stsad

aall

field teumerompa

al pipesand

onditiion phct.

oil pre

are generally based on the factored thrust and pipe wall resis- with a soil cover of 610 mm 2 ft. It was observed that the load-

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d.tance. The pipe wall resistance must be, indeed, greater than thefactored thrust to ensure safety against structural failure. Verticalsoil pressure at the pipe crown level and pipe outside diameter arethe two important factors for determination of the factored thrust.When the flexible pipes are buried under shallow depths, the ver-tical crown pressure is mainly influenced by the live load effect.Soil backfill quality, pipe geometrical and material properties,pipe installation condition, and loading configuration are also

ing plate with a contact area of 305 by 305 mm 12 by 12 in.punched into the soil as the bearing capacity of the soil backfillexceeded. This led to a stress increase at the pipe crown andeventual failure of the pipe with a reversal of curvature local wallbending. Most pipe failures occurred at vertical pipe deflectionsbetween 1.9 and 2.9% Conard et al. 1998.

Published literature indicates that there is very limited infor-mation on the pipe-soil system behavior with a soil cover of lessthan 610 mm 2 ft and without a pavement structure, especiallyfor pipes with a nominal diameter equal to or greater than900 mm 36 in.. Therefore, full-scale field tests were carried outat the Florida DOT FDOT maintenance yard on Springhill Roadin Tallahassee during December 2001 to May 2002 Arockiasamyet al. 2004. The field test was conducted to investigate thebehavior of buried thermoplastic and metal flexible pipes underthe application of static concentrated wheel loads including adynamic load allowance factor. The main objective was to evalu-ate the short-term responses of the pipe-soil system and the pipejoint performance under different soil cover depths without thepavement, which is considered as an extreme case during theconstruction phase.

In this paper, the pipe installation in the field and the testprocedure are first described. Then, the pipe-soil system responsesare presented and discussed with emphasis on pipe deflections,

1Professor and Director, Center for Infrastructure and ConstructedFacilities, Dept. of Civil Engineering, Florida Atlantic Univ., Boca Raton,FL 33431.

2Professor and Director, Dev. & Research for Str. and Rehab.DRSR, Dept. of Construction Engineering, Univ. of Quebec/Ecole deTechnologie Superieure, Montreal PQ, Canada H3C 1K3.

3Graduate Student, Dept. of Mechanical Engineering, Florida AtlanticUniv., Boca Raton, FL 33431.

Note. Discussion open until July 1, 2006. Separate discussions mustbe submitted for individual papers. To extend the closing date by onemonth, a written request must be filed with the ASCE Managing Editor.The manuscript for this paper was submitted for review and possiblepublication on October 6, 2004; approved on March 1, 2005. This paperis part of the Journal of Performance of Constructed Facilities, Vol. 20,No. 1, February 1, 2006. ASCE, ISSN 0887-3828/2006/1-2127/$25.00.

JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES ASCE / FEBRUARY 2006 / 21Full-Scale Field Teunder Live Lo

Madasamy Arockiasamy1; Omar Ch

Abstract: This paper describes the procedure and results of thediameter pipes subjected to a highway design truck loading. Ndetermine pipe-soil system response under live load application. Csoil pressures around and above the pipes, deformed cross-sectionthe buried flexible pipes, embedded with highly compacted gradedvisible joint opening or structural distress. Under shallow burial cadequate for installation of the flexible pipes during the constructpipes based on the truck load response and repeated loading effe

DOI: 10.1061/ASCE0887-3828200620:121

CE Database subject headings: Soil-structure interaction; Sdistribution; Highways; Trucks.

Introduction

Flexible pipes, corrugated high-density polyethylene HDPE,polyvinyl chloride PVC, and metal pipes are gaining popularityfor use as buried underground conduits for road way and highwaygravity-flow applications. In these applications, the pipes mustsupport soil overburden, groundwater, and loads applied at theground surface due to vehicular traffic. The flexible pipe designand installation are currently based on American Association ofState Highway and Transportation Officials AASHTO require-ments and Department of Transportation DOT design practice.

