Bass, B.J., and Beaver, J.L. 1

Comparison of Field Measurements from Deep Burial Test Installation of Two 24 in. Diameter1

Corrugated High Density Polyethylene Pipes with 2D Soil-Structure Interaction Finite Element2

Analysis34

5

6

7

Corresponding Author: Brent J. Bass, Simpson Gumpertz & Heger Inc., 41 Seyon St., Building 1, Suite8

500, Waltham, MA 02453, phone: 781.907.9327, fax: 781.907.9009, bjbass@sgh.com9

10

Jesse L. Beaver, Simpson Gumpertz & Heger Inc., 41 Seyon St., Building 1, Suite 500, Waltham, MA11

02453, phone: 781.907.9272, fax: 781.907.9009, jlbeaver@sgh.com12

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Submission Date: 1 August 201516

Word Count: 4,13217

Figure Count: 518

Table Count: 819

Total Equivalent Word Count: 7,38220

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Bass, B.J., and Beaver, J.L. 2

ABSTRACT1

A field test program was developed and implemented to monitor two 24 in. diameter corrugated high-2

density polyethylene pipes under 20 ft of fill. The test compared performance of two corrugated pipe wall3

geometries and provided data for comparison to design calculations and finite element models. Test pipes4

were installed in compacted sand embedment overtopped by granular stone dust backfill placed in5

accordance with manufacturer requirements. Backfill densities were measured by nuclear density tests.6

The authors instrumented the pipe sections with bonded resistance strain gages and displacement sensors,7

and soil pressure cells embedded in the backfill above the pipes. Instrumentation data were recorded8

during the installation and backfilling, continuing for over 10,000 hrs. The authors modeled the9

installation using two-dimensional (2D) soil-structure interaction (SSI) finite element analysis in10

CANDE-2007 software for comparison to field-measurements. Instrumentation configuration and11

measurements were compared to AASHTO design calculations in a TRB 2015 paper. This paper12

compares measured values at the end of the test to theoretical results from finite element analysis.13

14

15

Bass, B.J., and Beaver, J.L. 3

INTRODUCTION1

Two 20 ft long parallel runs of instrumented 24 in. diameter corrugated high-density polyethylene2

(HDPE) pipes were installed under 20 ft of fill in late spring 2012. The two runs of pipe were installed in3

a single partial trench (positive projecting embankment) with 6 ft clear spacing and embankment backfill4

placed above (Figure 1). Two locations were instrumented with displacement transducers, strain gages,5

and soil pressure cells. The installation had active instrumentation for initial installation to over6

10,000 hrs after completion of embankment fill placement.7

8

9

FIGURE 1 As-built installation cross-section looking north.10

11

The instrumented pipes were installed in compacted sand embedment overtopped by granular12

stone dust backfill placed in accordance with manufacturer requirements. Backfill densities were13

measured during installation using a nuclear density gage, allowing for determination of the soil load14

above the pipe and confirmation of target embedment stiffness. Instrumentation data were recorded15

during backfill placement through the end of the test. Detailed information about instrumentation,16

including measurements and comparison to AASHTO design (1) are presented in (2).17

A two-dimensional (2D) soil-structure interaction (SSI) finite element model (FEM) of the18

installation was developed in CANDE-2007 (CANDE) (3). CANDE model inputs include pipe material19

and geometry, soil types and compaction, embankment geometry, and construction increments. The FEM20

uses a non-linear soil model to represent embedment soil stiffness. Outputs of interest from the pipe21

model include hoop thrust, bending moment, and displacement. Output for the soil includes vertical and22

lateral pressures.23

24

PIPE SAMPLES, CORRUGATION, AND MATERIAL PROPERTIES25

We instrumented four 10 ft lengths of pipe in our laboratory. We installed instrumentation 2 ft from the26

ends of each 10 ft length, then joined them to form two 20 ft lengths with the instrumented sections near27

the center joint. The 20 ft lengths were installed in two parallel runs, Runs A and B. Runs A and B had28

different corrugation geometries. Run A had an overall deeper corrugation, and Run B had a greater unit29

area, moment of inertia, and pipe stiffness (EI/0.149R3) (Table 1).30

Bass, B.J., and Beaver, J.L. 4

TABLE 1 Profile Section Properties1

2

PipeRun

Area, A(in.2/in.)

