Construction Practices for Rigid and Flexible Pipes

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Construction Practices for Rigid and Flexible
Pipes
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Pipe Backfill Detail (4 ft. or less Below
Proposed Base)
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Pipe Backfill Detail (gt 4 ft. Below Proposed
Base)
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Notes

• The reinforcement fabric shall be rolled out
  parallel to the centerline of the road and shall
  be placed as shown in the details. The fabric
  shall be placed so that it is taut and the fabric
  shall be pinned on the 1.51 and 201 transition
  using 6 minimum pins. The pins shall be placed
  at a 15 spacing along all edges and at all
  corners prior to placing fill on the fabric. The
  reinforcement fabric shall be measured by the
  actual surface area covered to the nearest square
  yard. No allowance will be made for overlaps.
• The aggregate base course Cl 3 or Cl 5 backfill
  shall be compacted in layers not to exceed 6
  inches using a hand-held vibratory plate
  compactor or a hand-held mechanical tamper to the
  top of the pipe and within a distance of 2 feet
  on either side of the pipe.
• This standard corresponds to new/replaced
  centerline pipes only (including ramps). It does
  not include pipes in approaches.

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Problems Encountered with Centerline Pipes

• Poor Compaction Around Pipe
• Heaving of Shallow Pipes Due to Frost Action
• 201 transitions are not installed properly
• R1 Reinforcement fabric is not installed properly
• Pipes in a submerged condition should be
  dewatered prior to backfilling to allow adequate
  compaction

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Pipe Compaction
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Backfilling Around Pipes
Cannot overstate the importance of maintaining
lift thickness and using proper compaction
equipment.
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Compaction Equipment
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(No Transcript)
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Settlement Over Culverts
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Settlement Over Culverts
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Heaving of Large Structural Plate Pipe I-94
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Use of High Density Foam to Limit Frost
Penetration
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Compaction and Box Culverts
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Heave Over Shallow Box Culverts Pipes
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Construction Alternatives for Rigid and Flexible
Pipe

• 2007 Construction Conference Annual Meeting
• March 2007
• John Wolf
• NDDOT Materials Research Division

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Pipe Alternatives being used by the NDDOT

• Polymer Coated Corrugated Steel Pipe
• Under consideration as an allowable alternative
  for centerline culverts.
• Specified through the use of a Special Provision.
• Currently used by a number of DOTs as an
  allowable pipe alternative to RCP.
• High Density Polyethylene (plastic) Pipe
• Used as an allowable pipe alternative for
  approach pipe conduit. Also under consideration
  for centerline culverts.
• Included on NDDOT Standard Drawings D-714-14 and
  D-714-17.
• Currently used by a number of DOTs as an
  allowable pipe alternative for culverts and storm
  drains.

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Benefits of Rigid and Flexible Pipe

• Rigid Pipe (i.e. RCP)
• Very durable against almost all conditions.
• Requires low minimum fills for live loading.
• Does not rely as heavily on high levels of
  compaction for structural support. However,
  adequate compaction is still needed to prevent
  settlement and some structural support.
• Flexible Pipe (i.e. CMP and HDPE pipe)
• Reduced material and installation costs.
• Material weight is greatly reduced.
• Reduced number of sections and joints.
• Utilizes engineering properties of supporting
  soils.
• Coatings and material selection can provide
  excellent service life in the proper application.

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Load Distribution of Rigid and Flexible Pipe

• Rigid pipe transfers most of the pipe load
  through the pipe walls to the pipe bedding.
  Minimal deflections (2 or less).
• Flexible pipe supports the pipe load with both
  the pipe walls and the surrounding soil envelope.
  Some deflection is allowed.

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Background on Polymer Coated CSP

• Installations dating back over 30 yrs
• Used by an expanding number of DOTs
• Montana, California, Nebraska
• KLJ has used coated pipe on county projects for
  nearly 20 years.
• Completed NDDOT Projects
• NH-7-002(057)033 in 2006
• NH-7-002(055)043 in 2006
• NH-2-281(026)030 in 2006
• IM-5-094(034)053 in 2006
• Hwy 16 S of Golva in 2003
• Upcoming Projects
• AC-TIP-5-012(030)046
• HPP-TES-1-804(023)072

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What do we want to look for?

