Seismic Vulnerability Assessment of Urban Metro Tunnels: Influence of Material Properties and Cover Depth through Numerical Modelling

Structures constructed, either above or below the ground, are susceptible to damage by seismic vulnerabilities.In underground structures, especially tunnels, these vulnerabilities may lead to catastrophic failure causing infrastructural damage and loss of human lives.Therefore, construction of tunnels in urban regions require understanding of complex geological ground conditions for designing the underground tunnel system resistant against vulnerable seismic conditions.Studies indicate concerns in underground tunnels, during and post seismic effect, which require engineering assessment to ensure the tunnel structural safety.Hence, mechanical behaviour analysis of the tunnel lining is essential to determine the influence under varying conditions and its susceptibility to different ground motions.The current study analyses the seismic vulnerability impact on tunnel lining under variability in ground material characteristics and overburden depth.The analysis determines the ground motion impact in both x and y directions to comprehend the tunnel lining behaviour and further improve its seismic resistance.The behaviour is analysed to compare different mechanical parameters required for tunnel lining design in both the directions.To carry out this, three analytical frameworks: linear static, eigenvalue, and nonlinear time history analysis, defines the methodology utilised to simulate the seismic behaviour analysis under different scenarios.This is numerically simulated using finite element software, MIDAS GTS NX, analysing the structural sensitivity against combined variation in material characteristics and overburden depth for different seismic ground motions.The study utilises acceleration time-history plots of the Tokachi and Tohoku Coast ground motions to understand the behaviour.The analysis for different analysed cases suggests significant influence of material characteristics on maximum displacement, axial force, and bending moment compared to the seismic impact.In this, higher tunnel overburden depth leads to higher axial force and bending moment on tunnel lining depicting the influence of overburden depth.Thus, the results obtained using numerical analysis provide comprehensive behaviour of the tunnel lining, which can be utilised by designers for enhancing the seismic resistance.