The AASHTO designs of buried thermoplastic and metal pipesJ. Perform. Constr. Facion Flexible PipesApplication

al2; and Terdkiat Limpeteeprakarn3

sts on high-density polyethylene HDPE, PVC, and metal largeical simulations using finite element method are performed torisons of field test data with the predicted responses are made forprofiles, and pipe deflections. The field test results indicated that

with silt, demonstrated good performance without exhibiting anyons, the AASHTO specified deflection limit of 5% is found to bease, and a vertical deflection limit of 2% is suggested for HDPE

ssure; Flexible pipes; Culverts; Storm sewers; Live loads; Load

other important factors that govern the soil pressure distributionover the buried flexible pipes.

Literature review, conducted on buried flexible pipes subjectedto live load application, indicates that a minimum soil cover overthe pipe crown appears to be the most important parameter onpipe-soil system responses. Watkins and Reeve 1982 performedfield tests on corrugated polyethylene pipes, with pipe diametersranging from 381 to 610 mm 15 to 24 in.. The test pipes weresubjected to the concentrated wheel load, and it was found that asoil cover of 305 mm 1 ft over the pipe crown appeared toprovide adequate protection against an excessive pipe deflection.Lohnes et al. 1997 conducted the field test on the HDPE pipesl. 2006.20:21-27.

Table 1. Pipe Geometric Properties

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d.deformation of cross-sectional pipe profile, and soil pressuresaround and above the pipes. Recommendations are made for thevertical pipe deflection limit and the minimum soil cover depthbased on the field test results and published literature.

Field Installation of Flexible Pipes

Description of Flexible Pipes and InstrumentationSix flexible pipe types, investigated in this field-test program, are6.1 m 20 ft long, and have two different nominal pipe diam-eters: 900 and 1,200 mm 36 and 48 in.. The test pipes includedhigh-density polyethylene pipes PE36a, PE36b, and PE48, poly-vinyl chloride pipe PVC36, aluminum pipe Al36, and steelpipe St36. The metal pipe profile consists of the spiral-rib typewith 1919191 mm 3/43/471/2 in. corrugation. Thethermoplastic pipe wall profiles have been presented elsewhereChaallal et al. 2004. The pipe geometries and material proper-ties are shown in Tables 1 and 2, respectively.

During the pipe installation, linear variable differential trans-ducers LVDTs were used to measure vertical pipe deflections. Aspecial device, designed and built at the FDOT StructuralResearch Center, Tallahassee, was used for measuring cross-sectional pipe profiles during live load application at differentlocations along the pipe length. The earth pressure cells were usedto monitor the soil pressure during live load application. Thesepressure cells were located approximately 3,048 mm 10 ft alongthe pipe length from one end. For the 900-mm diameter pipes, thepressure cells were positioned at locations approximately 25 mm1 in. away from the pipesoil interface, and above the pipes atvarying soil depths, as shown in Fig. 1. The positions of thepressure cells around the 1,200-mm pipes were very similar tothose of the 900-mm diameter pipes with the exception that thepressure cells placed above the pipe crown were at differentdepths Arockiasamy et al. 2004. To ensure an accurate reading,the pressure cells were calibrated in the FDOT laboratory beforeinstallation in the field. A data acquisition system was used torecord the measured soil pressures. Strain gauges were also in-strumented in the interior surface of the buried pipes in the pipecrown, shoulder, springline, haunch, and invert regions.

Designation PE36a

Nominal pipe diameter mm 900Average inside pipe diameter mm 914Average outside pipe diameter mm 1,059Minimum pipe wall thicknessa mm 3.18Cross-sectional area per unit length mm2 10.19Moment of inertia per unit length mm4 6,555aFor the thermoplastic pipes, the minimum thickness denotes the inner li

Table 2. Pipe Properties and Idealized Pipe Wall Thickness for Three-DDesignation PE36a PE36

Modulus of elasticity MPa 760 760Poissons ratio 0.40 0.40Idealized pipe wall thickness mm 48.26 36.8322 / JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES AS

