OTC 6055

Submarine Pipeline On-Bottom Stability: Recent AGA Researchby D.W. Allen, Shell Development Co.; W.F. Lammert and J.R. Hale, Brown & Root U.S.A. Inc.;and V. Jacobsen, Danish Hydraulic Inst.

Copyright 1989, Offshore Technology Conference

This paper was presented at the 21st Annual OTC in Houston, Texas, May 1-4, 1989.

This paper was selected for presentation by the OTC Program Committee following review of information. contained in an abstract sUb~itted by the author(s). Contents of t~e paper,as presented, have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The matenal, as presented.. does not necessanl.y reflectany position of the Offshore Technology Conference or its officers. Permission to copy is restricted to an abstract of not more than 300 words. illustratIons may not be copied. Theabstract should contain conspicuous acknowledgment of where and by whom the paper is presented.

In addition to the hydrodynamic force program,model tests on pipe/soil interaction forces havebeen conducted on loose sands, dense sands, andsoft clays. The effect of pipeline oscillation onthese interaction forces was also analyzed toprepare empirical formulations of the lateral soilresistance developed by oscillatory pipe movements.

BACKGROUND

On-bottom stability design of submarinepipelines has traditionally been based on thestatic balance between applied hydrodynamic forces

b. to develop analysis tools capable ofpredicting the governing forces anddetermining their effect on pipelinestability, and

c. to produce practical calculationprocedures.

The major portion of the research has focusedupon hydrodynamic forces. Large scale model testson stationary submarine pipelines exposed tocurrents, waves and combined waves and currentshave been conducted for pipelines resting on aseabed, partially buried pipelines, and pipelinesresting in shallow trenches. Similar tests havealso been conducted to determine the reduction ofhydrodynamic force which is realized if the pipemoves under the influence of the wave or wave andcurrent loadings. The subsequent analyses of themeasured forces have resulted in force coefficientsapplicable in common industry formulas and in forcecoefficients for use in more refined and accurateforce calculation procedures.

This research effort was planned, coordinatedand monitored by an ad-hoc committee composed ofrepresentatives from A.G.A. member companies withassistance from the consultants used to perform thevarious research projects.

121

Recently, the Pipeline Research Committee ofthe American Gas Association (A.G.A.) has sponsoredseveral research projects in the area of submarinepipeline on-bottom stability. This coordinatedresearch effort has focused on, and resulted in,development of simulation software for design, andthe preparation of design guidelines.

Analytical models for both the hydrodynamicand pipe/soil interaction forces have beendeveloped and implemented into the pipe dynamicanalysis software. This software is designed topredict the motions of a pipeline exposed tocurrent and an irregular sea-state. Based uponresults of the model tests and computersimulations, pipeline on-bottom stability designcalculation procedures have been prepared in adesign handbook.

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References and figures at end of paper

INTRODUCTION

a. to obtain an accurate assessment andverification of the forces which governpipeline stability,

ABSTRACT

This paper describes a research program inpipeline on-bottom stability, sponsored by theA.G.A., which has been underway since 1983. Theresearch program has been conducted as a series ofseparate projects coordinated in "building block"fashion. Although the target product was definedin general terms, the full extent of the work wasnot initially conceived as one large, singleproject. Instead, the research was executed as aseries of tasks involving numerous organizationsand researchers. Throughout the work, results ofearlier tasks were used to define new tasks

. required to reach the desired objectives. Theseobjectives were:

2 SUBMARINE PIPELINE ON-BOTTOM STABILITY: RECENT AGA RESEARCH OTC 6055

New Force Model (1986)

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Analysis of the measured results from the 1985tests was performed using least squares fit,Fourier decomposition, and maximum force datareduction methods. Based on these results, ananalytical model, capable of accurately predictingboth the magnitude and temporal variation of dragand lift forces on a stationary pipe, resti~g onthe seabed, was developed (Jacobsen et al. •

Stationary Pipe Tests (1985-1986)

The large scale model tests conducted in 1985included some ±4000 odd tests. As reported byBryndum et al. , these tests included testconditions of current only, regular or irregularwaves only, and current combined with eitherregular or irregular waves. The test program wasdesigned to cover a wide range of the significantnon-dimensional parameters, includingKeulegan-Carpenter number, current to wave ratio,Reynolds number, pipe roughness, and seabedroughness. Secondary effects of seabed roughness,irregularity, and scaling effects were also.investigated. Ranges for the basic test parametersare given in Table 2.

