• TABLE OF CONTENTS
HIDE
 Title Page
 Dedication
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Literature review
 Equipment and facilities
 Simulation and analyses of NDT...
 Testing program
 Analyses of field measured NDT...
 Interpretation of in situ penetration...
 Pavement stress analyses
 Conclusions and recommendation...
 Appendix
 Reference
 Biographical sketch
 Copyright














Title: Evaluation of layer moduli in flexible pavement systems using nondestructive and penetration testing methods
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Permanent Link: http://ufdc.ufl.edu/UF00090204/00001
 Material Information
Title: Evaluation of layer moduli in flexible pavement systems using nondestructive and penetration testing methods
Series Title: Evaluation of layer moduli in flexible pavement systems using nondestructive and penetration testing methods
Physical Description: Book
Creator: Badu-Tweneboah, Kwasi,
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Bibliographic ID: UF00090204
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
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Resource Identifier: alephbibnum - 001036909
oclc - 18287379

Table of Contents
    Title Page
        Page i
    Dedication
        Page ii
    Acknowledgement
        Page iii
        Page iv
    Table of Contents
        Page v
        Page vi
        Page vii
        Page viii
        Page ix
    List of Tables
        Page x
        Page xi
        Page xii
        Page xiii
    List of Figures
        Page xiv
        Page xv
        Page xvi
        Page xvii
        Page xviii
        Page xix
        Page xx
    Abstract
        Page xxi
        Page xxii
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
    Literature review
        Page 6
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    Equipment and facilities
        Page 55
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    Simulation and analyses of NDT deflection data
        Page 71
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    Testing program
        Page 136
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    Analyses of field measured NDT data
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    Interpretation of in situ penetration tests
        Page 288
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    Pavement stress analyses
        Page 316
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    Conclusions and recommendations
        Page 331
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    Appendix
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    Reference
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    Biographical sketch
        Page 491
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    Copyright
        Copyright
Full Text










EVALUATION OF LAYER MODULI IN FLEXIBLE PAVEMENT SYSTEMS
USING NONDESTRUCTIVE AND PENETRATION TESTING METHODS





By

KWASI BADU-TWENEBOAH


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


1987














DEDICATED TO MY FAMILY, ESPECIALLY MY SISTER, ABENA KYEM

AND GRANDFATHER, ATTA KWAME, FOR THEIR CONTINUAL PRAYERS,

ENCOURAGEMENT AND SUPPORT DURING THE COURSE OF MY EDUCATION.



"A MIND IS A TERRIBLE THING TO WASTE."














ACKNOWLEDGMENTS

I would like to express my gratitude to Dr. Byron E. Ruth, chairman

of my supervisory committee, for his guidance, encouragement and con-

structive criticisms in undertaking this research work. I am also

grateful to Drs. F. C. Townsend, J. L. Davidson, M. Tia, J. L. Eades,

and D. P. Spangler for serving on my graduate supervisory committee. I

consider myself honored to have had these distinguished men on my com-

mittee.

I also owe sincere thanks to Dr. J. H. Schaub, chairman of the

civil engineering department, for the many times he gave help during the

course of my studies here, especially in my obtaining the grant award to

participate in the 1986 APWA Congress in New Orleans, Louisiana.

I would like to express my appreciation to the Florida Department

of Transportation (FDOT) for providing the financial support, testing

facilities, materials, and personnel that made this research possible.

I would like to thank the many individuals at the Pavement Evaluation

and Bituminous Materials Research sections of the Bureau of Materials

and Research at FDOT who contributed significantly to the completion of

this work. In particular, I am indebted to Messrs. W. G. Miley, Ron

McNamara, Ed Leitner, Don Bagwell, and John Purcell for giving so

generously of their time.

A very special word of thanks goes to Dr. David Bloomquist for his

significant contributions in conducting the in situ penetration tests








and for his helpful suggestions, advice, and friendship. The assistance

of Mr. Ed Dobson in the field work is also appreciated.

I would also like to thank Dr. F. Balduzzi of the Institute of

Foundation Engineering and Soil Mechanics of the Federal Institute of

Technology, Zurich, Switzerland, for inviting me to the institute, and

consequently helping me develop the interest to pursue active research

and further studies.

Last, but far from being the least, I would like to thank

Ms. Candace Leggett for her expertise and diligent skill in typing this

dissertation.














TABLE OF CONTENTS


Page

ACKNOWLEDGMENTS................................... ................. ii

LIST OF TABLES................. ................... ...... ..... ...... ix

LIST OF FIGURES.......................................... E..... xiii

ABSTRACT............o ......... .... o ....... ...................... xx


CHAPTER

1 INTRODUCTION ..... .......... ........................ .. 1

1.1 Background........ ... .... ........ .................... 1
1.2 Study Objectives ... .... .............. ... ... ...... .... ... 3
1.3 Scope of Study................................. ... .. 4

2 LITERATURE REVIEW .. ....................... ........... ... ... 6

2.1 Introduction......................... .............. 6
2.2 Elastic-Layer Theory................... ................ 7
2.2.1 General............ ....... ...... ........... 7
2.2.2 One-Layer System................................ 8
2.2.3 Two-Layer System............................. 9
2.2.4 Three-Layer System........................... 10
2.2.5 Multilayered or N-Layered Systems.............. 11
2.3 Material Characterization Methods...................... 13
2.3.1 General......................................... 13
2.3.2 State-of-the-Art Nondestructive Testing......... 15
2.3.2.1 General............................... 15
2.3.2.2 Static Deflection Procedures........... 16
2.3.2.3 Steady-State Dynamic Force-
Deflection................................ 21
2.3.2.4 Dynamic Impact Load Response........... 24
2.3.2.5 Wave Propagation Technique............. 29
2.3.3 NDT Data-Interpretation Methods................ 32
2.3.3.1 General ...... ...................... ....... 32
2.3.3.2 Direct Solutions ...................... 36
2.3.3.3 Back-Calculation Methods............... 41
2.3.4 Other In Situ Methods...............t......... 44








Page

2.4 Factors Affecting Modulus of Pavement-Subgrade
Materials ................................................... 47
2.4.1 Introduction..................................... 47
2.4.2 Temperature.................................. .. 48
2.4.3 Stress Dependency............................. 49

3 EQUIPMENT AND FACILITIES.................................... 55

3.1 Description of Dynaflect Test System.................... 56
3.1.1 Description of Equipment....................... 56
3.1.2 Calibration.................... ............... 59
3.1.3 Testing Procedure .............................. 59
3.1.4 Limitations...................................... 60
3.2 Description of the Falling Weight Deflectometer
Testing System.......................................... 60
3.2.1 The 8002 FWD..................................... 61
3.2.2 The 8600 System Processor........................ 61
3.2.3 The HP-85 Computer.............................. 63
3.2.4 Testing Procedure............................... 63
3.2.5 Advantages...... ... .............................. 64
3.3 BISAR Computer Program ................................. 64
3.4 Description of Cone Penetration Test Equipment.......... 65
3.5 Marchetti Dilatometer Test Equipment.................... 67
3.6 Plate Bearing Test...................................... 70

4 SIMULATION AND ANALYSES OF NDT DEFLECTION DATA.............. 71

4.1 BISAR Simulation Study................................ 71
4.1.1 General .......................................... 71
4.1.2 Dynaflect Sensor Spacing........................ 74
4.1.3 FWD Sensor Spacing............................... 74
4.2 Sensitivity Analysis of Theretical NDT
Deflection Basins....................................... 76
4.2.1 Parametric Study............................... 76
4.2.2 Summary of Sensitivity Analysis.................. 88
4.3 Development of Layer Moduli Prediction Equations........ 91
4.3.1 General .......................................... 91
4.3.2 Development of Dynaflect Prediction Equations.... 95
4.3.2.1 Prediction Equations for E .............95
4.3.2.2 Prediction Equation for E2 for
Thin Pavements............... .......... 103
4.3.2.3 Prediction Equations for E3............. 105
4.3.2.4 Prediction Equations for E4 ............ 108
4.3.3 Development of FWD Prediction Equations.......... 110
4.3.3.1 Prediction Equations for E ............. 110
4.3.3.2 Prediction Equations for E ........... 111
4.3.3.3 Prediction Equations for E ............. 113
4.3.3.4 Prediction Equations for E ............. 114








Page

4.4 Accuracy and Reliability of NDT Prediction Equations.... 119
4.4.1 Prediction Accuracy of Dynaflect Equations....... 119
4.4.1.1 Asphalt Concrete Modulus, E ............ 119
4.4.1.2 Base Course Modulus, E2,
for Thin Pavements...................... 123
4.4.1.3 Stabilized Subgrade Modulus, E ......... 123
4.4.1.4 Subgrade Modulus, E .................... 125
4.4.2 Prediction Accuracy of FWD Equations............. 127
4.4.2.1 Asphalt Concrete Modulus, E ............ 127
4.4.2.2 Base Course Modulus, E2.............. 129
4.4.2.3 Stabilized Subgrade Modulus, E ......... 132
4.4.2.4 Subgrade Modulus, E ................... 134

5 TESTING PROGRAM............. ................. .. ......... 136

5.1 Introduction..... o ..................................... 136
5.2 Location and Characteristics of Test Pavements.......... 137
5.3 Description of Testingn Procedures..................... 140
5.3.1 General .......... ...................... ....... 140
5.3.2 Dynaflect Tests........................................... ....... 142
5.3.3 Falling Weight Deflectometer Tests............... 142
5.3.4 Cone Penetration Tests.......................... 144
5.3.5 Dilatometer Tests..... .......................... 145
5.3.6 Plate Loading Tests................................. 145
5.3.7 Asphalt Rheology Tests.......................... 147
5.3.8 Temperature Measurements........................ 151

6 ANALYSES OF FIELD MEASURED NDT DATA......................... 153

6.1 General ... ... .................. .. .. ............... ... 153
6.2 Linearity of Load-Deflection Response.................. 153
6.3 Prediction of Layer Moduli.............................. 169
6.3.1 General.......................................... 169
6.3.2 Dynaflect Layer Moduli Predictions............... 171
6.3.3 FWD Prediction of Layer Moduli..................... 174
6.4 Estimation of El from Asphalt Rheology Data............. 178
6.5 Modeling of Test Pavements.............................. 181
6.5.1 General .................... ............. ..... ... 181
6.5.2 Tuning of Dynaflect Deflection Basins........... 182
6.5.3 Tuning of FWD Deflection Basins.................. 205
6.5.4 Nonuniqueness of NDT Backcalculation
of Layer Moduli ................................. 231
6.5.5 Effect of Stress Dependency.................... 233
6.6 Comparison of NDT Devices.............................. 236
6.6.1 Comparison of Deflection Basins.................. 238
6.6.2 Comparison of Layer Moduli...................... 253
6.7 Analyses of Tuned NDT Data.............................. 265
6.7.1 General ...................o .... ...... ....... 265
6.7.2 Analysis of Dynaflect Tuned Data................. 266








Page
6.7.2.1 Comparison of Measured and
Predicted Deflections................... 266
6.7.2.2 Development of Simplified Layer
Moduli Equations........................ 271
6.7.3 Analysis of FWD Tuned Data....................... 279
6.7.3.1 Comparison of Measured and
Predicted Deflections................... 279
6.7.3.2 Development of Prediction Equations..... 282

7 INTERPRETATION OF IN SITU PENETRATION TESTS.................. 288

7.1 General ................. ............................... 288
7.2 Soil Profiling and Identification....................... 289
7.3 Correlation Between ED and qc........................... 292
7.4 Evaluation of Resilient Moduli for Pavement Layers...... 302
7.4.1 General .......................................... 302
7.4.2 Correlation of Resilient Moduli with
Cone Resistance.................................. 304
7.4.3 Correlation of Resilient Moduli with
Dilatometer Modulus.............................. 308
7.5 Variation of Subgrade Stiffness with Depth.............. 312

8 PAVEMENT STRESS ANALYSES..................................... 316

8.1 General ................................................. 316
8.2 Short-Term Load Induced Stress Analysis................. 318
8.2.1 Design Parameters................................ 318
8.2.2 Comparison of Pavement Response and
Material Properties.............................. 319
8.2.3 Summary ....................................... 330

9 CONCLUSIONS AND RECOMMENDATIONS.............................. 331

9.1 Conclusions................ ..... ...................... 331
9.2 Recommendations ........................ ......... 334

APPENDICES

A FIELD DYNAFLECT TEST RESULTS................................. 338

B FIELD FWD TEST RESULTS ...................................... 354

C COMPUTER PRINTOUT OF CPT RESULTS............................ 379

D COMPUTER PRINTOUT OF DMT RESULTS............................ 406

E RECOVERED ASPHALT RHEOLOGY TEST RESULTS...................... 432

F RECOMMENDED TESTING AND ANALYSIS PROCEDURES FOR THE
MODIFIED DYNAFLECT TESTING SYSTEM............................ 456

G PARTIAL LISTING OF DELMAPS1 COMPUTER PROGRAM................. 463


viii








Page

REFERENCES.......................................................... 478

BIOGRAPHICAL SKETCH................................................. 491














LIST OF TABLES


Table Page

2.1 Summary of Deflection Basin Parameters...................... 35

2.2 Summary of Computer Programs for Evaluation of
Flexible Pavement Moduli from NDT Devices.................... 42

4.1 Range of Pavement Layer Properties........................... 73

4.2 Sensitivity Analysis of FWD Deflections for ti = 3.0 in. .... 86

4.3 Sensitivity Analysis of FWD Deflections for t t ,
and t3....................................................... 87

4.4 Sensitivity Analysis of FWD Deflections for E =
600 ksi and ti = 3.0 in. ....... ...... ......... .......... 89

4.5 Pavements with Dynaflect E1 Predictions Having More
Than 10 Percent Error................ ....... ............. 121

4.6 Pavements with Dynaflect E2 Predictions Having More
Than 10 Percent Error.......................... ............ 124

4.7 Comparison of Actual and Predicted E3 Values for
Varying t ................................................... 126

4.8 Prediction Accuracy of Equation 4.18--Error
Distribution as a Function of t ............................. 128

4.9 Prediction Accuracy of Equation 4.19--Error
Distribution as a Function of t ............................ 130

4.10 Pavements with E1 Predictions Having 15 Percent
or More Error......................... .............. ....... 131

4.11 Pavements with E2 Predictions Having 20 Percent
or More Errors............................................... 133

5.1 Characteristics of Test Pavements.......................... 138

5.2 Summary of Tests Performed on Test Pavements................. 143

5.3 Plate Loading Test Results................................... 148








5.4 Viscosity-Temperature Relationships of Recovered
Asphalt from Test Pavements.................................. 149

5.5 Temperature Measurements of Test Pavement Sections........... 152

6.1 Typical Dynaflect Deflection Data from Test Sections......... 170

6.2 Typical FWD Data from Test Sections......................... 172

6.3 Layer Moduli Using Dynaflect Prediction Equations............ 173

6.4 Layer Moduli Using FWD Prediction Equations.................. 176

6.5 Comparison Between NDT and Rheology Predictions
of Asphalt Concrete Modulus................................. 180

6.6 Comparison of Field Measured and BISAR Predicted
Dynaflect Deflections ....................................... 183

6.7 Dynaflect Tuned Layer Moduli for Test Sections............... 203

6.8 Predicted Deflections from Tuned Layer Moduli................ 204

6.9 Comparison of Field Measured and BISAR Predicted
FWD Deflections ..................................... ...... 206

6.10 FWD Tuned Layer Moduli for Test Sections..................... 227

6.11 Predicted FWD Deflections from Tuned Layer Moduli............ 228

6.12 Comparison Between Re-Calculated and Tuned FWD
Layer Moduli............................................... 230

6.13 Illustration of Nonuniqueness of Backcalculation of
Layer Moduli from NDT Deflection Basin...................... 232

