Reinforcement optimization of fiber reinforced concrete linings for conventional tunnels

摘要

Tunnel linings are generally reinforced with conventional rebars that are placed to resist tensile stresses. As far as the service conditions are concerned, in recent years durability issues have became of paramount importance, especially for underground infrastructures. Durability design generally requires rebar protection against corrosion that can be achieved by reducing concrete porosity and crack width. The former can be obtained by using a matrix with a low water/cement ratio while the latter can be achieved by using a diffused reinforcement; to this aim, discrete fibrous reinforcement may represent an optimal solution. In fact, the addition of fibers into concrete may provide noticeable residual tensile strength at a crack, linking the two adjacent faces of any crack due to the bridging effect provided by its enhanced toughness. The latter also provides a significant resisting contribution against diffused tensile stresses acting in the structural element. However, when localized stresses (due to bending actions) occur, they are more efficiently resisted by localized reinforcement (rebars). Within this framework, this paper aims at investigating the behavior of FRC final tunnel linings, excavated with conventional method. Numerical non-linear analyses were carried out by considering different load conditions in order to achieve a reinforcement optimization based on the combination of conventional (rebars) and fiber reinforcement (FRC). The procedure is applied to a real case of a road tunnel.