Structural Behavior of Precast Tunnel Segments Reinforced by Macro-synthetic Fibers During Temporary Loading Phases

Fibre Reinforced Concrete (FRC) has been increasingly used in precast tunnel linings. FRC, with or without conventional reinforcement could be an adequate solution for fulfilling the structural requirements. The design process of segmental concrete linings in ground conditions generally refers to the final permanent embedded in ground condition as well as to temporary phases. Among these temporary phases, the TBM thrust jack phase is a crucial loading condition during construction, which may noticeably govern the segment design. Tunnel elements having an internal diameter of 3.50 m and a thickness of 0.20 m were studied through full-scale tests to shed new lights on the possible use of macro-synthetic fibres in segmental lining. Precast segments were tested under bending in order to reproduce typical flexural conditions occurring during de-moulding, storage and transportation. Moreover, in order to study lining behaviour during TBM operations, segments were also tested under high concentrated loads for reproducing the excavation phase. Three main reinforcement solutions have been analysed: macro-synthetic fibres only (MSFRC segments), combination of an optimized amount of rebars and macro-synthetic fibres (Hybrid segments) and the reference solution made by conventional bars reinforcement (RC segments).