Seismic response and fragility evaluation of circular tunnels in the Himalayan region: Implications for post-seismic performance of transportation infrastructure projects in Jammu and Kashmir

The expanding infrastructural projects together with the prior historical records of significant earthquakes including the deadliest 2005 Kashmir earthquake in the Himalayan region, urge to assess the seismic vulnerability and risk of Jammu and Kashmir. This paper attempts to assess the seismic vulnerability of circular tunnels using the fragility function for various seismic environments. To accomplish this, the seismic performance of tunnels is quantified for each hazard zone with a diverse typology and seismic scenario. Microzonation results aided in defining the four hazard zones based on seismic severity. Zone A, B, C, and D are seismic zones with severe, high, moderate ad low Seismic Hazard Indexing (SHI). Tunnel performance is evaluated for each hazard zone, and empirical correlations for damage indices are defined. For Zone A, the fragility curves presented for minor, moderate, and extensive damage states for both shallow and deep tunnels appear to be extremely catastrophic. For various slippage conditions, the variation of flexibility and racking ratios for tunnels with shallow and deep overburden depths is significant. The proposed fragility curves are used to evaluate the seismic risk of a roadway network that includes A, B, and C routes that pass through Jammu. The risk matrices and probability function revealed that all tunnels on Route A are extremely vulnerable to damage. Extensive portal collapse and tunnel lining failure will render this route inoperable during the post-seismic phase. The developed empirical correlations, fragility curves, and risk matrices will serve as a ready-to-use tool for tunnel design engineers working on any Himalayan infrastructure project.