2009 ACC Presentation -Schilling Permeable by mgi72364

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									PERMEABLE DRAINAGE LAYERS
   IN AIRFIELD PAVEMENTS

  33rd Annual Airports Conference
  March 3, 2010 – Hershey, PA



  Presented by: Dave Schilling, P.E.
Outline


  •   What is it?
  •   Resource Information
  •   Design Parameters
  •   Real World Examples
  •   Discussion Points
  •   Questions
What is it?


  • Evolution –
     Good subsurface drainage has long been known
     to contribute to pavement life. Modern base
     materials, placement and higher loads have
     contributed to reduced permeable drainage
     paths

  • Permeable Drainage Layer –
     A layer in the pavement structure that
     specifically designed to allow rapid horizontal
     drainage of water from the pavement structure
History


 Commonly Used in Roadway
 Pavements Since the 1980s –
 Reference: NCHRP Synthesis 239, "Pavement Subsurface Drainage Systems"
    which is an up date of the previous Synthesis 96 with the same title.

 Report found that the cost effectiveness of drainage systems is recognized by
    the following conclusions:
 •   "Pavement subsurface drainage is a major factor in extending the life of a
     pavement."
 •   "Although performance indicators to quantify the benefits of pavement
     subsurface drainage systems have not been established, use of a
     permeable base with a free-draining outlet system generally has
     demonstrated the best performance of all subsurface drainage strategies."
 •   "The cost of pavement drainage system is high in terms of materials,
     construction, and maintenance, but the extended pavement life anticipated
     appears to make these systems cost-effective.“
Its Use

 FAA Advisory Circular 150/5320-5C, Change 1:
What is it?
Resources


FAA Advisory Circular
  150/5320-5c, Change 1
Surface Drainage Design

Available at:
http://www.faa.gov/regulations_polic
ies/advisory_circulars/index.cfm




Status of FAA Guide
Specifications?
Resources



 Tri-Services (Military)-
    UFC 3-230-06A
 Subsurface Drainage
 Available at
 http://www.wbdg.org/ccb/DOD/UFC/ufc_3_230_06a.pdf


 Industry – Innovative Pavement Research
    Foundation (IPRF) Stabilized and
    Drainable Base in Rigid Pavement
    Systems – Available at:
 http://www.iprf.org/products/IPRF-01-G-002-02-1-
     Final%20Report.pdf
Components

 • Aggregate Types:
    • Rapid Draining Material (RDM) – permeability of
      1,000 to 5,000 ft/day – usually mechanically
      stabilized
    • Open Graded Material (OGM) – permeability
      greater than 5,000 ft/day – usually chemically
      stabilized (asphalt binder or cement)
 • Stabilization
    • Usually stabilized with asphalt-binder or cement.
      Mechanically stabilized tends to be very sensitive
      to construction equipment (rutting)
 • Bond Breakers / Separation Layers
    • Filter fabrics, fine aggregate
Aggregate Gradation
Design Parameters


 • Design intent is drain rainfall that infiltrates the pavement
   from a 2-year, 1-hour rainfall event within a 24-hr period

    Thickness design (in inches):
 Where:
    • Infiltration coefficient (F) – assumed to be 50% per FAA / UFC
        recommendations for future deteriorated pavement
    • Rainfall Index (R) – from local IDF curves (in/hour)
    • Effective porosity (ne) – Recommended at 0.32 for OGM and
        0.25 for RDM

 Example:
 (w/ R= 1.4 in/hr):

 • Per IPRF Report, minimum thickness is 4-inches
Design Parameters


 • Per FAA / UFC guidance, assumes 85% of rainfall is to be
   discharged within 24-hrs (assumes some water is in the layer
   prior to the following rain event).

 Time (in days)
 Where:
    • Effective porosity (ne) – assumed 0.32 for OGM (recommended)
    • Drainage Path Slope Length (L) – calculated
    • Slope of Drainage Path (i) – in percent (say 1.50%)
    • Permeability of Material (k) – in feet / day (say 2,000 ft/day)

 Example:
 (w/ L= 75.7-ft )
 [see next slide]
Design Parameters


 • Slope length – geometric length of longest drainage path.

    Length (in feet):


 Where:
    • Transverse Length (Lt ) – in feet (say 75-ft or 1/2 of runway)
    • Transverse slope (it ) – in percent (say 1.50%)
    • Longitudinal slope (ie ) – in percent (say 0.20%)

 Example:
Real World Applications

  Memphis International   Nashville International
    Runway 18R-36L           Runway 13-31
     (B-747 traffic)         (B-747 traffic)
Real World Applications

   Detroit International   East WV Regional (Martinsburg, WV)
  Runway 3R-21L/9R-27L               Runway 8-26
      (B-747 traffic)                 (C-5 traffic)
Real World Applications

  NW Arkansas Regional   Chicago – O’Hare Int’l
     Runway 17-35          Runway 10C-28C
     (B-747 traffic)         (B-747 traffic)
Real World Applications
(ATPB)
Real World Applications
(ATPB)
Real World Applications
(CTPB)
Discussion Points


 Placement within a pavement structure
   • Per IPRF Report, there is no consensus. However, UFC /
     FAA design guidance is predicated on the assumption
     that water infiltrates from the top side. Groundwater
     effects are slower and generally mitigated through edge
     perimeter drains.

   • Per FAA AC 5320-5c, Change 1, Paragraph G-3.4
      • Rigid pavements: “…should be placed directly
         beneath the concrete slab.”
      • Asphalt pavements: “…should be placed directly
         beneath the surface layer or beneath a graded,
         crushed aggregate base course.”
Discussion Points


 Per FAA AC 150/5420-6E (sandwich layer?)
   • Appears to be a dated concern. Was applicable in the
     50s and 60s with the advent of quick pavement
     strengthening due to heavier jet aircraft. Tendency was
     to use crushed aggregate to reduce asphalt thickness
     and cost however, this process trapped water. A
     stabilized drainage layer is designed to mitigate trapped
     water.

   • Is currently allowed by FAA Advisory Circular 150/5320-
     5c, Change 1
Discussion Points


 Consideration as a stabilized layer?
    • Per FAA AC 150/5320-6e, Rigid Pavement designs with
      aircraft greater than 100,000-lbs require a stabilized
      layer. Although the drainage layer is “stabilized” with
      asphalt binder or cement, the support value is
      unknown.
    • Per FAA AC 150/5320-5c, Change 1, Paragraph G-3.4.1,
      “… the drainage layer along with any granular
      separation layer is considered a base layer, and
      structural benefit may be realized from the layers.”
    • Conservative estimates are to equate it to a P-209
      crushed aggregate basestone although higher support
      values may be achievable with stabilization and meet
      the purposes of a stabilized layer.
Discussion Points


 Bond Breakers / Separation Layers
   • Concern is with cement paste or pavement materials
     infiltrating into the drainage layer. Condition could clog
     drainage paths and “lock-in” pavements. IPRF Report
     performed field tests to determine that a layer of choke
     stone (3/8-inch minus) provided adequate drainage
     characteristics and separation.
   • Per FAA AC 150/5320-5c, choke stone recommended
     with unstabilized drainage layers. Separation layer is
     recommended in paragraph G-3.4.3 from migration of
     fines from underlying layers. Material can consist of
     geotextile fabrics or graded aggregate.
Questions????

								
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