J. Perform. Constr. FaciBurial Depths, Trench Width, Bedding, and BackfillMaterials

A total of thirty-six 36 pipes were buried and tested under threedifferent burial depths: 0.5D, 1D, and 2D. These three depthscorrespond to 457, 914, and 1,829 mm 1.5, 3, and 6 ft, and 610,1,219, and 2,438 mm 2, 4, and 8 ft, for the 900- and1,200-mm-diameter pipes, respectively. A minimum trench widthwas maintained so as not to be less than the greater of either 1.5times the pipe outside diameter plus 305 mm 12 in. or the pipeoutside diameter plus 406 mm 16 in. AASHTO 1998. Thebottom of the trench had a minimum of a 152-mm 6-in. thickbedding layer consisting of the 19 mm 34 in. crushed limestoneoverlaying the undisturbed natural soil. The soil backfill was clas-sified as poorly graded sand with silt SP-SM in accordancewith ASTM Standard D2487 ASTM 1995, and the native soilhas a similar soil property. The soil backfill was placed surround-ing or above the buried pipes in lifts of 152 or 305 mm 6 or12 in., and compacted before adding the subsequent lifts. A tightcontrol of the backfill compaction was also made to ensure that aminimum dry density equivalent to 95% of the Standard Proctormaximum dry density was achieved.

Field Tests of Flexible Pipes

Applied Axle Loads with Impact FactorsA 142-kN 32-kip axle load was used to simulate the standarddesign highway loading in this study. Impact load factors wereincluded in the simulation using the dynamic load allowance IMgiven below LRFD AASHTO specifications 1998:

IM = 33 1.0 0.125DE 1

where DE=depth of soil cover above the pipe crown ft. Basedon computed impact factors, a maximum axle load of 154 kN34.6 kips was required for 2D burial depth, and 72 and 181 kN38.6 and 40.6 kips for 1D and 0.5D burial depths, respectively,for the 900-mm diameter pipes, For the 1,200-mm diameterpipes, axle loads of 142, 166, and 177 kN 32, 37.3, and

PE48 PVC36 Al36 St36

1,200 900 900 9001,208 902 907 9101,339 985 947 9223.43 4.91 1.91 2.0114.76 10.44 1.19 1.50

10,094 2,393 55 61ckness at the interior pipe wall.

onal Finite Element Modeling

PE48 PVC36 Al36 St36

760 2,760 68,950 199,9600.40 0.37 0.33 0.30

53.34 26.67 5.08 7.11imensi

bPE36b

900911

1,0543.07CE / FEBRUARY 2006

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d.39.9 kips were required for the pipes with 0.5D, 1D, and 0.5Dburial depths, respectively.

Critical Load Case Determination and Test VehiclesThe positions of test vehicles along the pipe length were deter-mined to be one of the critical parameters for evaluation of theperformance of the pipes and the joints. Three different load casesI, II, and III were initially proposed and evaluated in the studyFig. 2a. In the load case II, a second vehicle was added tosimulate the two-lane traffic. Boussinesq 1883 introduced thesolution for the stresses produced at any point in a homogeneous,elastic, and isotropic medium as the result of a point load appliedon the surface of an infinitely large half space. Using the Bouss-inesq theory, the critical load case was determined based on thecomputed stresses at the pipe crown level. It was found that theload case II was the critical one the measured soil pressures alsoconfirmed this finding, and used for all test pipes.

Two different trucks, the tandem dump truck and the FDOTtruck, were used for the required load simulation. These truckswere loaded with concrete blocks based on the required axle loadsfor different test pipes and burial depths. The tandem dump truckwas chosen for the pipes with 2D burial depth due to the ease ofmaneuverability over the narrow and limited space in the field.Using the Boussinesq theory, it was determined that the tandemdump trucks only produced 7080% of the required pressures atthe pipe crown for the test pipes with 1D and 0.5D burial depthsArockiasamy et al. 2004. Therefore the FDOT trucks wereselected to simulate the required truck loads.