6.14 Comparison of Deflections Measured at Different Load
Levels .................................. ... ........ ........ 235

6.15 Comparison Between Tuned Layer Moduli and Applied
FWD Load............. ...................................... 237

6.16 Comparison of the Asphalt Concrete Modulus for
the Test Sections.............................................. 254

6.17 Comparison of the Base Course Modulus for the
Test Sections................................................ 258

6.18 Comparison of the Subbase Modulus for the
Test Sections................................................ 259

6.19 Comparison of the Subgrade Modulus for the
Test Sections ................................................ 260








6.20 Ratios of Dynaflect Moduli to FWD Moduli for Test Sections... 262

6.21 Correlation Between Measured and Predicted FWD
(9-kip Load) Deflections ......... ..... ........... ....... 281

7.1 Relationship Between ED and qc for Selected Test
Sections in Florida....................................... 298

7.2 Correlation of NOT Tuned Base Course Modulus (E2)
to Cone Resistance .......................................... 305

7.3 Correlation of NDT Tuned Subbase Modulus (E3) to
Cone Resistance......................................... ..... 306

7.4 Correlation of NDT Tuned Subgrade Modulus (E4) to
Cone Resistance............................... ..... ............ 307

7.5 Relationship Between Resilient Modulus, ER and
Cone Resistance, qc......... ...... ... ..... ................... 308

7.6 Correlation of NDT Tuned Subbase Modulus to
Dilatometer Modulus.......................................... 309

7.7 Correlation of NDT Tuned Subgrade Modulus to
Dilatometer Modulus ................... ................. ..... 310

7.8 Relationship Between Resilient Modulus, ER and
Dilatometer Modulus, ED...................................... 311

7.9 Effect of Varying Subgrade Stiffness on Dynaflect
Deflections on SR 26A...................................... 314

8.1 Material Properties and Results of Stress Analysis
for SR 26B (Gilchrist County); a) Input Parameters
for BISAR; b) Pavement Stress Analysis....................... 320

8.2 Material Properties and Results of Stress Analysis
for SR 24 (Alachua County); a) Input Parameters
for BISAR; b) Pavement Stress Analysis....................... 321

8.3 Material Properties and Results of Stress Analysis
for US 441 (Columbia County); a) Input Parameters
for BISAR; b) Pavement Stress Analysis....................... 322

8.4 Material Properties and Results of Stress Analysis
for SR 15C (Martin County); a) Input Parameters
for BISAR; b) Pavement Stress Analysis....................... 323

8.5 Material Properties and Results of Stress Analysis
for SR 80 (Palm Beach County); a) Input Parameters
for BISAR; b) Pavement Stress Analysis....................... 324

8.6 Summary of Pavement Stress Analysis at Low Temperatures...... 326








8.7 Effect of Increased Base Course Modulus on Pavement
Response on SR 80; a) Input Parameters for BISAR;
b) Pavement Stress Analysis.................................. 329


xiii














LIST OF FIGURES


Figure Page

2.1 Well-Designed Pavement Deflection History Curve.............. 18

2.2 Typical Annual Deflection History for a Flexible Pavement.... 20

2.3 Typical Output of a Dynamic Force Generator.................. .. 22

2.4 Schematic Diagram of Impulse Load-Response Equipment......... 25

2.5 Characteristic Shape of Load Impulse......................... 26

2.6 Comparison of Pavement Response from FWD and
Moving-Wheel Loads. a) Surface Deflections;
b) Vertical Subgrade Strains................................. 28

2.7 Empirical Interpretation of Dynaflect Deflection
Basin. a) Basin Parameters; b) Criteria...................... 34

2.8 Dynaflect Fifth Sensor Deflection-Subgrade
Modulus Relationship.................. ........ ......... 40

2.9 Temperature Prediction Graphs. a) Pavements More
Than 2 in. Thick; b) Pavements Equal to or Less
Than 2 in. Thick............................................ 50

3.1 Typical Dynamic Force Output Signal of Dynaflect............ 57

3.2 Configuration of Dynaflect Load Wheels and Geophones
in Operating Position........................................ 58

3.3 Schematic of FWD Load-Geophone Configuration and
Deflection Basin ............................................ 62

3.4 Schematic of Marchetti Dilatometer Test Equipment............ 69

4.1 Four-Layer Flexible Pavement System Model.................... 72

4.2 Dynaflect Modified Geophone Positions........................ 75

4.3 Typical Four-Layer System Used for the Sensitivity
Analysis ..................................................... 77








4.4 Effect of Change of El on Theoretical FWD (9-kip Load)
Deflection Basin................................... ........ 79

4.5 Effect of Change of E2 on Theoretical FWD (9-kip Load)
Deflection Basin ............................................. 80

4.6 Effect of Change of E3 on Theoretical FWD (9-kip Load)
Deflection Basin ........................................... 81

4.7 Effect of Change of E4 on Theoretical FWD (9-kip Load)
Deflection Basin............................................. 82

4.8 Effect of Change of tI on Theoretical FWD (9-kip Load)
Deflection Basin............................................. 83

4.9 Effect of Change of t2 on Theoretical FWD (9-kip Load)
Deflection Basin............................................. 84

4.10 Effect of Change of t3 on Theoretical FWD (9-kip Load)
Deflection Basin............................................. 85

4.11 Effect of Varying Subgrade Thickness on Theoretical FWD
(9-kip Load) Deflection Basin................................ 90

4.12 Variation in Dynaflect Deflection Basin with Varying
E2 and E3 Values with t, = 3.0 in. ......................... 93

4.13 Variation in Dynaflect Deflection Basin with Varying
E and E4 Values with t, = 3.0 in. .......................... 94

4.14 Relationship Between El and D1 D4 for t, = 3.0 in ....... 96

4.15 Relationship Between E1 and D1 D4 for t, = 6.0 in. ........ 97

4.16 Relationship Between El and Di D4 for tI = 8.0 in. ........ 98

4.17 Variation of Ki with ti for Different E2 Values.............. 100

4.18 Variation of K2 with t for Different E2 Values.............. 101

4.19 Relationship Between E2 and Di D4 for t, = 1.0 in. ........ 104

4.20 Comparison of E4 Prediction Equations Using Modified
Sensor 10 Deflections .................................... 109

4.21 Relationship Between E4 and FWD Deflections for Fixed
E E and E Values with t1 = 3.0 in. .................... 116

4.22 Relationship Between E4 and FWD Deflections for Fixed
El, E2, and E3 Values with t1 = 6.0 in. ..................... 117

5.1 Location of Test Pavements in the State of Florida........... 139








5.2 Layout of Field Tests Conducted on Test Pavements........... 141


6.1 Surface Deflection as


6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

6.10

6.11

6.12

6.13

6.14


Surface

Surface

Surface

Surface

Surface

Surface

Surface

Surface

Surface

Surface

Surface

Surface

Surface


Load on SR 26A........... 155


Deflection

Deflection

Deflection

Deflection

Deflection

Deflection

Deflection

Deflection

Deflection

Deflection

Deflection

Deflection

Deflection


as a Function of Load on


Function

Function

Function

Function

Function

Function

Function

Function

Function

Function

Function

Function

Function


6.15 Comparison of Measured and Predicted Dynaflect
Deflections for SR 26A--M.P. 11.912.........................

6.16 Comparison of Measured and Predicted Dynaflect
Deflections for SR 26B--M.P. 11.205..........................

6.17 Comparison of Measured and Predicted Dynaflect
Deflections for SR 26C--M.P. 10.168..........................

6.18 Comparison of Measured and Predicted Dynaflect
Deflections for SR 24--M.P. 11.112..........................

6.19 Comparison of Measured and Predicted Dynaflect
Deflections for US 301--M.P. 11.112.........................

6.20 Comparison of Measured and Predicted Dynaflect
Deflections for I-10A--M.P. 14.062...........................

6.21 Comparison of Measured and Predicted Dynaflect
Deflections for I-10B--M.P. 2.703............................

6.22 Comparison of Measured and Predicted Dynaflect
Deflections for I-10C--M.P. 32.071...........................


Load

Load

Load

Load

Load

Load

Load

Load

Load

Load

Load

Load


SR 26C...........

SR 24...........

US 301...........

US 441............

I-10A............

I-10B ............

I-10C.............

SR 715............

SR 12............

SR 15C ...........

SR 26B............

SR 15A............

SR 15B...........


156

157

158

159

160

161

162

163

164

165

166

167

168








6.23 Comparison of Measured and Predicted Dynaflect
Deflections for SR-15A--M.P. 6.549..........................

6.24 Comparison of Measured and Predicted Dynaflect
Deflections for SR 15B--M.P. 4.811...........................

6.25 Comparison of Measured and Predicted Dynaflect
Deflections for SR 715--M.P. 4.722............................

6.26 Comparison of Measured and Predicted Dynaflect
Deflections for SR 715--M.P. 4.720............................

6.27 Comparison of Measured and Predicted Dynaflect
Deflections for SR 12--M.P. 1.485.............................

6.28 Comparison of Measured and Predicted Dynaflect
Deflections for SR 80--Section 1............................

6.29 Comparison of Measured and Predicted Dynaflect
Deflections for SR 80--Section 2........... .................

6.30 Comparison of Measured and Predicted Dynaflect
Deflections for SR 15C--M.P. 0.055...........................

6.31 Comparison of Measured and Predicted Dynaflect
Deflections for SR 15C--M.P. 0.065...........................


6.32 Comparison of Measured and
(Normalized to 1-kip Load)

6.33 Comparison of Measured and
(Normalized to 1-kip Load)

6.34 Comparison of Measured and
(Normalized to 1-kip Load)

6.35 Comparison of Measured and
(Normalized to 1-kip Load)

6.36 Comparison of Measured and
(Normalized to 1-kip Load)

6.37 Comparison of Measured and
(Normalized to 1-kip Load)

6.38 Comparison of Measured and
(Normalized to 1-kip Load)

6.39 Comparison of Measured and
(Normalized to 1-kip Load)

6.40 Comparison of Measured and
(Normalized to 1-kip Load)


Predicted FWD Deflections
for SR 26A--M.P. 11.912........... 208

Predicted FWD Deflections
for SR 26B--M.P. 11.205........... 209

Predicted FWD Deflections
for SR 26C--M.P. 10.168........... 210

Predicted FWD Deflections
for SR 26C--M.P. 10.166........... 211

Predicted FWD Deflections
for SR 24--M.P. 11.112............ 212

Predicted FWD Deflections
for US 301--M.P. 21.585........... 213

Predicted FWD Deflections
for US 441--M.P. 1.236........... 214

Predicted FWD Deflections
for I-1OA--M.P. 14.062............ 215

Predicted FWD Deflections
for I-1OB--M.P. 2.703............. 216


xvii


194


195


196


197


198


199


200


201


202








6.41 Comparison of Measured and
(Normalized to 1-kip Load)

6.42 Comparison of Measured and
(Normalized to 1-kip Load)

6.43 Comparison of Measured and
(Normalized to 1-kip Load)

6.44 Comparison of Measured and
(Normalized to 1-kip Load)

6.45 Comparison of Measured and
(Normalized to 1-kip Load)

6.46 Comparison of Measured and
(Normalized to 1-kip Load)

6.47 Comparison of Measured and
(Normalized to 1-kip Load)

6.48 Comparison of Measured and
(Normalized to 1-kip Load)

6.49 Comparison of Measured and
(Normalized to 1-kip Load)


Predicted FWD Deflections
for I-10C--M.P. 32.071............ 217

Predicted FWD Deflections
for SR 15A--M.P. 6.546............ 218

Predicted FWD Deflections
for SR 15A--M.P. 6.549............ 219

Predicted FWD Deflections
for SR 15B--M.P. 4.811............ 220

Predicted FWD Deflections
for SR 715--M.P. 4.722............ 221

Predicted FWD Deflections
for SR 715--M.P. 4.720........... 222

Predicted FWD Deflections
for SR 12--M.P. 1.485............. 223

Predicted FWD Deflections
for SR 15C--M.P. 0.055............ 224

Predicted FWD Deflections
for SR 15C--M.P. 0.065........... 225


6.50 Comparison of Measured NDT Deflection Basins on SR 26C--
M.P. 10.166.................................................. 239

6.51 Comparison of Measured NDT Deflection Basins on US 301--
M.P. 21.585.................................................. 240

6.52 Comparison of Measured NDT Deflection Basins on US 441--
M.P. 1.237................................................... 241

6.53 Comparison of Measured NDT Deflection Basins on SR 12--
M.P. 1.485 ..................... ............ ........ ....... 242

6.54 Comparison of Measured NDT Deflection Basins on SR 26B--
M.P. 11.205.................................................. 243

6.55 Comparison of Measured NDT Deflection Basins on SR 15A--
M.P. 6.549................................................... 244

6.56 Comparison of Measured NDT Deflection Basins on SR 715--
M.P. 4.722................................................... 245

6.57 Comparison of Measured NDT Deflection Basins on SR 26A--
M.P. 11.912...................... ......... .................... 246

6.58 Comparison of Measured NDT Deflection Basins on SR 24--
M.P. 11.112....................................................... 247


xviii








6.59 Comparison of Measured NDT Deflection Basins on I-10A--
M.P. 14.062.................................................. 248

6.60 Comparison of Measured NDT Deflection Basins on I-10B--
M.P. 2.703................................................... 249

6.61 Comparison of Measured NDT Deflection Basins on I-1OC--
M.P. 32.071................................................. 250

6.62 Comparison of Measured NDT Deflection Basins on SR 15B--
M.P. 4.811.................................................... 251

6.63 Comparison of Measured NDT Deflection Basins on SR 15C--
M.P. 0.055....... ......... ............................... 252

6.64 Relationship Between Asphalt Concrete Modulus, E and
Mean Pavement Temperature.................................... 256

6.65 Comparison of Dynaflect and FWD Tuned Layer Moduli........... 261

6.66 Relationship Between Predicted and Measured Dynaflect
Modified Sensor 1 Deflections.............................. 267

6.67 Relationship Between Predicted and Measured Dynaflect
Modified Sensor 4 Deflections.............................. 268

6.68 Relationship Between Predicted and Measured Dynaflect
Modified Sensor 7 Deflections............................... 269

6.69 Relationship Between Predicted and Measured Dynaflect
Modified Sensor 10 Deflections .............................. 270

6.70 Relationship Between E12 (Using Equation 6.8) and D D .... 274


6.71

6.72

6.73

6.74

6.75

7.1

7.2

7.3

7.4

7.5


Relationship Between E12 (Using Equation 6.9) and D1 D ....

