Assessing seismic impact and fragility of circular tunnels in North Gyeongsang, South Korea: enhancing post-seismic road route functionality

The North Gyeongsang region in South Korea has demonstrated significant seismic activity over the past two decades. This study assessed the zone-specific performance and vulnerability of lined tunnels, incorporating structural material properties and surrounding geological conditions as primary influential parameters, along with variations in tunnel lining, to develop intensity–response relationships. For Zone E, the seismic fragility curves (SFCs) generated for minor, moderate, and extensive damage levels for both shallow and deep tunnels indicate a high level of catastrophic risk. These proposed SFCs are employed to assess tunnels planned for a proposed road network in Pohang. The findings revealed that Route P2 represents the optimal choice, whereas Route P3 is the least suitable for ensuring the safest design. This analysis includes the formulation of a tunnel-specific risk matrix, which is utilized to define the functionality of each route in post-seismic scenarios within the study area. The combined use of SFCs, risk matrices, and road functionality maps provides a valuable engineering resource for professionals engaged in the earthquake-resistant design and assessment of underground structures in South Korea. This methodology will assist disaster management authorities in risk mitigation and ensuring safe traffic flow on transportation networks.