Vertical Deflection Limit of Presentation at OTEC Buried Profile …€¦ · structural performance of the pipe. At 140 ft, 5.2% deflection, dimples became pronounced but were not

Vertical Deflection Limit of Buried Profile-Wall HDPE Drain Pipes (abstract No. 118)

Vertical Deflection Limit of Buried Profile-Wall HDPE Drain Pipes (abstract No. 118)

PI: Dr. Teruhisa (Terry) Masada, Faculty Advisor

Co-PI: Xiao Han, Ph.D. Student

Civil Engineering DepartmentRuss College of Engineering & TechnologyOhio University, Athens, OH

10:30-12:00 October 28 (Wed.), 2015

Presentation at OTEC

Session 72Buried ConduitMechanics

2

Introduction Introduction

• Thermoplastic pipelines have been utilized extensively below the ground surface to:

• 1) Provide utility service (water, natural gas, electricity, …) to customers;

• 2) Serve as alternatives to more conventional concrete and metal culverts; and

• 3) Serve as cheaper alternatives to short-span bridges.

3

IntroductionIntroduction

• In transportation related projects, HDPE pipe culverts are becoming more common than PVC pipe culverts.

• Structural health of the underground plastic pipes is vital to the overall infrastructure asset management.

• Structural conditions of buried HDPE pipes must be evaluated during and after construction. HDPE pipes are soft and flexible. They can deform much more easily than pipes made from other materials.

4


• HDPE pipes come with profiled wall sections.

(a) Straight Wall

(b) Corrugated Wall

(c) Profile Wall

(a) Straight Wall

(b) Corrugated Wall

(c) Profile Wall

Straight wall Profile wall

Corrugated Wall + Liner

5


• Because they are flexible, HDPE pipes interact with surrounding soil to resist dead and live loads. Soil-Pipe Interaction

• Plastic pipes require high-quality structural soil fill (backfill) to be able to perform well.

Ohio University - Ohio Research Institute for Transportation and the Environment

6


Springline

Crown

Invert

Bedding

Foundation Soil

SoilEnvelope

SoilEnvelope

Cover

Special Terms Used

7


• Potentially Critical Regions Located in Pipe Cross-Section:

CrownCompressive Strain (outside wall);Tensile Strain (inside wall)

SpringlineCompressive Strain (inside wall);Tensile Strain (outside wall)Cracking; Buckling

InvertStresses/Strains are significant when pipe sits directly on rigid media (ex. bedrock.).

8


• Limiting the maximum vertical deflection usually takes care of all concerns about the HDPE pipe’s structural performance.

• What will be the largest vertical deflection which can assure sound structural performance in varied field installation/service conditions for HDPE pipe culverts?


9

ObjectiveObjective

• The main goal of the OU study was to establishthe threshold vertical deflection values forthermoplastic pipes installed in a variety ofinstallation conditions


10

MethodologyMethodology

• Task 1: Literature Review• Summarize documented field performance cases for buried HDPE pipes

• Task 2: ASSHTO LRFD Design Calculations• Apply AASHTO LRFD method calculations to correlate vertical deflections to

performance limiting conditions for HDPE pipes

• Task 3: Computer Simulations• Use industry standard computer software CANDE to also correlate vertical

deflections to performance limit conditions for HDPE pipes

• Task 4: Development of Charts• Combine the results from all three tasks to draw conclusions and develop

charts concerning threshold vertical deflections for HDPE pipes


11

Task 1: Literature ReviewTask 1: Literature Review

• Hurd, J. O. (1985). "Field Performance of Corrugated Polyethylene Pipe Culverts in Ohio."

• Flattening occurs at vertical deflections exceeding15%.

• Wall buckling occurs at vertical deflections exceeding 25%.

• The vertical deflections of HDPE pipes without apparent flattening, buckling, and dent are less than 10%.

• The vertical deflections at the pipe joints are general slightly larger than those throughout the rest of the culvert.


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• There is no increase in vertical deflection after 2 to 4 years within pipes less than 10% deflection.

• Shallow cover and heavy truck traffic do not appear to be detrimental to the structural performance of pipes. Deflection appears to be built into the culverts instead of caused by highway loading.


