Pipeline Floatation Assessment in Liquefiable Soil

Bonjean, David; Erbrich, Carl; Zhang, George

doi:10.4043/19668-ms

Cited by 8 publications

(10 citation statements)

References 2 publications

(4 reference statements)

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“…This suggests that in the short term liquefaction is a possibility, but in the long term it is much less likely. Of course, as described above (and by Bonjean et al, 2008), this is provided the enhanced pore pressures are not sufficient to cause the pipe to float upwards through the soil owing to enhanced pipe buoyancy overcoming the reduced soil resistance. (b) The second possibility is that the pipe experiences a buckling event, known as upheaval buckling, which causes the soil to liquefy.…”

Section: Liquefaction Eventsmentioning

confidence: 96%

“…as described by Sumer et al Bonjean et al (2008)) or seismic events. In these cases, if the excess pore water pressures are not sufficient to liquefy the soil completely, then there is the possibility that consolidation around the pipe will occur, and the soil density will increase (such as indicated in Fig.…”

Section: Liquefaction Eventsmentioning

confidence: 97%

“…More complex versions vary the angle for the slip planes (e.g. White et al, 2001;Bonjean et al, 2008); however, for loose sands, where the angle of dilation is close to zero, the vertical slip plane assumption is adequate. Note that in this paper both the slip plane segments and the weight of the soil between the centre of the pipe and the crown of the pipe are taken into account; otherwise there will be no capacity for H/D less than 0 .…”

Section: Simple Model For Pipe Uplift Resistancementioning

confidence: 98%

“…just after trenching) before there has been any chance for shakedown of the soil skeleton. Bonjean et al (2008) consider the slightly more complex case of pipeline flotation before the soil has fully liquefied owing to the increases in the pore pressure regime, which will reduce the soil resistance (through modified equation (1)) and increase the pipe buoyancy (through equation (5)). Their concern is the flotation of pipes during a storm event, which causes a build-up of excess pore pressure but is not sufficient to cause full liquefaction of the soil.…”

Section: Implications For Buried Pipeline Design Flotationmentioning

confidence: 99%

“…Consider the potential for flotation of a buried offshore pipeline in sand. The net force acting on the pipe will depend on the overall density of the pipeline and the effect of any excess pore pressures developed around the pipe (see also Bonjean et al (2008) for a detailed analysis). Assuming that the excess pore pressure varies linearly with depth from the seabed surface, then a simple approximation would give a net force (downward positive) on the pipe of…”

Section: Implications For Buried Pipeline Design Flotationmentioning

confidence: 99%

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Uplift of shallowly buried pipe sections in saturated very loose sand

Byrne¹,

Schupp²,

Martin³

et al. 2013

Géotechnique

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Offshore pipelines are often buried to protect them from damage, and to provide additional thermal insulation. In sandy soils the pipes are trenched using jet-trenching or ploughing. In both cases the nature of the trenching operation means that the backfill material can be placed over the pipe in an extremely loose state. If the pipe then undergoes a small displacement or vibration, liquefaction of the backfill material may occur, and the resistance to upward movement of the pipe can be reduced. To explore this experimentally, an instrumented model pipe section was pulled vertically upwards at different rates in very loose, saturated, fine, uniform sand (representative of a North Sea sand). The instrumentation allowed for the measurement of the force on the pipe section as well as the excess pore water pressure regime around the pipe. The results show that, for sand at a relative density of zero, there is a reduction of capacity at the faster uplift rates. A simple analytical model, using the vertical slip model (for uplift resistance) modified to account for the development and dissipation of excess pore water pressures around the pipe, is used to predict the results from the experiments. Implications for the design of buried offshore pipelines in sand are discussed. INTRODUCTIONThis paper considers the problem of a short section of pipe that moves upwards in saturated loose fine sand. This problem is very important for understanding the likely performance of offshore pipelines buried in sandy or silty seabed soils. The pipe must be buried to a sufficient depth that any upward forces are resisted by the reaction of the soil, but not so deeply that the trenching operation becomes uneconomic. The pipe may experience a net upward force due to a very low combined pipe/fluid weight, the development of excess water pressures around the pipe, or a phenomenon known as upheaval buckling. Although it is recognised that buckling or flotation of an offshore pipeline is a three-dimensional problem, the present sudy is confined, as in many other studies, to the plane-strain problem of a short pipe section moving upwards through the soil. This allows the soil resistance to be measured accurately in laboratory tests, normalised against relevant parameters and used in pipeline design. The experiments reported here have been carried out in saturated, very loose fine sand, with a particular focus on the effect of uplift rate on soil resistance. A number of studies of pipes moving through dry (and hence fully drained) sand have been published, but little information is available in the public domain relating to pipes moving through saturated sand at different rates. The recent work by Bransby & Ireland (2009) highlighted that pipes in loose to medium dense saturated sand under faster rate loading experienced increased capacities, most likely due to a dilative sand response. The work presented below focuses on very loose sand, and shows substantial reductions in capacities for faster rate loading. As well as presenting novel experi...

