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BMT predicts geotechnical pipeline hazards

BMT predicts geotechnical pipeline hazards

BMT Fleet Technology, in association with the PRCI and the US Department of Transport (USDOT), has developed advanced soil-pipe interaction design and assessment modelling tools that can predict geotechnical hazard events on pipeline infrastructure.

By Dr Abdelfettah Fredj, BMT Fleet Technology, Kanata, ON, Canada

The linear nature of buried pipelines results in the risk of interaction with a range of geotechnical hazards involving natural forces, including active slopes, land surface subsidence, frost heave, and washout. Ground movements induced by these geotechnical hazards can subject a pipeline to axial, lateral flexural, and vertical flexural loading. While pipeline materials are generally ductile, and thus resistant to elevated strain states, USDOT statistics suggest that, in the ten-year period between 1999 and 2000, approximately 30 pipeline failures could be attributed to natural forces.

Techniques to predict geotechnical-hazard-induced pipeline displacements, loads, stresses, or strains are not well described in design standards or codes of practice. In response, the results of geotechnical site observations, successive in-line inspections, or pipeline instrumentation, are used to infer pipeline displacement or strain accumulation. These techniques are often augmented through the application of finite element analysis. The practice of using finite element analysis for soil-pipe interaction has developed in recent years and has proven to be a useful tool in evaluating the pipeline behaviour in response to ground movement.

Figure 1: Axial ground movement (the soil in front of the pipe is hidden, for clarity).

BMT Fleet Technology Ltd (BMT), with support from the Pipeline Research Council International (PRCI), the USDOT, and pipeline operating companies, has developed advanced soil-pipe interaction design and assessment modelling tools. These tools provide guidance by simulating and forecasting pipe deformations and stress or strain states generated due to the progression of geotechnical hazard events. Risk mitigating measures, or modified designs based upon the information provided by a tool of this type, can be implemented to preclude transmission interruption, environmental contamination, damage to neighbouring assets, and potential harm to the public.

The BMT soil-pipe interaction numerical simulation is a three-dimensional soil continuum analysis process that is capable of considering large deformations, non-linear material behaviour, and a range of soil types and properties. The performance demonstrated by the model is difficult to meet considering Winkler-type models (i.e. soil modelled using springs) and Lagrangian soil models1. Using the LS-DYNA discrete-element method (DEM) and the smooth-particle hydrodynamic method (SPH), BMT has validated that numerical simulation tools can predict soil displacements and pipe deformation and strains for a variety of full-scale laboratory and instrumented operating pipeline geotechnical hazard events 2, 3, 4.

When the modelling tools are used to consider a slope-failure event causing soil movement along the pipeline, it can understand the pipe’s current strain condition, as well as forecast the response of the pipeline to future ground movement. As the ground movement progresses, tensile strains are generally developed at the top of the slope while compression strains develop at the toe of the slope. Soil uplift or mounding at the toe of the slope can result in local pipe bending and result in pipeline buckling or wrinkling.

Figure 2: Lateral ground movement and graph of critical width (the soil above the pipe is hidden for clarity).

By considering a shell pipe model, the pipe strain distribution, wrinkle or buckle formation, and post-formation in-service behaviour of the wrinkle or buckle, can be explicitly simulated to understand the rate of damage accumulation.

The modelling tool can also be applied to ground movements perpendicular to the pipe’s axis, where some soil can flow around the pipe and the remainder applies pressure to the pipe, promoting displacement and bending. By studying these loading events, the strain in the pipeline has been demonstrated to be determined by the pipe geometry, soil properties, and magnitude and direction of soil movement, as well as the width of the mobile soil mass. Narrow soil-movement masses or very wide masses produce lower peak pipe strains than those associated with the critical movement width for a given geotechnical hazard scenario.

By considering the strains generated by the geotechnical hazard event, the potential for girth-weld failure or the onset of buckling or wrinkling can be evaluated. Using advanced soil-pipe interaction numerical simulation tools the current and future safety of the pipeline can be considered. The application of theses advanced tools in engineering assessments and mitigation measure development has considered a range of applications, including slope movement along and transverse to the pipeline, lateral spreading due to liquefaction, surface faulting, subsidence, excavation process effects, wrinkle bend integrity management, and the strain-relief scenarios. These tools are also being used to identify trends in pipe response to geotechnical events and develop engineering-design and assessment guidance that can be applied in the absence of these complex modelling tools.

For more information visit the BMT Fleet Tech website.

This article was featured in the December edition of Pipelines International. To view the magazine on your PC, Mac, tablet, or mobile device, click here.


Acknowledgements

The geotechnical-hazard assessment work presented in this article was completed by the team at BMT Fleet Technology (BMT) led by Dr A. Fredj, A. Dinovitzer, Dr A. Hassannejadasl, and Rick Gailing. BMT gratefully acknowledges the technical direction and sponsorship of PRCI and USDOT (PHMSA) related to the information discussed in this article.

References

  1. Konuk, I, Yu, S., Fredj, A., 2006. Do Winkler models work: a case study for ice scour problem, 25th OMAE Proceedings, OMAE2006-92335.
  2. Fredj, A., Dinovitzer, A., Hassannejadasl, A., Gailing, R., Sen, M., 2016. Application of the discrete element method (DEM) to evaluate pipeline response to slope movement, IPC2016-64508.
  3. Dinovitzer, A., Fredj, A., Sen, M., 2014. Pipeline stress relief and evaluation of strain measurement technology at amMoving slope, IPC2014-33497.
  4. Fredj, A., Dinovitzer, A., 2012. Simulation of the response of buried pipelines to slope movement using 3D continuum modelling, IPC2012-31516

 

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