Relationship Between E3 and D4 D ..........................

Relationship Between E4 and D o..............................

Simplified Flow Chart of DELMAPS1 Program ...................

Relationship Between E4 and FWD D6 and D7....................

Variation of qc and FR with Depth on SR 12...................

Variation of ED and KD with Depth on SR 12...................

Variation of qc and ED with Depth on SR 26A..................

Variation of qc and ED with Depth on SR 26C..................

Variation of qc and ED with Depth on US 301...................


275

276

277

280

287

290

291

293

294

295


xix








7.6 Variation of qc and ED with Depth on US 441.................. 296

7.7 Variation of qc and ED with Depth on SR 12................... 297

7.8 Correlation of ED with qc.................................. 300














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy


EVALUATION OF LAYER MODULI IN FLEXIBLE PAVEMENT SYSTEMS
USING NONDESTRUCTIVE AND PENETRATION TESTING METHODS

By

Kwasi Badu-Tweneboah

December 1987


Chairman: Byron E. Ruth
Major Department: Civil Engineering


A research study was conducted to develop procedures for the eval-

uation of layer moduli in flexible pavement systems using in situ non-

destructive (NDT) and penetration tests. The Bitumen Structure Analysis

in Roads (BISAR) elastic layer computer program was used to simulate

Dynaflect and Falling Weight Deflectometer (FWD) load-deflection

response for typical flexible pavements in the state of Florida. A

field testing program consisting of Dynaflect, FWD, cone penetration,

Marchetti Dilatometer, and plate bearing tests was conducted on fifteen

pavement sections in the state of Florida. Cores of the asphalt con-

crete pavement were collected for laboratory low-temperature rheology

tests. This provided a reliable and effective method of predicting the

asphalt concrete modulus.

A modified Dynaflect geophone configuration and simplified layer

moduli prediction equations which allow a layer-by-layer analysis of

Dynaflect deflection measurements were developed. Multiple linear








regression equations with relatively good prediction accuracy were

obtained from analyses of FWD deflection data. Different layer moduli

values were obtained from the Dynaflect and FWD deflection basins for

the various test sections.

The penetration tests provided means for identifying the soils and

also assessing the variability in stratigraphy of the test sites. Good

correlations between cone resistance, qc, and dilatometer modulus, ED,

for sandy soils and soils above the water table were obtained. Pavement

layer moduli determined from NDT data were regressed to qc and ED for

the various layers in the pavement. The correlations were better with

qc than with ED, and also for the base and subbase layers than the
variable subgrade layer. The penetration tests can be used to supple-

ment NDT evaluation of pavements especially in locating zones of weak-

ness in the pavement or underlying subgrade soils.

The effects of moisture, temperature, and the properties of the

asphalt binder on the performance and response characteristics of

flexible pavements were demonstrated using short-term load-induced

stress analyses on five of the test pavements.


xxii














CHAPTER 1
INTRODUCTION


1.1 Background

In recent years, the use of layered elastic theory to evaluate and

design highway and airfield pavements has become increasingly popular

vis-a-vis existing empirical methods. The elastic layer approach, also

called mechanistic analysis, has obvious advantages over empirical

methods which are based on the correlation between the maximum deflec-

tion under a load and pavement performance. It allows a rational eval-

uation of the mechanical properties of the materials in the pavement

structure.

An essential part of the mechanistic process is determining real-

istic elastic modulus values for the various layers in the pavement

structure. Current methods to determine the modulus of pavement

materials include various laboratory testing procedures, destructive

field tests, and in situ nondestructive tests (NDT). The problems

associated with the simulation of in situ conditions such as moisture

content, density, loading history and rate of loading of the pavement in

the laboratory are well known and recognized. Destructive field tests,

such as the California bearing ratio (CBR) and plate tests are expen-

sive, time-consuming, and generally involve trenching the pavement,

which has to be subsequently repaired.

Nondestructive testing generally involves applying some type of

dynamic load or shock waves to the surface of the pavement and measuring





2

the response of the pavement. Among such methods are various seismic

techniques and surface dynamic loading tests. The basic concept behind

seismic or wave propagation techniques is the use of vibratory loads and

the resulting identification and measurement of the waves that propagate

through the media. These methods have not gained wide acceptance,

partly because of the relative sophistication required in field opera-

tion and in the interpretation of test data.

Surface loading tests generally involve the use of measured surface

deflections to backcalculate the moduli of the pavement layers. Among

the numerous types of devices used are the Dynaflect, Road Rater, and

Falling Weight Deflectometer (FWD). Such techniques have gained wide-

spread popularity partly because they are simple, time-efficient, and

relatively inexpensive, and partly because of their ability to model

real traffic load intensities and durations. However, there are no

direct theoretical solutions available at present to evaluate the

various layer moduli of the pavement from the measured surface deflec-

tions which generally represent the overall combined stiffness of the

layers. Instead, computerized iterative solutions, graphical solutions,

and nomographs are currently used to backcalculate pavement layer

moduli. All these techniques basically consist of using linear-elastic

programs in which calculated versus measured deflections are matched by

adjustment of pavement layer moduli E-values.

Those methods which are based on iterative procedures may need a

large amount of computer time to arrive at the correct moduli for the

pavement materials. In some cases, the required computer may not be

accessible (e.g., for direct field evaluation) or the expertise required

may not be available. Also, due to the inherent problems associated








with iteration methods, unique solutions cannot be guaranteed and dif-

ferent sets of elastic moduli can produce results that are within the

specified (deflection or layer moduli) tolerance. In addition, elastic

layer programs generally assume an average (composite) modulus for the

subgrade layer without regard to the variation of the underlying soil

properties with depth. For sites with highly variable subgrade stiff-

nesses, it becomes very difficult to analytically match measured deflec-

tion basins using a composite modulus for the subgrade layer. There-

fore, there is a need to find a more viable way to determine the E-

values of pavement materials for a rational mechanistic analysis.

Recent advances in in situ testing in geotechnical engineering have

led to improvements in the determination of important soil parameters

such as strength and deformation moduli. Unfortunately, the application

of the improved techniques to evaluate or design pavements has been very

limited. The Marchetti Dilatometer test (DMT) offers significant pro-

mise for providing a reliable and economical method for obtaining in

situ moduli of pavement layers, especially of the subgrade. There is

also the potential of determining in situ moduli from the cone penetra-

tion test (CPT) since several correlations between different deformation

moduli and cone resistance have been reported in the geotechnical liter-

ature. The CPT and DMT provide detail information on site stratifica-

tion, identification, and classification of soil types which makes them

attractive tests for the evaluation and design of pavements.


1.2 Study Objectives

The primary objective of this study is to develop procedures for

the evaluation of material properties in layered pavement systems using








NDT deflection measurements. This includes the development of layer

moduli prediction equations from NOT deflections.

The secondary objective is to evaluate the feasibility of deter-

mining the modulus of pavement layers and underlying subgrade soils

using in situ penetration tests and to evaluate the possible effects of

stratigraphy, water table and underlying subgrade soil properties on

surface deflections obtained from NDT.


1.3 Scope of Study

This investigation is primarily concerned with predicting pavement

layer moduli from nondestructive and penetration tests. It is hoped

that this will lead to improvements in the determination of layer moduli

for mechanistic evaluation and design of flexible pavement systems. The

initial part of the study consisted of developing layer moduli predic-

tion equations from computer-simulated Dynaflect and FWD deflection

data. A modified Dynaflect load-sensor configuration was utilized in

the theoretical analysis.

Field tests were conducted on fifteen pavement sections in the

state of Florida. Tests conducted consisted of Dynaflect, FWD, elec-

tronic CPT, DMT, and plate bearing tests. Also, cores of asphalt con-

crete pavement were collected for laboratory low-temperature rheology

tests. These were used to establish viscosity-temperature relationships

of the recovered asphalts which were then used to predict the moduli of

the asphalt concrete layers.

The field measured NDT data were analyzed to establish layer moduli

values for the test pavement sections. The layer moduli derived from

the Dynaflect and FWD nondestructive tests were compared with each other








and correlated to the results of the penetration tests. Simplified

layer moduli prediction equations were developed for the modified

Dynaflect testing system.

Five of the test pavements were selected for short-term load

induced stress analysis using actual wheel loadings and low temperature

conditions. The effects of age-hardened asphalt, soil type, moisture

content, weak base course and subgrade characteristics on layer stiff-

nesses were evaluated to assess the stress-strain response of the

different pavements.














CHAPTER 2
LITERATURE REVIEW

2.1 Introduction

A mechanistic pavement design procedure consists of analyzing the

pavement on the basis of the predicted structural response (stresses,

strains, and deflections) of the system to moving vehicle loads. Pave-

ment-layer thicknesses (surface, base, and subbase) are selected such

that the predicted structural response would be acceptable for some

desired number of load repetitions and under existing environmental

conditions. This approach is consistent with the conditions established

by Yoder and Witczak that

for any pavement design procedure to be completely
rational in nature total consideration must be
given to three elements. These elements are
(1) the theory used to predict failure or distress
parameter, (2) the evaluation of the pertinent
material properties necessary for the theory
selected, and (3) the determination of the rela-
tionship between the magnitude of the parameter in
question to the failure or performance level
desired.
(133, p. 24-25)

In the last several years, a concentrated effort has been made to

develop a more rational analysis and design procedures for pavements.

For flexible or asphalt concrete pavements, layered (7,19,20) and finite

element (33) theories have been used with some success to analyze pave-

ment response. The use of either theory requires that the materials

that make up the pavement be suitably characterized. Layered and finite

element theories use Young's modulus and Poisson's ratio to characterize








the stress-strain behavior of pavement materials. While some success

has been made in developing design theories, their limitations must also

be understood. Most pavement material responses differ from the assump-

tions of the theory used, and the "true" values of stress, strain or

deflection may differ from the predicted levels. However, a great deal

of engineering reliance is being placed upon the use of multilayered

linear elastic theory (133) in which the elastic modulus is an important

input parameter.

The thesis presented here is aimed at determining realistic modulus

values for the structural characterization of flexible pavement systems

using layered elastic theory. This chapter reviews previous work on

layer-system solutions, the methods of determining the elastic modulus

of pavement-layer materials, and some important factors influencing the

modulus of elasticity.


2.2 Elastic-Layer Theory

2.2.1 General

The type of theory used in the analysis of a pavement-layered

system is generally distinguished by reference to three properties of

material behavior response (133). They are the relationship between

stress and strain (linear or nonlinear), the time dependency of strain

under constant stress level (viscous or nonviscous), and the degree to

which the material can rebound or recover strain after stress removal

(plastic or elastic). These concepts have been clearly elucidated by

Yoder and Witczak (133). Considerable effort has been expended to

analyze pavement response using the above concepts. For example, the

finite element method (33), elastic-layer analysis based on Burmister's








theory (18,19,20) and the visco-elastic layer analysis (7) are all based

on these three properties of material behavior. As previously noted,

the type of theory most widely used at the present time is the

multilayered linear elastic theory. The development of multilayered

elastic solutions is presented below.

2.2.2 One-Layer System

The mathematical solution of the elastic problem for a concentrated

load on a boundary of a semi-infinite body was given by Boussinesq in

1885 (13). His solution was based on the assumption that the material

is elastic, homogeneous, and isotropic. Boussinesq's equation (133;

p. 28) indicates that the vertical stress is dependent on the depth and

radial distance and is independent of the properties of the transmitting

medium. There are several limitations of this solution when applied to

pavements. For example, the type of surface loading usually encountered

in flexible pavements is not a point load but a load which is distri-

buted over an elliptical area (133).

Further work with the Boussinesq equation expanded the solutions

for a uniformly distributed circular load by integration. Newmark (85)

developed influence charts for determination of stresses in elastic soil

masses. The charts are widely used in foundation work. Love (60) used

the principle of superposition to extend Boussinesq's solution to solve

for a distributed load on a circular area. Foster and Ahlvin (36)

presented charts for computing vertical stress, horizontal stress, and

vertical elastic strains due to circular loaded plates, for a Poisson's

ratio of 0.5. This work was subsequently refined by Ahlvin and Ulery

(4) to allow for an extensive solution of the complete pattern of








stress, strain, and deflection at any point in the homogeneous mass for

any value of Poisson's ratio.

Although most asphalt pavement structures cannot be regarded as

being homogeneous, the use of these solutions are generally applicable

for subgrade stress, strain and deflection studies when the modular

ratio of the pavement and subgrade is close to unity. This condition is

probably most exemplified by conventional flexible granular base/subbase

pavement structures having a thin asphalt concrete surface course (133).

Normally, in deflection studies for this type of pavement, it is assumed

that the pavement portion (above the subgrade) does not contribute any

partial deflection to the total surface deflection.

2.2.3 Two-Layer System

Since Boussinesq's solution was limited to a one-layer system, a

need for a generalized multiple-layered system was recognized.

Moreover, typical flexible pavements are composed of layers such that

the moduli of elasticity decrease with depth (133). The effect is to

reduce stresses and deflections in the subgrade from those obtained for

the ideal homogeneous case.

Burmister (18,19,20) established much of the ground work for the

solution of elastic layers on a semi-infinite elastic layer. Assuming a

continuous interface, he first developed solutions for two layers, and

he conceptually established the solution for three-layer systems. The

basic assumption made was full continuity between the layers, which

implies that there is no slippage between the layers. Thus, Burmister

assumed that the strain in the bottom of one layer is equal to the

strain at the top of the next layer, but the stress levels in the two








layers will differ as a function of the modulus of elasticity of each

layer.

2.2.4 Three-Layer System

Although Burmister's work provided analytical expressions for

stresses and displacements in two- and three-layer elastic systems, Fox

(38) and Acum and Fox (2) produced the first extensive tabular summary

of normal and radial stresses in three-layer systems at the intersection

of the plate axis with the layer interfaces. Jones (52) and Peattie

(89) subsequently expanded these solutions to a much wider range of

solution parameters. Tables and charts for the various solutions can be

found in Yoder and Witzcak (133) and Poulos and Davis (92). It should

be noted that the figures and tables for stresses and displacements have

been developed, respectively, for Poisson's ratios of 0.5 and 0.35, for

all layers, and on the assumption of perfect friction at all interfaces.

Hank and Scrivner (42) presented solutions for full continuity and

zero continuity between layers. Their solutions indicate that the

stresses in the top layer for the frictionless case (zero continuity)

are larger than the stresses presented for the case of full continu-

ity. In an actual pavement, the layers are very likely to develop full

continuity; hence, full continuity between layers should probably be

assumed.

Schiffman (100) extended Burmister's solution to include shear

stress at the surface for a three-layer system. Mehta and Veletsos (73)

developed a more general elastic solution to a system with any number of

loads. They extended the solution presented by Burmister to include

tangential forces as well as normal forces.








