Precast tunnel segments reinforced by macro-synthetic fibers during TBM operations: an experimental and numerical study

In the scientific community and among designers there is a growing interest on macro-synthetic fibers for use in underground structures, especially for precast tunnel segmental linings. Segment reinforcement is generally designed according to the design actions on tunnel segments, resulting from segment transportation, placing process and ground pressure in the final state. In particular, during construction, the high-concentrated forces exerted by TBM jacks are the most critical factors, which could lead to undesirable cracks. Within this framework, the present study investigates the possibility of using polypropylene (PP) fiber reinforcement in hydraulic precast tunnel segments. In a first phase, point-load experimental tests on full-scale tunnel segments of a hydraulic tunnel were carried out. In a second phase, based on data initially retrieved, a reliable numerical model was developed. The latter was used for numerically simulating the segment behavior during TBM operations by including Fiber Reinforced Concrete (FRC) post-cracking properties through a non-linear concrete crack model. Different reinforcement configurations (fiber reinforcement and traditional rebars) were considered, as well as possible irregularities that can occur during this temporary phase.