Deformation behavior of D-Shaped shallow tunnels under dynamic loading conditions

Underground tunnels have offered a quick and cost - effective alternative for storage, traffic, and transportation in many countries. Due to intensive and more frequent occurrences of worldwide terrorism attacks on urban tunnels, there is a need to develop a methodology for designing underground structures that can withstand such attacks [14]. Therefore, in the present study, the physical modeling of D-Shaped shallow tunnels is carried out to understand tunnel behavior when subjected to a high rate of impact loading (projectile). To understand the tunnel deformation behavior, an extensive experimental investigation is performed on the physical model of the tunnel in synthetic rockmass subjected to impact loads. For rock-tunnel modeling, three different cover depths are considered. The impact loads of varying magnitude are applied at the center using drop hammer equipment. The deformation of the tunnel crown is measured along the tunnel length by means of a linear variable differential transducer (LVDT). Further, the finite element method based numerical investigation is carried out by using Abaqus/CAE numerical tool. The validation of the numerical model is performed by using the experimental results. It is found that the cover depth plays a vital role in determining the overall stresses and deformation when the tunnel is subjected to either static or dynamic loading. From the experimental and numerical investigations, it has been observed that the tunnel with the lowest cover depth experience excessive deformation, and the zone of influence, i.e., area through which crack propagates, is less. The maximum deformation along the tunnel length is observed in the D-Shaped shallow tunnel as compared to the Circular Shape tunnel.