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 Whiting Chair 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 Presenters Richard L. Boudreau, PE Anand J. Puppala, PhD, PE John 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 M R 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 Soil CBR R-value Unbound Aggregate Base Structural Layer Coefficient

History of M r and Design Design Method Layer AASHTO 1972 Interim Guide AASHTO 1986 Design Guide AASHTO 1993 Design Guide MEPDG Subgrade soil support M r M r M r Base layer coeff. layer coeff. M r /layer coeff. M r

What is Resilient Modulus? AASHTO Definition: A measure of the elastic property of soil recognizing certain non-linear characteristics. Resilient Modulus = M r Resilient Modulus = elastic modulus (mod. of elasticity) Resilient Modulus = stress/strain Resilient 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 M R of subgrades and bases

Webinar Objective: How Do I Obtain Resilient Modulus? Different methods to measure M R of subgrades and bases Laboratory test methods AASHTO T307 Setup

Webinar Objective: How Do I Obtain Resilient Modulus? Different methods to measure M R 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 M R of subgrades and bases Laboratory test methods Field: Destructive & nondestructive test methods Empirical and semiempirical 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, PE rlboudreau@comcast.net President Boudreau Engineering, Inc. 5392 Blue Iris Court Norcross, Georgia 30092 404.388.1137 www/boudreau-engr.com resilient 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 Design Anand J. Puppala, PhD, PE Professor The University of Texas at Arlington Arlington, TX 76019 anand@uta.edu NCHRP Synthesis 382 Summary TRB WEBINAR

Outline Introduction on Synthesis Resilient Modulus, M R Surveys Geotechnical/Materials Group Pavement Design Group Methods for Determining M R Laboratory Methods Non-destructive Methods Intrusive Methods Correlations Useful Practices: Summary

Resilient Modulus Resilient Modulus (M R ) Analogous to Elastic Modulus

Resilient modulus (M R ) 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 Different methods to measure M R 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 M R Geotechnical and materials group of 50 DOTs Pavement design group of 50 DOTs Literature information of M R Laboratory M R 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 M R 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% M R from laboratory tests, field studies and correlations Overall satisfaction of using M R for pavement design is low Limitations of Using M R 1. Constant modification of test procedures 2. Measurement difficulties 3. Design related issues

Synthesis: Laboratory Methods Chapter 3 (Pages 22-41)

Laboratory Tests for M R Repeated Load Triaxial Test

Laboratory Tests for M R : 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 pulse 2. Loading - 0.1 sec and relaxation - 0.9 sec Triaxial Unit with Data Acquisition & Control Panel Unit

Laboratory Methods for M R : Resonant Column (RC) Test To study dynamic properties of geologic materials where, G= small strain-shear modulus; E= Poisson s ratio ρ= soil density; L= sample length F r = resonant frequency; I R = polar moment of inertia of soil I o = 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 M R Tests: Summary M R studies from the literature are presented in three phases: Phase I: M R Literature before 1986 Phase II: M R Literature between 1986 and 1996 Phase III: M R Literature after 1996

Phase I: M R 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: M R Literature Between 1986 and 1996 Studies of laboratory and field equipment to determine the M R Evaluation of AASHTO T-292, T-294 and P-46 Displacement measurement system - Realistic M R Testing on local subgrades and unbound bases Development of various local models to predict resilient properties

Phase III: M R 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 M R 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 M R 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 M R 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 M R 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 % R 2 = 0.44

Direct (D): Soil Properties (S) Based Models MRDS 2 For the Illinois subgrades, the equation is where, M R = resilient modulus measured at σ d = 6 psi for soils with a relative compaction of 95% as per AASHTO T99 % CLAY= clay content in percent PI= plasticity index in percent % SILT= silt content in percent CLASS= 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 1,155 B= constant, varies from 369 to 555 R= -value (AASHTO T190) For fine-grained soils whose R-values are 20, A=1,000 and B= 555 For R>20 with σ d = 6 psi and σ 3 = 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, M R = resilient modulus (Mpa) q c = cone resistance (Mpa) f s = sleeve friction (Mpa) σ c or σ 3 = confining stress (kpa) σ v = vertical stress (kpa) w= water content in decimal number format γ d = dry unit weight (kn/m 3 ) γ w = unit weight of water(kn/m 3 )

Indirect (I) Models: 2 Parameter Models MRI2-1 Confining stress (σ 3 ) is used as a tress attribute and the equation is where k 1 and k 2 = 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, ρ a = atmospheric pressure σ 1 and σ 2 = major and intermediate principal stresses, respectively σ 3 = minor principal stress θ= bulk stress= σ 1 + σ 2 + σ 3 Note: This model is primarily used for granular soils

Indirect (I) Models: 2 Parameter Models MRI2-3 Use the deviatoric stress (σ d ) as the lone stress attribute in and the equation is where, k 1 and k 2 = model constants (dimensionless) ρ a = atmospheric pressure σ d = 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 (σ d ) as the lone stress attribute where, k 1 and k 2 = model constants (dimensionless) σ d = 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 test Light 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 Design Level 1 input parameters are necessary AASHTO T 307: Moduli values at various combinations of stress levels Level 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/DOT Office of Materials and Road Research

Acknowledgements Special thanks to the following organizations: Ammann, Bomag, Caterpillar, and Sakai CNA Consulting Engineers Colorado School of Mines Federal Highway Administration Iowa State University Loughborough University Minnesota Department of Transportation Minnesota Local Road Research Board University of Illinois University of Minnesota University 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 Framework Environment Traffic Materials 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 Plan Moisture testing Roller compaction value Corrective actions to be taken Quality Assurance by Owner includes: Review and approval of the Contractor s QC plan QA testing using the light weight deflectometer (LWD) dynamic cone penetrometer (DCP) and moisture tests Review and approval of the Contractor s QC report Archive of electronic QC and QA data

Import Aerial Photography

Apply Quantitative Statistics to IC Data

MnPAVE Design Soil Modulus Input 1000 800 Frequency 600 400 Median 200 35% 35% 0 15% 15% 0 20 40 60 80 100 120 140 160 180 200 220 E (MPa)

LWD Target Values LRRB Inv 860 Grading 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

2.5 Deflection Target Value vs Gravimetric Moisture Content 2.0 Deflection TV (mm) 1.5 1.0 0.5 0.0 6 8 10 12 14 16 18 20 22 24 26 28 Gravimetric Moisture Content (percent) Plastic Limit=15 Plastic Limit=20 Plastic Limit=25 Plastic Limit=30

Deflection Target Value vs Field Moisture 2.5 Deflection TV (mm) 2.0 1.5 1.0 0.5 0.0 70 75 80 85 90 95 100 105 110 Field Moisture as a Percent of Optimum Moisture Standard Proctor (percent) 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