trb webinar: estimating stiffness of subgrade and...

TRB Webinar: Estimating Stiffness of Subgrade

and Unbound Materials for Pavement Design

Today’s Presenters and Moderator

Nancy Whiting, Purdue University, whiting@purdue.edu

Richard Boudreau, Boudreau Engineering, Inc., rlboudreau@comcast.net

Today’s Presenters and Moderator

Anand Puppala, University of Texas, Arlington, anand@uta.edu

John Siekmeier, Minnesota Department of Transportation, john.siekmeier@dot.state.mn.us

Find the report here:Download: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_382.pdf

Purchase: http://books.trbbookstore.org/syh382.aspx

Introduction to Webinar

Nancy WhitingChair of TRB AFP70 Mineral Aggregates Committee

Research Scientist at the Applied Concrete Research Initiative at Purdue University

whiting@ecn.purdue.edu

Estimating Stiffness of Subgrades and Unbound Materials for Pavement Design

NCHRP Synthesis 382 Summary

Estimating Stiffness of Subgrades and Unbound Materials for Pavement Design

NCHRP Synthesis 382 Summary

PresentersRichard L. Boudreau, PEAnand J. Puppala, PhD, PEJohn Siekmeier, PE

Webinar Objective

The main focus of this workshop is to prepare you to understand what resilient modulus is,

how it relates to pavement performance, and most importantly, how to derive a value

for your pavement designs.

This webinar is not a workshop describing how to design a pavement.

Outline• Introduction

– Why Resilient Modulus?• Surveys

– Geotechnical/Materials Group– Pavement Design Group

• Methods for Determining MR – Laboratory Methods– Non-destructive Methods– Intrusive Methods– Correlations

• Useful Practices: Summary• A State’s Perspective

Outline• Introduction

– Why Resilient Modulus?• Surveys

– Geotechnical/Materials Group– Pavement Design Group

• Methods for Determining MR – Laboratory Methods– Non-destructive Methods– Intrusive Methods– Correlations

• Useful Practices: Summary• A State’s Perspective

Outline• Introduction

– Why Resilient Modulus?• Surveys

– Geotechnical/Materials Group– Pavement Design Group

• Methods for Determining MR – Laboratory Methods– Non-destructive Methods– Intrusive Methods– Correlations

• Useful Practices: Summary• A State’s Perspective

Outline• Introduction

– Why Resilient Modulus?• Surveys

– Geotechnical/Materials Group– Pavement Design Group

• Methods for Determining MR – Laboratory Methods– Non-destructive Methods– Intrusive Methods– Correlations

• Useful Practices: Summary• A State’s Perspective

Why Resilient Modulus?

“The main reason for using the resilient modulus or modulus or stiffness as the

parameter for subgrades and bases is that it represents a basic material property and

can be used in the mechanistic analyses for predicting different distresses such as

rutting and roughness”

What Does it Replace?

• Subgrade SoilCBRR-value

• Unbound Aggregate BaseStructural Layer Coefficient

History of M r and Design

Design Method

LayerAASHTO 1972 Interim Guide

AASHTO 1986 Design Guide

AASHTO 1993 Design Guide MEPDG

Subgrade soil support Mr Mr Mr

Base layer coeff. layer coeff. Mr /layer coeff. Mr

What is Resilient Modulus?AASHTO Definition:

“A measure of the elastic property of soil recognizing certain non-linear characteristics.”

Resilient Modulus = Mr

Resilient Modulus = elastic modulus (mod. of elasticity)Resilient Modulus = stress/strainResilient Modulus = stiffness

Resilient modulus ≠ strength

Loading Mechanism of a Pavement System

applied wheel load results in stresses and deflections throughout the pavement system

Webinar Objective: How Do I Obtain Resilient Modulus?

• Different methods to measure MR of subgrades and bases

Webinar Objective: How Do I Obtain Resilient Modulus?

• Different methods to measure MR of subgrades and bases– Laboratory test methods

AASHTO T307 Setup

Webinar Objective: How Do I Obtain Resilient Modulus?

