Numerical Modeling of Buried HDPE Pipelines Subjected to Normal Faulting: A Case Study Xiaojian Xie, a) Michael D. Symans, b) Michael J. O’Rourke, b) Tarek H. Abdoun, b) Thomas D. O’Rourke, c) Michael C. Palmer, c) and Harry E. Stewart c) A systematic study is presented herein on the seismic response of buried pipelines subjected to ground fault rupture in the form of normal faulting. In this study, advanced computational simulations are conducted in parallel with physical testing using a geotechnical centrifuge. For the numerical simulations, the pipeline was modeled using isotropic 3-D shell elements and the soil was modeled using either 1-D spring elements or 3-D solid (continuum) elements. The results from continuum finite-element analyses are compared with those from a Winkler-type model (in which the pipe is supported by a series of discrete springs) and with results from centrifuge tests. In addition, via appropriate modeling of the soil-pipe interaction, the q-z relation of the soil medium is elu- cidated for normal faulting events. The numerical analysis results demonstrate the potential for continuum modeling of events that induce pipe-soil interaction and results in improved understanding of pipe-soil interaction under normal faulting. [DOI: 10.1193/1.4000137] INTRODUCTION Major earthquakes result in rupture at the ground surface. The rupture involves relative displacement in a horizontal plane (strike-slip fault), relative displacement in a vertical plane (normal or reverse fault), or a combination of the two (oblique faults). The response of buried pipelines to seismic faulting has been the subject of numerous research investigations. Physical tests that have been conducted as part of these investigations, along with associated development of numerical models, have often focused on simplified conditions for evaluating the soil-pipe interaction. For example, there have been tests to evaluate soil-pipe interaction wherein plane strain conditions are simulated (all locations along the pipe are assumed to experience the same relative displacement with respect to the soil) and thus a two-dimensional (2-D) plane strain model is utilized. In relation to normal and reverse faulting, some past studies have utilized 2-D plane strain models to study the uplift resistance of pipes buried in sand (soil-pipe interaction) and the corresponding failure mechanism (e.g., Trautmann and O’Rourke 1985, Ng and Springman 1994, White et al. 2001, Chin et al. 2006, Earthquake Spectra, Volume 29, No. 2, pages 609–632, May 2013; © 2013, Earthquake Engineering Research Institute a) Offshore Structural Engineer, American Bureau of Shipping, Houston, TX 77060 b) Dept. of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 c) School of Civil and Environmental Engineering, Cornell University, Ithaca, NY 14853 609