Moment ofInertia, I(in.4/in)

Distance fromCentroid to

Inner Fiber, yin

(in.)

Distance fromCentroid to

Outer Fiber, yout

(in.)

CorrugationDepth,yin + yout

(in.)

PipeStiffness,

PS(lb/in./in.)

A 0.290 0.132 0.674 1.373 2.047 36.6B 0.353 0.139 0.738 1.070 1.808 38.4

3In addition to the pipe section property inputs, CANDE requires input of pipe material properties4

(Young’s modulus). For comparison to the approximately 10,000-hr test, we used a modulus5

representative of 10,000-hr load duration from ASTM D6992 (4) tensile creep tests. These tests were6

performed at a constant stress of 500 psi, similar to the 510 psi maximum expected pipe service stress.7

From the test results, we estimated 30,000 psi as an appropriate 10,000-hr modulus for the model.8

9

TEST INSTALLATION10

11

General Description12

The test site consisted of a subtrench plus embankment installation (positive projecting embankment) to13

facilitate 20 ft of soil over the instrumented sections. The two runs were laid in the north-south direction14

with blind-end bulkheads at the north ends. 30 ft of non-instrumented pipe was added at the south end of15

each run to provide man-access from the embankment toe. The installation included trench drainage and16

ventilation pipes.17

18

Soil Materials, Placement, and Timeline19

Table 2 provides a soil materials summary including results from grain size distribution tests and20

maximum dry densities per the modified Proctor test (MPD) in accordance with ASTM D1557 (5)21

Procedure C. ASTM D6938 (6) wet unit weight tests were performed on the bedding, embedment, and22

embankment fill.23

24

TABLE 2 Soil Material Summary25

26

Material DescriptionASTM D2487 (7)

or D2488 (8)Classification

AASHTOM145 (9)

Classification

Maximum Dry Density,Modified Proctor Test

(pcf)

In Situ Firm, Stable,Well-Graded Sand

with Silt

SW-SM(D2488)

N/A N/A

Bedding andEmbedment

Well-Graded Sandwith Silt

SW-SM(D2487)

A-1-B 120.5

EmbankmentFill

Granular Stone Dust SM(D2487)

A-1-B 135.5

N/A = Data not available as test was not performed for in situ soil.27

The pipes were installed with 9 in. of well-graded sand with silt bedding, compacted by two28

passes of a Wacker WP1550 walk-behind vibrating plate compactor. Three field compaction tests were29

performed on the bedding to determine the average wet unit weight of 114 pcf, equal to 92% MPD.30

Embedment soil (well-graded sand with silt) was placed in 6 in. nominal lifts to 2 ft over the31

pipes and the soil pressure cells were installed. Each embedment layer was compacted with one pass of32

the plate compactor. Workers shovel-sliced the embedment material into the haunches. Fifty-three field33

Bass, B.J., and Beaver, J.L. 5

compaction tests were performed on the embedment resulting in a weighted-average wet unit weight of1

106 pcf or 83% MPD.2

Embankment fill (granular stone dust) was placed in 1 ft lifts. The first four lifts were compacted3

with a single pass of a roller compactor. The final fill depth of 20.6 ft at the top of embankment was4

achieved 12 days after placement of the initial embedment lift. Sixty-four field compaction tests were5

performed on the embankment fill to determine a weighted-average wet unit weight of 129 pcf, equal to6

