Designing Pipelines in Areas with Moderate or High Seismic Risk : Geohazard Assessment Beyond EC8 Provisions
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During the last decades hundreds of onshore or offshore oil and gas pipelines have been constructed all over the world. It is evident that the geohazard assessment of these pipelines is one of the most important issues of their design. However, in some areas that are characterized by moderate or high seismicity the geohazard assessment is much more demanding and challenging, since many issues are directly or indirectly associated to a potential earthquake. The current paper aims to illustrate the main topics of geotechnical earthquake engineering that have to be coped with for the proper design of pipelines. In the first part of the paper the verification of the pipeline segments against wave propagation loading is described in detail after an extensive review of the impact of local site effects (such as valley and topography) on the ground surface motion. Emphasis is given on the second part of the study, which deals with the distress of pipelines due to permanent deformations that may be caused by a fault rupture, soil liquefaction phenomena, and/or seismic slope instabilities. These permanent deformations are of great importance since they are regarded in general as a more severe loading than wave propagation. Additionally, the paper deals with the provisions of seismic standards, such as EC8, which do not cover sufficiently all the aforementioned issues. It is shown that the complexity of the specific problems requires advanced modeling and realistic simulation on a case-by-case basis. Characteristic case studies of pipelines in seismic prone areas are also presented.
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