• Different methods to measure MR of subgrades and bases– Laboratory test methods– Field: Destructive &

non-destructive test methods

lightweight deflectometer (LWD)

Webinar Objective: How Do I Obtain Resilient Modulus?

• Different methods to measure MR of subgrades and bases– Laboratory test methods– Field: Destructive & non-

destructive test methods– Empirical and semi-

empirical correlations

Usefulness of Resilient Modulus

• Used to define fundamental material properties

• Used to predict stress, strain, and displacement

• Used to develop performance models• Used in current AASHTO pavement design

guide• Used in mechanistic design approach

Richard L. Boudreau, PErlboudreau@comcast.net

PresidentBoudreau Engineering, Inc.5392 Blue Iris CourtNorcross, Georgia 30092404.388.1137www/boudreau-engr.comresilient modulus specialists

Anand Puppala

• Professor in Civil Engg at Univ of Texas at Arlington

• Conducted Research with Both LaDOT and TxDOT

• Authored/Co-Authored Several Papers on Resilient Modulus of Subgrades

• Consultant on the NCHRP Synthesis 382

Estimating Stiffness of Subgrades and Unbound

Materials for Pavement DesignAnand J. Puppala, PhD, PE

ProfessorThe University of Texas at Arlington

Arlington, TX 76019anand@uta.edu

NCHRP Synthesis 382 Summary

TRB WEBINAR

Outline Introduction on Synthesis

– Resilient Modulus, MR

Surveys– Geotechnical/Materials Group– Pavement Design Group

Methods for Determining MR – Laboratory Methods– Non-destructive Methods– Intrusive Methods– Correlations

Useful Practices: Summary

Resilient Modulus Resilient Modulus (MR) – Analogous to Elastic Modulus

Resilient ModulusResilient modulus (MR)

“The main reason for using the resilient modulus or modulus or stiffness as the parameter for subgrades and bases is that it represents a basic material property and can be used in the mechanistic analyses for predicting different distresses such as rutting and roughness”

Different methods to measure MR of subgrades and bases– Laboratory test methods– Field: Destructive & non-destructive test methods– Empirical and semi-empirical correlations

Synthesis of NCHRP 382

Nationwide surveys to gather information on MR– Geotechnical and materials group of 50 DOTs– Pavement design group of 50 DOTs

Literature information of MR– Laboratory MR tests– In situ non-destructive test methods– Existing in situ intrusive test methods – Direct correlations– Indirect correlations

Survey Questionnaire: Chapter 2

Survey Results

28 respondents encountered silty clay subgrade 22 respondents used crushed stone aggregates in unbound base layers

Survey Results Total 40 respondents out

of 50 requests (80%)

24 respondents used 1993 AASHTO design guide to design pavement

18 and 19 respondents use MR obtained from different methods other than laboratory and field measurement for subgrades and unbound bases, respectively

Summary of Surveys

Overall response is more than 80% MR from laboratory tests, field studies and correlations Overall satisfaction of using MR for pavement design is low

Limitations of Using MR

1. Constant modification of test procedures2. Measurement difficulties3. Design related issues

Synthesis: Laboratory Methods

Chapter 3 (Pages 22-41)

Laboratory Tests for MR

Repeated Load Triaxial Test

Laboratory Tests for MR: Repeated Load Triaxial Test

AASHTO T-274, T-292, T-294, T-307-99

Specimen preparation methods Stress levels simulates the specimen location Confining pressure simulates overburden

pressure Axial deviatoric stress:

1. Cyclic stress (actual applied cyclic stress)

2. Constant stress (seating load on the soil specimen)

Test Specification:1. Haversine shaped wave load pulse2. Loading - 0.1 sec and relaxation - 0.9 sec

Triaxial Unit with Data Acquisition

& Control Panel Unit

Laboratory Methods for MR: Resonant Column (RC) Test

To study dynamic properties of geologic materials

where, G= small strain-shear modulus; E= Poisson’s ratioρ= soil density; L= sample lengthFr= resonant frequency; IR= polar moment of inertia of soil Io= polar moment of inertia of driver system