13


• Hashash, N., Selig, E. T. (1989). "Results of Field Measurements on Polyethylene Pipe Taken in August 1988."

• A 24-in profile-wall HDPE pipe was buried in the embankment and only loaded by soil dead load. The deflection, stress and strain are recorded with the rise of cover thickness. The maximum soil cover height was 100 ft.

• 24-in corrugated and profile HDPE pipes are installed in a trench with 5-ft depth and 6-ft width. The backfill is well-graded crushed limestone under 100% compaction. The load is soil dead load only.


14


Height of Fill (ft)

Avg. Vertical Stress (psi)

Avg. Horizontal

Stress (psi)

Avg. Strain at Crest

(%)

Avg. Strain at Centroid

(%)

Avg. Circumferential Strain

(%)

Avg. Vertical

Deflection (%)

Avg. Horizontal Deflection

(%)2.5 2.87 2.17 0.000 0.000 0.21 0.00 0.00

15.0 6.27 6.00 0.228 0.115 0.32 N/A N/A

17.0 6.63 7.53 0.287 0.118 0.32 0.67 0.46

20.0 6.83 8.37 0.153 0.020 0.32 N/A N/A

36.0 9.23 16.17 0.218 0.097 0.38 0.97 0.40

55.0 11.27 26.83 0.271 0.264 0.47 1.58 0.51

63.0 12.67 30.23 0.442 0.292 1.06 2.27 0.68

76.0 15.93 40.47 0.775 0.718 1.15 3.22 0.59

95.0 17.67 N/A 1.455 1.149 1.26 4.02 0.64

99.0 16.83 N/A 1.662 1.333 1.30 4.04 0.61


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• At 95-ft soil cover, the average deflection of corrugated pipe is 3.4%, and the average deflection of profile pipe is 4.4%.

• The max. vertical deflection is 7.2%, and no local distress or structural damage observed.


16


• Hsuan, Y.G., McGrath, T. J. (1999). NCHRP Report 429: HDPE Pipe: Recommended Material Specifications and Design Requirements. National Academy Press, Washington, D.C.

• Field performances of buried HDPE pipes in various regions of the U.S. are surveyed and presented in this report.


17


Year Installed

Pipe Type and

Diameter

Backfill Type and Depth

Pavement Type and Thickness

Daily Traffic

Vertical Deflection

Conditions

<1985Corrugated

15 in

granular and native soil

3 ft

asphalt/

light 13.3%circumferential crack appears slip at outlet

1981Corrugated

24 in

gravel bank run ODOT 304

1 ft

asphalt15 in

light 14.6%

circumferential and longitudinal crack due to

vehicle impact and mower damage at pipe ends

1983Corrugated

24 inODOT 304

2 ftasphalt

/mediu

mmax 8.3% all good

1984Corrugated

12 in

ODOT 411 limestone

5 ft

asphalt/

light 8.3% all good

1982Corrugated

15 ingravel

4.5 ~ 6 ftasphalt15 in

light 10% all good


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Year Installed

Pipe Type and

Diameter

Backfill Type and Depth

Pavement Type and Thickness

Daily Traffic

Vertical Deflection

Conditions

1983Corrugated

15 inmixed

1 ftasphalt

/light 13.3% all good

1995Profile30 in

sand8 ft

unpaved/

none 10%circumferential crack;

deflection at joints

1994Profile42 in

unknown3 ft

asphalt6 in

medium

average 9.5%

circumferential crack growth from 1 to 4.5 in in

one year


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• Moser A. P. (2000). "Structural Performance of 42-inch (1050mm) Corrugated Smooth Interior HDPE Pipe."

• Dr. Moser conducted three tests on 42-inch diameter profile-wall HDPE pipes. The pipes were buried in the embankment constructed using a silty-sand (SM) backfill material. The compaction level was different among the three tests. The load was applied using hydraulic cylinders to simulate dead load.


20


• Test 1. The relative compaction level on backfill was 75%.

