Effect of blast inside tunnel on surrounding soil mass, tunnel lining, and superstructure for varying shapes of tunnels

In this study, a finite element (FE) analysis of shallow tunnels exposed to a blast inside the tunnel, with soil as surrounding medium and a structure at ground level, was performed. The ConWep program, developed by the US Army, was used to simulate blast loading using ABAQUS/Explicit (R). Drucker-Prager (D-P) plasticity model, concrete damage plasticity (CDP), and Johnson-Cook (J-C) plasticity models were used to define the behavior of the soil, concrete, and reinforcement, respectively. FE analysis was carried out to compare the damages to the superstructure with variation in the cross-sectional shapes of the tunnel under internal blast loading. Three tunnel shapes (circular, rectangular, and horseshoe cross-sections) were considered in the FE analysis. An explosive of 100 kg TNT was located at the center of the cross-section of the tunnel. The response of the tunnel in terms of displacement and stress at critical locations was computed. The results showed that changes in the cross-section of the tunnel affect the stability of the tunnel, even when keeping all other factors constant. It was observed that the intensity of the stresses was the highest for a rectangular tunnel and lowest for a circular tunnel. Furthermore, it was also determined that the tunnel with a rectangular cross-section experienced the maximum displacement in the reinforced concrete (RC) lining compared with the horseshoe and circular tunnels. The displacement measured at critical structural members of the superstructure was found to be the highest for the tunnel with a rectangular cross-section and lowest for the tunnel with a circular cross-section.