• Padded spacers used during Transport.
• Pipe secured and handled with straps or padded
  equipment. (NO CHAINS!)
• Repair any damaged coating prior to installation
  with manufacturer provided coating material.
• Trench is shaped to a height deep enough to cover
  the pipe and the minimum fill.
• Make sure joints are tightly secured with
  connection bands coated with polymer coating.
• Compact aggregate backfill in 6 lifts with
  vibratory compactors.

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Transporting Handling

• Padded Spacers used to separate pipe.
• Secured and handled using nylon straps.

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Damaged Coating

• Damage can be caused by shipping and unloading.
  
• Unloading should be done under the
  supervision NDDOT inspector.
• When handled according to the SP procedure,
  significantly less coating damage was identified.

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Repair material and procedure

• Repair procedure are identified in the SP for
  Polymer coated CSP.
• Repair material is provided by the pipe
  manufacturer.
• Repair material can be applied using a paint
  brush and requires minimal set time before the
  product can be handled (less than 5 min).

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Trench Installation

• Trench should be constructed according to
  approach pipe detail.
• For pipes installed before the roadway
  embankment has been placed, embankment should be
  placed at the location of the pipe prior to the
  trench excavation.

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Placing the Pipe
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Compaction
Vibratory compaction in 6 lift thicknesses. Well
compacted fill around the pipe helps to support
the pipe load. Well compacted material reduces
settlement and deflection in the pipe.
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Compaction (continued)

• Fill directly over the pipe should be free of
  any rocks that may cause point loading on the
  pipe.
• Minimum fill height is 12 for AASHTO H-25
  loading.
• Live loads for construction traffic shall be in
  accordance with the manufacturers recommendation.

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Minimum Cover for Flexible Pipe Under Temporary
Loading

• Construction vehicles sometimes exceed design
  loads, and warrant a temporary live load
  consideration.
• Mounding and compacting additional cover over the
  pipe may be necessary during construction in
  situations where pipe has little cover.
• The Modern Sewer Design, Fourth Edition gives the
  following guidelines for min cover requirements
  assuming the AASHTO H-25 load distribution
• 1 foot for vehicles between 0 and 30 tons
• 2 feet for vehicles between 30 and 60 tons
• 3 feet or more for vehicles over 60 tons

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Finished Installation
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High Density Polyethylene (HDPE) Pipe
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• PE pipe has been used as a liner for
  rehabilitated culverts.
• Flowable fill has been used in some urban areas
  to limit trench size and reduce the need for
  compaction.
• HDPE is being used by city municipalities in
  North Dakota.
• HDPE was estimated to save 20 to 30 over RCP on
  a recent Bismarck city project.

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Bennifits of HDPE Pipe

• Meets requirements for AASHTO H-25 loads with a
  12 inch min cover with proper backfill material
  and compaction.
• Reduced installation time and material cost.
• Withstands aggressive environments.
• Becoming increasingly used and available locally.
• Improved hydraulic characteristics.
• Very light and easy to handle. Does not require
  special equipment to install.

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Construction Considerations for HDPE Pipe

• HDPE pipe requires trench installation.
  Embankment shall be placed to the top of the pipe
  zone prior to installation.
• Aggregate backfill shall be used around the pipe
  according to D-714-14.
• The 6 aggregate bedding shall be loosely
  compacted to allow for pipe seating.
• When live loads are present, minimum cover shall
  be as determined by the manufacturers
  recommendations.
• Use corrugated steel end sections one size larger
  then the specified pipe (common Industry
  practice).
• Mandrel testing shall be performed by the
  contractor under the supervision of an engineer
  to check for 5 deflections in accordance to
  standard 714.03 A.9.

Pipe Conduit Detail D-714-14
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Summary

• Cost savings of Polymeric CSP are evident.
• Savings of 17 to 53 of RCP prices were seen in
  the 2006 projects.
• An average cost savings of 34 of the project bid
  price for RCP.
• The saving on IM-5-094(034)053 based on 2005
  average bid price for 1210 feet of storm drain
  was over 140,000.
• Material costs and alternative bids will help
  reduce the bid price.
• Flexible pipe are structurally capable of
  performing as centerline culverts when the design
  requirements are followed.
• Flexible pipe can be installed with smaller
  equipment and in less time than RCP.

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Questions?
John Wolf Materials Research North Dakota
DOT 701-328-6915 jowolf_at_nd.gov Sources Modern
Sewer Design, Fourth Edition 1999. Published by
the American Iron and Steel Institute