Nonlinear collapse simulation of Daikai Subway in the 1995 Kobe earthquake: Necessity of dynamic analysis for a shallow tunnel

This research conducts dynamic time-history analysis and a modified cross-section racking deformation (MCSRD) method to analyze the collapse mechanism of the Daikai Subway during the 1995 Kobe earthquake using FLAC2D. A simplified approach to consider the nonlinear behavior of a structure element is imported and combined with the FLAC2D built-in nonlinear soil constitutive models to accurately consider the nonlinear interaction between the soil material and structure. Based on the proposed framework, the damage evolution process of the Daikai Subway station can be traced by the dynamic time-history analyses. The collapse pattern roughly agrees with field observation. Regarding the MCSRD method, the critical member of the central column is identified but the internal forces did not reach its limit state; this may be because inertial force is neglected, which is a characteristic of the pseudo-static method. Therefore, it is recommended to conduct dynamic time-history analysis for a shallow buried tunnel in soft soil because the inertial force may largely influence the seismic characteristics.