Additional tests on partially buried pipelineswere performed in the current flume during 1986 asan extension of the 1985 test program. Results ofthese tests indicated that both in-line and liftforces are reduced due to the less exposed pipe.It has also been concluded from these tests thatthe effect of partial burial can be considered byusing a reduction factor depending only on thedegree of burial.

To describe hydrodynamic force variations overa wave cycle, a Fourier series representation ofthe drag and lift forces was adopted during this

hydrodynamic forces. The identification of thegoverning non-dimensionalized parameters and waveplanning of the initial test program were conductedduring 1983-84. Model tests on stationary pipeslaying on the seabed were conducted in 1985. In1986, a new wave force model was developed andadditional model tests were performed on partiallyburied pipelines. All of the above work onhydrodynamic forces has br3n previously reportra indetail by Jacobsen et al. and Bryndum et al. •Following the initial test program in 1985-86, asecond test program was defined for 1987 with thepurpose of determining the reduced hydrodynamicloadings on pipelines in shallow trenches. During1986-1987, use of the analytic wave force modeldeveloped from the 1985. test program establishedthat pipe movement during a wave cycle couldproduce significant reductions in hydrodynamicloads. To quantify this reduction in loadings, atest program for moving pipelines was defined and athird set of wave and cYsrent tests were c£gductedin 1988 (Bryndum et al. , Jacobsen et al. ). Inthese tests, oscillatory flow conditions weredeveloped around the pipe by moving the model pipeand seabed rather than by causing the body of testwater to oscillate. The tests and the analyticmodel developed from these tests are brieflydescribed below.

The research that has been performed by the A.G.A.in each of the above work areas is furtherdescribed below (also, see Table 1).

The research in the area of hydrodynamicforces has included large scale model tests and thedevelopment of an analytic approach, capable ofaccurately predicting the temporal variation of

HYDRODYNAMIC FORCES

122

This basic design dilemma (underestimatedhydrodynamic forces but seemingly conservativeresults) provided the basis for several A.G.A.research projects. In 1987, results from a threeyear long effort on the tfPESTAB project werereported (Wolfram et al. ), and a similar jointindyztry study has been reported by Palmer etal•• Concurrently, the A.G.A.'s research wasdeveloping, and it is this work which is brieflypresented in this paper.

Each of the individual projects is associatedwith one of the four following work areas:

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a. Hydrodynamic Forcesb. Pipe/Soil Interaction Forcesc. Computer Software Developmentd. Development of Design Guidelines

Beginning in ~he late 1950's, the work ofGrace Bnd Nicinski , S,rpkaya , Sarpkaya andRajabi , Grace and Zee and others indicated thathydrodynamic coefficients in oscillatory flow couldbe substantially larger than those for steady flowcon~itions. Furthermere, the work ofl~ryndum etal. , Jacobsen et al. , Verley et al. , and othershas clearly demonstrated that the time variation ofhydrodynamic lift forces is substantially differentfrom that predicted by the Morison type equation.However, the higher hydrodynamic force coefficientsdid not initially gain widespread acceptancebecause the industry has recognized that their usewith the traditional design methodology would leadto unrealistic weight coating requirements forsubmarine pipelines.

and resisting soil forces as depicted in Figure 1.Typically, applied hydrodynamic forces from bothand current action were computed using thefamiliar Morison equation with drag and lift forcecoefficients based on Todel tests conducted insteady flow conditions. The resisting soil forcewas typically characterized as a frictional force,with friction coefficients based on sliding pipetests or on simple foundation design theory.

