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

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

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

This is the ideal design…

This is the call from the PM…

…and this is what we end up with

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

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

WE NEED X-RAY VISION!

Or do we admit defeat?!?!

Time to call the Geo-folks!

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

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

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

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

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. Construction platform - Meet compaction and deflection criteria during construction of the pavement section. Cost-effective design Cost-effective design No contractor claims No contractor claims

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

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

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

What does chemical stabilization look like?

Mechanical Spreader

Soil Mixer

Sheepsfoot Roller

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

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

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

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