Generic design of HPNG pipelines against liquefaction-induced lateral spreading

G. Bouckovalas

The design of high pressure oil and gas pipelines in liquefaction prone areas remains a challenging task. The reason is that such pipelines are particularly susceptible to (vertical and/or horizontal) liquefaction-induced permanent ground displacements (PGDs). For instance, lateral spreading induced PGDs towards the free face of a watercourse may be significant (from tens of cm up to a few meters), with the peak PGD values appearing in the close proximity of the free face. In cases where a buried steel pipeline crosses such a watercourse, the area near the free face is also where the pipeline transitions downward under the waterbed, thus forming an S-shaped geometry in the vertical plane and making this area the most prone for high tensile and bending strains. In addition, case-specific non-linear numerical analyses (e.g. finite element analyses FEA) may become quite cumbersome due to the (3D) geometrical nonlinearity of the pipeline routing and the PGD non-uniformity with distance along the pipeline. In view of the above practical design difficulties, the presentation will focus on an alternative “generic” (as opposed to “case-specific”) design procedure: the typical pipeline response at areas prone to liquefaction-induced lateral spreading is examined via parametric FEA for a distinct number of representative cases of ground topography, liquefiable soil stratigraphy and pipe characteristics, for a wide range of applied PGDs. On top of gaining insight into the pipeline response at such areas, the presented FEA comprise a framework for an efficient liquefaction verification of the pipeline. This framework conservatively replaces case-specific analyses, which may prove a very costly and time-consuming alternative for lengthy pipeline projects in seismically prone areas.