89% MPD.7

8

Instrumentation9

Test pipe instrumentation consisted of displacement transducers, strain gages, and soil pressure cells. We10

instrumented two vertical cross-sections (Sections 1 and 2) of each pipe run. The instrumented cross-11

sections were positioned 2 ft north (Section 1) or south (Section 2) of the joint between the two 10 ft12

sections. Instrumentation details for each sensor type are provided in (4). An instrumentation cross-13

section at Section 1 with sensor naming conventions is shown in Figure 2.14

15

16

FIGURE 2 Section 1 instrumentation and sensor naming conventions.17

18

Displacement Transducers19

We measured displacements and circumferential shortening using draw wire rotational resistance20

displacement transducers (draw wires). Section 1 (Figure 3) included vertical, horizontal, and two21

diagonal diameter measurements, plus a circumferential shortening draw wire (housing near right of22

figure). Section 2 had only vertical and horizontal diameter measurements.23

24

Bass, B.J., and Beaver, J.L. 6

1

2

FIGURE 3 Instrumentation at Section 1.3

4

Strain Gages5

We installed sixteen bonded resistance strain gages, eight per pipe run, at Section 1. We installed four6

gages at each springline, two on the interior surface corrugation valley and two on the exterior surface7

crest (Figure 2).8

9

Soil Pressure Cells10

We installed three vibrating wire pressure transducer soil pressure cells within the embedment soil. We11

installed one soil pressure cell 1.15 ft above and centered over the top of each pipe profile (Figure 2), 1 ft12

north of Section 1, with the third pressure cell centered between the pipes.13

14

MEASUREMENT RESULTS15

16

Manual Measurements17

We measured inside diameter and internal circumference by man-entry approximately 10,250 hrs after18

completing embankment construction (Table 3). We measured the diameter using a tape measure with19

1/16 in. increments. We measured circumference with a π-tape, directly reading an equivalent diameter 20

for a circular shape. Deflection data is presented as a change in diameter relative to Day 0 π-tape 21

measurements (23.75 in. for Run A and 24.16 in. for Run B). Negative measurements indicate a reduction22

in diameter or circumference.23

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25

Bass, B.J., and Beaver, J.L. 7

TABLE 3 Pipe Deflection and Circumferential Shortening from Manual Measurements at1

10,000 hrs2

3

Measurement Run A Run BSection 1 Section 2 Section 1 Section 2

Vertical Deflection (%) -3.7 -4.2 -2.8 -4.3Horizontal Deflection (%) 0.6 1.1 0.4 0.9Circumferential Shortening Strain (%) -1.0 -1.1 -0.9 -0.8

4

Electronic Measurements5

We started data collection on pipe sensors on Day 0 with unloaded pipes and on soil pressure cells when6

the fill depth allowed for their installation. Data acquisition continued for 10,000 hrs after completion of7

earthwork.8

Draw Wires9

Draw wire data at the end of the test is presented in Table 4. Negative deflection is a decrease in diameter.10

Displacement data was generally stable for the 10,000 hrs of data acquisition on all but four gages:11

• Draw Wires B-2-H and A-1-H stopped functioning on Days 390 and 419, respectively.12

• Draw Wire A-2-V had a -0.3% change in vertical deflection in a 17-hr period on Day 323 then13

remained around -3.7%. We are unsure of what caused this sudden change and omit this data from14

Table 4.15

• Draw Wire B-1-H showed a steady reduction in horizontal deflection over the last six months,16

reaching 0.0%.17

TABLE 4 Draw Wire Deflection or Circumferential Shortening Strain at 10,000 hrs1819

Location Draw Wire No. Run A(%)

Run B(%)

Section 1, Vertical A/B-1-V -3.4 -3.3Section 2, Vertical A/B-2-V -- -3.6Section 2, Horizontal A/B-2-H 0.6 --Section 1, Diagonal A/B-1-D1 -0.5 -0.7Section 2, Diagonal A/B-1-D2 -1.2 -0.7Section 1, Circumferential A/B-1-Circ -0.8 -0.9

20

Vertical deflections were -3.3% to -3.6%, similar to manual measurements. The one horizontal21

draw wire still working at the end of the test showed a value much lower than the vertical deflection22

results but similar to manual measurements. The two pipe runs had similar magnitudes of circumferential23

shortening strain from draw wires and manual measurements.24

Strain Gages25

Six of the sixteen electrical resistance strain gages failed during backfilling. All failed gages were inside26

gages, four on Run A and two on Run B. An additional inside gage failed on Run B in the first two27

weeks, leaving B-In-W-2 as the only functional inside gage. Seven strain gages remained functional28

throughout the test. Gage failure can be attributed to difficulty bonding to the highly curved, smooth29

