Sustainability assessment of different reinforcement alternatives for precast concrete segmental linings

Nowadays, several tunnels bored with Tunnel Boring Machines (TBM) are already in service and various dozens are being constructed around the world. The internal support of these usually consist of precast concrete segmental rings with a low – moderate amount of concrete since these elements are mainly compressed in service conditions and low tensile stresses only appear during initial transient situations (demoulding, stocking, transportation, manipulation and thrust of the jacks). Structural fibres have proved to be an interesting solution to replace part or the total amount of the rebars. In fact, fibre reinforced concrete (FRC) has already been applied in more than fifty TBM constructed tunnels so far. However, the use of FRC is not consolidated yet in this type of tunnels due to the lack of specific design methods until the publication of the last version of the Model Code 2010 as well as the high inertia to change exhibited by the technical community. In this scientific contribution, a multi-criteria decision-making model based on the MIVES method is proposed for assessing the sustainability index of precast concrete segments. This model is able to take into account the three main pillars of the sustainability (economic, environmental and social). By using this model, different reinforcement alternatives (rebars, fibres or the hybrid solution) can be assessed for specific boundary conditions (e.g., tunnel and segment geometry, concrete dosages, transport distances, risks during the manufacturing of the segments). Likewise, this model is designed to minimize the subjectivity of the decision and to facilitate the task of deciding which concrete reinforcement strategy is the most suitable in terms of sustainability. Finally, the model is used to assess the sustainability of different precast concrete segments (with different reinforcement solutions), which are potential alternatives to be used in a real tunnel placed in the metropolitan area of Barcelona.