Numerical analysis of buried pipelines response to bidirectional non-uniform seismic excitation

The multi-directional, spatially variable earthquake motion is a primary cause of pipeline damage during earthquakes. A comprehensive finite element model considering soil nonlinearity and pipeline-soil interaction nonlinearity was established and validated based on shaking table tests and then employed to investigate the difference in response of buried pipelines subjected to longitudinal unidirectional (UD) and bidirectional (BD) horizontal non-uniform excitations. The responses were evaluated in terms of the acceleration and axial strain time histories along with the peak axial strain, hoop strain, and radial strain in the pipeline cross-section. The results demonstrate that the strain response and axial force of the pipeline under BD excitation are 50%-70% larger than under UD excitation. The large difference is attributed to the increase in maximum frictional force and the delay of the strain growth inflection point under the BD excitation. It was also observed that the pipeline cross-section experienced only lateral ovalization under the UD excitation. For the BD excitation, the cross-section experienced both lateral ovalization and vertical ovalization. Finally, the existence of the Y-direction seismic component in the BD excitation did not significantly change the X-direction acceleration response of the pipeline but increased the peak values.