2002- 17REV
Final Report
BEST PRACTICES FOR THE
DESIGN AND
CONSTRUCTION OF LOW
VOLUME ROADS
REVISED
Technical Report Documentation Page
1. Report No. 2. 3. Recipients Accession No.
MN/ RC – 2002- 17REV
4. Title and Subtitle 5. Report Date
November 2003
6.
BEST PRACTICES FOR THE DESIGN AND CONSTRUCTION
OF LOW VOLUME ROADS
REVISED
7. Author( s) 8. Performing Organization Report No.
Eugene L. Skok, David H. Timm, Marcus L. Brown, Timothy R. Clyne
and Eddie Johnson
9. Performing Organization Name and Address 10. Project/ Task/ Work Unit No.
11. Contract ( C) or Grant ( G) No.
Department of Civil Engineering
University of Minnesota
500 Pillsbury Drive SE
Minneapolis, MN 55455
( c) 74708 ( wo) 123
12. Sponsoring Organization Name and Address 13. Type of Report and Period Covered
Final Report
14. Sponsoring Agency Code
Minnesota Department of Transportation
Research Services Section
395 John Ireland Boulevard Mail Stop 330
St. Paul, Minnesota 55155
15. Supplementary Notes
http:// www. lrrb. org/ PDF/ 200217REV. pdf This is a revised manual.
16. Abstract ( Limit: 200 words)
This report presents information about the use of the mechanistic- empirical procedure ( MnPAVE) in
designing hot- mix asphalt pavements in Minnesota. Researchers developed the MnPAVE software
program using information from the Minnesota Road Research Project ( Mn/ ROAD) test facility and
from 40- year- old test sections around Minnesota. MnPAVE procedures use Equivalent Standard Axle
Loads ( ESALs) to evaluate traffic loading, and the report includes methods to estimate these values
for design purposes over a 20- year design life, as well as a procedure to measure vehicle type
distributions. In addition, the report presents an evaluation of subgrade soils for each thickness design
procedure, summarizes Minnesota Department of Transportation specifications that relate to
embankment soil construction and to construction of the pavement section materials, and recommends
specific density or quality compaction using a control strip. It also includes best practices on setting up
projects most effectively to follow specifications.
17. Document Analysis/ Descriptors 18. Availability Statement
Mechanistic- Empirical
Soil Factor
Pavement Section
Construction Specifications
R- Value
ESAL’s
Resilient Modulus
Subgrade Soil
Granular Equivalent
Flexible Pavement Thickness
Design
No restrictions. Document available from:
National Technical Information Services,
Springfield, Virginia 22161
19. Security Class ( this report) 20. Security Class ( this page) 21. No. of Pages 22. Price
Unclassified
Unclassified
241
BEST PRACTICES FOR THE DESIGN AND
CONSTRUCTION OF LOW VOLUME
ROADS- REVISED
Final Report
Prepared by:
Eugene L. Skok
Timothy R. Clyne
Eddie Johnson
David H. Timm
Marcus L. Brown
University of Minnesota
Department of Civil Engineering
November 2003
Published by:
Minnesota Department of Transportation
Research Services Section
MS 330
395 John Ireland Boulevard
St. Paul, MN 55155
This report represents the results of research conducted by the authors and does not necessarily represent the views
or policy of the Minnesota Department of Transportation/ and or the Center for Transportation Studies. This report
does not contain a standard or specified technique
TABLE OF CONTENTS
Chapter 1 INTRODUCTION AND SUMMARY
1.1 Introduction................................................................................................................... .... 1- 1
1.2 Minnesota Thickness Design ............................................................................................. 1- 4
1.2.1 Soil Factor Design Procedure ................................................................................... 1- 4
1.2.2 R- Value Procedure.................................................................................................... 1- 5
1.2.3 MnPAVE Procedure ................................................................................................. 1- 6
1.2.4 Procedure( s) to Use in 2001- 02?............................................................................... 1- 7
1.3 Traffic Estimates................................................................................................................ 1- 8
1.4 Subgrade ( Embankment) Soil ............................................................................................ 1- 8
1.4.1 Background ............................................................................................................... 1- 8
1.4.2 Drainage.................................................................................................................... 1- 9
1.4.3 Subgrade ( Embankment) Soil Construction ........................................................... 1- 10
1.4.3.1 General........................................................................................................... 1- 10
1.4.3.2 Specifications................................................................................................. 1- 10
1.4.3.3 General Design Considerations...................................................................... 1- 10
1.4.3.4 Construction Notes and Procedures ............................................................... 1- 11
1.4.3.5 Subgrade Enhancement.................................................................................. 1- 12
1.5 Pavement Section Materials............................................................................................. 1- 13
1.5.1 General.................................................................................................................... 1- 13
1.5.2 Pavement Layer Construction................................................................................. 1- 14
1.5.2.1 General........................................................................................................... 1- 14
1.5.2.2 Specifications................................................................................................. 1- 14
1.5.2.3 Field Control Procedures to Meet Specifications .......................................... 1- 15
1.5.2.3.1 General.................................................................................................. 1- 15
1.5.2.3.2 Granular Bases ...................................................................................... 1- 16
1.5.2.3.3 Hot Mix Asphalt Mixtures .................................................................... 1- 17
1.6 Summary and Recommendations .................................................................................... 1- 19
Chapter 2 THICKNESS DESIGN PROCEDURES
