On the Mitigation of the Risk of Prefabricated Tunnel Linings: the ACCIDENT Project

Underground structures, and in particular tunnels, are assuming a strategic role in the construction field. The traffic management in the underground, e.g. railway tunnels, roads and subways, or providing other services, e.g. pipes for water supply or hydropower and sanitation, represents a growing need for civilized countries. The paper presents some new design aspects aimed at the construction of prefabricated lining segments for urban tunnels in soft ground, able to ensure adequate structural performance under exceptional loads, such as fire and explosion within the structure. The design problems and the advantages resulting from the adoption of high performance fiber reinforced materials, like High Performance Fibers Reinforced Cementitious Composites (HPFRCC) and Steel Fibre Reinforced Concrete (SFRC) and Textiles (TRC) are described, pointing out the critical issue in the design of a new prototype characterized by a layered structure. A dynamic meso-scale characterization carried out by using a shock-tube suitably designed and a full scale test reproducing an internal explosion in a concrete pipe embedded in a soft soil, aimed at checking some crucial assumptions used in the segment design are briefly described. The main aim of these tests is the evaluation of reliability in modeling prediction. The results are instrumental to optimize a full scale prefabricated tunnel segment designed according to the New Model Code: its construction allowed us to verify all the technological details and to compute a more reliable estimation of the real production costs and an effective evaluation of the advantages in terms of serviceability and exceptional loads resistance.