• At 40 ft, deflection 10% and a dimpling pattern started at 3 and 9 o'clock. The center distance between dimples was about the same as the rib spacing. At 55 ft, 14.5% vertical deflection, hinging was noted at 3 and 9 o'clock. At 60 ft, 16.5% deflection, hinging was very apparent and become more pronounced at 3 and 9 o'clock. Test ended at 69 ft, 20% deflection.


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• At 70-ft soil cover, 8.7% deflection, small dimples began to form near 3 and 9 o'clock. At 82 ft, 11% deflection, waffling pattern formed. At 110 ft, 16.5% deflection, hinging started at 4 and 9 o'clock. Test ended at 110 ft.


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• At 110 ft, 3.5% deflection, dimpling pattern began at 3 and 9 o'clock and spread toward the top of the pipe as load increased. This pattern was like a wavy checkerboard in appearance and the beginning of localized instability. The dimpling was extremely small and would not affect the structural performance of the pipe. At 140 ft, 5.2% deflection, dimples became pronounced but were not judged to be a performance limit of the pipe. At 170 ft, 6.7% deflection, first signs of wall crushing were noted at 10 o'clock. At 225 ft, 9.4% deflection, waffling and wall crushing became more pronounced but the pipe did not fail. Test ends at 225 ft.


23


• Sargand, S. M. and Masada, T. (2011). “Field Service Conditions of the Oldest Corrugated HDPE Pipe Culvert Under Ohio's Roadway."

• In this ASCE journal paper, the ORITE researchers reported the field conditions of a 24" diameter corrugated HDPE pipe culvert that had served under SR 145 (Noble County) under a shallow soil cover and low pH (4-5) drainage flow. The pipe was installed in 1981 under a cover of 1.0 to 1.3 ft.


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• Vertical Deflection Data


Location Along Pipeline Data Collected in 1982 Data Collected in 2004

Outlet End 0.0 0.0

Middle of Section 1 -1.5% -1.0%

End of Section 1 -5.2% -5.2%

Joint -7.3% -8.3%

Middle of Section 2 0.5% 1.0%

Inlet End 0.0 0.0

AVERAGE -2.3% -2.3%

The pipe was observed to be functioning well, with no signs ofstructural distress (wall crushing, wall buckling, cracking, …).

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Task 2: AASHTO CalculationsTask 2: AASHTO Calculations

• The AASHTO LRFD Bridge Design Specifications (2013 Interim Revisions to the Six Edition 2012).

• The vertical deflection, combined tensile strain, combined compressive strain, and buckling strain are computed through the formulas presented in Section 12: Buried Structures and Tunnel Liners.

• The live load and load combination are set up according to Section 3: Loads and Load Factors.

• The complete assumptions of parameters and formulas are listed in "AASHTO Equations".


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Scanned Wall Profile of Each HDPE Pipe Diameter

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Nominal Diameter

(in)

Inside Diameter

(in)

Outside Diameter

(in)

Inner Liner Thickness

(in)

Wall Area (in2/in)

Moment of Inertia I(in4/in)

Dist. toCentroid c

(in)

12 12.15 14.45 0.035 0.217 0.035 0.43

24 24.08 27.80 0.059 0.324 0.137 0.74

30 30.00 35.10 0.059 0.378 0.277 0.86

36 36.00 41.70 0.067 0.401 0.400 1.00

42 41.40 47.70 0.070 0.458 0.572 1.21

48 47.60 53.60 0.070 0.495 0.570 1.17

60 59.50 66.30 0.070 0.578 0.860 1.32


General Dimensions of Each HDPE Pipe Diameter

[Comment] Above dimensions based on ADS Product Note 3.107.

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Nominal Diameter

S (in)

w-crest (in)

w-liner (in)

w-valley (in)

w-web (in)

t-crest (in)

t-liner (in)

t-valley (in)

t-web (in)

12 0.787 1.181 0.591 0.984 0.079 0.039 0.098 0.098

24 1.378 2.165 0.787 1.575 0.098 0.079 0.118 0.118

30 1.575 2.559 1.181 1.969 0.118 0.079 0.197 0.177

36 2.165 2.953 0.984 1.772 0.197 0.157 0.236 0.197

42 2.362 3.543 0.984 2.362 0.157 0.118 0.197 0.197

48 2.362 3.543 1.181 2.362 0.197 0.118 0.236 0.217

60 2.756 4.134 1.378 2.756 0.236 0.157 0.256 0.256


Detailed Dimensions of Each HDPE Pipe Diameter

[Note] “w” = width; and “t” = thickness.