Fig. 1. Location of pressure cells for 36-in. diameter pipes with a0.5D; b 1D; and c 2D burial depths

Fig. 2. a Three different load cases. b Tire dimension andJOURNAL OF PERFORMANC

J. Perform. Constr. FaciTest Vehicle Position and Data RecordingFig. 2b shows the tire positions of the two rear axles of theFDOT truck for pipes with 0.5D burial depth. The rear axle ofeach truck was exactly over the center of the buried pipe. Fig. 3shows a typical test setup for the pipes with 0.5D and 1D burialdepths. The tire positions for 1D burial depth are also similar tothat of the 0.5D burial depth, except that the location of the firstFDOT truck from the pipe end was 762 mm instead of 556 mm.In the case of 2D burial depth, the two rear axles of each tandemdump truck were positioned symmetrically with respect to theburied pipes.

The pipe deflections, soil pressures, and pipe wall strains at theinstrumented pipe sections were monitored and recorded 1 priorto, 2 immediately upon load application, and 3 immediatelyafter load removal. Additional measurements of pipe wall strainswere also recorded after 1530 min of load application.

Analytical Investigations

Finite Element Analysis for Pipe-Soil SystemNumerical simulations based on finite element FE method werecarried out to study the pipe-soil system behavior under the

ion of the first FDOT truck for pipes with 0.5D burial depth

Fig. 3. Two FDOT trucks in position over the test pipe with 0.5burial depthE OF CONSTRUCTED FACILITIES ASCE / FEBRUARY 2006 / 23

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d.application of truck loading. Both two- and three-dimensional FEanalyses were performed based on modeling the pipesoil inter-face conditions as fully bonded. The pipes with 2D burial depthwere modeled using a two-dimensional FE code, CANDE-89 pro-gram Musser 1989. The CANDE-89 modeling is based on atwo-dimensional plane strain formulation, in which the loadedfootprint length is assumed to be infinite. The finite footprints,caused by the required wheel loads, were idealized as a singlestrip load with an infinite length using the approach suggested byKatona 1990. Gravel and sandy silt with 95% compaction wereselected for the bedding and in situ soil materials, and sandy siltwas used for both the trench fill and the backfill with the samecompaction level.

A general-purpose three-dimensional FE program, ANSYSVersion 5.7, 2000, was used to model the pipes with all three2D, 1D, and 0.5D burial depths. Three assumptions made in thethree-dimensional modeling are small displacement theory, time-independent response, and linearly isotropic elastic material. For2D burial depth, the pipe-soil system was modeled taking advan-tage of the symmetry of axle loads Fig. 4a. In the case of 1Dand 0.5D burial depths, the buried pipe was subjected to unsym-metrical axle loads. Therefore the system was idealized consider-ing the full pipe together with the soil Fig. 4b. All three trans-lational degrees of freedom were fixed at the bottom boundary,and only the horizontal translational degrees of freedom wererestrained along the two lateral boundaries Figs. 4c and d. Thepipe material properties and idealized pipe wall thicknesses usedfor the models are shown in Table 2. For the soil modeling, thePoissons ratio was assumed to be 0.38, and the soil moduli forpipes with 0.5D, 1D, and 2D burial depths were taken as 19.6,31.4, and 43.2 MPa 2,845, 4,552, and 6,259 psi, respectively.The detailed procedures for obtaining the idealized thickness andsoil moduli were discussed elsewhere Arockiasamy et al. 2004.

Pipe DeflectionIn addition to the results from FE analyses, the maximum pipedeflection was also computed using two different semi-empirical

Fig. 4. Three-dimensional FE modeling of the pipe-soil system:solid modeling for 2D burial depth a and for 1D and 0.5D b,boundary condition for 2D burial depth c, and for 1D and 0.5Dburial depth d24 / JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES AS

J. Perform. Constr. Facimethods: the modified Iowa formula Eq. 2 by Watkins andSpangler 1958 and the modified Meyerhofs formula Eq. 3by Sargand et al. 1998.

x =DLKWcr3

EI + 0.061Er32

where x=horizontal deflection; DL=deflection lag factor;K=bedding constant; E=modulus of soil reaction Hartley andDuncan 1987; Wc=vertical soil pressureo.d.; o.d.=pipe out-side diameter; r=pipe mean radius; EI=stiffness factorPS 0.1493r3; and PS=pipe stiffness.

x

D% =

33.75E

1 + 2H/D2

1 + H/DH/D3

where H=average soil cover over the pipe=H0+0.215r;H0=height of soil cover over the pipe crown; v=vertical stressat depth H; and D=nominal pipe diameter.

