Examination of the performance of viaduct with pile groups underoblique-slip fault creeping: a case study in Chegualin Fault, Taiwan

    Since the 1999 Chi-Chi Earthquake, earthquake engineering has devoted much effort to the issues of fault rupture-engineering structure interaction in Taiwan. So far, the Central Geology Survey of Taiwan has announced 36 active faults. Due to natural terrain conditions, linear traffic structures are difficult to avoid crossing the fault zone. However, the current design code rarely considers the effects of long-term fault creeping displacement in the assessment of structural performance. This study aims to develop a numerical-based performance examination approach for the viaduct with pile group foundations subjected to long-term fault offset. The area where the High-Speed Rail of Taiwan crosses the Chegualin Fault was selected as the case study. Remote-sensing survey and structural monitoring both indicated that the viaduct has been offset by approximately 30 cm due to fault creeping since 2006. The ratio between right-lateral and uplift movements is approximately 7:1. This study adopted coupled FDM-DEM technique as the numerical tool, and first validated its performance by physical sandbox tests. We used non-cohesive soil as the overburden material and polyethylene hollow foam tube as the foundation piles. Several key factors, including the Riedel shear bands, fault extended distance, tri-shear zone, pile cap deformation, were compared between numerical and sandbox models. Next, full-scale numerical modeling was calibrated based on in-situ structural monitoring data. The comparison of bridge pier displacement shows approximately 80% agreement between simulation and monitoring data. We found that the deformation of piles was dominated by the location of the fault tip. Simulation shows that the maximum rigid-body rotation of the pile cap will occur close to the fault tip. The cap of each pile group exhibits differential rotations and displacements behaviors, resulting significant superstructure distress. Based on the simulation, the performance of the High-Speed Rail in the study area was expected to fail meeting the current design code of Taiwan after 50 years.