses, defects on the tunnel lining can arise. Cracks can then be caused by improper load application by the TBM thrust jacks (due to uncorrected inclination or eccentricities). Further defects can be caused by non-uniform ring joints and this needs to be taken into account in the design and construction of the lining. Because the precast segments are not supported uniformly by the previous ring, they are subjected to a transient bending moment that can jeopardise their integrity and performance during both the excavation phase and service life. The proposed hybrid solution of FRC segments with Glass Fibre Reinforced Polymer (GFRP) reinforcement presented in this paper can overcome these situations, which cannot be satisfied with FRC-only segments, by means of an “elastic-return action” provided by the GFRP reinforcement. Two full-scale tests simulating the TBM thrust, for which irregular support conditions were taken into account, were carried out. Based on the obtained results, it is concluded that the proposed hybrid solution shows almost full recovery of the initial geometry with residual crack widths measuring 79% less compared to the FRC-only solution.