Field Test Results and Comparisons

Vertical Pipe Deflections during InstallationThe vertical pipe deflections during installation were measuredand recorded only for the metal pipes and the HDPE1,200-mm-diameter pipe with 2D burial depth. Fig. 5 shows themeasured pipe deflection versus depth of soil backfill. It can beseen that the values undergo an increase during the placement andcompaction of the soil backfill from the pipe invert level to thepipe crown, then exhibit a slight decrease after the soil backfillwas placed above the pipe crown, and have no significant changeuntil the end of the installation. These observations were similarto those reported by Fleming et al. 1997 where an increasein the pipe diameter along the vertical axis was observed in theheavily compacted sand installation. The maximum pipe

Fig. 6. Comparison of pipe deflections for the PE36a pipe

Fig. 5. Vertical pipe deflection during the pipe installationCE / FEBRUARY 2006

l. 2006.20:21-27.

the data obtained prior to load application, and during load appli-

FE A

Soil p

8

Field

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d.deflections, recorded when the backfill was filled up to the pipecrown level, were approximately 0.2, 1.1, and 0.5% for the steel,aluminum, and HDPE 48-in. diameter pipes, respectively. Thusthe deflection design limit of 5% specified in AASHTO 1998 isfound to be adequate for flexible pipes during the installationunder shallow burial applications.

Pipe Deflections during Live Load ApplicationThe vertical pipe deflection due to the effect of live load applica-tion was found to have a maximum value of 0.6% 5 mm in thePE36a pipe with 0.5D burial depth. This value compared reason-ably with the finding in the field test on HDPE pipes reported byMcGrath et al. 2002. Fig. 6 shows comparisons of the measuredhorizontal deflection x and vertical pipe deflection y withthe predicted values based on the modified Iowa formula, themodified Meyerhof formula, as well as CANDE and ANSYSanalyses for the PE36a pipe. It can be seen that the analyticalvalue based on the three-dimensional FEM prediction ANSYSanalysis compares reasonably with the measured value. Theother methods tend to overestimate to a considerable extent. Inthe case of pipes with 1D and 2D burial depths, the measured andpredicted values were small less than 3 mm.

Cross-Sectional Pipe ProfileNo significant deformation was observed for all the test pipesexcept that the two HDPE 900-mm-diameter pipes with 0.5Dburial depth experienced a small deformation at the pipe crownregion. Fig. 7 shows different measured cross-sectional pipe pro-files for the PE36a pipe. These pipe profiles are plotted based on

Fig. 7. Measured cross-sectional profiles with and withoutmagnification for the PE36a pipe

Table 3. Comparisons of Measured Soil Pressures with Predicted Values

Pressurecellpositions

PE36a PE36b PE4

FEM Field FEM Field FEM

P1 8 21 8 14 6P2 26 38 25 17 22P3 52 51 50 58 39P4 40 39 41 66 37P5 104 125 83 106 66P6 509 101 508 438 211Note: N/A: data not available; FEM: finite element method.JOURNAL OF PERFORMANC

J. Perform. Constr. Facication with and without 5-time magnification. A pipe profile com-puted from the three-dimensional FE analysis also indicates asimilar pattern. It can be seen that the pipes generally tend todeform to the heart shape defined by Rogers 1988, in whichthe pipe crown flattens and the shoulders become relatively morecurved. This behavior confirmed that the buried pipes were em-bedded in a well-compacted quality soil.

Soil PressuresTable 3 shows the measured and predicted soil pressures aroundand above the pipes with 0.5D burial depth. It is readily seen thatthe predicted soil pressures from the three-dimensional FE analy-sis at the pipe crown and springline are generally in the samerange with the measured values. The magnitudes of soil pressuresfor pipes with 1D and 2D burial depths are small when comparedto those with 0.5D burial depth, and the data can be found else-where Arockiasamy et al. 2004.