HDPE surface in these small diameter pipes, high thrust strains, curvature changes from bending, large30

service temperature ranges, moisture, and external embedment impingement. Table 5 presents strain gage31

data at 10,000 hrs. Negative values show compression from combined thrust and bending.32

33

TABLE 5 Strain Gage Measurements at 10,000 hrs34

Bass, B.J., and Beaver, J.L. 8

1

Location Gage No. Run AStrain

(%)

Run BStrain

(%)

Inside Surface, West Springline, Section 2 A/B-In-W-2 -- -0.28Outside Surface, East Springline, Section 1 A/B -Out-E-1 -0.72 --Outside Surface, East Springline, Section 2 A/B -Out-E-2 -0.83 -0.39Outside Surface, West Springline, Section 1 A/B -Out-W-1 -0.41 --Outside Surface, West Springline, Section 2 A/B -Out-W-2 -0.06 -0.49

2

Pairs of gages at nearby locations (different by 1 or 2 in their numbering) should show a similar3

response. The two Run A west springline gages (A-Out-W-1 and A-Out-W-2) registered very different4

strains of -0.41% and -0.06%. Gage A-Out-W-2 showed a consistent reduction in strain from 2,000 hrs to5

10,000 hrs that indicates likely gage failure. We exclude the -0.06% value from further discussion.6

Soil Pressure Cells and Vertical Arching Factor7

Soil pressure cell data can be used to approximate a vertical arching factor (VAF). VAF is the ratio of the8

soil load carried in the wall of a buried structure divided by the weight of the soil prism above the pipe9

outside diameter to the ground surface. The VAF may be calculated using springline hoop thrust to10

determine the soil load in the pipe wall. The VAF can also be calculated as the ratio of the soil pressure11

directly over the pipe divided by the free field vertical pressure (unit weight times height of fill).12

For a fill height of 20.6 ft, with embedment material to 2 ft above the pipes, and the average13

moist unit weights given above, the free-field vertical pressure at the soil pressure cell locations, 1 ft14

above the pipes, is 17.4 psi. Measured vertical soil pressures at the end of the test were 11.2 psi, 13.8 psi,15

and 20.1 psi for Run A, Run B, and between the pipe runs, respectively. Using soil pressure to calculate16

VAF gives VAF = 0.64 for Run A, VAF = 0.79 for Run B, and a ratio of 1.16 times the free field pressure17

for the soil column between pipes. Some additional arching may occur in the 1 ft height between the18

pressure cells and the top of pipes.19

20

CANDE FINITE ELEMENT ANALYSIS21

22

Model Description23We created a two-dimensional plane strain FEM of the test installation using the computer program24

CANDE. The model incorporates nonlinear soil behavior using the Duncan/Selig hyperbolic model with25

soil properties developed by Selig for SIDD concrete pipe installations and later adopted by AASHTO.26

We modeled all placed soils as SW soils in CANDE, representative of the sand embedment and27

stone dust backfill used. We based soil compaction levels in the model on field density test28

measurements. Compaction levels for Duncan/Selig soil model parameters are based on maximum29

density per the standard Proctor test (11). For example, SW95 soil is representative of the sand bedding30

material compacted to 95% maximum dry density per the standard Proctor test (95% SPD). Recall that31

field density tests reported modified Proctor densities (MPD). To convert from modified to standard32

Proctor densities, we increased the reported compacted density by 5%. Thus, 90% MPD in the field33

measurements is 95% SPD for input into CANDE. Model soil properties are summarized in Table 6.34

Figure 4 shows the model finite element mesh near the pipes with soil zones depicted by different colors.35

36

37

Bass, B.J., and Beaver, J.L. 9

TABLE 6 Soil Properties used in CANDE Finite Element Model1

2

Zone MaterialColor inModel

Description Soil Model UnitWeight

(pcf)