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Section: Liquefaction Eventsmentioning

confidence: 96%

Section: Liquefaction Eventsmentioning

confidence: 97%

Section: Simple Model For Pipe Uplift Resistancementioning

confidence: 98%

Section: Implications For Buried Pipeline Design Flotationmentioning

confidence: 99%

Section: Implications For Buried Pipeline Design Flotationmentioning

confidence: 99%

See 3 more Smart Citations

Uplift of shallowly buried pipe sections in saturated very loose sand

Byrne¹,

Schupp²,

Martin³

et al. 2013

Géotechnique

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Pipe–Seabed Interaction

White

Bransby

2018

Encyclopedia of Maritime and Offshore Engineering

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Subsea pipelines rest on or in the seabed, and therefore their behavior and condition depends on pipe–seabed interactions. Pipelines expand and contract during operation and can also be loaded by hydrodynamic action, turbidity flows, or debris flows. These actions are resisted by seabed reaction forces in the vertical, axial, and lateral directions. In some situations, the pipeline may be deliberately buried, for example, to allow overtrawling, provide thermal insulation, or prevent expansion‐induced buckling. However, in many cases, the pipeline may be laid directly onto the seabed. It may self‐bury through the action of sediment transport, remain only partially embedded into the soil, or some intermittent combination of these effects along its route. Assessments of pipe–seabed interaction forces for all the abovementioned burial conditions begin with estimation of the as‐laid (or as‐constructed) embedment. Classical methods such as limit plasticity underpin solutions for embedment and the limiting pipe–soil resistance in each direction. The critical uncertainties are usually the operative soil strength—which is affected by the seabed disturbance during the lay (or backfilling) process and throughout the operating life—and the pipeline embedment (or cover depth). Specific geotechnical testing technologies have evolved to reduce uncertainties in pipe–seabed assessments, including tools for determining the near‐seabed (and disturbed) soil strength and the pipe–soil interface strength at very low stresses. The associated analysis methods also aim to quantify the variability of the seabed reaction forces along the pipeline. The abovementioned predictions of pipe–seabed interaction behavior are performed to feed into structural analyses of the pipeline, which often use a reliability‐based framework. Pipe–soil interaction assessments require close collaboration between the pipeline and geotechnical experts due to the inherent influence of soil–structure interaction, as well as the aim of tailoring the geotechnical assessment to address the particular design criticalities, which vary depending on the seabed and pipeline conditions.

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Pipeline Soil Interactions

Wang

Guo

2022

Encyclopedia of Ocean Engineering

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Pipeline Floatation Assessment in Liquefiable Soil

Cited by 8 publications

References 2 publications

Uplift of shallowly buried pipe sections in saturated very loose sand

Uplift of shallowly buried pipe sections in saturated very loose sand

Pipe–Seabed Interaction

Pipeline Soil Interactions

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