Concrete tunnel segments with combined traditional and fiber reinforcement: optimization of the structural behavior and design aspects

This research work concerns shield driven tunnels made in ground conditions. The reinforcement of precast tunnel segments is designed with respect to several mechanics, temporary and permanently loading conditions. These elements are generally made of ordinary reinforced concrete. Fiber Reinforced Concretes (FRC) are composite materials with a cementitious matrix and a discontinuous reinforcement, the fibers, that may be made of metal, glass, synthetic or natural materials. Fiber Reinforced Concrete (FRC) could be a competitive design alternative for tunnel segments as it would allow time reduction in handling and placing the curved reinforcement that has to be used in ordinary RC elements. FRC represents a minimum reinforcement spread out everywhere into the segment, especially in the concrete cover, which in the ordinary segments need to be often considerably thick for the fulfillment of the fire protection and durability requirements. The principal aim was to evaluate the opportunities offered by SFRC (Steel Fiber Reinforced Concrete) in precast tunnel elements. It is of main interest the combination of traditional and fiber reinforcement in order to achieve a good lining structural response with respect to the principal mechanisms governing the design process of tunnel segments.