Pressure-impulse diagrams for SFRC underground tunnels

In this work, a numerical procedure based on a simplified FE model for the analysis of underground tunnels subjected to internal explosion is proposed. The procedure can provide a valuable tool for designers for checking the structural tunnel safety in case of an internal blast event. The tunnel geometry considered is that adopted for the Brescia metro line. It has an inner diameter of about 8.15 m, a length of about 13.7 km and is located from about 23.1 m below the surface (distance measured from the surface to the centre of the tunnel). Six segments and a smaller key segment (6+1) compose the tunnel. The segment average length is of about 1.5 m. The FE model is firstly tested under serviceability static loads. Dynamic analyses are carried out in order to reproduce the blast scenario. Aim of this work is the pressure-impulse (p-i) diagrams generations for underground tunnel in case of internal explosion. Limit state criteria based on ultimate flexural and shear capacities are introduced. Two tunnel structural solutions are considered: A traditional solution where the lining section is made of R/C and a new solution in which a layered precast tunnel segment is made of different fibre-reinforced cementitious composites.