Subgrade: Its Just Dirt. Isnt it? Daniel N. Frchette, PhD, PE - - PowerPoint PPT Presentation

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Subgrade: Its Just Dirt. Isnt it? Daniel N. Frchette, PhD, PE - - PowerPoint PPT Presentation

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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

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SLIDE 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

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SLIDE 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

Sustainable Asphalt Pavements Workshop 2 March 22, 2017

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SLIDE 3

Introduction

  • What is Subgrade?
  • MAG –
  • ADOT –
  • FHWA –
  • DNF – ?

Sustainable Asphalt Pavements Workshop 3 March 22, 2017

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SLIDE 4

Pavement Components

4 Sustainable Asphalt Pavements Workshop March 22, 2017

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SLIDE 5

Pavement Components

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Pavement Components

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SLIDE 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

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SLIDE 8

Construction Specifications – Portland Cement Concrete

Sustainable Asphalt Pavements Workshop 8 March 22, 2017

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SLIDE 9

Construction Specifications – Asphaltic Concrete

Sustainable Asphalt Pavements Workshop 9 March 22, 2017

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Construction Specifications – Aggregate Base

Sustainable Asphalt Pavements Workshop 10 March 22, 2017

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SLIDE 11

Construction Specifications – Subgrade

Sustainable Asphalt Pavements Workshop 11 March 22, 2017

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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

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Soil Type

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  • Soils Map of Arizona

(USDA-NRCS)

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Swell Potential Map – Phoenix Area

14 Sustainable Asphalt Pavements Workshop March 22, 2017

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Swell Potential Map – Tucson Area

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SLIDE 16

Collapsible Soils

16 Sustainable Asphalt Pavements Workshop March 22, 2017

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SLIDE 17

Environmental Effects/ Climatic Conditions

  • Elevation
  • Temperature
  • Precipitation
  • Seasonal Variation Factor

17 Sustainable Asphalt Pavements Workshop March 22, 2017

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SLIDE 18

Seasonal Variation Factor vs Elevation

18 Sustainable Asphalt Pavements Workshop March 22, 2017

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Seasonal Variation Factor vs Temperature

19 Sustainable Asphalt Pavements Workshop March 22, 2017

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Seasonal Variation Factor vs Precipitation

20 Sustainable Asphalt Pavements Workshop March 22, 2017

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SLIDE 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

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SLIDE 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

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SLIDE 23

Case Study – I-17 Widening

23 Sustainable Asphalt Pavements Workshop March 22, 2017

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SLIDE 24

Case Study – I-17 Widening

  • Swell Potential Map – Phoenix Area

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Case Study – I-17 Widening Project Soils

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  • Subgrade Criteria
  • Percent Passing No. 200 Sieve
  • Plasticity Index (PI)
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SLIDE 26

Case Study – I-17 Widening

March 22, 2017 Sustainable Asphalt Pavements Workshop 26

  • R-Value Data
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SLIDE 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

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SLIDE 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

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SLIDE 29

Summary

  • What is Subgrade?
  • MAG –
  • ADOT –
  • FHWA –
  • DNF –
  • Subgrade: Foundation for the pavement
  • Largest variability, Know the least about

Sustainable Asphalt Pavements Workshop 29 March 22, 2017

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