Visual Observations of Pipe Joint Opening and PipeDistressObservations of the performance of pipe joints were made onlyfor the pipes with 0.5D burial depth via visual examination. Dueto the safety concern, the pipe joints were not inspected duringlive load application; therefore the joints were photographed atone of the pipe ends using a zoom camera to observe joint dislo-cation, if any, and inspected for joint opening immediately afterremoval of the truck loading. Neither visible pipe joint openingswere observed in this study nor did the test pipes exhibit anyvisible localized bulging, wall buckling, wall crushing, cracking,or tearing of the pipe.

Discussions

Pipe Deflection Limit for HDPE PipesUnder shallow burial conditions and static loading configuration,pipe deflection limits have been reported by Iowa State UniversityKlaiber et al. 1996; Lohnes et al. 1997; Conard et al. 1998;Phares et al. 1998, Texas Tech University Jayawickrama et al.2002, Ohio University Sargand et al. 1998, and Florida AtlanticUniversity Reddy 1999. The deflections at pipe failure werefound to be varying from 2 to 8%. These published data indicatethat vertical pipe deflection limits are dependent to a large extenton the pipe diameter and the position of the loaded contact area.

nalysis for Pipes with 0.5D Burial Depth

ressure kPa

PVC36 Al36 St36

FEM Field FEM Field FEM Field

9 14 11 29 11 5927 30 27 25 26 2653 73 50 76 48 7037 50 37 44 36 4594 90 86 113 113 72

502 492 503 166 505 222E OF CONSTRUCTED FACILITIES ASCE / FEBRUARY 2006 / 25

l. 2006.20:21-27.

Table 4. Changes in Vertical Pipe Diameter Due to Repeated LoadingEffect adapted from Faragher et al. 2000

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d.Faragher et al. 2000 conducted field tests on buried plasticpipes with diameters of 6101,067 mm 2442 in.. These pipeswere buried under a soil cover of 914 mm 3 ft without a pave-ment structure and tested with 1,000 passes of a heavy testvehicle to study the effect of the repeated loading on vertical pipedeflections. They reported that the pipe deflections increased rap-idly during the initial loading cycles, and the rate of deformation,thereafter, reduced considerably with increasing number of cyclesof loading. In this study the backfill soil was normally compactedFaragher et al. 2000. In order to account for higher soil com-paction, the vertical pipe deflection corresponding to the 50thload pass may, then, be assumed as the value of the initial deflec-tion. The effect of the repeated loads on HDPE pipes may beestimated using the deflections at the 1,000th load pass. Table 4shows that the vertical deflections at the 1,000th load pass areapproximately three 3 times those at the 50th load passFaragher et al. 2000.

The maximum vertical pipe deflection can be estimated to be1.8% based on a magnification of three 3 over the observedmaximum deflection of 0.6% in the present study. Therefore it issuggested that the maximum deflection be limited to 2% forHDPE pipes with shallow burial conditions. In the present study,a soil cover of 457 mm 1.5 ft was used for the900-mm-diameter HDPE pipes; however, further studies may benecessary to examine the repeated loading effect.

Soil PressuresThe computed soil surface pressures were 648 and 634 kPa94 and 92 psi for the 900- and 1,200-mm-diameter pipes,respectively. These values were calculated based on the tire-truckloads of 44.4 and 45.1 kN 10,150 and 9,975 lbs and the tire-contact area of 229 by 305 mm 9 by 12 in.. The measured soilpressures at the pipe crown are 19, 16, 14, 11, and 18% of thecomputed soil pressures for the PE36a, PE36b, PVC36, St36, andAl36 pipes, respectively. Moreover, in the case of the PE48 pipe,the measured pipe crown pressure was only 7%. It is readily seenthat the measured soil pressure for the HDPE 1,200-mm-diameterpipe is approximately 2 to 3 times less than those of the HDPE900-mm-diameter pipes. This indicates that an additional soilcover of 152 mm 6 in. significantly contributes to lower the soilpressure at the pipe crown.