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• The constrained soil modulus is set at 1 ksi and 3 ksi. The unit weight of backfill with various constrained modulus is assumed according to the recommended values listed in user`s manual of CANDE.

• The modulus of HDPE pipe material is considered in terms of short term and long term. The short-term modulus is 110 ksi, and long-term (50-years) modulus is 22 ksi.


Unit Weight (pcf) Constrained Modulus (ksi)130 1145 3

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• AASHTO calculations are based on pipe wall strains, not on pipe wall stresses.

• The critical strains for HDPE pipe wall are 5% (tensile) and 6.15% (compressive). Calculations show that compressive strains in the pipe wall tend to reach the compressive strain limit well before tensile strains reach the tensile strain limit. Thus, a focus is placed on compressive strains in pipe wall.

• The dead load on the pipe is continuously increased to the failure of the pipe.

• The loading cases have "dead load only" as well as "dead and live loads".


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Short-Term & Long-Term Strain vs. Ver. Def., Ms = 1 & 3 ksi, Dead Load Only

32



Short-Term Buckling Ratio vs. Ver. Def., Ms = 1 & 3 ksi, Dead Load Only

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• When the vertical deflection is held constant, higher constrained modulus induce higher strains in the pipe wall.

• The critical vertical deflection in the long-term service condition is less than the critical vertical deflection in the short-term service condition, especially for the HDPE pipes buried in the lower modulus backfill.

• If the vertical deflections are smaller than 7.5%, the combined compressive strain will not surpass 6.15% limit in most cases, except when the pipes are buried in the 3-ksi modulus backfill material and under the long-term service condition.

• Wall buckling failure is not a concern when vertical deflections are held below 12%.


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Short-Term Strain and Buckling Ratio vs. Ver. Def., Ms = 1 & 3 ksi, Dead and Live Load

35


• Combined compressive strain in the pipe wall never reach the strain limit even when the cover thickness is as low as 1 ft.

• When the soil cover thickness is held constant, the combined compressive strain decreases as the soil modulus increases.

• The portion of combined compressive strains caused by the live load diminishes with the soil cover. At the cover thickness of 15 ft, combined compressive strains occurred under the dead and live loads become the same to those under the dead load only.

• Under the dead and live loads, wall buckling failure mode is not a concern even at a cover thickness of 1 ft.


36

Task 2: ValidationsTask 2: Validations


Sargand, S. M. and Masada, T. (2011). “Field Service Conditions of the Oldest Corrugated HDPE Pipe Culvert Under Ohio's Roadway."

A 24-in diameter corrugated HDPE pipe had served State Route 145 (Noble County) from 1981. The pipe was installed under a cover of 1 to 1.3 ft, and the constrained modulus of soil is estimated to be around 1 ksi. The pipe was subjected to the dead and live loads. The vertical deflection was 8.3% in 2004. No overstraining/no buckling was observed.

Based on AASHTO calculation`s results, the vertical deflection of 24-in diameter HDPE pipe under live load is 8.16%, and max. combined compressive strain is 3.48% (<6.15%), and buckling ratio is 0.62 (<1.0).

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Task 3: CANDE SimulationsTask 3: CANDE Simulations

• Culvert Analysis & Design (CANDE) computer software

• Originally developed by Dr. Michael Katona & his team

• Latest version is CANDE 2007

• Pipe represented by a series of column/beam elements

• Soils represented by a number of quadratic elements

• Requires a detailed mesh with material properties, boundary condition statements, construction sequences, and loading instructions


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Model Half-Mesh

39


• The computer simulations were made for 12-in, 24-in, 36-in, 48-in, and 60-in diameter HDPE pipes.

• The installation modes included embankment (positive projection) mode, trench mode, and negative projection mode.