In the traditional design approach, designsea-state conditions are typically represented by asingle regular wave height and period. This typeof design practi2e is similar to that described inDnV's 1976 Rules. For oscillatory flowconditions, the traditional design approach hasbeen shown to be inaccurate due to its simplisticmodels for hydrodynamic and pipe/soil interactionforces. The method has, however, been successfullyused in many parts of the world for many years, andit is generally felt that the method yieldsconservative results. Note that rec3ntly, DnV haspublished a new recommended practice , the accuracyof which is yet to be determined.

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OTC 6055 ALLEN, LAMMERT, HALE AND JACOBSEN 3

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COMPUTER SOFTWARE DEVELOPMENT

The apparent stability obtained from traditionalpipeline design indicated that the soil resistanceforces could be larger than assumed. Recentresearch in pipe/soil interacti?n includes that18described by ¥gennodden et al. 'l~agner et al. ,Morris et al. and Palmer et al. . The workcompleted during the A.G.A.'s research includeslarge scale model tests, and the development of amodel to predict pipe/soil interaction.

The pipe/soil interaction tests performed duringthis research (see table 5) were performed usingthe same test flume, carriage17ystem, etc. as thatreported by Brennodden et al. on the PIPESTABproject. Testing procedures, instrumentation, etc.were also similar, with the exception that thetests were conducted in only the displacementcontrolled fashion, and lift forces were notapplied to the pipe test section. Details of thetest procedures, data reduction methods, test20results etc.2~ave been reported by Brz2nodden ,Lieng et al. ,and Brennodden et al. •

Computer software development was coordinatedto stay abreast of the findings from the model testprograms. In 1984, development of dynamicstability analysis software was initiated, andincluded irregular sea simulation and a threedimensional finite element program 2~ model thepipe dynamics (Borgman and Hudspeth ). A simpletwo dimensional finite e~~ent model was nextdeveloped (Michalopoulos ) in order to improve thecomputational efficiency for use on microcomputers.The microcomputer based dynamic analysis programwas the basis for the software developments of thisresearch.

The work of the researchers listed above as well asthat of the A.G.A. has shown that when a pipe isoscillated in either a force or displacementcontrolled manner, the pipe will tend to dig intothe soil, and the ability of the soil to resistlateral loads will increase. In soils which aretypical of soft marine sediments, the tendency ofthe pipe to embed itself into the seabed can bepronounced (as illustrated on Figure 5), and theincrease in lateral soil resistance significant.This type of increase in soil resistance is notconsidered in the traditional static stabilitydesign method, since the implication of this methodis that the pipe does not move under wave andcurrent loadings •. Recent research has focused onmeasuring the development of lateral resistancewhich can be attributed to oscillatory pipemovement, and it has been shown that even smallpipe oscillations (say 5% of the pipe diameter) canproduce a significant increase in soil resistancedue to the pipe penetration into the seabed.

The data measured during the tests was reduced to aform consistent with that required to provideinformation for development of an energy basedpipe/soil interaction model which was envisaged atthe outset of the test program. Based on thereduced data, an empirical model of the pipe/soilinteraction was developed and has been implementedinto the pipe dynamics software package.

123

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Moving Pipe Tests (1988)

The promising results of the partially buried pipetests led to a second model test program conductedduring 1987. These tests were designed to studythe reduction in hydrodynamic forces experienced bypipes sitting in narrow bottom, shallow trenches.Trench configurations tested during the program areshown in Figure 4. Measured data from the testswere reduced in a fashion similar to that for theprior test programs. Similar to the partiallyburied pipe tests, it was also concluded that thesheltering effect of the trenches could be wellrepresented by applying a reduction factor to thetime histories generated for a completely exposedpipe. The ranges of relevant parameters includedin the tests are given in Table 3.

