Seismic performance evaluation of high ground stress soft rock tunnels using incremental dynamic analysis

Soft rock tunnels excavated under high ground stress are particularly vulnerable to seismic loading due to their low stiffness and complex rock-lining interaction. This study presents a performance-based seismic evaluation of a deep-buried soft-rock tunnel using Incremental Dynamic Analysis (IDA) implemented in MIDAS GTS NX. A two-dimensional numerical model of a semicircular tunnel with a diameter of 10 m and a burial depth of 500 m is subjected to incrementally scaled earthquake records representing moderate and strong seismic excitations. Key engineering demand parameters, including displacement, base shear, and drift ratio are evaluated, and IDA-based fragility curves are developed to quantify damage exceedance probability. Unlike most exciting tunnel seismic studies that rely on linear or single-intensity dynamic analyses, this study integrates IDA with fragility assessment to systematically capture nonlinear response evolution and record-to-record variability of deep-buried soft rock tunnels under high ground stress. The results indicate pronounced nonlinear deformation and amplification of internal forces with increasing seismic intensity, with maximum displacement and base shear increasing by approximately 90 % and 50 %, respectively. The findings demonstrate the effectiveness of IDA as a vibration-based performance evaluation tool for underground structures and provide new insights for the seismic design of tunnels in high-stress and seismically active regions.