2.2.5 Multilayered or N-Layered Systems

A general analysis of a multilayered system under general condi-

tions of surface loading or displacement, or both was developed indepen-
\
dently by Schiffman (99) and Verstraeten (125). Schiffman (99) con-

sidered the general solutions for stresses and displacements due to non-

uniform surface loads, tangential surface loads, and slightly inclined

loads, but no numerical evaluations were presented. Verstraeten (125)

presented a limited analysis of the four-layered elastic problem. He

first derived expressions for the stresses and displacements for the

general case and performed numerical calculations for the particular

case of four-layered systems with continuous interfaces. The analysis

by Verstraeten included not only a uniform normal surface stress, but

also two types of surface shear stresses: (1) uniform one-directional

shear stress and (2) a uniform centripetal shear stress.

Recently, the Chevron Research Corporation (74) and the Shell Oil

Company (32) have developed computer programs for multilayered solutions

of the complete state of stress and strain at any point in a pavement

structure. Notable programs of interest are the BISTRO and BISAR pro-

grams by Shell (32), and the various forms of CHEVRON program by the

Chevron Research Corporation. These computer solutions are essentially

an extension of Burmister's work that permit the analysis of a structure

consisting of any number of layers supported by a semi-infinite sub-

grade, and under various loading conditions. In reality, it is only the

CHEVRON N-LAYER program (74) which is suitable for any number of layers.

All the others are restricted to a maximum number of layers. BISAR

(32), for example, can handle nine pavement sub-layers of known thick-

nesses plus the semi-infinite subgrade or bottom layer.








Several investigators have verified the validity of Burmister's

theory with the actual mechanical response of flexible pavements.

Foster and Fergus (37) have compared the results of extensive test

measurements on a clayey silt subgrade to theoretical stresses and

deflections based on Burmister's theory and reported satisfactory

agreement. The discrepancy between actual and theoretical stresses and

displacements can be mainly attributed to the assumption of a homoge-

neous and isotropic material, the rate-dependent behavior of some

materials such as asphalt, and a circular loaded area representing the

wheel load. Nielsen (86) has made a detailed study in this area. His

review of the magnitude and distribution of stresses within a layered

system revealed regions where vertical and shearing stresses were criti-

cal. His studies concluded that the layered-elastic theory is in every

respect consistent and that it is possible to establish fundamental

patterns of pavement performance based upon this theory. This suggests

that the elasticity theory could be used more extensively.

The moderators of the Fifth International Conference on the Struc-

tural Design of Asphalt Pavements (76) concluded that the use of linear

elastic theory for determining stresses, strains, and deflections is

reasonable as long as the time-dependent and nonlinear response of the

paving materials are recognized. They noted that the papers presented

at the conference confirmed that multilayer elastic models generally

yield good results for asphalt concrete pavements.

Barksdale and Hicks (10) compared the multilayered elastic approach

with the finite element method and recommended the use of the former for

pavement analysis since only two variables are needed (modulus and

Poisson's ratio). Pichumani (91) used the BISAR computer program for








the numerical evaluation of stresses, strains, and displacements in a

linear elastic system. He demonstrated that predicted vertical, radial,

and shear stress distribution were noticeably affected by slight changes

in the assumed material moduli. Pichumani's work demonstrated the need

for proper and extensive material characterization.


2.3 Material Characterization Methods

2.3.1 General

The use of multilayered elastic theory has provided the engineer

with a rational and powerful basis for the structural design of pave-

ments, for pavement evaluation, and for overlay design. In this theory,

the complete stress, strain, and displacement pattern for a material

needs only two material properties for characterization, namely the

elastic modulus (E), and the Poisson's ratio (u). Generally, the effect

of Poisson's ratio is not as significant as the effect of the modulus

(133, pp. 280-282; 88; 59, p. 160). Thus, E is an important input

parameter for pavement analysis using the layer theory.

Many tests have been devised for measuring the elastic modulus of

paving materials. Some of the tests are arbitrary in the sense that

their usefulness lies in the correlation of their results with field

performance. To obtain reproducible results, the procedures must be

followed at all times. The various possible methods for determining the

elastic modulus of pavement materials include laboratory tests, destruc-

tive field tests, and in situ nondestructive tests.

Laboratory methods consist of conducting laboratory testing on

either laboratory-compacted specimens or undisturbed samples taken from

the pavement. Yoder and Witzcak (133) describe various laboratory








testing methods with the diametral resilient modulus test (8), indirect

tension test (9), and the triaxial resilient modulus test (1) being the

most popular. The latter is useful for unbound materials such as base

course and subgrade soils, while the other two are for bound materials

like asphalt concrete and stabilized materials. Monismith et al. (78)

studied the various factors that affect laboratory determination of the

moduli of pavement systems. They concluded that

. it is extremely difficult to obtain the same
conditions that exist in the road materials (mois-
ture content, density, etc.) and the same loadings
(including loading history) in the laboratory as
will be encountered in situ. . Thus the best
method of analysis would appear to be to determine
an equivalent modulus which when substituted into
expressions derived from the theory of elasticity,
will give a reasonable estimate of the probable
deformation.

(78, p. 112)

Destructive field tests include, among others, several different

plate load tests (8) and the California Bearing Ratio (CBR) test (8).

These tests require trench construction and subsequent repair of the

pavement, and like the laboratory test methods, usually call for an

elaborate and costly testing program. The delays associated with such

programs are prohibitive especially for routine pavement analysis

studies.

The third method involves the extraction of pavement-layer proper-

ties from in situ nondestructive testing (NDT). NDT methods have gained

wide popularity in the last few decades because of their ability to

collect data at many locations on a highway or airfield in a short

time. Therefore, a great deal of research effort has been concentrated

on this area. A review of the various types of NOT equipment available

and the associated interpretation tools is presented below.








2.3.2 State-of-the-Art of Nondestructive Testing

2.3.2.1 General. Nondestructive testing (NDT) consists of making

nondestructive measurements on a pavement's surface and inferring from

the responses the in situ characteristics related to the structural ade-

quacy or loading behavior (79). Among such methods are various seismic

techniques (associated with time measurements) and surface loading tests

(associated with deflection measurements). The latter is more popular

because surface deflection is the most easily measured structural

response of a pavement. The idea of using deflection measurements to

evaluate the structural integrity of pavements dates back to 1938 when

the California Division of Highways used electrical gages implanted in

roadways to measure displacements induced by truck loads (134).

There are currently several NDT procedures being used for pavement

investigations. Each of the procedures can be placed into one of the

following four general classes:

1. Static force-deflection,

2. Steady-state vibratoryy) dynamic force-deflection,

3. Dynamic impulse force-deflection, and

4. Wave propagation.

As their names imply, the first three categories are associated with

deflection measurements due to application of force or load. The fourth

category--wave propagation--measures the length and velocity of force-

induced waves traveling through the pavement system. A detailed

description and evaluation of many of these NDT devices and procedures

has been presented by Bush (21), Moore et al. (79), and Smith and Lytton

(109). In the following pages, a brief description of the principles

involved and equipment available for each class will be presented.








2.3.2.2 Static Deflection Procedures. Measurement systems that

determine the pavement response to slowly applied loads are generally

termed static deflection systems. In these systems, the loading.methods

may consist of slowly driving to or from a measurement point with a

loading vehicle, or by reacting against a stationary loading frame. The

maximum resilient or recoverable deflection at the surface of the pave-

ment is measured.

The most commonly used equipment in this class is the various forms

of the Benkelman beam devices. Other equipment that had been used

include the plate bearing test (8), Dehlen Curvature Meter, Traveling

Deflectometer, Lacroix-LCPC Deflectograph, and the French Curviameter.

The last three devices are essentially automation of the Benkelman beam

principle. The French Curviameter, for example, measures both the

deflection and curvature of the pavement, under an 18-kips rear axle

load, with tire pressure maintained at 100 psi (24). Most of the

automated devices have been used widely in Europe and other parts of the

world, except for the Traveling Deflectometer which was built for the

California Department of Transportation and has been in use by that

agency for several years (109).

The major advantages of the static deflection procedures are the

simplicity of the equipment and the large amount of data that has been

accumulated with these devices. The most serious problem with this type

of measurement technique is the difficulty in obtaining an immovable

reference point for making the deflection measurements. This makes the

absolute accuracy of this type of procedure questionable. In addition,

since most of the devices generally measure a single (maximum)








deflection only, it is impossible or difficult to determine the shape

and size of the deflection basin.

In spite of their shortcomings, the large amount of data developed

using static deflection techniques makes such procedures an important

part of structural pavement evaluation. For this reason, several inves-

tigators have attempted deflection comparison and correlations from the

static devices with those measured by the dynamic devices. The

following is a list of concepts developed from the deflection response

of a pavement using static NDT (79):

1. For adequately designed pavements, the deflections during the same

season of the year remain approximately constant for the life of the

pavement.

2. There is a tolerable level of deflection that is a function of

traffic type, volume and the structural capacity of the pavement as

determined by the pavement's structural section. This tolerable

level of deflection can be established through the use of fatigue

characteristics of the pavement structure.

3. Overlaying of a pavement will reduce its deflection. The thickness

required to reduce the deflection to a tolerable level can be esta-

blished.

4. The deflection history of a well-designed pavement undergoes three

phases in its behavior (71). A typical curve representing these

phases is shown in Figure 2.1.

a. In the initial phase, immediately after construction, the pave-

ment structure consolidates and the deflection shows a slight

decrease.
































TRAFFIC---


Figure 2.1


Well-Designed Pavement Deflection History Curve (71)








b. During the functional or service phase, the pavement carries the

anticipated traffic without undue deformation and the deflection

remains fairly constant or shows a slight decrease.

c. The failure phase occurs as a result of both traffic and envi-

ronmental factors. In this phase the deflection increases

rapidly and there is a rapid deterioration resulting in failure

of the pavement structure.

5. The deflection history of a pavement system varies throughout the

year due to the effects of frost, temperature, and moisture. A

typical annual deflection history of a pavement subjected to frost

action, as shown in Figure 2.2, can be divided into the following

four periods (103):

a. The period of deep frost when the pavement is the strongest.

b. The period during which the frost is beginning to disappear from

the pavement structure. During this period, the deflection

rises rapidly.

c. The period during which the water from the melting frost leaves

the pavement structure and the deflection begins to drop.

d. The period during which the deflection levels off with a general

downward trend as the pavement structure continues to slowly dry

out.

6. For a given flexible pavement structure it is generally known that

the magnitude of the deflection increases with an increase in the

temperature of the bituminous surfacing material. This is due to a

decrease in the stiffness of the bituminous surfacing. The effect

of temperature varies with the stiffness of the underlying layers.

As the stiffness of the underlying layers increases, the effect of















Cn 32

Period of : Period of Slow
Deep Frost ) Strength Recovery
C)


0


,.J
LL




--- I I 1 I I I I
DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV
MONTH


Figure 2.2 Typical Annual Deflection History for a Flexible Pavement (103)








an increase in temperature on deflection of the total structure

decreases.

2.3.2.3 Steady-State Dynamic Force-Deflection. Essentially, all

steady-state dynamic deflection measurement systems induce a steady

state sinusoidal vibration in the pavement with a dynamic force genera-

tor. The dynamic force is superimposed on the weight of the force gen-

erator, resulting in a variation of force with time as shown in Figure

2.3. The magnitude of the peak-to-peak dynamic force is less than twice

the static force to insure continuous contact of the vibrator with the

pavement (79). This means there must always be some amount of dead

weight or static force applied. As the dynamic peak-to-peak loading is

increased, this preload must also be increased (109).

Deflections are usually measured with inertial motion sensors. For

pure sinusoidal motions at any fixed frequency, the output of such sen-

sors is directly proportional to deflection. Thus, to measure deflec-

tion it is only necessary to determine the calibration factor (output

per unit of deflection) for the measurement frequency. In general,

either an accelerometer or a velocity sensor may be used to measure

deflections. The latter type is commonly called a geophone and is the

type normally employed in dynamic deflection measurements.

There are several different types of steady-state dynamic deflec-

tion equipment that are currently being used for nondestructive struc-

tural evaluation of pavements. Only two of them have been used exten-

sively and are available commercially--the Dynaflect and the Road

Rater. The others have been designed and constructed by agencies

involved in pavement research, namely the U.S. Army Waterways Experiment

Station (WES), the Federal Highway Administration (FHWA), the Illinois


































N)

o
0
U.








TIME -+



Figure 2.3 Typical Output of a Dynamic Force Generator (79)








Department of Transportation, and the Koninklijke/Shell Laboratorium,

Amsterdam, Holland. Detailed descriptions of the various vibratory

equipment can be found in References 21, 79, 109. The Dynaflect was

used in this study and a description of the device will be given later

in this report.

When one considers the difficulty in obtaining a reference point

for deflection measurements, the real advantage of a steady-state dyna-

mic deflection measurement system becomes apparent. An inertial refer-

ence can be employed to measure dynamic deflections. That is, the mag-

nitude of the deflection change (the peak-to-peak value) can be compared

directly to the magnitude of the dynamic force change (peak-to-peak

value). For a given value of dynamic force, the lower the deflection,

the stiffer the pavement is (79).

Although the dynamic response of a pavement system approaches its

static (or elastic) response at low frequencies, exactly what value of

driving frequency is low enough to determine the elastic characteristics

of a pavement is somewhat questionable. As the driving frequency be-

comes low it becomes difficult to generate dynamic forces and the output

of inertial motion sensors becomes very small. These factors combine to

make it difficult to obtain accurate low frequency dynamic deflection

measurements (79). Other technical limitations of vibratory equipment

include the need for a heavy static preload for the heavier devices and

the nonuniform loading configurations (109).

The deflection measurements that result represent the stiffness of

the entire pavement section. Although some significant accomplishments

have been made in separating the effects of major parts of the pavement

structure, the separation of the effects of all of the various








components of the structure with deflection basin measurements has not

yet been accomplished (63). The study presented herein is aimed at

developing an approach that would allow a layer-by-layer analysis of the

Dynaflect vibratory deflection basin.

2.3.2.4 Dynamic Impact Load Response. Essentially, all impact

load testing methods deliver some type of transient force impulse to the

pavement surface and measure its transient response. The equipment uses

a weight that is lifted to a given height on a guide system and is then

dropped. Figure 2.4 illustrates this schematically. By varying the

mass of the falling weight or the drop height or both, the impulse force

can be varied.

The width or duration of the loading pulse (loading time) is

controlled by the buffer characteristics, Figure 2.4, and it closely

approximates a half-sine wave (Figure 2.5). The duration of the force

is nominally 25-30 msec, Figure 2.5, which approximates the load

duration of a vehicle traveling 40 to 50 mph (123). The peak magnitude

of the force can be determined approximately by equating the initial

potential energy of the system to the stored strain energy of the

springs (buffer system) when the mass is momentarily brought to rest

(11,105). Thus


F = (2Mghk)1/2 Eqn. 2.1


where

M = mass of the falling weight,

h = drop height,

k = spring constant, and

g = acceleration due to gravity.























M



*


0oo o00 o oo
OD~ I- I^ 0 0


II,'Il
11111.


