Uplift Mechanisms of Pipes Buried in Sand

Cheuk, C.Y.; White, David; Bolton, M. D.

doi:10.1061/(asce)1090-0241(2008)134:2(154)

Cited by 158 publications

(80 citation statements)

References 11 publications

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“…This phenomenon has been observed in previous studies, and is linked to intermittent slumping of sand around the pipe periphery into the voids beneath (Trautmann et al, 1985;Dicken, 1994;Cheuk et al, 2008;O'Loughlin & Barron, 2012).…”

Section: Uplift Responsesupporting

confidence: 65%

The effect of radial fins on the uplift resistance of buried pipelines

Tom¹,

O’Loughlin²,

White³

et al. 2017

Géotechnique Letters

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This paper investigates the potential for increasing the uplift resistance of buried pipelines through the addition of radial fins on the pipe circumference. Experiments conducted in loose sand showed that fins extending by 20% of the pipe diameter increase the vertical peak uplift resistance by up to 25%, depending on embedment depth and fin configuration. A limit equilibrium solution -based on known values of peak friction and dilation angles -predicts the uplift resistance within 13% of the measurements. The trends of peak uplift resistance with embedment and fin configuration were also replicated in numerical analyses conducted using a non-associated Mohr-Coulomb soil model. The numerically predicted peak uplift resistances were within 10 and 21% of the experimental values for rough and smooth interfaces, respectively. Soil failure mechanisms from the numerical analyses were broadly consistent with that assumed in the limit equilibrium solution. However, the experimentally observed mechanisms differed subtly, with a limited extent of lifted soil above the pipe and circulatory flow occurring from above to beneath the pipe. This mechanism was approached in the numerical analyses for a smooth interface by specifying a small negative dilation angle, which had minimal effect on the predicted peak uplift resistance.

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Section: Uplift Responsesupporting

confidence: 65%

The effect of radial fins on the uplift resistance of buried pipelines

Tom¹,

O’Loughlin²,

White³

et al. 2017

Géotechnique Letters

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“…Schaminee et al, 1990;Bransby et al, 2002) and numerical modelling approaches (e.g. Dickin & Laman, 2007;Cheuk et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Uplift mobilisation resistance of subsea pipelines in loose sand

Ivanović¹,

Oliphant

2014

Géotechnique Letters

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Upheaval buckling (UHB) is a well-known phenomenon associated with buried high-pressure hightemperature pipelines. A large number of research studies have been undertaken in the last two decades on developing reliable uplift resistance mobilisation models from which the current standards and recommendations are based. This paper examines Technip's extensive database consisting of experimental and numerical studies concerning sandy backfills only. The peak uplift mobilisation distances obtained are compared with the current DNV recommendations and a recent experimental study undertaken at the University of Cambridge. The trends obtained indicate differences associated specifically with the lower backfill cover depths and suggest that the current recommendations need to be updated. A new improved peak mobilisation distance model, which is able to capture the relevant data with a distinction made between very loose and loose sand backfill, is offered.

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“…At greater depths, where the confining stresses are higher, there will be a transition to a flow-around mechanism (Schupp et al, 2006;Byrne et al, 2008;Cheuk et al, 2008). The depth of transition depends on the density of the sand and the peak friction angle.…”

Section: Simple Model For Pipe Uplift Resistancementioning

confidence: 99%

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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Uplift Mechanisms of Pipes Buried in Sand

Cited by 158 publications

References 11 publications

The effect of radial fins on the uplift resistance of buried pipelines

The effect of radial fins on the uplift resistance of buried pipelines

Uplift mobilisation resistance of subsea pipelines in loose sand

Uplift of shallowly buried pipe sections in saturated very loose sand

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