Stationary Pipe Tests in Shallow Trenches (1987)

research. Inertial forces are computed in the samefashion as with the Morison type equation. Anextensive data base, established from the Fourierdecomposition of the regular wave forces, forms thebasis for the method, which also includes theimportant wake effect (i.e •• the eff~ct the wakecreated in the previous half wave cycle has on theforces experienced by the pipe in the present halfwave cycle). Table look up and interpolation ofthe Fourier coefficients and phase relationshipsfrom this data base are performed based onKeulegan-Carpenter number, current to wave ratio,pipe roughness and seabed roughness. For regularwave and current conditions, the interpolatedcoefficients and phase relationships are used todirectly compute the variation of forces. Theeffectiveness of the new force model in comparisonto the traditional Morison type equation isdemonstrated in Figure 2.

Similar to the hydrodynamic aspects of on-bottomstability, there has been a large volume ofresearch into the interaction between the pipe andthe seabed. Interest in this aspect of the problemwas spurred by the experimental verification thatactual hydrodynamic forces are larger than thoseassociated with the traditional design methodology.

PIPE/SOIL INTERACTION FORCES

During 1986 and 1987, dynamic simulations ofpipelines were conducted using the A.G.A.'s pipedynamics software and the new hydrodynamic forceformulations. These simulations includedcomparison of different methods to consider theeffect of pipe movement on hydrodynamic drag andlift forces. In order to select the mostappropriate force reduction method, a series ofmodel tests were planned (see table 4). In thesetests, the pipe would be allowed to move. Re~~lts

of these tests are lEPorted by Bryndum et al. ,and Jacobsen et al.

The method has also been adapted for irregular waveforce computations. The f~aptation is described indetail by Jacobsen et al. ,and it has shownexcellent capability of reproducing irregular waveforce time series recorded during the model tests(based on input of the free stream velocity timeseries) as is shown in Figure 3.

4 SUBMARINE PIPELINE ON-BOTTOM STABILITY: RECENT AGA RESEARCH OTC 6055

Enhancements and modifications to the dynamic small movements (less than 0.5 pipeanalysis software during this research program diameters).include: b. In sands with relative density less

a. incorporation of the new model for than about 50 percent (in the top soilhydrodynamic forces on stationary pipes, layer), the programs predict that a

b. modification of the program to include pipe designed to be stable with thethe effect of pipe embedment and shallow traditional method will be stable andtrenches on hydrodynamic forces, will undergo only small movements

c. inclusion of a method to reduce the c. In softer clay and looser sand thanhydrodynamic forces for moving pipes, and indicated in a) and b) above, it

d. incorporation of the pipe/soil appears that the traditional designinteraction model. method yields conservative results and

there may be the opportunity to reduceThe arrangement of”the dynamic ana$~sis weight coating designs.

software is discussed by Lammert et al. . d. In harder clay and denser sand thanAlthough the software is relatively easy to use, indicated in a) and b) above, dynamicthe nature of dynamic analysis does not lend itself simulations indicate that the tradi-well to the stability design process. In order to tional design method yields a pipemake the results of the hydrodynamic forces and design that will undergo net movementspipe/soil interaction tests available to the design (several pipe diameters and larger).engineer in a practical form, a simplified analysis e. The new hydrodynamic force formulationprocedure has also been developed and computerized. strongly influences the degree of netThe simplified analysis is based on a quasi-static pipe movement predicted during asimulation of the pipe during an assumed, short dynamic simulation. Dynamic analysesstorm build-up period just prior to the design based on use of free stream velocitysea-state. Based on this simulation, an embedment in the Morison type equation introduceof the pipe is predicted. Stability of the pipe is a large bias in the applied forcesthen checked for the significant and maximum bottom when currents are included in thevelocities which are expected during the design analysis. With the new force formu-sea-state. This check is based on a static balance lation, the applied forces are notof forces as in the traditional design method, but nearly as strongly biased and muchthe hydrodynamic forces applied to the pipe are smaller net movement of pipe isrealistic and the available soil resistance force predicted.is based on the prior loading history of the pipe.The2grocedure is described in detail by Hale et In the above comparisons, traditional designal. and illustrated in Figure 6. is characterized as follows:

