TRB Webinar: Estimating Stiffness of Subgrade
and Unbound Materials for Pavement Design
Today’s Presenters and Moderator
Nancy Whiting, Purdue University, [email protected]
Richard Boudreau, Boudreau Engineering, Inc., [email protected]
Today’s Presenters and Moderator
Anand Puppala, University of Texas, Arlington, [email protected]
John Siekmeier, Minnesota Department of Transportation, [email protected]
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
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, [email protected]
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 [email protected]
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: [email protected]
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