Summary
This paper addresses lateral pipe/soil interaction behavior at the large
displacements that occur with lateral buckling of a pipeline.
Force-displacement-response models were developed by the Safebuck
joint-industry project (JIP) to replace the use of simple friction-coefficient
approximations. Such simplistic models are unrealistic for modeling large
lateral displacements or the building of soil berms that occurs with cyclic
lateral loading.
The models are based on large- and small-scale tests carried out by the
Safebuck JIP on deepwater soils from the Gulf of Mexico and west Africa, as
well as on kaolin clay. To this database was added project-specific test
data donated by JIP participants.
Four stages of pipe/soil interaction are considered:
- Embedment of the pipe at installation.
- Breakout during buckle formation on the basis of different levels of
initial pipe embedment.
- Large-amplitude lateral displacement as the buckle forms.
- Cyclic lateral displacement influenced by the building of soil
berms.
While breakout loads have been the subject of much research and published
papers on pipeline stability, there is little guidance on modeling lateral
resistance at the large displacements experienced in lateral buckling.
There is also little guidance on modeling subsequent large-amplitude cyclic
behavior, which occurs with each shutdown and restart of the
pipeline.
New equations were proposed where appropriate, and recommended models for
each part of the characteristic response were developed. These models provide a
valuable basis for lateral- buckling design guidance. They currently are being
applied by JIP participants on a number of projects in which pipelines are
being designed for lateral buckling.
Background of the Safebuck JIP. The aim of the Safebuck JIP
(Bruton et al. 2005) is to raise confidence in the lateral-buckling-design
approach and to improve understanding of the related phenomenon of pipeline
walking. Experimental work is being undertaken at the Welding Inst. on
low-cycle fatigue-materials performance and at Cambridge U. on axial- and
lateral-pipe/soil interaction.
The JIP has been very well supported by the offshore industry. BP,
ConocoPhillips, ExxonMobil, Petrobras, and Shell, as well as the U.S.
Government through the Minerals Management Services, participated in Phase I,
with installation contractors and suppliers represented by Allseas,
JFE-Metal One, Technip, and Tenaris. Additional participants
including Acergy, Chevron, Statoil, and Saipem have joined Phase II, which
will run through 2005 and 2006.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
3 May 2006
- Revised manuscript received:
25 July 2006
- Manuscript approved:
27 July 2006
- Version of record:
20 September 2006
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