The simplified design calculation has been a. Design wave: Significant wave height,verified using the more sophisticated dynamic Zero crossing period, Longanalysis software. This verification has been crested wave theoryperformed by simulating the build-up sea-state b. Hydrodynamic coefficients:period with the dynamic analysis software. The Drag (Cd) = 0.7results show that the simplified analysis Lift (Cl) = 0.9conservatively estimates pipe embedments predicted Inertia (Cm) = 3.29by the more detailed dynamic analysis. c. Soil friction: Sand = 0.7

Clay= 0.4DESIGN CAT”TUATION RESULTS

Results from analyses using the simplified DESIGN GUIDELINESdesign procedure indicate that in most casestraditionally designed pipes are more than To collect and summarize the importantadequately weighted to resist pipe movement. Only findings relating to on-bottom pipeline stabilityin very hard soils (where the pipe cannot from the body of research performed by the A.G;A.,penetrate) does the new design procedure indicate a set of design guidelines were developed. Thethat traditionally designed pipes may move. Figure guidelines are written as a reference tool to be7 illustrates the trend of results from the used by the design engineer when performing weightsimplified analysis when compared to the coating design. They supplement the analysis toolstraditional design procedure. and research reports with discussions and

flowcharts of the total design process, and showAt this time, there has not been sufficient how stability design fits into that process.

experience with the completed software to develop a Details of the stability design process andwide range of general conclusions regarding the philosophy are discussed as well as explanations ofresults to be expected. However, several general the physical phenomena modeled. Details of dataconclusions are as follows: collection techniques and route and soil surveys

are also presented. Finally, general discussionsa. In clays which have undrained shear about related items which may need to be considered

strengths less than about 80 psf, the simultaneously are also provided (e.g.programs predict that a pipe designed to installation, shore approach, pipeline crossings,be stable with the traditional method soil erosion and scour).will be stable and will undergo only

124

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. —

OTC 6055 ALLEN, LAMMRRT, HALE AND JACOBSEN 5

SUMMARY Conference, Paper No. OTC 2898,Houston, 1977.

The results of the work reported here providethe basis for a more rigorous approach to on-bottom 6. Sarpkaya, T. and Rajabi, F., “Hydrodynamicstability design of submarine pipelines. With the Drag on Bottom-Mounted Smooth and Roughmore rigorous approach, realistic hydrodynamic Cylinders in Periodic Flow,” Proc. offorces are used, and these forces are larger than Eleventh Offshore Technology Conference,the forces used in the traditional on-bottom Paper No. OTC 3761, Houston, 1979.stability design method. Due to the larger appliedhydrodynamic forces, the results of the work 7. Grace, R.A. and Zee, G.T.Y., “Wave Forcesindicate that some movement of the pipe can be on Rigid Pipes Using Ocean Test Data,”expected in typical marine sediments. However, Journal of the Waterway, Port, Coastal andthere is also indication that small movements of Ocean Division, ASCE, Vol. 107, No. WW2,the pipe will cause the pipe to embed if the bottom pp. 71-92, 1981.sediments are not too dense (non-cohesive soils) ortoo stiff (cohesive soils). Associated with this 8. Bryndum, M.B., Jacobsen, V., and Brand,embedment is substantial increase in soil L.P., “Hydrodynamic Forces From Wave andresistance forces, which in turn may limit the Current Loads on Marine Pipelines,” Proc.pipeline movements. of Fifteenth Offshore Conference, Paper No.

OTC 4454, Houston, 1983.The experimental research and computer

programs developed during this project have been 9. Jacobsen, V., Bryndum, M.B., and Fredsoe,incorporated into a design guideline thereby J., “Determination of Flow Kinematics Closefacilitating more accurate and reliable stability to Marine Pipelines and Their Use indesign. Stability Calculations,” Proc. of

Sixteenth Offshore Technology Conference,ACKNOWLEDGMENTS Paper No. OTC 4833, Houston, 1984.

