WisDOTs Policy on Select Materials in Subgrades

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WisDOTs Policy on Select Materials in Subgrades

• Frozen Four Workshop
• Madison, WI
• October 8, 2008

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Presentation Highlights

• Brief History and Introduction of WisDOT Select
  Materials Policy
• Design Details and Information
• Recent Research Findings

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Historical Background

• Mid-90s Subgrade Process Review
• Address Cost Over-runs Attributed to Soils
• Team Established - Findings
• Greatest subgrade stress during construction
• Few subgrade problems after paving
• Do what is necessary to pave roadway
• Change orders during construction are costly in
  time and money
• About 2/3 of state has difficult soils

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Historical Background Contd.

• Recommendations From Study Team
• Developed list of 22 items
• Use of select materials in subgrades ranked as
  highest priority
• Assemble a team to investigate further and
  provide guidance

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Historical Background Contd.

• Departmental Directions Team Goals
• Use select materials in the upper portion
• of subgrades
• Limit the use to areas of difficult soils
• Provide details/guidance for usage
• Develop WisDOT policy for inclusion in
• design manual (FDM)

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Historical Background Contd.

• Results of Team Discussions
• Eight different methods/options of materials
• Desire for all alternatives to provide
• equivalent performance
• Selection of particular alternative is based
• on local conditions/availability /cost and
• identified in the soils report
• Estimate total impacts/costs
• to the Department

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Areas of Inclusion
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Select Material Alternatives

• Breaker Run Stone
• Breaker Run Stone w/Geogrid
• Grade 1 Granular Backfill
• Grade 2 Granular Backfill or Select Borrow
• Pit Run Sand and Gravel
• Pit Run Sand and Gravel w/Geogrid
• Flyash, Lime, Cement Stabilization
• Salvage Materials or Industrial By-products
• with optional Geogrid

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Breaker Run Stone
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Breaker Run Stone

• Crushed Material From Quarry Face
• Processed Through the Primary Crusher
• Acceptance Based On Visual Inspection
• Desire At least One Fracture Face on 50
• of the R 1½ Material
• Approximate Gradation -
• Sieve Percent Passing
• 5 100
• 1½ 20 - 50
• 10 0 - 10

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Granular Backfills
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Grade 1 2 Granular Backfills

• Generally Sand Materials
• Gradations -
• Maximum Percent Passing
• Sieve Grade 1 Grade 2
• 4 100 100
• 40 75 -
• 100 15 30
• 200 8 15

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Pit Run Sand and Gravel
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Pit Run Sand and Gravel

• Obtained From Naturally Occurring Sand and Gravel
  Deposits
• Minimum 50 Retained on 1½ Sieve
• Approximate Gradation -
• Sieve Percent Passing
• 6 100
• 2 0 - 75
• 10 0 - 40

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Stabilization and Recycled Matls
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Drainage Implications

• Drainage Concern With Thick Layers
• Do Not Want to Create Bath-tub Sections
• Complicated By Different Thicknesses
• Special Cross-section Details Developed
• Daylight Where Possible
• Drains Where Necessary

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Policy Guidelines

• Use in Upper Portion of Subgrades Constructed in
  Difficult Soils as Shown on Plans Begin 2006
• Will be Used in Identified Areas Unless Exception
  Justified in Soils Report
• Will Not be Used in Areas Outside of Identified
  Areas Unless Justification is Provided
• Soils Report Will Provide Recommendation of
  Appropriate Alternative Material
• May be Used in Segments of Project (2000-3000)

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Policy Guidelines Contd.

• Use on Projects With Significant Earthwork
  Volumes
• Will be Used in Both Cuts and Fills (Some
  exceptions for rock or dense cut areas)
• One of Eight Alternative Designs Should be
  Selected and Shown on the Plan
• Appropriate Bid Items Included in Plan
• Considered Part of Subgrade
• Must Adjust Earthwork Quantities
• Account For in Pavement Design

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Incorporating Benefits Into Pavement Design

• Primary Purpose is to Facilitate Construction
• Recognize that Subgrade is Improved
• Realize That Some Benefit to Pavement Structure
• Alternatives Reduce pavement structure or
  extend pavement life
• Investigated Methods to Account for Benefits

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WisDOT Pavement Design

• Using Outdated AASHTO 1972 Methods
• Compute Structural Numbers Using
• Soil Support Value (SSV) for asphalt
• Subgrade Modulus (k) for concrete
• Soil Strength Numbers Arrived at Using DGI
  System, Based on Soil Pedology
• Separate PCC and HMA Design Methods
• Moving to New AASHTO MEPDG

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Asphalt Pavement Design
Subgrade Strength Based on DGI and Correlated to
SSV
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Concrete Pavement Design

• Compute Pavement Thickness Using Standard Design
  Procedures
• Deduct ½ inch From Computed Thickness
• Recommendations Based on Sensitivity Analyses

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Estimated Costs (For Planning)
Alternative Cost/Mile Breaker
Run Stone 110 k Breaker Run Stone
w/Geogrid 150 k Grade 1 Granular
Backfill 95 k Grade 2 Granular
Backfill or 95 k Select
Borrow Pit Run Sand and Gravel 105
k Pit Run Sand and Gravel 145 k
w/Geogrid Flyash, Lime, Cement Stabilization
90 k Salvage Materials or Industrial
100 k By-products Late-90s
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Cost/Benefit

• Est. Cost for Policy is 8 M - (180 Lane Miles)
• Cost offset by reduced bid prices
• Reduction in contractor claims
• Reductions in contract administration costs
• Other Benefits
• Reduction in structural pavement designs
• Provides solid base for paving operations
• Reduction in future pavement rehab. costs

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Recent Research In Area

• Five Recent Research Projects With UW-Madison
• One deals with geosynthetic reinforcement
• Two deal with industrial byproducts/flyash
• Two deal with equivalency of alternatives and
  inclusion into pavement design
• Implementation Study

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Summary of Recent Research

• Major Findings
• Provided recommended material thicknesses
• Provided recommended modulus and layer
  coefficients for pavement design
• Added geogrid-reinforced alternatives
• Deleted breaker run geogrid option
• Provided geogrid property recommendations
• Investigated specific recycled and
• stabilized materials

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Research Recommendations
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Future Directions

• Review/Analyze Research Findings
• Compare to Existing Knowledge/Guidelines
• Potential Adoption of Results - Revision of
  Existing Guidelines
• Continue Use of Select Materials

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Questions/Comments ??