An Overview of the Seismic Verification Analyses Performed for Natural Gas Pipeline Networks

The purpose of this paper is to present an overview of the various seismic analyses performed and the measures taken to ensure the mechanical integrity of the natural gas pipeline networks in Greece. Design of large pipeline networks in an open countryside is a complicated issue and involves many disciplines and works, such as, preliminary geological investigation, topographical investigation, detailed geotechnical investigation, adjustment of pipeline routing (if necessary) according to the detailed investigation results and finally pipeline stress verification due to stresses induced by seismic loading caused either by soil lateral spreading during a seismic event or by the rupture of active faults. Engineering judgment and previous experience are important to determine the best pipeline routing, however, due to the large seismic events occurring in Greece, measures are always necessary to improve the seismic response of pipeline networks. Loading of buried pipelines, due to earthquake induced permanent ground displacements (active fault rupture and lateral spreading) is displacement controlled. Various analyses were performed to evaluate the maximum ground surface acceleration and its reduction with depth, which control the outcome of the liquefaction potential. The results of the liquefaction analyses were used to compute permanent ground displacements. These displacements as well as the active fault displacements were applied to critical parts of the pipeline network and elasto-plastic analyses were performed to compute the resulting pipeline stresses and strains. Various mitigation measures have been taken to release pipeline stresses, such as changing (where possible) the pipeline routing, widening the pipeline trench in critical areas, using a light-weight backfill material, increasing the pipeline thickness, etc. The paper will present an overview of the various analyses performed and will summarize the measures taken to improve the seismic response of the pipeline network.