Other Test Methods Studied Academic Research Simple Shear Test Hollow Cylinder Test Cubical Triaxial Test Bender Element Test – Simple and Inexpensive

Cubical Triaxial Test Bender Element Test

Laboratory MR Tests: Summary

MR studies from the literature are presented in three phases:

Phase I: MR Literature before 1986Phase II: MR Literature between 1986 and 1996Phase III: MR Literature after 1996

Phase I: MR Literature Before 1986

Development of test procedures

Equipment modifications to test cohesive subgrades / granular bases

Development of appropriate models to represent the resilient behavior

Few correlations based on soil properties to predict resilient properties

Phase II: MR Literature Between 1986 and 1996

Studies of laboratory and field equipment to determine the MR

Evaluation of AASHTO T-292, T-294 and P-46

Displacement measurement system - Realistic MR

Testing on local subgrades and unbound bases

Development of various ‘local’ models to predict resilient properties

Phase III: MR Literature After 1996

Modifications of AASHTO test procedure from T-294 to T-307

Research on the use of AASHTO T-294 and T-307 methods

Development of a large MR database of subgrades

Use of shear modulus to determine resilient modulus

Resilient Modulus - Unsaturated soil testing (MnDOT)

– Most Subgrades are unsatuated

– Suction controlled Triaxial Tests?

Field Studies for MR

Non-Destructive Studies

Chapter 4 (Pages 42-56)

Non-Destructive Methods To measure deflections of pavement sections under impulse loads To estimate the stiffness properties of layers – back calculation Predicted deflections match with the measured deflections

Devices: Dynaflect Falling Weight Deflectometer (FWD) Geogauge Light Falling Weight or Potable Deflectometer (LWD)

Dynaflect Falling Weight Deflectometer

Non-Destructive Methods

Geogauge Seismic Pavement Analyzer (SPA)

Non-Destructive Methods

Light Falling Weight or Portable Deflectometers (LWD)

PRIMA 100 Equipment

LOADMAN PFWD

Summary of Findings Most DOTs use FWDs – Design moduli is a fraction of FWD moduli

Design Moduli – Varies from state to state; is a function of shear

strain level as suggested by Nazarian et al. 1996

Several FWD Back-calculation Programs – EVERCALC, ELMOD and

MODULUS

PSPA and DSPA – Used in TxDOT

LWDs – Several DOTs are using them for both Subgrades and Bases

Issues with respect to stress (Irwin, 1995) & moisture content and

temperatures (White et al. 2007)

Field Studies for MR

Intrusive Methods

Chapter 4 (Pages 57-65)

Cone Penetrometers

Dynamic Cone Penetrometer Static Cone Penetrometer

Dynamic Cone Penetrometer (DCP)

CPT Results: RLT Results

Resilient Moduli Correlations:

Direct & Indirect

Chapter 5 (Pages 66-82)

Direct (D): Soil Properties (S) Based Models

Based on multiple linear regression tools

Selected correlations should be evaluated with the soil test database

MRDS 1 MR is f(degree of saturation and compaction moisture content) For clays A-7-6 type, the equation is

where, w= compaction moisture content in %S= degree of saturation in %R2= 0.44

Direct (D): Soil Properties (S) Based Models

MRDS 2 For the Illinois subgrades, the equation is

where, MR= resilient modulus measured at σd= 6 psi for soils with a relative compaction of 95% as per AASHTO T99

% CLAY= clay content in percentPI= plasticity index in percent% SILT= silt content in percentCLASS= AASHTO classification for A7-6 soils

Direct (D): Soil Properties (S) Based Models

MRDS 3 Recommended by Asphalt Institute (1982), the equation is

where, A= constant, varies from 772 to 1,155B= constant, varies from 369 to 555R= -value (AASHTO T190)

For fine-grained soils whose R-values are ≤20, A=1,000 and B= 555

For R>20 with σd= 6 psi and σ3 = 2 psi, the equation is

Direct (D): In Situ Tests (I) Based Models

MRDI 1 (DCP)