Figure 2.4 Schematic Diagram of Impulse Load-Response Equipment (105)


*1\jj\































TIME


Figure 2.5


Characteristic Shape of Load Impulse (105)








The response of the pavement to the impulse loading is normally

measured with a set of geophones placed at varying radial distances from

the center of the plate. These deflection measurements can, in princi-

ple, be used to characterize the structural properties of the pavement

layers.

Three manufacturers currently market impulse testing equipment in

the United States. These are the Dynatest, KUAB and Phoenix falling-

weight deflectometers. The Dynatest falling-weight deflectometer (FWD)

is the most widely used impulse loading device in North America and

Europe (109). Its newest version--the Dynatest 8000 FWD testing

system--was used in this study and will be described later in this

report. Other experimental impulse testing devices have been evaluated

by Washington State University and Cornell Aeronautical Laboratory (79).

The impulse testing machines have several advantages over other NDT

instruments. The magnitude of the force can be quickly and easily

changed to evaluate the stress sensitivity of the pavement materials

being tested. Perhaps the greatest advantage is the ability to simulate

vehicular loading conditions. Several investigators (11,35,46) have

compared pavement response in terms of stresses, strains, and deflec-

tions from an FWD-imposed load to the response of a moving wheel load.

All these comparisons have shown that the response to an FWD test is

quite close to the response of a moving wheel load with the same load

magnitude. Figure 2.6 shows such an example of pavement response com-

parison.

However, the deflection basin produced by an impulse loading device

is symmetrical about the load and Lytton et al. (63) have argued that

the deflection basin under a moving wheel is not symmetrical about the










750-




E 500-

00

OSL
O L.
M 250-
U.0
LL O


0 -

0


600

/

x< 0
400
/c
2 400


I- LLA



na
n --------I---


250 500
DEFLECTION (gm)
FROM MOVING WHEEL LOAD

a) Surface Deflections


200


400


VERTICAL STRAIN (x 10-6)
FROM MOVING WHEEL LOAD
b) Vertical Subgrade Strains


Figure 2.6


Comparison of Pavement Response from FWD and
Moving-Wheel Loads (35)


750


600








load in any pavement structure. Thus, the impulse load of a FWD is not

an exact representation of a moving wheel load. Moreover, the response

from the impact testing technique is similar to other types of dynamic

deflection testing in the sense that it represents characterization of

the entire structure. The technique does not provide information that

readily separates the effects of its various layers. Finally, the

parameters that cause plastic deformation in the structure are not

readily determinable from impact testing (79).

2.3.2.5 Wave Propagation Technique. Wave propagation provides

methods for the determination of the elastic properties of individual

pavement layers and subgrades. Unlike the three previous methods of

NDT, these methods are not concerned with the deflection response of the

pavement. Rather, they are concerned with the measurement of the velo-

city and length of the surface waves propagating away from the load

surface (127).

There are two basic techniques for propagating waves through pave-

ment structures: (1) steady-state vibration tests and (2) seismic

(impulse) tests. Generally, three types of waves are transmitted when a

pavement surface is subjected to vibration. These are

1. Compression or primary (P) waves,

2. Shear (S) waves, and

3. Rayleigh (R) waves.

The P and S waves are body waves while the R wave is a surface wave.

Raleigh waves are the dominant waves found in the dissipation of energy

input from a vibrator on a semi-infinite half-space (75). Also, because

P and S waves attenuate rapidly with radial distance from the vibration








source, R waves are the typical waves measured in the wave propagation

technique.

Wave propagation theory is based upon the fact that in a homoge-

neous isotropic half space subjected to an external disturbance, waves

travel at velocities that may be expressed as (59, p. 153; 79; 127)


Vs= (G) 2 -E /2 Eqn. 2.2a
p 2(1 + u)p

V = E(1 u) /2 Eqn. 2.2b
P p(1 + v)(1 2p)


VR = aVs Eqn. 2.2c


where

Vs = shear wave velocity,

Vp = compression wave velocity,

VR = Rayleigh wave velocity,
G = shear modulus,

E = Young's modulus,

P = Poisson's ratio,

p = mass density, and

a is a function of Poisson's ratio and varies from 0.875

for P = 0 to 0.995 for P = 0.5.

In general, R and S waves are not particularly dependent on Poisson's

ratio, but the value of compression wave velocity is strongly dependent

on Poisson's ratio (59,79).

Field test procedures for the wave propagation measurements involve

two general types of tests. Raleigh wave velocities are determined from








steady-state vibratory pavement responses and compression wave veloci-

ties are measured from impulse (seismic) tests. The former usually

follows procedures developed by researchers at the Royal Dutch Shell

Laboratory (43,53,93), the British Road Research Laboratory (79), and

the Waterways Experiment Station (79). They utilized a mechanical

vibrator for low-frequency vibrations (5-100 Hz) and a small electro-

magnetic vibrator for the high-frequency work (43,53). The general

procedure currently in use is to place the vibrator on the pavement

surface and set the equipment in operation at a constant frequency.

Details of the procedure can be found in Reference 79.

Seismic tests may be conducted to determine the velocity of com-

pression waves, which can be used with the shear wave (or Rayleigh wave)

velocity to compute Poisson's ratio. One such method is the hammer-

impulse technique in which the pavement is struck with a light hammer

and the resultant ground motion is observed at one or more points with

horizontal motion geophones. However, this method is only good for

soils where the velocity of the materials increases with depth. It is

not applicable to layered pavement systems where strong, high velocity

layers occur at the top and grow progressively weaker with depth. How-

ever, Moore et al. (79) report that this procedure has been used to

obtain compression wave velocities of pavement layers during construc-

tion.

A method of using surface waves to structurally characterize pave-

ments is currently in the research stage at the University of Texas at

Austin (80,81,82). The technique, called Spectral Analysis of Surface

Waves (SASW), determines shear wave velocity at soil or pavement sites.

The elastic shear and Young's moduli profiles are then calculated under








the assumption of homogeneous, isotropic, and elastic medium. The SASW

method is essentially a seismic procedure. An iterative inversion

process is used to interpret the shear wave velocity profiles (81).

Laboratory procedures are available for the determination of the

elastic properties of pavement and soil specimens using wave propagation

techniques. However, the laboratory procedures require that samples of

the pavement material be obtained for testing. Therefore, it may not be

considered as a nondestructive technique. Two laboratory procedures

that parallel the field vibratory procedures and which may be applicable

to pavement design are the resonant column and the pulse methods (79).

The most difficult aspect of the wave propagation techniques is

that of interpretation and analysis of test results. The wave propaga-

tion method of testing relies on the ability to interpret the data

obtained in the field so that the characteristics of the structure

beneath the surface may be determined (79). Because of the inherent

complexities involved, such techniques have not gained wide acceptance.

2.3.3 NDT Data-Interpretation Methods

2.3.3.1 General. Considerable emphasis has been placed upon

determining the elastic properties of pavement layers using NDT data.

Most of this work has been concentrated on the first three types of NDT

procedures, those associated with deflection measurements. The fourth

category, the wave propagation method, has not gained wide acceptance

because of the relative sophistication required in the field operation

and in the interpretation of test data. However, the interpretation of

measured surface deflection basins has gained widespread popularity with

the advent of NDT procedures. There is a general agreement among








pavement engineers that the measured surface deflection basins from NDT

can provide valuable information for structural evaluation of a pave-

ment.

Methods for the interpretation of NDT data can be placed into two

categories: empirical or mechanistic methods. Empirical procedures

directly relate NDT response parameters to the structural capacity of a

pavement. Most of these methods (48,56) do not involve direct or

indirect theoretical analysis. Instead, they are based upon the cor-

relation between the maximum deflection under a load (static NDT or

wheel load) and pavement performance.

In an attempt to improve the empirical procedures, other research-

ers have relied on the use of deflection basin parameters (90) or semi-

empirical correlations (79) for pavement evaluation. Figure 2.7 shows

an example of basin parameters and the criteria used to evaluate a pave-

ment. Table 2.1 lists some of the deflection basin parameters that have

been developed for NDT data evaluation of pavements (120). Most of the

basin parameters do not relate directly to the elastic parameters of the

pavement section.

Semi-empirical procedures usually involve correlation of modulus

values to other known pavement parameters. For example, Heukelom and

Foster (43) have developed a correlation between modulus E (in psi) from

wave propagation techniques and the California Bearing Ratio (CBR)

value. This correlation, though later refined by WES (79), is of the

form


E = 1500 (CBR)


Eqn. 2.3











ligid Force Wheels


SCI


DMD = Dynaflect Maximum Deflection (Numerical Value of Sensor No. 1)
SCI = Surface Curvature Index (Numerical Difference of Sensor No. 1 and
No. 2)
BCI = Base Curvature Index (Numerical Difference of Sensor No. 4 and
No. 5).
a) Basin Parameters


b) Criteria


Figure 2.7 Empirical Interpretation of Dynaflect Deflection Basin (90)


DMD SCI BCI CONDITION OF PAVEMENT STRUCTURE
GT 0.11 Pavement and Subgrade Weak
GT 0.48
GT 1.25 LT 0.11 Subgrade Strong, Pavement Weak
GT 0.11 Subgrade Weak, Pavement Marginal
LT 0.48
LT 0.11 DMD High, Structure Ok
GT 0.11 Structure Marginal, DMD Ok
GT 0.48
LT 1.25 LT 0.11 Pavement Weak, DMD Ok
GT 0.11 Subgrade Weak, DMD Ok
LT 0.11 Pavement and Subgrade Strong0.48
LT 0.11 Pavement and Subgrade Strong







Table 2.1 Summary of Deflection Basin Parameters


Parameter Definitiona NDT Deviceb


Dynaflect maximum deflection (DMD)

Surface curvature index (SCI)
Base curvature index (BCI)

Spreadability (SP)





Basin slope (SLOP)
Sensor 5 deflection (W )
5
Radius of curvature (R)
Deflection ratio (Qr)
Area, in inches (A)

Shape factors (F F )
1 2


Tangent slope (TS)


DMD = d
1
SCI = d d
1 2
BCI = d d
4 5
SP = ( Idi /5d )x 100
i=1 to 5
SP = ( Idi /4d ) x 100
i=1 to 4
SLOP = d d
1 5
W = d
5 5
R = r2/{2.dm[(dm/dr) 111]}

Qr = r/do
A = 6[1 + 2(d /d ) + 2(d /d ) +
2 1 3 1
F = (d d )/d
1 1 3 2
F = (d d )/d
2 2 4 3
TS = (d dx)/x


Dynaflect
Dynaflect, Road Rater model 400
Dynaflect

Dynaflect


Road Rater model 2008


Dynaflect
Dynaflect

Benkelman beam
FWD, Benkelman beam
(d /d )] Road Rater model 2008
4 1
Road Rater model 2008


a d = deflection; subscripts 1,2,3,4,5 = sensor locations; o = center of load; r = radial distance;
m = maximum deflection; x = distance of tangent point from the point of maximum deflection.
b The NDT device for which the deflection parameter was originally defined.

Source: Uddin et al. (120)








and is the most widely used correlation (133). Other correlations (79)

have been made between E and plate bearing subgrade modulus, K. It

should be recognized that the conditions of dynamic testing generally

yield moduli in the linear elastic range. Conventional tests such as

the CBR and plate bearing tests produce deformations that are not

completely recoverable and, therefore, are partly in the plastic range.

Thus, one would expect some variation in the correlation between E

modulus and pavement parameters, such as K and CBR.

Mechanistic analysis of NDT data is usually performed by one of the

following:

1. Direct relationship between deflection parameters and the

elastic moduli of the pavement layers.

2. Inverse application of a theoretical model by fitting a

measured deflection basin to a deflection basin using an

iterative procedure.

3. A combination of 1 and 2.

The above mechanistic methods employ deflection data from either vibra-

tory or impulse loading equipment. While these devices are dynamic in

nature, most of the mechanistic solutions are based on elasto-static

(19,32,74) and visco-elasto-static (7) models. Recently, an elasto-

dynamic model (54) has been used to interpret NDT data (66,67,105).

However, the use of dynamic analyses for interpretation of NDT data can

be considered to be in the research stage. Another significant obser-

vation is that almost all the mechanistic solutions available employ

layered theory or simplified versions of it. The only exception to this

is the use of a finite element model presented by Hoffman and Thompson

(45). A review of the various solutions is presented below.








2.3.3.2 Direct Solutions. Presently, there are no direct analy-

tical solutions that can uniquely determine the elastic moduli for a

multilayered pavement system using surface deflection measurements

alone. The so-called direct solutions have been developed for only two-

layer systems which usually involve graphical solutions, nomographs, or

in most cases only provide estimates for the subgrade modulus.

Scrivner et al. (102) presented an analytical technique for using

pavement deflections to determine the elastic moduli of the pavement and

subgrade assuming the structure is composed of two elastic layers.

Based upon the same assumption, Swift (113) presented a simple graphical

technique for determining the same two elastic moduli. Vaswani (124)

used Dynaflect basin parameters to develop charts for the structural

evaluation of the subgrade and its overlying layers for flexible pave-

ments in Virginia (see Table 2.1). The methods by Majidzadeh (64) and

Sharpe et al. (107), among others, employ similar basin parameters from

the Dynaflect or Road Rater to estimate the subgrade modulus and develop

charts to assess the overlying layers.

Jimenez (51) described a method for evaluating pavement-layer

modular ratios from Dynaflect deflections. The pavements were

considered to be three-layer systems, and the deflection data were used

to estimate ratios of the elastic moduli of the adjacent layers. The

ratios reduce the system from three values of elastic modulus to two

values of modular ratio. The major limitation of this method is that

the elastic modulus of the asphalt concrete layer must be known.

Wiseman (129) and Wiseman et al. (131) have, respectively, applied

the Hertz Theory of Plates and the Hogg Model to evaluate two-layered

flexible pavements using surface deflection basins. The Hertz theory is








an application of the analytical solution of a vertically loaded elastic

plate floating on a heavy fluid. The solution to this problem was

presented by Hertz in 1884 and was first applied to concrete pavement

analysis by Westergaard in 1926 (79). The Hogg model consists of an

infinite plate on an elastic subgrade. The subgrade can be either of

infinite extent or underlain by a perfectly rigid rough horizontal

bottom at a finite depth. Analysis of this model was reported by A.H.A.

Hogg in 1938 and 1944 (131). In both methods, the flexural rigidity of

the composite pavement which will best fit a measured deflection basin

is calculated.

Lytton et al. (62) and Alam and Little (5) have developed another

method based on elastic-layer theory for prediction of layer moduli from

surface deflections. This method makes use of the explicit expression

for deflection originally postulated by Vlasov and Leont'ev (126). The

major drawback of this technique is the need to develop several con-

stants, five in all, for which no analytical or test method exists as

yet. In applying this method, the authors (5,62) resorted to the use of

regression analyses and computer iterative solutions.

Cogill (28) presented a method which provides an estimate of the

stiffness of the pavement-layer materials. The method essentially is a

graphical presentation in which the deflections measured over a parti-

cular range of load spacing can be related to the stiffness of the pave-

ment material at a certain depth. The relationship is an approximate

one and is expressed with the aid of Boussinesq's formula.

All the methods presented above use deflection measurements

obtained from vibratory loading equipments--Dynaflect and Road Rater.

