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Chemically Treated Subgrade Stabilization

Chemically Treated Subgrade Stabilization. ODOT Geo/Hydro/HazMat Conference. Chemically Treated Subgrade Stabilization ODOT Pavement Services Rene’ A. Renteria, P.E. Pavement Design Engineer ODOT Geo/Hydro Tom Braibish, P.E. Region 1 Geo/Hydro Manager.

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Chemically Treated Subgrade Stabilization

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  1. Chemically Treated Subgrade Stabilization

  2. ODOT Geo/Hydro/HazMat Conference Chemically Treated Subgrade Stabilization ODOT Pavement Services Rene’ A. Renteria, P.E. Pavement Design Engineer ODOT Geo/Hydro Tom Braibish, P.E. Region 1 Geo/Hydro Manager

  3. Why Do We Need Subgrade Stabilization? • We can design to soft subgrade, typically fine-grained or “loose” consistency granular soils • The unknown condition is the moisture content during construction • Conservative to design for “worst case” • Lots of money to save if we can know ahead of time the extent of need

  4. Standard Practice to design pavement to meet “need”, then allow for Subgrade Stabilization as separate pay item

  5. This is the ideal design…

  6. This is the call from the PM…

  7. …and this is what we end up with

  8. What we want… Construction platform—meet compaction and deflection Cost-effective design No contractor claims What we need… What are the subsurface conditions? Where are the problem areas? What is the best alternative to obtain the desired results? Subgrade Performance

  9. What are the choices? • Sub-excavate and replace with stone embankment $$$ • Use Geosynthetics $$$$ • Reinforcement Geotextiles • Geogrids with and w/o geotextile • Chemically treat the subgrade $$ • How do we decide what to use?

  10. WE NEED X-RAY VISION!

  11. Or do we admit defeat?!?!

  12. Time to call the Geo-folks!

  13. Geo’s Responsibility… How are we going to answer these questions: • Where are the problem areas? • What are the subsurface conditions? • What is the best alternative to obtain the desired results?

  14. Where are the problem areas? Defining the problem involves several different disciplines and stakeholders: • Geology/Geotechnical • Pavements • Construction • Maintenance • Roadway • Environmental (As a general rule always include Environmental in on any discussions) • Others

  15. Where are the problem areas? Institutional Knowledge • Maintenance • Pavements Report Field reconnaissance • Observe tell-tale signs such as alligator cracking in pavements, patches • Look at the adjacent topography, surface drainage, ditches, wetlands, etc.

  16. What are the subgrade conditions? Subsurface Investigations • GeoProbe • Test Pits - Yes, test pits. But don’t go tearing up the road yet! Laboratory Testing • Soil Classification • Atterberg Limits • Moisture Content

  17. What is the best alternative to obtain the desired results? Again, What we want… • Construction platform - Meet compaction and deflection criteria during construction of the pavement section. • Cost-effective design • No contractor claims

  18. What is the best alternative to obtain the desired results? What are our tools? • Chemical Stabilization • Cement • Lime • Fly Ash • Removal and Replacement • Mechanical Stabilization • Geotextiles • Geogrids

  19. What is the best alternative to obtain the desired results? Cement Treatment • Typically applied to silty soils • Improves soils properties through: • Hydration of cement – continuous skeleton is formed • Increase in optimum moisture content • Cation exchange – reduces plasticity • Carbonation and Pozzlanic reactions • 4% to 8% cement, by weight, typical

  20. What is the best alternative to obtain the desired results? Lime Treatment • Typically applied to clayey soils • Improves soils properties through: • Cation exchange – reduces plasticity, makes soil friable and workable • Increase in optimum moisture content • 3% to 6% lime, by weight, typical

  21. What does chemical stabilization look like?

  22. Mechanical Spreader

  23. Soil Mixer

  24. Sheepsfoot Roller

  25. Design Resources • ODOT Standard Specifications • Section 00344 - Treated Subgrade • Portland Cement Association, PCA publications: • Soil-Cement Technology for Pavements: Different Products for Different Applications (IS327) • Evaluating the Performance of Soil-Cement and Cement-Modified Soil for Pavements: A Laboratory Investigation (RD120). • National Lime Association, NLA • Lime-Treated Soil, Construction Manual, Lime Stabilization & Lime Modification • Evaluation of Structural Properties of Lime Stabilized Soils and Aggregates, Volume 3: Mixture Design and Testing Protocol for Lime Stabilized Soils • ASTM, AASHTO • Methods of Testing for Moisture Density Relations of Soil-Cement Mixtures, ASTM D558; AASHTO T-134 • Methods of Wetting and Drying Test of Compacted Soil Cement Mixtures, ASTM D559; AASHTO T-135

  26. Construction ObservationYour work doesn’t end at PS&E… • Chemically stabilized soil recommendations need to be followed up with during construction. • Modify the mix design based on contractors methodology and observed performance. • This involves Geo, Construction, and the Contractor

  27. The key to a successful investigation is to always be aware of the site conditions around you…

  28. ?? QUESTIONS ??

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