Note: Those models are non-dimensional and are unit sensitive

Direct (D): In Situ Tests (I) Based Models

MRDI 2 (CPT) Expression valid for overburden stress conditions is

Expression valid for both overburden stress and traffic conditions is

where, MR= resilient modulus (Mpa)qc= cone resistance (Mpa)fs= sleeve friction (Mpa)σc or σ3= confining stress (kPa)σv= vertical stress (kPa)w= water content in decimal number formatγd= dry unit weight (kN/m3)γw= unit weight of water(kN/m3)

Indirect (I) Models: 2 Parameter Models

MRI2-1

Confining stress (σ3) is used as a tress attribute and the equation is

where k1 and k2= model constants (dimensionless)

Note: This model formulation does not address the deviatoric stress effects

Indirect (I) Models: 2 Parameter Models

MRI2-2

Bulk stress (θ) is used as a stress attribute and the equation is

where, ρa= atmospheric pressureσ1 and σ2= major and intermediate principal stresses, respectivelyσ3= minor principal stressθ= bulk stress= σ1+ σ2+ σ3

Note: This model is primarily used for granular soils

Indirect (I) Models: 2 Parameter Models

MRI2-3

Use the deviatoric stress (σd) as the lone stress attribute in and the equation is

where, k1 and k2= model constants (dimensionless)ρa= atmospheric pressureσd= deviatoric stress applied during triaxial test

Note: This model formulation does not consider confining stress effects. It is primarily used for cohesive soils

Indirect (I) Models: 2 Parameter Models

MRI2-4

Use deviatoric stress (σd) as the lone stress attribute

where, k1 and k2= model constants (dimensionless)σd= deviatoric stress applied during triaxial test

Note: This model is primarily used for cohesive soils

Indirect (I) Models: 3 Parameter Models

MRI3-1

MRI3-2 Replace the deviatoric stress with octahedral shear stress

MRI3-3

Indirect (I) Models: 3 Parameter Models

MRI3-4

Use the following stresses as their attributes:

Correlations Development

Note: MC- Moisture content MOIST- Optimum moisture

content SATU- Percent saturation COMP- Percent compaction S40 and S60- Percent passing

numbers 40 and 60 sieves CLY- Percent clay (CLY) SLT- Percent silt (SLT) SW- Percent swell (SW) SH- Percent shrinkage DEN- Density CBR- California Bearing Ratio

Useful Practices: Summary Laboratory Methods (Level 1 Parameters)

Repeated load triaxial test is the most preferred laboratory test

Field Methods – Non-destructive (Level 1 Parameters)Falling Weight Deflectometer test is the most preferred field testLight Falling Weight Deflectometers are upcoming test methods

Field Methods – Intrusive (Level 1 Parameters)Dynamic Cone Penetrometer is widely used

Correlations - Direct and Indirect (Level 2 Parameters)Different correlations available – Have some issues

For Better Pavement DesignLevel 1 input parameters are necessaryAASHTO T – 307: Moduli values at various combinations of stress levelsLevel 2 and Level 3 input parameters – Engg Judgment

LOCAL EXPERIENCE - VALUABLE

Action Items

Importance of “Level 1” input parameters for pavement design (lab and field) Use of “Level 2” moduli input (from correlations) Standardize the test procedures, both in laboratory and field conditions Address seasonal moisture variations and their effects on moduli

Define the design moduli and their correlation with various moduli

Develop the training modules that emphasize all of the above

Topic Panel

Judith Corley-Lay; Leo Fontaine; G. P. Jayprakash; Andrew Johnson; John

Siekmeier; Bruce Steven; Doc Zhang; Michael Moravec; Cheryl Richter & Jon Williams

THANK YOU

DOT Implementation of Moduli during Pavement Design and Construction

October 28, 2009

John Siekmeier, PE

Mn/DOTOffice of Materials and Road Research

Acknowledgements Special thanks to the following organizations:

Ammann, Bomag, Caterpillar, and SakaiCNA Consulting EngineersColorado School of MinesFederal Highway Administration Iowa State University Loughborough UniversityMinnesota Department of TransportationMinnesota Local Road Research BoardUniversity of IllinoisUniversity of MinnesotaUniversity of Wisconsin

Topics

Mechanistic-Empirical Design, MnPAVE Performance Based Construction Testing New Field Testing Techniques What We’ve Learned Next Steps

M-E in MN: MnPAVE for Local Roads Provides the FrameworkEnvironmentTrafficMaterials and Structure

Sponsor: MN Local Road Research Board Contact: Bruce.Chadbourn@dot.state.mn.us

Performance Based Construction QA

Achieve agreement between construction quality assurance, pavement design, and performance.