The authors wish to thank the Pipeline 10. Verley, R.L.P., Lambrakos, K.F., and Reed,Research Committee of the American Gas Association K “Prediction of Hydrodynamic Forces onfor permission to publish this paper. The authors S~~ Bed Pipelines,” Proc. of Nineteenthalso wish to thank present and past members of the Offshore Technology Conference, Paper No.ad hoc committee which has overseen the development OTC 5503, Houston, 1987.of the research described above; and in particularR. W. Patterson, and D. T. Tsahalis, two recent ad 11. Wolfram, W.R. Jr., Getz, J.R., and Verley,

hoc committee chairmen. Their contribution to the R.L.P., “PIPESTAB Project: Improved Designwork has been invaluable. In addition to the Basis for Submarine Pipeline Stability,vtauthors’ respective companies, there are other Proc. of Nineteenth Of:fshoreConference,organizations whose work has advanced the project Paper No. OTC 5501, Houston, 1987.to its completion and the authors wish to recognizetheir contribution. These include, L.E. Bergman, 12. Palmer, A.c., Steenfelt, J.S.,Inc.; Southwest Applied Mechanics, Inc.; McClelland Steensen-Bach, J.O., and Jacobsen, V.,Engineers, Inc.; and, SINTEF. “Lateral Resistance of Marine Pipelines on

Sand,” Proc. of Twentieth OffshoreREFERENCES Technology Conference, Paper No. OTC 5853,

Houston, 1988.1. Jones, W.T., “On-Bottom Pipeline Stability

in Steady Water Currents,” Proc. of Eight 13. Jacobsen, V., Bryndum, M.B., and Tsahalis,Offshore Technology Conference, Paper No. D.T. , “Prediction of Irregular Wave ForcesOTC 2598, Houston, 1976. on Submarine Pipelines,” Seventh Offshore

Mechanics and Arctic Engineering2. Det norske Veritas, “Rules for the Design,

Construction and Inspection of Submarineconferences PP. 23-329 Houston* Feb. 1988.

Pipelines and Pipeline Risers,” DnV, Oslo, 14. Bryndum, M.B., Jacobsen, V., and Tsahalis,1976. D.T., “Hydrodynamic Forces on Pipelines:

Model Tests,” Seventh Offshore Mechanics3. Det norske Veritas, “On-Bottom Stability and Arctic Engineering Conference, pp.

Design of Submarine Pipelines,” 9-21, Houston, Feb. 1988.Recommended Practice E305, October 1988.

15. Jacobsen, V., Bryndum, M.B., and Bonde,4. Grace, R.A. and Nicinski, S.A., “Wave Force C.L., “Fluid Loads on Pipelines - Sheltered

Coefficients from Pipeline Research in the or Sliding,” Proc. of the 21st OffshoreOcean,” Proc. of Eighth Offshore Technology Conference, Paper No. OTC 6056,Technology Conference, Paper No. OTC 2676, Houston, 1989.Houston, 1976.

16. Bryndum, M.B., Jacobsen, V., and Bonde,5. Sarpkaya, T., “In-line and Transverse C.L., “Hydrodynamic Forces on a Sliding

Forces on Cylinders Near a Wall in Pipeline - Model Tests,” Report by DanishOscillatory Flow at High Reynolds Numbers,” Hydraulic Institute to the American GasProc. of Ninth Offshore Technology Association, Horsholm, Denmark, 1988.

..-125

6 SUBMARINE PIPELINE ON-BOTTOM STABILITY: RECENT AGA RESEARCH OTC 6055

17. Brennodden, H., Sueggen, D., Wagner, D.A.,and Murff, J.D., “Full-Scale Pipe-SoilInteraction Tests,” Proc. of EighteenthOffshore Technology Conference, Paper No.5338, Houston, 1986.

18. Wagner, D.A., Murff, J.D., Brennodden, H.,and Sueggen, O., “Pipe-Soil InteractionModel,” Proc. of Nineteenth OffshoreTechnology Conference, Paper No. OTC 5504,Houston, 1987.

