Crack width design approach for fibre reinforced concrete tunnel segments for TBM thrust loads

Concentrated loads induced during the excavation stage by Tunnel Boring Machines (TBMs) is still a matter of discussion into the tunnelling construction field, this having a strong impact from both the technical (e.g., durability and service conditions) and the economic perspectives. Fiber reinforced concrete (FRC) has been gaining acceptance as a structural material for producing precast segments as this has proven to lead to various advantages respect to the traditional reinforced concrete, especially for improving the crack control during transient loading situations. In this sense, several experimental programs and numerical studies were previously carried out in which the different geometric and mechanical governing variables were analyzed and, from the results, valuable conclusions were derived. Nonetheless, there are still observed lacks and gaps related with the optimum reinforcement design (FRC strength class and/or amount of traditional steel bar reinforcement) which is often hindering the use of fibers as main reinforcement for concrete segments. The main purpose of the research consist in developing a parametric analysis related with the TBM-thrust effects on FRC segments by means of using a non-linear 3D FEM, previously calibrated with full-scale tests. The results are used to determine the range of FRC strength classes suitable for controlling the crack with during the TBM thrust phase. The results and conclusions are expected to be useful for tunnels designers when establishing the FRC mechanical requirements.Peer Reviewe