• The increments of soil cover thickness were the same as those applied in the AASHTO calculations. For the dead and live loads analysis, the cover thickness was increased from 1 to 15 ft.

• The analysis also addressed both short-term and long-term service conditions.


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Pipe Type Pipe ID Installation Mode Backfill Soil Cover & Loading

Corrugated HDPE

Short-termLong-term

12”24”36”48”60”

Embankment(or Positive

Projection Mode)

A-1 @ 90, 95% Compaction

Shallow; (D + L)Intermediate; (D + L)Deep; (D only)



A-3 @ 85, 90, 95% Compaction


[Note] * There are 42 different cases illustrated above for each pipe size.* Shallow (< 7 ft), Intermediate (7-15 ft), Deep (> 15 ft).

41



Pipe Type Pipe ID Installation Mode

Backfill Soil Cover & Loading

Corrugated HDPE

Short-termLong-term

12”24”36”48”60”

Trench(Trench Width is OD + 1 ft at each side of pipe. This

value is much greater than

AASHTO Min.12" Cover above

pipe top)





A-3 @ 85, 90, 95% Compaction


[Notes] * There are 42 different cases illustrated above per pipe size.* Shallow (< 7 ft), Intermediate (7-15 ft), Deep (> 15 ft).

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• The in-situ soil in the embankment mode and trench mode were both specified as SW-100.

• The backfill and bedding materials were the same during each analysis. In accordance with AASHTO M145 and ASTM 2487, CA-90 and CA-95 corresponded to A-1, SM-85 and SM-90 correspond to A-2, and SW-85, SW-90 and SW95 correspond to A-3.

• CA-90, CA-95, SM-85 and SM-90 were only applicable to Duncan formation. SW-85, SW-90 and SW95 were applicable to Duncan/Selig formulation


43


• Pipe wall strain limits were set at 6.15% (compressive).

• Pipe wall buckling strain limits were calculated for each pipe diameter size.


44



Combined Compressive Strain vs. Ver. Def., Dead Load, Embankment Mode & Trench Mode

45



Short-Term Buckling Ratio vs. Ver. Def., Dead Load, Embankment Mode & Trench Mode

46


• If the vertical deflections are smaller than 7.5%, the combined compressive strain will not surpass 6.15% limit in most cases, except when the pipes are buried in the SW-95 backfill material and/or under the long-term service condition.

• Wall buckling failure is not a concern as long as the vertical deflection is kept below 7.5% (only exception occurs with the SW-95 backfill).

• Compared to the pipes in the embankment mode, trench mode can help the pipes raise critical vertical deflection.

• The higher modulus backfill can cause higher strains in the pipe wall when the vertical deflection is constant.


47



Short-Term Strain vs. Ver. Def., Dead & Live Load, Embankment Mode & Trench Mode

48


• As shallow as 1-ft soil cover thickness, the combined compressive strain in 24-in diameter HDPE pipe wall is greater than 6.15% stain limit when backfill is SM-85 and CA-90 in embankment mode and CA-90 in trench mode. Combined compressive strain of other diameter pipes buried in any backfill types are all smaller than the strain limit, even when the soil cover thickness is only 1 ft.

• Under 2-ft cover thickness, 24-in diameter HDPE pipe wall never buckles regardless of which when backfill material is surrounding the pipe.

• The effect of live load on combined compressive strain disappeared when soil cover thickness approaches 15 ft.


49

Task 3: ValidationTask 3: Validation


Height of Fill

(ft)

Field Test Data CANDE Simulation

Dia. (in) Backfill Ver. Def. (%) Backfill Height of

Fill (ft) Ver. Def. (%)

99 24 CA-100 4.04

CA-90 99 8.72CA-95 99 6.98

CA-100 99 5.24(estimated)

Hashash, N., Selig, E. T. (1989). "Results of Field Measurements on Polyethylene Pipe Taken in August 1988."