The only approach for the direct estimation of layer moduli from impulse








load-deflection response (such as an FWD deflection basin) is the

concept of equivalent layer thickness (121,122) in which the layered

pavement system is transformed into an equivalent Boussinesq (13)

system. This concept, originally proposed by Odemark (87), is based on

the assumption that the stresses, strains, and deflections below a given

layer interface depend on the stiffness and thickness of the layers

above that interface. Although this approach obtains an explicit

solution for the subgrade modulus (121), it relies on estimates of the

asphalt concrete layer modulus and also employs certain modular ratios

to obtain the moduli of the various layers above the subgrade (25). The

method of equivalent thicknesses (MET) has also been incorporated into

some iterative computer programs which are discussed in the next

section.

Several investigators have obtained equations to directly determine

the subgrade modulus from one or more sensor deflections. For example,

Figure 2.8 shows the relationship between the subgrade modulus and the

Dynaflect fifth sensor deflection as summarized by Way et al. (128).

Keyser and Ruth (55) developed a prediction equation from five test road

sections in the Province of Quebec, Canada, by using the BISAR elastic-

layer program to match measured Dynaflect deflection basins. The

equation is of the form


-1.0006
E = 5.3966(D ) Eqn. 2.4
4 5


where E4 is subgrade modulus in psi, and Ds is Dynaflect fifth sensor

deflection in inches. This equation had an R2 of 0.997 (55), and is

similar to that of Ullidtz (see Figure 2.8). Godwin and Miley (41) have













100,000 I I I 1 1 1 1 1



SMajidazdeh, Ref. 17
S-\ Esg =(6115 x D5)-0984

c0 -ADOT Hyperbolic -
SEsg =(0.000013 + 0.00016 x D )1
ADOT Power Equation
10,000 -UlIdtz, Ref. 20---- -= 8800 x D0.58
Sq xa2 x(1.0 Nu2) 5200xD10
g r x D5 x 0.001
S-q = Load Pressure = 159.16 psi
< -a = Load Pressure = -2. Inches
C Nu = Poisson's Ratio = VO-
0 r = Fifth Sensor Distance from Load = 49.0 Inches \

D -McCullough, Ref. 18
Esg =4000xD51.2

1,000 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I
0.01 0.1 1.0 10.0
DYNAFLECT DEFLECTION, D5, mils


Dynaflect Fifth Sensor Deflection-Subgrade Modulus Relationship (128)


Figure 2.8








developed correlations between the base, subbase and subgrade moduli and

the second, third, and fourth Dynaflect sensor deflections, respec-

tively. However, the modulus values used in the correlation were the

surface moduli from plate bearing tests which suffers from the problem

of incorporating plastic and nonrecoverable deformations.

An approach using regression equations to estimate layer moduli has

been attempted by other investigators (83,120,132). This approach

usually involves analysis of computer-simulated NDT data using a theo-

retical model (usually layered elastic theory). The various investi-

gators reported success in the case of the subgrade modulus. To obtain

good correlations for the other layers (surface, base, subbase), certain

assumptions had to be made, such as the base course modulus being

greater than the modulus of the subgrade (83), or they had to resort to

computer-iteration programs (83,120).

2.3.3.3 Back-Calculation Methods. The method of iteratively

changing the layer moduli in a theoretical model to match the theoreti-

cal deflection basin to a measured basin is currently called back-

calculation in the literature. Initial developments of this procedure

utilized a trial-and-error approach (49,72) using the following steps:

1. Pavement-layer thicknesses, initial estimates of the pavement-layer

moduli, and the loading and deflection measurement configuration are

input into the model (usually a multilayer elastic computer

program).

2. The computed deflections at the geophone positions are compared with

those actually measured in the field.

3. The layer moduli used in the computer program are then adjusted to

improve the fit between the predicted and actual deflection basins.








4. This process is repeated until the two deflection basins are vir-

tually the same. The process may have to be repeated several times

before a reasonable fit is obtained.

Because of the time consuming nature (49) of the trial-and-error

method, many researchers have developed computer programs to perform the

iteration. Table 2.2 lists some of the self-iterative computer pro-

grams. The major differences among the various programs are the differ-

ent models, algorithms and tolerance levels used in the iteration pro-

cess. A few of these will be discussed here.

Anani (6) developed expressions for surface deflections in terms of

the modulus values of a four-layer pavement. However, he could not

obtain direct solutions to determine the moduli. Therefore he used an

iterative procedure to obtain the moduli from Road Rater deflection

basins. The computer programs reported by Tenison (114) and Mamlouk

(66) followed the successive approximation method of Anani (6). In the

overlay design program called OAF, Majidzadeh and Ilves (65) employed a

deflection matching technique for determining the in situ layer stiff-

nesses. While using field data to substantiate the applicability of the

procedure, they experienced difficulties and commented,

. the computed asphalt layer stiffness shows a
large variation, and in a few cases the asphalt is
stiffer than steel; nevertheless the values are
reasonable in a great majority of the cases . .

(65, p. 85)

The BISDEF computer program (23) is an improvement over the CHEVDEF

(22) to handle multiple loads and variable interface conditions. The

number of layers with unknown modulus values cannot exceed the number of

measured deflections. However, a maximum of four deflections are











Summary of Computer Programs for
of Flexible Pavement Moduli from


Evaluation
NDT Devices


Number Theoretical Applicable
Name Reference of Model Used NDT
Layers For Analysis Device


* Anani (6)


4
Layer


BISAR-Elastic


Road Rater 400


ISSEM4 Sharma and
Stubstad (106)

CHEVDEF Bush (22)


OAF Majidzadeh
and Ilves (65)


ILLI-PAVE


Hoffman and
Thompson (45)


Tenison (114)


FPEDD1 Uddin et al.
(118,120)

BISDEF Bush and
Alexander (23)


ELMOD Ullidtz and
Stubstad (123)

IMD Husain and
George (47)


DYNAMIC Mamlouk (66)


* not known or available


4 ELSYM5-Elastic
Layer


4(a)
Layer


CHEVRON-Elastic


3 or ELSYM5 Elastic
4 Layer

3 Finite Element


3 CHEVRON's N
Layer (Elastic)

3 or ELSYMS Elastic
4 Layer


4(a)


2, 3
or 4


BISAR Elastic
Layer
Vibrator, or FWD

MET-Boussinesq


3 or CHEVRON Elastic
4 Layer
for FWD

4 Elasto-dynamic


Road Rater 2008


Dynaflect,
Road Rater, or FWD

Road Rater 2008,
or FWD

Road Rater 2000


Dynaflect, FWD


Dynaflect,
Rater, WES


FWD


Road


Dynaflect, but
can be modified


Road Rater 400


(a) not to exceed number of deflections


Table 2.2








targeted during the iteration process, which is also limited to a

maximum of three loops. When applied to field measured deflections on

an airfield pavement in Florida (23), BISDEF predicted unreasonably high

values of the AC modulus for all the different NDT devices used in the

study. Also, Bush and Alexander (23) conceded that the program provides

the best results if the number of unknown layer moduli is three.

The ISSEM4 computer program (106) incorporates the principles of

the method of equivalent thicknesses (MET) into the ELSYM5 multilayered

elastic program to determine the in situ stress-dependent elastic

moduli. The parameters for the nonlinear stress-dependent relationships

(see Section 2.4.3) are established from FWD tests performed at differ-

ent load levels. The iteration process is seeded with a set of E-values

(106). The ELMOD program (123) also utilizes the MET principle and the

iteration procedure. Both programs provide relatively good solutions if

the asphalt concrete modulus is known.

ILLI-PAVE (45), the only program which utilizes a finite element

model, is specifically developed to handle Road Rater deflection data.

However, Road Rater deflection basins must be converted to equivalent

FWD deflection basins prior to being used in the program (45). Also,

the nonlinear stress-dependent material models incorporated into the

finite element method utilized relationships established from previous

laboratory material characterization procedures. It is also surprising

that the authors resulted to nomographs for specific applications of the

back-calculation model (45).

Most of the iteration programs listed above require a set of ini-

tial moduli--seed moduli--and therefore are user-dependent. Therefore

computational times and cost can be prohibitive. Unique solutions








cannot be guaranteed since an infinite number of layer modulus combina-

tions can provide essentially the same deflection basins. Moreover,

most of the iterative programs yield questionable base course and

subbase moduli. In some programs, adjustment of the field data are

required in order to improve the solution (6,47).

2.3.4 Other In Situ Methods

Cogill (27) presented a method involving the use of an ultrasonic

technique. The elastic modulus of the top layer can be accurately

determined; however, the modulus values for the other layers are

questionable. Kleyn et al. (58) and Khedr et al. (57) have developed

different forms of a portable cone penetrometer to evaluate the stiff-

ness of pavement layers and subgrade soils. However, these devices do

not provide direct modulus values but rather are based on correlations

with CBR and plate bearing parameters. Similarly, the Clegg Impact

tester, which was developed in Australia in the mid-1970s, relies on CBR

correlation for pavement evaluation applications (40). The problems of

the CBR and plate bearing tests have been discussed previously.

Maree et al. (70) presented an approach to determine pavement-layer

moduli based on a device developed to measure deflections at different

depths within a pavement structure. The device, called the multi-depth

deflectometer (MDD), is installed at various depths of an existing pave-

ment structure to measure the deflections from a heavy-vehicle simulator

(HVS) test. Maree et al. (70) suggested that effective moduli for use

in elastic-layer theory can be determined from correction factors esta-

blished from field measurements using the MDD at different times of the

year and under different conditions.








Molenaar and Beuving (77) described a methodology in which the FWD

and a dynamic cone penetrometer (DCP) were used to assess stress depen-

dent unbound pavement layers and the presence of soft interlayers.

However, the procedure does not provide any direct modulus correlation

but a graphical presentation of FWD surface modulus and DCP profiles.

Geotechnical engineers have, for several years, used various forms

of field tests to assess the engineering properties of soils for con-

struction purposes. Recent advances in exploration and interpretation

methods have led to improvements in the determination of important soil

parameters such as strength and deformation moduli. For example, the

following in situ techniques (26,30,50) are suitable for the determina-

tion of soil stiffness:

1. Menard Pressuremeter (PMT) and Self-Boring Pressuremeter (SBP)

tests.

2. Cone Penetration Test (CPT), including the mechanical,

electronic, and piezo-cone penetrometers.

3. Marchetti Dilatometer Test (DMT).

4. Plate Loading Tests (PLT), including Screw Plate Tests (SPL).

Some of these tests have the added advantage of providing detailed

information on site stratification, identification, and classification

of soil types. This is of great appeal since the variation of the

subgrade soil properties with depth can be accounted for rather than

assuming an average modulus value as conventionally used in multilayer

analysis.

Unfortunately, the application of the improved techniques to eval-

uate or design pavements has been very limited. As evident from the

previous sections, the material characterization part of a rational








pavement design program, though very important, is often treated with

considerable simplification and empiricism. Geotechnical engineers

often feel that structural engineers have little or no interest in those

parts of their work below the ground level. These feelings are cer-

tainly justified in the case of pavements (76). It is therefore not

surprising that most of the in situ geotechnical applications to pave-

ments rely on correlations with empirical pavement parameters such as

CBR to validate their proposed methods (40,57,58,77). The other known

applications of geotechnical in situ testing methods to evaluate the

stiffness of pavement structures are discussed below.

Briaud and Shields (14,15) have described the development and

procedure of a special pressuremeter test for pavement evaluation and

design. The pavement pressuremeter consists of a probe, tubing and a

control unit, and works on the same principle as the Menard pressure-

meter (30). They illustrated how the modulus values obtained from the

test can be used directly in multilayer mechanistic analysis. In order

to use empirical design charts, however, Briaud and Shields (15) also

developed a correlation between the pressuremeter modulus and the

bearing strength obtained from a Macleod plate test for two airport

pavements in Canada.

Borden et al. (12) have presented an experimental program in which

the dilatometer test (68) was used to determine pavement subgrade sup-

port characteristics. A major part of the testing program consisted of

conducting DMT and CBR tests in soil samples prepared in cylindrical

molds and also in a special rectangular chamber. A limited field test

was conducted on a compacted embankment constructed with one of the

soils used in the laboratory investigation. Although they report good








correlations between the dilatometer modulus and CBR value, the use of

the CBR test makes the study empirical, to say the least.



2.4 Factors Affecting Modulus of Pavement-Subgrade Materials

2.4.1 Introduction

The response characteristics of flexible pavement materials is a

complex function of many variables, which is far-fetched from the ideal

materials assumed in classical mechanics. In general, the behavior of

these materials is dependent upon many environmental and load vari-

ables. Specifically, the asphalt concrete response is primarily a

function of temperature and rate of loading. Due to its viscoelastic

nature (7,51), asphalt concrete materials become stiffer as the load

rate increases and the temperature decreases. The granular base course

and subgrade characteristics are dependent upon moisture content, dry

density, stress level, stress states, stress path, soil fabric, stress

history, and soil moisture tension (59,78,133).

Several researchers have presented relationships of resilient

modulus as a function of one or more variables, while keeping others

fixed or completely ignored. Most of these relationships were developed

from laboratory studies. A complete review of the relative effects of

the various factors on pavement-soil response, or the relationship

between modulus and other parameters measured in the laboratory can be

found in References 31, 44, 59, 78, 94, and 133. It is not the intent

of this discussion to review the various studies on this topic. The

discussion below will concentrate on two variables that are believed to

be very important in flexible pavement technology, especially when con-

sidering NDT and pavement evaluation. These factors are the temperature








of the asphalt concrete layer, and the stress dependency of base/subbase

and subgrade materials. This does not mean that the effects of the

other variables can be ignored or underestimated. For example, moisture

content has a considerable effect on the modulus of flexible-pavement

materials, especially for fine-grained subgrade soils (78).

2.4.2 Temperature

Temperature has a very important influence on the modulus of

asphalt-bound materials. The modulus of asphalt concrete decreases with

an increase in pavement temperature (51,78,111,133). The temperature of

the pavement also fluctuates with diurnal and seasonal temperature vari-

ations. In order to determine the variation of modulus with temperature

for flexible-pavement materials, the mean pavement temperature should be

established. Southgate and Deen (111) developed a method for estimating

the temperature at any depth in a flexible pavement up to 12 inches.

Figure 2.9 shows the graphical solution for the determination of the

mean pavement temperature with depth from the known temperatures. This

relationship has been recommended and in some cases incorporated into

many flexible pavement design procedures (47,65,107). Though, the

curves have been found to be reasonably accurate for other locations

(111), it would be more desirable to make a direct determination of this

temperature.