In Situ Red Firm, stable, well-graded soil Linear Elastic, E = 3,000 psi 120Bedding Orange Well compacted sand Duncan/Selig, SW95 114Haunches Blue Sand manually worked into place Duncan/Selig, SW80 106Embedment Yellow Moderately compacted sand Duncan/Selig, SW90 106Backfill Green Compacted stone dust Duncan/Selig, SW95 129

3

4FIGURE 4 CANDE Finite Element Model Mesh near Pipes (Green Soil Continues to 20.6 ft Total5

Cover (Not Shown)).6

7

The FEM includes incremental construction of soil lifts around and above the pipe. The initial8

construction increment consisted of the red in situ soil. We then placed soil fill (including bedding) at9

6 in. to 9 in. lifts around and above the pipes until reaching 6 ft of cover. Embankment fill was placed in10

12 in. lifts to 20.6 ft. We modeled the soil as fully bonded to the pipe.11

Boundary conditions along the sides of the model restrain lateral displacement and allow free12

vertical displacement. Fixed boundary conditions along the bottom of the model restrain movement in13

both the vertical and horizontal directions. We did not include construction live loads or compaction14

forces. Soils were placed at the compacted density. The soil model allows for increased soil stiffness15

with increased confinement provided by the fill above.16

We modeled the pipes using the linear-elastic basic pipe type in CANDE with beam element17

input properties including the area and moment of inertia shown in Table 1. We included a gravity line18

load for the pipe beam elements of 0.0119 lb/in. based on a 65 pcf unit weight for HDPE. We used a19

30,000 psi elastic modulus to evaluate results that correspond to the 10,000 hr test based on tensile creep20

testing.21

Bass, B.J., and Beaver, J.L. 10

Model Results1CANDE model outputs, including thrust, moment, and deflection are presented in Table 7 along with2

computed wall strains.3

4

TABLE 7 CANDE Model Results Summary(a)56

Behavior Run A Run BCrown(b) Springline(b) Crown(b) Springline(b)

Thrust (lb/in.) -60.5 -111.1 -66.6 -121.8Moment (in.-lb/in.) 27.1 -15.8 29.2 -16.3Thrust Strain(c) (%) -0.7 -1.4 -0.7 -1.2Outer Fiber Flexural Strain (%) -0.9 0.6 -0.8 0.4Inner Fiber Flexural Strain (%) 0.5 -0.3 0.5 -0.3Outer Fiber Combined Strain(d) (%) -1.7 -0.8 -1.4 -0.8Inner Fiber Combined Strain(d) (%) -0.3 -1.7 -0.1 -1.5Deflection(e) (%) -2.8 0.8 -2.6 0.8a. Negative strain is compression, positive bending occurs at crown, positive deflection is increased diameter.b. At controlling nodes near crown and springline (moment and thrust do not peak exactly at crown or springline).c. Considers effective area based on uniform compression strain.d. Considers effective area based on combined strain at inner or outer fibers.e. Vertical deflection presented in crown column, horizontal deflection in springline column.

7

We calculated strains from CANDE force output during post-processing based on pipe cross-8

section geometry and 30,000 psi elastic modulus. Circumferential shortening strain, calculated from the9

CANDE thrust results around the entire circumference of the pipes, was -0.9% strain and -0.8% strain for10

Runs A and B, respectively.11

A contour plot of vertical soil stress is shown in Figure 5. The superimposed red line is at an12

elevation approximately 1 ft above the pipes at the location of the soil pressure cells in the field test. The13

vertical soil pressures at this elevation in the model were 12.8 psi, 13.2 psi, and 19.5 psi for Run A,14

Run B, and between the pipes. The vertical soil pressure at the springline elevation between the pipes was15