Quantify alternative materials and construction practices.

Show economic benefit of improved materials. Reward good construction. This requires new specifications and new tools.

General QC/QA Procedure Quality Control by the Contractor includes:

Quality Control PlanMoisture testingRoller compaction valueCorrective actions to be taken

Quality Assurance by Owner includes:Review and approval of the Contractor’s QC planQA testing using the light weight deflectometer (LWD)

dynamic cone penetrometer (DCP) and moisture testsReview and approval of the Contractor’s QC reportArchive of electronic QC and QA data

Import Aerial Photography

Apply Quantitative Statistics to IC Data

0 20 40 60 80 100 120 140 160 180 200 2200

200

400

600

800

1000

Freq

uenc

y

E (MPa)

MnPAVE Design Soil Modulus Input

Median

15% 15%

35%35%

LWD Target Values LRRB Inv 860Grading Number Moisture Content LWD Modulus Zorn LWD Deflection Zorn*

GN % MPa mm

3.1-3.5 5 - 7 80 0.38

7 - 9 67 0.45

9 - 11 50 0.60

3.6-4.0 5 - 7 80 0.38

7 - 9 53 0.56

9 - 11 42 0.71

4.1-4.5 5 - 7 62 0.49

7 - 9 47 0.64

9 - 11 38 0.79

4.6-5.0 5 - 7 53 0.56

7 - 9 42 0.71

9 - 11 35 0.86

5.1-5.5 5 - 7 47 0.64

7 - 9 38 0.79

9 - 11 32 0.94

5.6-6.0 5 - 7 42 0.71

7 - 9 33 0.90

9 - 11 29 1.05

Deflection Target Value vs Gravimetric Moisture Content

0.0

0.5

1.0

1.5

2.0

2.5

6 8 10 12 14 16 18 20 22 24 26 28

Gravimetric Moisture Content (percent)

Def

lect

ion

TV (m

m)

Plastic Limit=15 Plastic Limit=20 Plastic Limit=25 Plastic Limit=30

Deflection Target Value vs Field Moisture

0.0

0.5

1.0

1.5

2.0

2.5

70 75 80 85 90 95 100 105 110

Field Moisture as a Percent of Optimum Moisture Standard Proctor (percent)

Def

lect

ion

TV (m

m)

Plastic Limit=15 Plastic Limit=20 Plastic Limit=25 Plastic Limit=30

Why Deflection Target Values? Design engineer determines allowable deflection

using the moduli of the layers in the pavement foundation and the load applied.

Design engineer determines allowable moisture content for material specified and defines the relationship between moisture and deflection.

Construction engineer measures deflection and moisture to verify that the design parameters have been achieved.

Roadmap: What’s Next Intelligent Compaction Specified in More Contracts Purchase LWDs for Performance Based QA Testing Specification Includes Design-Based Minimum Targets Specification Includes Design-Based Uniformity Targets Educate Designers, Opportunity to Refine/Validate Design MnPAVE Enhancements to Predict Construction QA Targets MnPAVE Enhancements to Include Unsaturated Mechanics Continued Participation with National Projects

NCHRP 21-09 Intelligent Compaction Specifications FHWA-led Intelligent Compaction Pooled Fund ASTM Test Standard Development

Conclusions Construction equipment and field tests are now available

that can measure the mechanistic properties used to design pavements and predict performance.

IC rollers allow operators to make better decisions and correct problem areas early.

IC rollers produce surface covering documentation that can be used to reward more uniform construction.

LWDs and DCPs can be used during construction quality assurance to efficiently verify design target values.

Thank You.

Questions?

www.dot.state.mn.us/materials/researchic.html