2.4.3 Stress Dependency

Laboratory studies presented in the literature (31,44,78,94) sug-

gest that the moduli of granular base materials and subgrade soils are

stress-dependent. The stiffness of the granular base has been found to

be a function of the bulk stress or first stress invariant. A stress-

stiffening model in which the modulus increases with the first stress











160
LL
0

a 120




I-
W 80


" 40

I-
0
0


40 80 120 160 200 240
PAVEMENT TEMPERATURE + 5
DAY MEAN AIR TEMPERATURE


a) Pavements More Than 2 in. Thick


o"- (b) Depth in
Pavement, -0
i- 0 Inches 1
S120- 2
-

t 80

c:
W 40- Depth in
0-
M 2 Pavement, Inches

0o l-- l I I0I I I
0 40 80 120 160 200 240
PAVEMENT TEMPERATURE + 5
DAY MEAN AIR TEMPERATURE

b) Pavements Equal to or Less Than 2 in. Thick


Figure 2.9 Temperature Prediction Graphs (111)








invariant is generally used to characterize granular base materials.

The relationship is of the form


K
E = K 9 2 Eqn. 2.5
1


where

E = granular base/subbase modulus,

6 = first stress invariant or bulk stress, and

K K = material constants
1 2

The subgrade stiffness, on the otherhand, has been found to be a

function of the deviator stress (stress difference). For fine-grained

soils, resilient modulus decreases with increase in stress difference

(78). The mathematical representation of the subgrade stiffness is of

the form



E = AaB Eqn. 2.6



where

E = subgrade modulus

a = stress difference, and

A, B = material constants for the subgrade

The constant B(slope) is less than zero for the stress-softening model,

while for the stress-stiffening model, the slope is greater than zero.

The stress-dependency approach of characterizing pavement materials

is of great importance for high traffic loadings. Situations in which

high traffic loadings occur are larger aircraft loadings in the case of

airfield pavements, and when heavy wheel loads and/or single tire








configurations (which result in higher stresses) are applied to flexible

highway pavements. For this reason, some of the NDT back-calculation

procedures have accounted for the stress dependency effect by incorpo-

rating Equations 2.5 and 2.6 into their algorithms (45,65,106). How-

ever, the problem of determining the material constants, A, B, K and
1
K still remains, especially when NDT deflection basins are used to
2
characterize the pavement. The most common approach is to use labora-

tory resilient moduli and regression analysis to determine these para-

meters (45,65,72). Thus, the material parameters will depend upon

sample preparation procedures, disturbance, prestress-strain conditions,

etc.

Other researchers (93,106,121) have suggested determining the mate-

rial constants from FWD tests conducted at three or more load levels.

However, it is not clear how viable this procedure is since the resul-

tant load-deflection response of a pavement is a combined effect of the

behavior of the individual layers. The relative contribution of each

layer is not clearly known. It is even more complex since the asphalt

concrete layer is dependent on the temperature and age-hardening

characteristics of the asphalt cement. Moreover, contrary to previous

belief, Thompson (116) has found that the material parameters are not

independent-of each other, especially for granular bases and subbases.

Uddin et al. (118,119,120) have applied the concepts of equivalent

linear analysis developed in soil dynamics and geotechnical earthquake

engineering to evaluate the nonlinear moduli. They concluded that the

in situ moduli derived from an FWD deflection basin (at 9000-1b. peak

force) are the effective nonlinear moduli and need no further correc-

tion. However, an equivalent linear analysis has to be performed to








correct the in situ moduli calculated for nonlinear granular materials

and subgrade soils from a Dynaflect deflection basin. These conclusions

were based on stress analysis comparisons of a single-axle 18-kip design

load, FWD (9000-lb. peak force) and Dynaflect loadings simulated in the

ELSYM5 elastic-layer program. An algorithm to perform this equivalent

linear correction has been incorporated into the FPPEDD1 self-iterative

computer program (120). However, results reported by Nazarian et al.

(81) tend to contradict the conclusions of Uddin et al. (120). Their

study involving FWD tests at 5- and 15-kip loads indicated that non-

linear behavior occurs at higher FWD loads, and is more predominant in

the base course layers than the subgrade.

These results and those from other research work indicate there is

disagreement as to what type of approach should be used when the effects

of nonlinearity and stress dependency are to be considered. There are

at least three schools of thought in this regard. The first group

believes that the use of an equivalent effective modulus in an elastic-

layer theory would provide reasonable response predictions. This

approach would eliminate the expense, time and complexity associated

with more rigorous methods such as finite element models (61). The

research works of Maree et al. (70), Roque (96), and Roque and Ruth (97)

on full-scale pavements tend to support this theory.

The second school of thought recommends that the nonlinear stress

dependent models (Equations 2.5 and 2.6) can be incorporated into an

elastic-layer program to predict reasonable response parameters. How-

ever, the asphalt concrete layer is treated as linear elastic. This

theory is supported by Monismith et al. (78), among others, and has been

used in iterative computer programs like OAF, ISSEM4, and IMD.








The third school of thought contends that layered elastic theory,

when used with certain combinations of pavement moduli, predicts tensile

stresses in granular base layers, even if gravity stresses are also

considered (16,45,112). Instead of using a layered approach, this group

prefers a finite element model in which the nonlinear responses of the

granular and subgrade materials are accurately characterized. Again,

the asphalt concrete layer is considered to be linear elastic. The

ILLI-PAVE finite element back-calculation program (45) is a classic

application of this theory.

In the finite element approach discussed above, researchers have

used, with limited success, various failure criteria and in some cases

arbitrary procedures to overcome the problem of tensile stresses

(16,112). For example, Brown and Pappin (16) used a finite element

program called SENOL with a K-0 contour model and found it to be capable

of determining surface deflections and asphalt tensile stresses but

unable to determine the stress conditions within the granular layer.

The asphalt layer was characterized as elastic with an equivalent linear

modulus. They therefore concluded that the simplest approach for design

calculations involves the use of a linear elastic-layered system pro-

vided adequate equivalent stiffnesses are used in the analysis. This

conclusion is shared by other investigators (10,61,96,97) and is the

philosophy behind the work presented in this dissertation.














CHAPTER 3
EQUIPMENT AND FACILITIES


Most of the methods available for determining the elastic moduli of

flexible pavements have been outlined in Chapter 2. These include the

use of nondestructive tests (NDT), laboratory methods and other in situ

test methods. The limitations of these methods and the need for a more

simple approach have also been highlighted. An approach which mechanis-

tically evaluates pavements with the use of NOT and/or in situ penetra-

tion tests is therefore developed in this study. This approach is

developed to simplify the mechanistic analysis and design process, and

to evaluate the effects of important variables involved in the determi-

nation of pavement layer moduli. The study consisted of the development

of moduli prediction equations from NDT data, field testing and analyses

of NDT and in situ penetration tests, and finally, comparison and eval-

uation of test data. Therefore, this chapter describes the equipment

and facilities used in the study.

The test equipment were either available at the Civil Engineering

Department of the University of Florida or at the Bureau of Materials

and Research, Florida Department of Transportation (FDOT). They are

essentially standard testing devices. This research was concerned with

their optimum use and application for a rational mechanistic design and

evaluation of asphalt concrete pavements.








3.1 Description of Dynaflect Test System

3.1.1 Description of Equipment

The Dynaflect, as previously mentioned, belongs to the dynamic

steady-state force-deflection group of NDT equipment. It is an electro-

mechanical device for measuring the dynamic deflection of a pavement

caused by oscillatory loading. The testing system (84,104,108) consists

of a dynamic force generator mounted on a small two-wheel trailer, a

control unit, a sensor assembly and a sensor (geophone) calibration

unit. The Dynaflect can be towed by and operated from any conventional

passenger carrying vehicle having a rigid trailer hitch and a 12-volt

battery system.

The oscillatory load is produced by a pair of counter weights

rotating in opposing directions and phased in such a manner that each

contributes to the vertical force of the other, but opposes the horizon-

tal force of the other, thereby canceling horizontal forces. The weight

of the unbalanced masses varies sinusoidally from 2500 Ibs. to 1500

Ibs., thereby producing a cyclic force of 1000 Ibs. peak-to-peak at a

frequency of 8 Hz (see Figure 3.1). The cyclic force is alternately

added to and subtracted from the 2000-1b. static weight of the trailer.

The 1000-1b. cyclic force is transmitted to the pavement through a pair

of polyurethane-coated steel wheels that are 4-in. wide and 16-in. in

outside diameter. These rigid wheels are spaced 20-in. center to center

(see Figure 3.2).

The pavement response to the dynamically applied load is measured

by five geophones located as shown in Figure 3.2. The first geophone

measures the deflection at a point midway between the rigid wheels while

the remaining four sensors measure the deflection occurring directly













1---1/f -A


f = Driving Frequency = 8 Hz



T
Peak-to-Peak
-- Dynamic Force
I= 1000 Ib


TIME


Typical Dynamic Force Output Signal of Dynaflect (108)


Figure 3.1














Housing and Tow Bar


Loading Wheels \ No.4 No.5
Geophones


(a) The Dynaflect System in Operating Position



Loading
Wheels Geophones


10 No.1 No. 2 No. 3 No. 4 No. 5
^ ~-A----^---*----^ --^
10" -12" 4-]-12" -H4-12" -I4-12" .J
4"
--T
h-n^

(b) Configuration of Load Wheels and Geophones.

Figure 3.2 Configuration of Dynaflect Load Wheels and
Geophones in Operating Position (108)








beneath their respective locations along the centerline of the trail-

er. However, the geophone configuration can be easily changed to a

desired pattern. Each geophone is equipped with a suitable base to

enable it to make proper contact with irregular surfaces (108).

Data are displayed by a digital readout for each sensor on the

control panel which is umbilically attached to the trailer and can be

placed on the seat of the towing vehicle beside the operator/driver.

All operations subsequent to calibration are performed from the control

panel by the operator/driver without leaving the towing vehicle.

3.1.2 Calibration

The Dynaflect unit is calibrated by placing the sensors on a cam-

actuated platform inside the calibrator furnished with each unit (108).

This platform provides a fixed 0.005-in. vertical motion at 8 cycles per

second. The corresponding meter reading of 5 mils is set in the control

unit by adjustment of an individual sensitivity control for each geo-

phone. Subsequent deflection measurements are thus comparisons against

this standard deflection.

3.1.3 Testing Procedure

The normal sequence of operation is to move the device to the test

point and hydraulically lower the loading wheels and geophones to the

pavement surface (84,108). A test is performed and the data of the 5

geophone deflection readings are recorded. At this point the operator

has the option of raising both the sensors and the loading wheels or

only the sensors. With the rigid wheels down and the pneumatic tires

lifted, the trailer may be moved short distances from one measuring

point to another at speeds up to 6 mph on the loading wheels (108).








When the rigid wheels are out of contact with the ground, the

trailer is supported on pneumatic tires for travel at normal vehicle

speeds. The sensors and loading wheels are raised and lowered by remote

control to enable such moves to be made quickly without need for the

operator/driver to leave the towing vehicle (84,104,108).

3.1.4 Limitations

The general limitations of dynamic steady-state NDT devices have

previously been described. In addition to those, the technical limi-

tations of the Dynaflect device include (109) peak-to-peak loading is

limited to 1000 lbs., load cannot be varied, frequency of loading cannot

be changed, the deflection directly under the load cannot be measured,

and it is difficult to determine the contact area.



3.2 Description of the Falling Weight
Deflectometer Testing System

The Falling Weight Deflectometer (FWD) is a deflection testing

device operating on the impulse loading principle. As described pre-

viously, there are various forms of the FWD, with the most widely used

one in the United States being the Dynatest Model 8000 FWD system. This

is the type used by the FDOT and in the study reported herein. There-

fore, this section describes the operating characteristics of the Dyna-

test FWD test system. Like the Dynaflect, the FWD is also trailer

mounted and can be easily towed by most conventional passenger cars or

vans.

The Dynatest 8000 FWD test system consists essentially of three

main components (34,110), namely

1. a Dynatest 8002 FWD,








2. a Dynatest 8600 System Processor, and

3. a Hewlett-Packard HP-85 Table Top Computer.

3.2.1 The 8002 FWD

The Dynatest 8002 FWD consists of a large mass that is constrained

to fall vertically under gravity onto a spring-loaded plate, 11.8 in. in

diameter, resting on the pavement surface (see Figure 2.4). A load

range of about 1500 to 24000 Ibs. can be achieved by adjusting the num-

ber of weights or height of drop or both. The impulse or impact load is

measured by using a strain-gauge-type load transducer (load cell). The

impact load closely approximates a half-sine wave (see Figure 2.5), with

a duration of 25-30 msec which closely approximates the effect of moving

dual-wheels with loads up to 24000 Ibs. (110).

Seven seismic deflection transducers or geophones in movable brack-

ets along a 2.25 m raise/lower bar are used to measure the response of

the pavement to the dynamically applied load. The geophones, which are

50 mm in diameter and 55 mm high, operate at a frequency range of 2 to

300 Hz (34). One of the geophones is placed at the center of the plate,

with the remainder placed at radial distances from the center of the

plate (see Figure 3.3). In its present form, the FDOT measures deflec-

tions at radial distances of 0, 7.87, 11.8, 19.7, 31.5, 47.2, and 63.0

in. from the plate center. These deflections are respectively called

D D D D D D and D in this study.
1 2 3 4 5 6 7
3.2.2 The 8600 System Processor

The Dynatest 8600 system processor is a microprocessor-based con-

trol and registration unit which is interfaced with the FWD as well as

the HP-85 computer (34,110). The processor is housed in a 19-in. wide












































Figure 3.3 Schematic of FWD Load-Geophone Configuration and
Deflection Basin (34)








case which is compact, light weight, and controls the FWD operation. It

also serves as a power supply unit for the HP-85 computer.

The system processor performs scanning and conditioning of the 8

transducer signals (1 load + 7 deflections). It also monitors the

status of the FWD unit to insure correct measurements.

3.2.3 The HP-85 Computer

The Hewlett-Packard Model 85 computer is used for input of control

and site/tests identification data as well as displaying, printing,

storing (on magnetic tape), editing, sorting, and further processing of

FWD test data (34,110).

3.2.4 Testing Procedure

The automatic test sequence is identified and programmed from the

HP-85 keyboard. This includes the input of site identification, height

and number of drops per test point, pavement temperature, etc. When the

operator enters a "START" command, the FWD loading plate and the bar

carrying the deflection transducers will be lowered to the pavement

surface, the weight will be dropped from the pre-programmed heightss,

and the plate and bar will be raised again. An audible "BEEP" signal

tells the operator that the sequence is complete, and that he/she may

drive onto the next test point. A complete measuring sequence normally

takes about one minute, exclusive of driving time between test points,

for three or four drops of the falling weight (34,110).

The measured set of data (1 load + 7 deflections) will be displayed

on the HP-85 for direct visual inspection, and the data will be stored

on the HP-85 magnetic tape cartridge, together with site identification

information, etc. The display, printed results, and stored results can

be in either metric or English units (34).








3.2.5 Advantages

The primary advantages of the Dynatest FWD, like many other impulse

deflection equipment, are that the created deflection basins closely

match those created by a moving wheel load of similar magnitude (11,45,

110,123), and the ability to apply variable and heavier dynamic loads to

assess stress sensitivity of pavement materials. The Dynatest FWD test

system has the added advantage that the resulting deflection basin is

constructed from seven deflection measurements compared to five and

three deflections in the KUAB and Phoenix Falling Weight Deflectometers,

respectively.



3.3 BISAR Computer Program

The analyses and evaluation of NDT deflection data in this study

involved the use of BISAR, an elastic multilayered computer program.

