Study on the influence of train formation and passenger capacity changes on long-term settlement of subway tunnels

Abstract The progressive settlement of subway tunnels induced by repetitive subway loading represents a fundamental challenge to both structural safety and passenger serviceability. Conventional prediction studies on long-term tunnel settlement commonly presuppose a fixed six-car subway operating at maximum passenger occupancy, thereby disregarding temporal variations in passenger flow and subway formation. Such simplified assumptions fail to capture the complexity of actual operational conditions. To bridge this gap, this paper adopts a data-mining strategy to classify real subway traffic into three representative scenarios: LPFP (Low Passenger Flow Period), MPFP (Medium Passenger Flow Period), and HPFP (High Passenger Flow Period). On this basis, comprehensive numerical simulations are carried out to quantitatively examine the influence of passenger flow fluctuations and subway formation on the dynamic response of soils surrounding tunnels. Furthermore, by integrating the differential principle, an explicit integral prediction framework is established for evaluating long-term tunnel settlement, whose accuracy is subsequently verified against in-situ monitoring data. The analysis reveals that both increasing passenger loading and extending subway formation considerably intensify cumulative settlement. Specifically, the settlement is reduced by 32.03% and 48.49% when passenger demand decreases from HPFP to MPFP and LPFP, respectively. Likewise, shortening subway length from 8 cars to 6 and 4 cars results in settlement reductions of 5.01% and 14.68%, respectively. In comparison with the traditional predictive model, the enhanced differential framework exhibits markedly improved alignment with real operational conditions and thereby demonstrates broader applicability to long-term settlement assessment. In addition, results indicate that approximately 77.19% of the total deformation occurs during the first decade of operation, with 80.20% of the cumulative settlement attributable to the progressive plastic strain of the soil mass.