FEA of Urban Rock Tunnels Under Impact Loading at Targeted Velocity

This paper presents the effect of impact load and weathering of surrounding rockmass on the deformation behavior of urban underground structures. The FEM based numerical simulation is carried out by varying overburden depths, impact energy, and rock weathering grade. Based on this study, it is suggested that subsidence in tunnel under dynamic loading conditions are basically the function of impact energies, engineering characteristics of surrounding rock mass, depth and diameter of U/G structure, and induced stresses. Overburden depth and weathering grade are found to be the critical parameters in the study. It is observed that the tunnel crown deformation increases with increase in weathering grade. It is also found that the weathering of rock affects the depth of penetration of hammer. The depth of penetration of hammer is large in case of highly weathered Basalt rock as compared to Fresh rock. It is noticed that the increase in cover depth decreases the tunnel deformation and mises stresses around the tunnel periphery. Hence, the tunnels at deeper depth are more stable as compare to the tunnels with lesser overburden depth under dynamic loading conditions. In present work, parametric study is carried out for different rockmasses, subjected to impact loading. The findings of this work suggests that the synthetic rockmass, which is prepared in the laboratory, can be used to replicate in-situ conditions by representing weathered rockmass. Finally, the investigation is performed for the prototype model, and the dynamic response of tunnel lining is computed. The tunnel reinforcement is safe against impact loading, whereas the concrete lining is failed completely at the crown of tunnel and the significant amount of failure is observed along the tunnel length. Hence, the improvement in the tunnel lining material and thickness is required.