BISAR is an acronym for Bitumen Structures Analysis in Roads. The

program, developed by Koninklijke/Shell Laboratorium, Amsterdam,

Holland, is a general purpose program for computing stresses, strains

and displacements in elastic multilayered systems subjected to one or

more uniform loads, acting uniformly over circular surface areas (32).

The surface loads can be combinations of a vertical normal stress and

unidirectional tangential stress.

The use of BISAR to compute the state of stress or strain in a

pavement requires the following assumptions (32):

1. Each layer of pavement acts as a horizontally continuous, isotropic,

homogeneous, linearly elastic medium.

2. Each layer has finite thickness except for the lower layer, and all

are infinite in the horizontal direction.








3. The surface loading can be represented by uniformly distributed ver-

tical stresses over a circular area.

4. The interface conditions between layers can vary from perfectly

smooth (zero bond) to perfectly rough (complete bonding) conditions.

5. Inertial forces are negligible.

6. The stress solutions are characterized by two material properties,

Poisson's ratio and Young's modulus for each pavement layer.

BISAR was used over other layered-theory programs because of its

availability, tested--and proven--reliability and accuracy (72,91,96),

and, also, its ability to handle variable layer interface conditions.

For example, McCullough and Taute (72) found that the ELSYM5 program (3)

which is based on the CHEVRON program (74) predicts unrealistic deflec-

tions in the vicinity of the load. They therefore recommended the use

of BISAR in computing fitted deflection basins, especially if the

deflection measurements are made near the loading point. Also, Ruth et

al. (98) reported correspondence with Mr. Gale Ahlborn, who developed

the ELSYM5 program, that the program is unreliable for certain unpre-

dictable combinations of material properties.


3.4 Description of Cone Penetration Test Equipment

The cone penetration test equipment consisted of a truck-mounted

hydraulic penetration system, electronic cone penetrometers (95) and an

automated data acquisition system. Detailed descriptions of the truck

and its features have been presented by Davidson and Bloomquist (30).

The hydraulic system serves two functions (29): leveling the truck

and penetrating the cone. The leveling system consists of four








independently controlled jacks. The front two jacks are connected to a

2 ft. x 7 ft. reaction plate; the back two to separate 15-in. circular

pads. The vehicle is lifted off the ground and leveling assured by

means of a spirit level. The penetrating system consists of a 20-ton

ram assembly located in the truck to achieve maximum thrust from the

reaction mass of the vehicle. Two double-acting hydraulic cylinders

provide a useable vertical stroke of 1.22 m. Prior to testing, the rams

are used to raise the telescoping roof unit. When locked in the raised

position, the unit allows full travel of the rams (29,30).

The cone penetrometers are of the subtraction type configuration,

with tip and friction strain gauges mounted on the central shaft

(29,95). Cone bearing is sensed by compression in the first load cell,

while the sum of cone plus friction is sensed in the rear load cell.

The friction value is then obtained by subtraction, which is done

electronically (29). The cones used also measure pore water pressure

and inclination. A cable, threaded through the 1-meter long push rods,

transmits the field recording signals to the data acquisition system.

The University of Florida currently has three electric cones, with

rated capacities of 5, 10 and 15 metric tons. Each measures tip

resistance, local friction, pore pressure, and inclination. The 5- and

10-ton cones are of standard configuration with 10-cm tip areas and 150-

cm friction sleeves. The larger 15-ton cone has the capability of

testing in much stiffer soil materials. All three cones contain

precision optical inclinometers which output the angular deviation of

the cone from the vertical during penetration (30).








The electronic data acquisition system is capable of printing and

plotting penetration data directly on the job site. It consists of a

microprocessor with 128 k magnetic bubble memory, an operator's console

with keypad, an Okidata microline 82A printer and an HP 7470A graphics

plotter. The computer is programmed with preset limits defined to

protect the probe from overloading. If a limit is exceeded, the

computer automatically stops the test and displays the cause of the

abort (29,30).

The electronic cone penetration testing equipment has several

advantages, such as a rapid procedure, continuous recording, high

accuracy and repeatability, automatic data logging, reduction, and

plotting. The CPT provides detailed information on site stratification,

identification, and classification of soil types. Results have also

been correlated with several basic soil parameters, including different

deformation moduli. For example, Schmertmann's method (101) of

computing settlements in sands requires the in situ variation of Young's

modulus. This is obtained from the CPT cone bearing resistance.


3.5 Marchetti Dilatometer Test Equipment

The Marchetti Dilatometer test (DMT) is a form of penetration test

and is fully described in References 17, 29, 68 and 69. Basically, the

test consists of pushing into the ground a flat steel blade which has a

flush-mounted thin circular steel membrane on one face. At the desired

depth intervals (usually every 20 cms) penetration is stopped, and

measurements are taken of the gas pressure necessary to initiate

deflection and to deflect the center of the membrane 1.1 mm into the








soil. These two readings serve as a basis for predicting several

important geotechnical parameters, using experimentally and semi-

empirically derived correlations (17,50,68). The DMT sounding provides

indications of soil type, preconsolidation stress, lateral stress ratio

at rest (Ko), Young's modulus (E), constrained modulus (M), shear

strength in clays and angle of shearing resistance in sands.

The major components of the dilatometer test equipment are the

dilatometer blade, the gas-electric connecting cable, a gas-pressure

source, and the read-out (control) unit. Figure 3.4 shows a schematic

diagram of this equipment. In addition there is a calibration unit,

adaptors, electric ground cable and a tool kit containing special tools

and replacement parts. Detailed descriptions and functions of the

various components are presented by Bullock (17) and Marchetti and

Crapps (69).

The dilatometer blade, as shown in Figure 3.4, consists of a stain-

less steel blade, 94 mm wide and 14 mm thick, bevelled at the bottom

edge to provide an approximate 16-degree cutting edge. A 60 mm stain-

less steel circular membrane is centered on and flush with one side of

the blade.

The control unit, housed in an aluminum carrying case, contains

various indicators, a pressure gauge and the controls for running the

test. The control unit gauge used in the current study had a range of

0-40 bars. Higher and lower range units are also available. This gauge

provides the gas pressure readings for the dilatometer test.

The dilatometer blade is advanced into the ground using standard

field equipment. The blade can be pushed or driven by one of the

following methods (29):

















Pressure Gauge
Buzzer

High
Pressure
Tubing -


To Pressure
r Source

Regulator Valve


Drill Rods


SFriction Reducer Ring


(/ I --- Diaphragm (60mm diam)



'm-- ,DMT Blade
14mm-







Figure 3.4 Schematic of Marchetti Dilatometer Test Equipment (69)








1. Using a Dutch Cone Penetrometer rig. This method is believed to

yield the highest productivity, up to 250 or more tests per day.

2. Using the hydraulic capability of a drill rig.

3. Using the SPT rig hammer or similar lighter equipment.

4. With barge-mounted equipment or by wireline methods for underwater

testing.


3.6 Plate Bearing Test

The plate bearing test conceptually belongs to the static force-

deflection group of NDT procedures (79). However, it can also be con-

sidered as a destructive field test since the testing requires the

construction and subsequent repair of a trench or test pit. The plate

bearing test consisted of the repetitive-static type of load test out-

lined in ASTM Test Procedure D 1195-64 (8). The main objective in this

test is to measure the deformation characteristics of flexible pavements

under repeated loads applied to the pavement through rigid, circular

plates. Burmister's two-layer theory (18,19,20) is generally used to

interpret plate load testing results (133).

The test equipment used by the Florida Department of Transportation

consists of a 12-inch diameter steel plate, loading system, deflection

gauges and supports (41). A trailer loaded with a huge rubber container

filled with water is used as a reaction. A hydraulic jack assembly is

used to apply and release the load in increments. A detailed descrip-

tion of the repetitive-static plate load test is provided in ASTM test

standards (8, pp. 258-260).














CHAPTER 4
SIMULATION AND ANALYSES OF NDT DEFLECTION DATA


4.1 BISAR Simulation Study

4.1.1 General

The Dynaflect and FWD loading-geophone patterns were simulated in

the BISAR elastic-layer computer program to predict surface deflection

data for four-layer pavement systems. A flexible pavement structure was

modeled as a four-layer system with parameters shown in Figure 4.1.

The selection of layer thicknesses and moduli was based on typical

ranges in parameters representative of Florida's flexible pavement

systems. In general, the limerock base and stabilized subgrade thick-

nesses were fixed at 8 in. and 12 in., respectively. Table 4.1 lists

the range of layer parameters used in the theoretical analysis. The

subgrade was generally characterized as semi-infinite in thickness with

an average or composite modulus of elasticity. However, the effect of

bedrock at shallow depth was also assessed by varying depth to bedrock

in a five-layer system. Poisson's ratio was fixed at 0.35 for all the

pavement layers since it has negligible effect on computed deflections.

In using the layered theory to generate and analyze NDT deflection

data certain assumptions had to be made. The following assumptions were

made with the use of the BISAR program:

1. Pavement materials are homogeneous, isotropic, and linearly

elastic. Therefore, the principle of superposition is valid for

calculating response due to more than one load.





















I 1


E2 2 H12



E3, 3 H3
E4, P4 3 H3



E4,I H4 = .


Four-Layer Flexible Pavement System Model


Figure 4.1















Range of Pavement Layer Properties


Layer Layer Layer Poisson's Layer Modulus
Layer Layer Thickness
Number Type iness Ratio (ksi)
(in.)


1 Asphalt 1.0 10.0 0.35 75 1,200
Concrete


2 Limerock 8.0 0.35 10 170
Base


Stabilized
3 Subgrade 12.0 0.35 6 75
(Subbase)


4 Subgrade Semi-infinite 0.35 0.35 200
(Embankment)


Table 4.1








2. Pavement layers are continuously in contact at the interfaces with

shearing resistance fully mobilized between them, so that the four

layers act together as an elastic medium of composite nature with

full continuity of stresses and displacements.

3. The Dynaflect and FWD dynamic loads are modeled as static circular

loads. Thus, the peak-to-peak dynamic force of the Dynaflect is

modeled as two pseudo-static loads of 500 Ibs. each uniformly

distributed on circular areas. The peak dynamic force of the FWD is

assumed to be equal to a pseudo-static load uniformly distributed on

a circular area representing the FWD loading plate.

4. Thickness and Poisson's ratio of each layer are assumed to be known.

4.1.2 Dynaflect Sensor Spacing

In order to determine the optimum locations of the five Dynaflect

sensors, additional ones were included in the BISAR simulation study.

These sensors were placed at intermediate positions near the loaded

wheel and first two (standard) sensors, with hope of detecting the

primary response of the upper pavement layers (surface and base

course). Figure 4.2 illustrates the loading and modified geophone

array.

The Dynaflect was modeled in the BISAR program using two circular-

loaded areas, with deflection measurement positions as shown in Figure

4.2. Each load is 500 Ibs. in weight, and the contact area used in this

study was 64 in.2, resulting in an equivalent radius of 4.5 in.

4.1.3 FWD Sensor Spacing

The conventional sensor spacing used by the FDOT and four

additional sensor locations were utilized in the analytical study.

Sensors were placed at radial distances of 0, 7.87, 11.8, 16.0, 19.7,






















Spacing


GEOPHONE NO.
Conventional Modified


Figure 4.2 Dynaflect Modified Geophone Positions


@-X








24.0, 31.5, 36.0, 47.2, 63.0, and 72.0 in. from the center of the FWD

plate. The deflection measured by the last sensor (at radial distance

of 72.0 in.) is called D in this study. Sensors at 16, 24, and 36 in.

were only used to better define the deflection basin and were not incor-

porated in the analysis for prediction equations, which is described

later in this chapter. Thus, eight deflection locations were actually

used in the analysis. These are called D1, D2, D3, D4, D5, D6, D7, and

D8 to represent, respectively, radial distances of 0, 7.87, 11.8, 19.7,

31.5, 47.2, 63, and 72 in. from the center of the FWD plate.

The FWD was modeled in the BISAR program as a circular loaded area

with deflection measurement positions as stated previously. The radius

of the loaded area was 5.91 in., and a load of 9 kips was used which

corresponds to one-half of an 18-kip single-axle wheel loading.


4.2 Sensitivity Analysis of Theoretical NDT Deflection Basins

4.2.1 Parametric Study

Pavement surface deflection data generated from BISAR were ini-

tially evaluated to see the effect of rate of change of each layer

modulus and/or thickness on the NOT deflection basins. This was accom-

plished by using the pavement section shown in Figure 4.3 as a typical

Florida pavement under warm temperature conditions. Using the informa-

tion in Figure 4.3, each parameter (modulus and thickness) for a given

layer was doubled or halved while the others were kept unchanged. For

example, the E value of 10 ksi was increased to 20 ksi without changing

E E2, E3 and the layer thicknesses. BISAR was then used to calculate

the NDT deflections. The original E value was also halved to 5 ksi and

the theoretical deflections were computed with BISAR. This procedure was

















,',',',',ASPHALT CONCRETE' ,'
%%\` '\E1 = 150 ksi ^^^^^
\\%%^/^/^^ *VI\\\\\\^\\\\ \ .^ \\\ *
p p% ,p ,,,,,, I-1 pp ~P P K .
*,.b'U 0 /./,y --0 . 0. -,1oo.*o;
.O.' .:O. LIMEROCK BASE COURSE.'..O
C OO0O :E =85 ksi.o.k-c;.




.' .-. . ..* ....... ::. ..


SSTABILIZED SUBGRADEAY:', Y
(SUBB'AS E(SU B B AS E).





... ...-....... ....: ...::........
.. .. ........


Semi-Infinite


Figure 4.3 Typical Four-Layer System Used for the Sensitivity Analysis








repeated for all layer moduli and thicknesses. The NDT device used in

the parametric study was the FWD with a 9-kip loading and sensor spacing

as previously described. However, the findings also apply to the

Dynaflect loading system, under the principle of superposition and

linear elastic theory.

Figures 4.4 through 4.10 show the effect of change of either

modulus or thickness on the FWD deflection basins. The rate of change

of deflections is most pronounced with changes in E as compared with

the moduli of the upper pavement layers. In the case of the layer

thicknesses, the effect is most apparent with changes in the base course

thickness, t It is possible that the t2 effect was due to the high E2

relative to E3 and E4.

Table 4.2 shows the percent change in deflections as a result of

doubling or halving each layer modulus while keeping the other para-

meters unchanged for the pavement section shown in Figure 4.3. The

table shows that changes in E4 affect the deflections to the greatest

degree. The percent change in deflection is highest for any sensor

position when the E4 value is changed. This change with regard to E4

also increases substantially for the sensors further away from the load

center. The table thus suggests that E4 contributes the most to the FWD

deflections.

Similar comparisons were also made for changes in deflections for

t values of 1.5 and 6.0 in. The effect of layer thicknesses, ti, t2,

and t3, on the theoretical FWD deflections were also studied and the

results are summarized in Table 4.3. In this table, t2 seems to have

the most effect. The effect of tI on the deflections becomes negligible

when the original value (t. = 3.0 in.) is halved.




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