subgrade it s just dirt isn t it
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Subgrade: Its Just Dirt. Isnt it? Daniel N. Frchette, PhD, PE - PowerPoint PPT Presentation

Subgrade: Its Just Dirt. Isnt it? Daniel N. Frchette, PhD, PE Senior Associate Geotechnical Engineer, Amec Foster Wheeler Environment & Infrastructure, Phoenix, AZ Daniel.Frechette@amecfw.com Outline of Presentation


  1. Subgrade: It’s Just Dirt. Isn’t it? Daniel N. Fréchette, PhD, PE Senior Associate Geotechnical Engineer, Amec Foster Wheeler Environment & Infrastructure, Phoenix, AZ Daniel.Frechette@amecfw.com

  2. Outline of Presentation • Introduction • Pavement Components • Specifications • Factors that Influence Subgrade Performance • Mitigation Strategies for Poor Subgrade • Case Study – I-17 Widening Project • Summary 2 Sustainable Asphalt Pavements Workshop March 22, 2017

  3. Introduction • What is Subgrade? MAG – • ADOT – • FHWA – • DNF – ? • 3 Sustainable Asphalt Pavements Workshop March 22, 2017

  4. Pavement Components 4 Sustainable Asphalt Pavements Workshop March 22, 2017

  5. Pavement Components 5 Sustainable Asphalt Pavements Workshop March 22, 2017

  6. Pavement Components 6 Sustainable Asphalt Pavements Workshop March 22, 2017

  7. Summary of Pavement Components • Manufactured/Produced Components • Portland Cement Concrete • Asphaltic Concrete • Base Course • Naturally Occurring • Subgrade 7 Sustainable Asphalt Pavements Workshop March 22, 2017

  8. Construction Specifications – Portland Cement Concrete 8 Sustainable Asphalt Pavements Workshop March 22, 2017

  9. Construction Specifications – Asphaltic Concrete 9 Sustainable Asphalt Pavements Workshop March 22, 2017

  10. Construction Specifications – Aggregate Base 10 Sustainable Asphalt Pavements Workshop March 22, 2017

  11. Construction Specifications – Subgrade 11 Sustainable Asphalt Pavements Workshop March 22, 2017

  12. Factors Influencing Subgrade Performance • Soil Type • Plasticity • Percent fines (% < No. 200) • Swell potential • Collapse potential • Environmental Effects/ Climatic Conditions • Elevation • Temperature • Precipitation/Moisture • Drainage 12 Sustainable Asphalt Pavements Workshop March 22, 2017

  13. Soil Type • Soils Map of Arizona (USDA-NRCS) 13 Sustainable Asphalt Pavements Workshop March 22, 2017

  14. Swell Potential Map – Phoenix Area 14 Sustainable Asphalt Pavements Workshop March 22, 2017

  15. Swell Potential Map – Tucson Area 15 Sustainable Asphalt Pavements Workshop March 22, 2017

  16. Collapsible Soils 16 Sustainable Asphalt Pavements Workshop March 22, 2017

  17. Environmental Effects/ Climatic Conditions • Elevation • Temperature • Precipitation • Seasonal Variation Factor 17 Sustainable Asphalt Pavements Workshop March 22, 2017

  18. Seasonal Variation Factor vs Elevation 18 Sustainable Asphalt Pavements Workshop March 22, 2017

  19. Seasonal Variation Factor vs Temperature 19 Sustainable Asphalt Pavements Workshop March 22, 2017

  20. Seasonal Variation Factor vs Precipitation 20 Sustainable Asphalt Pavements Workshop March 22, 2017

  21. Mitigation Strategies for Poor Subgrade • Over-Excavation and Replace • Over-Excavation and Recompaction • Geogrid with Geotextile • Lime or Cement Treated • Alternative Engineering Solutions 21 Sustainable Asphalt Pavements Workshop March 22, 2017

  22. Case Study – I-17 Widening • Project Location • Project Soils • Subgrade Characterization (R-Value Evaluation) • Alternatives Evaluated • Final Design 22 Sustainable Asphalt Pavements Workshop March 22, 2017

  23. Case Study – I-17 Widening 23 Sustainable Asphalt Pavements Workshop March 22, 2017

  24. Case Study – I-17 Widening • Swell Potential Map – Phoenix Area 24 Sustainable Asphalt Pavements Workshop March 22, 2017

  25. Case Study – I-17 Widening Project Soils • Subgrade Criteria • Percent Passing No. 200 Sieve • Plasticity Index (PI) 25 Sustainable Asphalt Pavements Workshop March 22, 2017

  26. Case Study – I-17 Widening • R-Value Data 26 Sustainable Asphalt Pavements Workshop March 22, 2017

  27. Case Study – I-17 Widening Alternatives Evaluated Alternatives Evaluated • Over-Excavation and Replace • Viable alternative • Over-Excavation and Recompaction • Not viable, soils not collapsible • Geogrid with Geotextile • Strain compatibility concerns • Lime or Cement Treated • ADOT did not want to pursue • Alternative Engineering Solutions • Evaluate impact of lower R-value on pavement thickness 27 Sustainable Asphalt Pavements Workshop March 22, 2017

  28. Case Study – I-17 Widening Alternatives Evaluated Alternatives Evaluated • Over-Excavation and Replace Viable alternative • • Over-Excavation and Recompaction Not viable, soils not collapsible • • Geogrid with Geotextile Strain compatibility concerns • • Lime or Cement Treated ADOT did not want to pursue • • Alternative Engineering Solutions Evaluate impact of lower R-value on pavement thickness • 28 Sustainable Asphalt Pavements Workshop March 22, 2017

  29. Summary • What is Subgrade? MAG – • ADOT – • FHWA – • DNF – • • Subgrade: Foundation for the pavement • Largest variability, Know the least about 29 Sustainable Asphalt Pavements Workshop March 22, 2017

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