On the use of macro synthetic fibres in precast tunnel segments

The effectiveness of tunnel segments reinforced with 12 kg/m3 polymeric macro-fibres in addition to a minimum steel reinforcement ratio has been assessed. Precast tunnel segments have been adopted to test this fibre-reinforced solutions for structural elements, in which the longitudinal reinforcement has been designed to comply only with EC2 minimum reinforcement requirements for no seismic design situations. This experimental campaign is the final step of a wider research, aimed at investigating an optimized mixture for the use of the polymeric fibres ISTRICE, as well as investigating the performance of some structural elements such as slabs, beams and tunnel segments, which are produced by using such a mix design. The experimental programme has been devised in such a way that in a first stage the structural behaviour of a fibre-reinforced tunnel segment has been first of all investigated under a 3 point bending test at 7 days after casting, mainly to underline the behaviour that this element would have in an initial movement phase. In a second stage the effectiveness of the fibre reinforced solution has been checked testing the tunnel segment under a lateral compression at 28 days, to highlight the behaviour of the element during the assembly stage with the advancing of the TBM. The results, analysed in terms of maximum load bearing capacity and crack openings highlight the effectiveness of the proposed structural polymeric fibre-reinforced concrete combined with a minimum steel reinforcement solution, which, also in view of their easiness of execution and reduced invasiveness, can stand as a reliable alternative to traditional reinforced tunnel segments.