Design of Buried Pipelines against Permanent Ground Displacements

Synopsis

Permanent ground displacements (PGDs) consist one of the most critical loading conditions that need to be taken into account for the design of buried pipelines. In earthquake-prone areas, such displacements are mainly associated to fault rupture, sloping ground failure, or liquefaction-induced lateral spreading. Nevertheless, they may also originate from underground works (e.g. tunneling), differential settlement (e.g. due to lowering of the groundwater table) or heave (e.g. expansive soils undergoing large climatic variations). Especially in the case of step-like deformations, the axial and bending strains developing on the pipeline may become fairly large and lead to rupture, either due to tension or due to buckling. Apart from the detrimental effects that such a rupture can have to social and economic activities, the ecological disaster that may result from the leakage of environmentally hazardous materials should also be highlighted.

The numerical techniques currently utilized in practice for the rigorous performance-based design of pipelines will be initially reviewed. Attention will be drawn to the importance of accurately modelling the non-linear behaviour of pipeline steel, non-linear soil-pipeline interaction effects and second order effects induced by large displacements, which make the corresponding numerical analyses highly demanding in terms of both expertise and computational effort. Emphasis will be then given to recently-developed simplified analytical methodologies for the estimation of the developing pipeline strains. A series of methodologies will be presented, focusing on strike-slip, normal and oblique fault crossings, as well as on cases of differential settlement or heave. These methodologies are based on simple equilibrium and displacement compatibility equations to derive the axial forces applied to the pipeline, while they adopt a combination of beam-on-elastic-foundation and elastic-beam theory to calculate the developing bending moments. Large-displacement non-linearities are indirectly taken into account, while material non-linearities are introduced through an equivalent-linear iterative solution scheme that considers the actual distribution of stresses on the pipeline cross-section. Furthermore, attention will be drawn to the effect of bends existing within the pipeline’s unanchored length, where the pipeline strains may even exceed the strains developing at the PGD zone and become critical for the design.

Based on comparisons with benchmark numerical analyses, it will be demonstrated that the proposed simplified methodologies provide fairly accurate predictions while remaining relatively easy to program and utilize, at least for preliminary design and verification purposes. Finally, the insight provided by the analytical solutions will reveal a number of conclusions of practical interest to pipeline design applications.

About the speaker

Dr Dimitris Karamitros is a Lecturer in Civil Engineering at the University of Bristol, since 2013. He holds a 5-year Diploma Degree (2004) and a PhD Degree (2010) in Civil Engineering from the National Technical University of Athens (NTUA), where he was also employed as a Research Assistant (2004-2010) and Associate (2010-2013). Dr Karamitros has co-authored more than 40 scientific publications (11 in peer-reviewed journals), he has received more than 190 citations of his scientific work (h-index=7, i10-index=6), he is a member of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE) and he has served as a Reviewer for several Journals. His research interests include the performance-based design of buried pipelines, the constitutive modelling of sands and the associated numerical implementation, the numerical simulation of earthquake-induced liquefaction, the liquefaction performance of shallow footings and pile foundations, seismic ground response and dynamic soil-structure interaction. As a Chartered Engineer of the Technical Chamber of Greece, Dr Karamitros has undertaken geotechnical consultancy on several areas, with particular emphasis on the seismic design of natural gas pipelines.

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Presentation slides

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Further information

This evening meeting is organised by SECED and chaired by Dr Stavroula Kontoe (Imperial College London). Non-members of the society are welcome to attend. Attendance at this meeting is free. Seats are allocated on a first come, first served basis. Tea and biscuits will be served from 5.30pm - 6pm. For further information, please contact Greg James (tel. 020 7665 2229).