20.2 psi.16

17

Bass, B.J., and Beaver, J.L. 11

1

23

FIGURE 5 Contour Plot of Vertical Stress (psi) from CANDE Model Output.4

5

We calculated VAFs from CANDE analysis results using two methods: (1) based on vertical6

soil stress 1 ft above the pipes and the assumed free field vertical overburden pressure of 17.4 psi, and (2)7

from the beam element springline thrust and vertical soil stress between pipes at the springline elevation8

and the calculated soil prism load at the springline elevation. We calculated the soil prism load at the9

springline of the pipes to be 240 lb/in. (each springline) and the free field vertical overburden soil10

pressure to be 18.9 psi.11

VAFs calculated from CANDE vertical soil stress were 0.74, 0.76, and 1.12 at an elevation 1 ft12

above the pipes for Run A, Run B, and between the pipes, respectively. VAFs calculated from springline13

thrust and vertical soil stress at the springline elevation between pipes were 0.46, 0.51, and 1.07 for14

Run A, Run B, and between the pipes, respectively.1516

DISCUSSION OF MEASURED DATA AND COMPARISON TO CANDE OUTPUT17

18As reported in (2), for a 75-year design life installation, the maximum allowable cover height for the test19

installation conditions to meet the AASHTO 1.95 dead load factor and thermoplastic pipe resistance20

factors would be 12.5 ft and 16.5 ft for Run A and Run B, respectively.21

22

Deflection23Manual deflection and circumferential strain measurements (Table 3) showed similar order of magnitude24

but greater variability than electronic measurements (Table 4). The greater variability of manual25

measurements is likely due to the nature of taking manual measurements in the tightly confined 24 in.26

diameter space.27

FEM results showed less vertical deflection (2.8% and 2.6% for Runs A and B, respectively) than28

the instrumentation measured values (3.3% to 3.6%). FEM results gave horizontal deflections of 0.8% for29

both pipes. Manual horizontal deflection measurements ranged from 0.4% to 1.1%, enveloping the FEM30

results and instrumentation results (0.6% for Run A). Run A has 5% lower moment of inertia than Run B.31

This lower bending stiffness should result in greater deflection, which is reflected in the FEM results but32

is less apparent in the manual data. Draw wire deflection data does not show a significant difference33

between runs.34

FEM results showed -0.9% and -0.8% circumferential strain for Runs A and B, respectively. All35

circumferential shortening measurements were similar in magnitude to the FEM results, however the36

Bass, B.J., and Beaver, J.L. 12

instrumentation values showed Run A (-0.8%) to have slightly less shortening than Run B (-0.9%). The1

corrugation unit area of Run A is 82% of that of Run B, therefore greater circumferential shortening is2

expected in Run A. This is reflected in CANDE results and manual measurements but not in3

instrumentation results.4

All vertical deflections at 10,000 hrs were of an acceptable magnitude to meet pipeline5

serviceability criteria and design assumptions, with a maximum allowable deflection of 5% in (1).6

7

Strain8Measured and theoretical strains at the end of the test are summarized in Table 8.9

10

TABLE 8 Measured and Theoretical Strain(a) at End of Test11

12

Location MethodRun A

(% Strain)Run B

(% Strain)

Springline Inner FiberField Test Strain Gage -- -0.3

CANDE Combined Strain -1.7 -1.5

Springline Outer FiberField Test Strain Gage -0.4 to -0.8 -0.4 to -0.5

CANDE Combined Strain -0.8 -0.8a. Negative strain is compression.

13

Measured and computed strains were less than the approximate 2.5% compression strain limit14

(based on 5% ultimate strain and a factor of safety for dead load of 1.95) allowed in design (2). However,15

this measurement process does not adequately address the effects of local buckling on the material strains16

at stiffer regions of the corrugation cross-section and this test was only to 10,000 hrs, whereas the typical17

design life is 75 years.18

With positive horizontal deflections, we expect the springline-measured strain magnitude at the19

inside fiber (-0.3%) to be greater than the outside fiber (-0.45%) at the same springline location. This was20

not observed in the measurement results although the trend did exist in the CANDE results. Since nearly21

all inside surface strain gages failed, the last remaining measurement (-0.3%) may not be reliable. These22

measurements may have been affected by initiation of local buckling of the corrugation wall. Springline23

outer fiber strain gage measurements were close to the CANDE results. The high inside gage loss rate is24

likely from the curvature change due to bending on the HDPE substrate.25

FEM results showed greater inside fiber combined strain in Run A than Run B.26

27

Soil Pressures and Vertical Arching Factors28Measured vertical soil pressures at an elevation 1 ft above the pipes (11.2 psi, 13.8 psi, and 20.1 psi for29

