Comparative study on the seismic response and seismic fragility evaluation of pile-supported box-type versus traditional railway subgrades

A novel pile-supported box-type subgrade (PBS) is proposed to address the seismic shortcomings of traditional earthwork (TE) in high-speed railways. Three-dimensional finite element models of PBS and TE were established and compared under PGA levels of 0.1 g, 0.2 g, and 0.4 g. PBS reduced dynamic displacement by 33%-39%, showed lower peak accelerations with stronger high-frequency attenuation, and achieved a stress attenuation rate of 89.6%, indicating enhanced energy dissipation and wave-impedance matching. Fragility curves (PGA as IM, displacement as demand) further shifted right for PBS with higher IM50, implying a lower probability of damage exceedance than TE at the same intensity. The rigid “box-pile-soil” collaborative system therefore substantially improves seismic stability, supporting PBS deployment in seismically active and geologically complex regions.