Vertical Deflections of HDPE Pipes after the installations

The estimated vertical deflection of 24-in dia. HDPE diameter pipe is higher than the measured value. In CANDE simulation, combined compressive strain and buckling ratio are respectively smaller than their limits when the backfill is CA-95. Since the strains and buckling ratio will decrease with the rise of compaction level, the 24-in dia. HDPE pipe has no failure under 99-ft cover thickness, and the actual pipe in the field test exhibited no signs of failure.

50

Task 4: ComparisonsTask 4: Comparisons

Dia. (in)Ms = 1 ksi Ms = 3 ksi

ST LT ST LT12 15.0 8.2 10.9 6.624 13.2 7.3 9.4 6.130 13.7 7.5 9.7 6.236 13.0 7.2 9.2 6.142 12.3 6.9 8.8 5.948 12.6 7.0 8.8 5.960 12.4 6.9 8.7 5.8

Average 13.2 7.3 9.4 6.1


Maximum Vertical Deflections (%), AASHTO Calculations

[Note]: Dia. = diameter of the pipe; Ms = constrained modulus of the backfill; ST = short-term service condition; LT = long-term service condition.

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Task 4: ComparisonsTask 4: Comparisons

BackfillType

12-in 24-in 36-in 48-in 60-in

ST LT ST LT ST LT ST LT ST LT

CA-90 7.8 8.2 7.4 7.9 7.9 8.3 6.3 8.1 5.9 8.2CA-95 7.7 7.7 7.2 7.4 7.4 7.7 6.1 7.5 5.8 7.7SM-85 6.5 6.7 6.0 6.3 6.1 6.5 4.9 6.2 4.5 6.3SM-90 7.2 6.4 6.6 6.0 6.5 6.2 5.3 6.0 4.8 6.0SW-85 8.4 8.9 9.5 9.1 9.5 9.2 9.4 8.8 9.6 8.8SW-90 8.2 7.4 8.6 7.4 8.3 7.5 8.2 7.4 8.2 7.5SW-95 5.6 6.0 6.0 6.2 6.1 6.6 5.9 6.5 5.6 6.6


Maximum Vertical Deflections (%), CANDE Simulation

[Note]: ST = short-term service condition; LT = long-term service condition.

52

ConclusionConclusion

• Although conservative, the AASHTO LRFD method largely pointed out that 7.5% vertical deflection limit can protect HDPE pipes from developing structural failures/major distress.

• CANDE is even more conservative than the AASHTO method, as its stiffness based formulation makes the pipe stiffer and also it suffers from convergence problems in some cases.

• Performing two separate analyses using the short-term and long-term pipe material moduli does not really make sense for HDPE pipes servicing in the field.


53


* Actual pipe-soil system in the field acts as a viscoelastic system.


Time

Short-Term

Long-Term

Actual

Vert

ical

Def

lect

ion

54


• Documented field performance data uncovered during the literature review are littered with cases where the HDPE pipes have performed fine at vertical deflections larger than 7.5% (less than 10%).

• Also, a limited volume of strain gage readings available from OU’s Thermoplastic Pipe Deep Burial project indicate the strains in the HDPE pipe walls are less than half of what are estimated by the AASHTO method.

• [Main Conclusion] For the HDPE pipes buried in 1-ksi and 3-ksi backfill materials, a 7.5% vertical deflection limit is sufficient for both short-term and long-term service conditions.


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• [Additional Note] The HDPE pipe’s vertical deflection window can be extended if the pipe is allowed to peak during the initial backfilling stage.


Peaking

7.5%DeflectionLimit

8.5 to 9.5%DeflectionLimit

1 to 2%

56

AcknowledgementAcknowledgement

• We would like to thank ODOT for supporting this research study.


www.ohio.edu/engineering

Thank you!

PI: Xiao Han, Graduate StudentCo-PI: Teruhisa (Terry) Masada, Faculty Advisor

Civil Engineering DepartmentRuss College of Engineering & TechnologyOhio University, Athens, OHTel: (740) 593-2474Fax: (740) 593-0625E-Mails: [email protected]

[email protected]

Documents

Vertical Deflection Limit of Presentation at OTEC Buried Profile …€¦ · structural performance of the pipe. At 140 ft, 5.2% deflection, dimples became pronounced but were not