Run A, Run B, and between the pipes, respectively) were similar to FEM results (12.8 psi, 13.2 psi, and30

19.5 psi, respectively). VAFs computed from these results, therefore, were also comparable. Calculated31

VAFs from FEM springline thrust and soil pressure values (0.46 for Run A, 0.51 for Run B, and 1.0732

between pipes at the springline) were significantly lower than those calculated from FEM vertical soil33

pressures (0.74, 0.76, and 1.12 for Run A, Run B, and between the pipes, respectively). This shows the34

effects of additional vertical soil arching under the pressure cells and over the top half of the pipes.35

36

CONCLUSIONS37

Deflection and circumferential strain measurements at the end of the 10,000 hr test installation were of38

comparable magnitude to FEM results although instrumentation vertical deflections were slightly higher.39

FEM deflections were consistent with expectations when comparing results from the two pipe runs with40

different cross-sections. Instrumentation results showed no conclusive difference between pipe runs.41

Bass, B.J., and Beaver, J.L. 13

Reliable strain gage installation on HDPE pipes is difficult to achieve. Springline outer fiber1

strains calculated from FEM results were comparable to measured values. FEM showed trends consistent2

with expectations for flexible pipes with positive horizontal deflections.3

Vertical arching factors computed from vertical soil pressures (measured or from FEM) showed4

consistent trends expected for flexible pipes that shed load to the adjacent soil column when installed in5

granular fill that is well compacted around the pipes.6

7

ACKNOWLEDGEMENT8The test installation, data processing, and modeling were funded by Advanced Drainage Systems Inc.9

10

Bass, B.J., and Beaver, J.L. 14

REFERENCES1

1) AASHTO LRFD Bridge Design Specifications, 2012 Edition. AASHTO, 2012.2

2) Bass, B.J., B.R. Vanhoose, and J.L. Beaver. Comparison of Field Measurements from Deep3

Burial Test Installation of Two 24 in. Diameter Corrugated Plastic Pipes with the AASHTO4

Thermoplastic Pipe Design Method. Proceedings of the Transportation Research Board5

Conference 2015, Washington, D.C., 2015.6

3) Mlynarski, M., M.G. Katona, and T.J. McGrath. Modernize and Upgrade CANDE for Analysis7

and LRFD Design of Buried Structures. NCHRP Report 619, Transportation Research Board,8

National Research Council, 2008.9

4) ASTM D6992-03(2009). Standard Test Method for Accelerated Tensile Creep and Creep-10

Rupture of Geosynthetic Materials Based on Time-Temperature Superposition Using the Stepped11

Isothermal Method. ASTM International, 2009.12

5) ASTM D1557-12. Standard Test Methods for Laboratory Compaction Characteristics of Soil13

Using Modified Effort (56,000 ft-lbf/ft3 (2,700 kN-m/m3)). ASTM International, 2012.14

6) ASTM D6938-10. Standard Method of Test for In-Place Density and Water Content of Soil and15

Soil-Aggregate by Nuclear Methods (Shallow Depth). ASTM International, 2010.16

7) ASTM D2487-11. Standard Practice for Classification of Soils for Engineering Purposes17

(Unified Soil Classification System). ASTM International, 2011.18

8) ASTM D2488-09a. Standard Practice for Description and Identification of Soils (Visual-Manual19

Procedure). ASTM International, 2009.20

9) AASHTO M145-91 (2008). Standard Specification for Classification of Soils and Soil-Aggregate21

Mixtures for Highway Construction Purposes. AASHTO, 2011.22

10) ASTM D698-12s1. Standard Test Methods for Laboratory Compaction Characteristics of Soil23

Using Standard Effort (12,400 ft-lbf/ft3 (600 kN-m/m3)). ASTM International, 2012.24

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