Fig. 8 shows the measured soil pressures normalized by thevalues at the pipe crown at 0 for pipes with 0.5D burial depth.It can be seen that the pressures at pipe springline at 90 areonly 4055% of those at pipe crown for the HDPE pipes, and thatthe values are about 70, 80, and 98%, for the aluminum, PVC,and steel pipes, respectively. This suggests that for pipes with thesame diameter and soil cover depth, the HDPE pipes attractedmore load at the pipe crown region than other three pipes; the

Soiltype

Vertical pipe diameter change%

Ratioa50 load passes 1,000 load passes

Gravel 0.4 1.1 2.8Sand 0.75 2.4 3.2aRatio of the pipe diameter changes at the 50th load pass to those at1,000th load pass.26 / JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES AS

J. Perform. Constr. FacistifferPVC and metalpipes appeared to distribute concen-trated wheel loading at the soil surface to pipes various regionsbetter when compared to the HDPE pipes.

It is also interesting to point out that the pressures at thehaunch region at 135 for all of the pipes except the PE48 pipeare only approximately 1535% of those at the pipe crown. Anexamination of the measured soil pressures at the pipe invert at180 also shows that the pressures are generally in the samerange as those at the haunch region Fig. 8. Therefore one caninfer that the test pipes received good soil support throughout thelower portion of the pipes.

Summary and Conclusions

The present study investigates the pipe-soil system responsesunder live load application including dynamic impact load effects.One of the important factors for the current design method ofburied thermoplastic and metal pipes is the vertical soil pressureat the pipe crown. Field test results show that when an additionalsoil cover of 152 mm 6 in. is introduced, the vertical soil pres-sure, at the pipe crown, of the larger HDPE pipe reduces 2 to 3times compared to those of the smaller HDPE pipes. The othertwo important factors are the vertical pipe deflections during in-stallation and live load application. The AASHTO specified de-flection limit of 5% is found to be adequate for the flexible pipesduring the installation phase. A vertical deflection limit of 2% issuggested for the HDPE pipes during the construction phase forroad way and highway applications. Although a soil cover of457 mm 1.5 ft was used for the 900-mm-diameter HDPE pipesin the present study, further studies may be necessary to examinethe repeated loading effect.

Acknowledgments

The writers wish to express sincere thanks to Florida Departmentof Transportation FDOT for the financial support of the studypresented in this paper Research Project: Experimental and Ana-lytical Evaluation of Flexible Pipes for Culverts and StormSewers, Contract No. BC-775, Principal investigator: Dr M.Arockiasamy, Project Manager: Marc Ansley. The writers wishto express their appreciation to Dr. P. Scarlatos, Professor andInterim Chairman, Department of Civil Engineering, and Dr. KarlK. Stevens, Dean, College of Engineering, Florida AtlanticUniversity for their continued interest and encouragement.

Fig. 8. Normalized measured soil pressures for a HDPE pipes andb PVC and metal pipesCE / FEBRUARY 2006

l. 2006.20:21-27.

References

American Association of State Highway and Transportation OfficialsAASHTO. 1998. AASHTO LRFD bridge design specifications,Washington, D.C.

Arockiasamy, M., Chaallal, O., Limpeteeprakarn, T., and Wang, T.2004. Experimental and analytical evaluation of flexible pipes forculverts and storm sewers, Vol. III: Field experimental work and nu-merical analysis, Contract No. BC-775, Florida Department ofTransportation.

ASTM. 1995. Classification of soils for engineering purposes: Unifiedsoil classification system. D 2487-93, Annual Book of ASTMStandards, ASTM, Philadelphia.

Boussinesq, J. 1883. Application des potentials a letude de lequilibreet du mouvement des solides elastiques, Gauthier-Villars, Paris.

Chaallal, O., Arockiasamy, M., and Limpeteeprakarn, T. 2004. Labo-ratory testing for determination of stiffness characteristics of largediameter thermoplastic gravity-flow drainage pipes. 83rd TRBAnnual Meeting, Transportation Research Board, Washington, D.C.

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