The Seismic Response Of Buried Gas Pipelines In Inhomogeneous Soil

  • Nick Psyrras

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Buried gas pipelines constitute lifeline systems whose uninterrupted operation is critical to the well-being of the community. Given that these systems are spatially extended, their unavoidable exposure to seismic hazards such as wave propagation is an issue of concern requiring better understanding. This thesis is concerned with the performance of gas transmission pipes buried in laterally inhomogeneous soil during earthquake ground shaking. The broad goal is to identify which conditions can lead to failure, particularly buckling, and characterize those failure mechanisms.
The dynamic soil-pipe interaction problem was approached numerically and experimentally. A rigorous yet efficient two-step numerical methodology involving a global and a local model was developed to capture the response at site, soil-pipe interaction, and pipeline levels. Critical states of ground deformation for the pipe were identified by considering a range of case studies and generic site scenarios. The worst-case ground deformations were obtained for a combination of high site impedance contrast, soft soil and long-period input excitations. Under strong excitations, the soil response was nonlinear with sharp horizontal and vertical differential movements. When subjected to such soil load profiles, it was found that a pipeline with relatively high radius-to-thickness ratios, low internal pressure, and high surface roughness can experience plastic buckling. The instability was governed by interaction between axial load and bending moment, while the critical loads and strains were found to be much lower than those under pure axial compression.
Shaking table tests of a scale model of a long pipeline laid through a three-block configuration of sands were also performed. The results overall confirmed the significant pipe strain concentrations at soil interfaces predicted by the numerical models. Strains were maximized at resonant frequencies and also increased notably with surface acceleration. Models more advanced than the commonly used beam on springs are necessary to capture this complex localised response pattern.
Date of Award23 Jun 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorAnastasios Sextos (Supervisor) & Adam J Crewe (Supervisor)

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