19. Morris, D.V., Webb, R.E., and Dunlap, W.A.,“Self-Burial of Laterally Loaded OffshorePipelines in Weak Sediments,” Proc. ofTwentieth Offshore Technology Conference,Paper No. OTC 5855, Houston, 1988.

20. Brennodden, H., “Pipe-Soil InteractionTests in Sand and Soft Clay,” Report No.STF69 F87018, a SINTEF report to theAmerican Gas Association, Trondheim,Norway, 1988.

21. Lieng, J.T., Sotberg, T., and Brennodden,H “Energy Based Pipe-Soil InteractionM~~els,” Report No. STF69 F87024, a SINTEFreport to the American Gas Association,Trondheim, Norway, 1988.

22. Brennodden, H., Sotberg, T., Leing,J Verley, R., “An Energy BasedP~~e-Soil Interaction Model,” Proc. ofthe 21st Offshore TechnologyConference, Paper No. 6057, Houston,1989.

23. Bergman, L.E. and Hudspeth, R., “The Effectof Random Seas on Pipeline Stability -Volumes I & II,” a Pipeline ResearchPublication of the American GasAssociation, Arlington, VA, 1984.

24. Michalopoulos, C.D., “Effect of Random Season Pipeline Stability - Phase 11,” aSouthwest Applied Mechanics, Inc. report tothe American Gas Association, Houston,1986.

25. Lammert, W.F., Hale, J.R., and Jacobsen,v “Dynamic Response of SubmarineP~~elines Exposed to Combined Wave andCurrent Action,” Proc. of the 21stOffshore Technology Conference, Paper No.6058, 1989.

26. Hale, J.R., Lammert, W.F., and Jacobsen,v “Improved Basis for Static StabilityA~~lysis and Design of Marine Pipelines,”Proc. of the 21st Offshore TechnologyConference, Paper No. 6059, Houston, 1989.

Table 1 Scope of Coordinated Research Effort

Work Area 1984 1985 1986 1987 1988

hydrodynamic Desk study, Model tests ‘Model tests Model tests Model tests on?orces program on stationary on stationary, on stationary moving pipe.

planning. pipe. partially pipe in shallowburied pipe. trenches.“Improvedhydrodynamicforceformulation(Fourierseries).

?ipe/Soil Model tests Pipe/soil interaction[interaction with forced force.?orces oscillations

in “sandsandclay.

:omputer Irregular Irregular wave Fourier series ●Pipe/soil interaction;oftware wave simulation force force model implemented.development simulation. and pipeline formulation “Results of moving pipe tests

dynamics implemented. implemented.‘Simplified quasi-staticmethod developed.

Design Geotechnical Hydrographic/ ‘Version 1.0 of guidelinesGuidelines aspects of hydrodynamic completed.

guidelines aspects “Seminar presented.prepared. prepared.

-.

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. —

Table 2 Test Parameter Range for 1985 Hydrodynamic Force Tests

.

Test pipe diameter - 200 mm and 400 mm

Pipe hydraulic roughness range - fine, medium, rough (10-5

to 5X10-2)

Seabed hydraulic roughness range - fine, medium, rough (10-3

to 5X10-2)

Maximum average current in flume - 0,69 m/see

Steady Regular Irregular

Current Waves Waves

Reynolds number (x 105) 0.3 - 2.4 0.5 - 3.6 0.7 - 2,5

Keulegan-Carpenter number - 3 - 160 10 - 70

Current to Wave ratio O - 1.6 0 - 1.2

Note: Keulegan-Carpenter number and current-to-wave ratio

for irregular waves based on significant velocity and

peak period of bottom velocity spectrum.

Table 3 Test Parameter Range for 1987 Hydrodynamic Force Tests

for Pipe in Narrow, Shallow Trenches

.

Test pipe diameter - 200 mm

Width of trench bottom - 1 pipe diameter

Trench depth to pipe

diameter ratio - 0.5 to 1.0

Slope of trench sides - 11° to 18°

Direction of flow - Perpendicular to pipe

Pipe hydraulic roughness range - 10-3

Seabed hydraulic roughness range - 10-3

Maximum average current in flume - 0.69 m/see

Steady Regular Irregular

Current Waves Waves

Reynolds number (x 105) 0.3 - 1.2 0.5 - 3.6 -

Keulegan-Carpenter number -

Current

Note:

to Wave ratio

Keulegan-Carpenter number

for irregular waves based

5 - 100 -

0.0 - 1.4 -

and current-to-wave ratio

on significant velocity and

peak period of bottom velocity spectrum.

127

Table 4 Test Parameter Range for 1988 Hydrodynamic Force Tests

for Moving Pipe

Test pipe diameter - 200mmPipe hydraulic roughness range - 10-3

Seabed hydraulic roughness range - 10-3

Maximum average current in flume - 0.69 mlsec

Steady Regular Irregular

Current Waves waves——

Reynolds number (x 105) 0.3 - 1.2 0.5 - 3.6 -

Keulegan-Carpenter number - 10 - 60 10 - 30Current to Wave Ratio 0.0 - 0.8 0.0 - 0.5

Note: Keulegan-Carpenter number and current-to-wave ratio

for irregular waves based on significant velocity and

peak period of bottom velocity spectrum.

Table 5 Test Parameter Range for 1987 Pipe/Soil

Interaction Tests

Type of Test

Test Pipe Diameter -

Submerged Weight

of pipe

Amplitude of Pipe

Oscillations

Soil Types

—

Simple breakout (no pipe oscillations),

Regular oscillatory (displacement

controlled),

Random force tests

0.5m and l.Om

0.25kN/m to 2.0 kN/m

O.lm to 0.5m

Loose sand (relative density = 0.05)

Dense sand (relative density = 0.46)

Soft clay (undrained shear strength

= 1.4 kPa)

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-.— -.—

MEA FY, iJFf FORCE N/M

------ EST FY. LIFTFORCE N/M (FOURIER k4flHoo)

400

300

200

100

0

Rg. 3-Measured and predicted lift force using Fouriermethod test 863 (KC=30, a= Uc /Uw =0.48)

u-.

.2 +/0= 0,5;0=3

-TIH

. ‘/D= !.O; a=5

A H/D= ]. Cl; a=3

Fig. 4–Trench configuration for hydrodynamic forcemodel test on pipes in shallow trenches

n ‘----------,., ..~,,,,,—[+;,;

●

o(CONTINUED PIPE OSCILLATION)

●

●

““’””-”---’’-i’---vE‘“E~,

Fig. 5–Embedment of pipe in soft sediments

RANDOM WAVE

SIMULATION PROGRAM“WSIMQ”

(!+, TP, etc. ) ,~(ON BOITOM)

I L& Ul,lo, U,,l OO,

*

Tz

A.G.A.“FORCE”MODULE

!

HYDRODY

FORCES

dAMIC

I

uMAX 1

HISTORY DEPENDENTSOIL MODEL

IIHISTORY DEPENDENTSOIL RESISTANCE &EMBEDMENT Pl?EDICTICh!

1

STATIC STABILITY CHECK

(Ucj) u,/,(y ? ‘1/,IXI $ ‘MAX)

I

Fig. 6–Simplified qasi–static stability analysis program

131

A_

.—. ~~_—— .—-_— . .. . . _., — . _ ., , __ ~ —— ._—_——_—_._—.— .-— — .————— —= c-_ ~

. —

I

1-‘1~ CONSERVATIVEx .—— ——— ——— —.. ——— .—. . ———c) _7RAoTlToTlAL.mE?51GNa3wQ_n

0 ——— ——— .—— — UNCONSERVATIVE——— ——. .—— ———7WOTTiOmLmE31GN

!Eg SIMPUFIED

ANALYSIS

INCREASING SOIL SIRENGTH -

Fig. 7–Comparison of stability requirements

132

A_ —.——

.—. ~~_—— .—-_— . .. . . _., — . _ ., , __ ~ —— ._—_——_—_._—.—.

.-— — .————— —= c-_ ~

—