2.1 Background and Introduction ............................................................................................ 2- 1
2.2 Soil Factor Design.............................................................................................................. 2- 1
2.3 Stabilometer R- Value Design ............................................................................................ 2- 3
2.4 MnPAVE Design ............................................................................................................... 2- 5
2.4.1 General...................................................................................................................... 2- 5
2.4.2 Set Up........................................................................................................................ 2- 7
2.4.3 Start Up ..................................................................................................................... 2- 7
2.4.3.1 Control Panel ................................................................................................... 2- 7
2.4.3.2 General Operation............................................................................................ 2- 7
2.4.4 Inputs......................................................................................................................... 2- 8
2.4.4.1 General............................................................................................................. 2- 8
2.4.4.2 Climate Inputs ( Seasonal Design).................................................................... 2- 8
2.4.4.3 Structural Inputs............................................................................................... 2- 9
2.4.4.4 Traffic Inputs ................................................................................................. 2- 11
2.4.5 Outputs.................................................................................................................... 2- 12
2.5 Which Procedure Should be Used in 2001- 02? ............................................................... 2- 12
Chapter 3 TRAFFIC PREDICTIONS
3.1 Background and Definitions .............................................................................................. 3- 1
3.2 Determination of AADT .................................................................................................... 3- 2
3.3 Determination of HCADT ................................................................................................. 3- 3
3.4 ESAL Calculations............................................................................................................. 3- 3
3.4.1 Estimate AADT ........................................................................................................ 3- 3
3.4.2 Vehicle Type Distribution......................................................................................... 3- 4
3.4.3 Determination of ESAL Factors by Vehicle Type.................................................... 3- 5
3.4.4 Determination of Growth Factor............................................................................... 3- 6
3.4.5 Design Lane Distribution.......................................................................................... 3- 7
3.4.6 ESAL Calculation Spreadsheet................................................................................. 3- 7
3.5 Summary and Conclusions ................................................................................................ 3- 9
Chapter 4 SUBGRADE ( EMBANKMENT) SOIL DESIGN AND CONSTRUCTION
4.1 Background..................................................................................................................... ... 4- 1
4.2 Soil Surveys and Sampling ................................................................................................. 4- 2
4.3 Subgrade Soil Design Factors............................................................................................. 4- 3
4.3.1 General....................................................................................................................... 4- 3
4.3.2 Laboratory Testing................................................................................................... 4- 4
4.3.2.1 AASHTO Soil Classification........................................................................... 4- 4
4.3.2.2 Stabilometer R- Value........................................................................................ 4- 6
4.3.2.3 Resilient Modulus ............................................................................................. 4- 7
4.3.3 Field Measurements of Subgrade Resilient Modulus ............................................. 4- 11
4.3.3.1 General............................................................................................................ 4- 11
4.3.3.2 Falling Weight Deflectometer......................................................................... 4- 11
4.3.3.3 Dynamic Cone Penetrometer .......................................................................... 4- 13
4.3.3.4 Additional In Situ Factors............................................................................... 4- 14
4.3.4 Use of Subgrade Design Factors.............................................................................. 4- 16
4.3.4.1 General............................................................................................................ 4- 16
4.3.4.2 Soil Factor....................................................................................................... 4- 16
4.3.4.3 R- Value........................................................................................................... 4- 16
4.3.4.4 MnPAVE......................................................................................................... 4- 16
4.4 Subgrade ( Embankment) Soil Construction ..................................................................... 4- 18
4.4.1 General..................................................................................................................... 4- 18
4.4.2 Specifications........................................................................................................... 4- 19
4.4.3 General Design Considerations................................................................................ 4- 21
4.4.4 Construction Notes and Procedures ......................................................................... 4- 21
4.5 Subgrade Enhancement..................................................................................................... 4- 21
4.5.1 General..................................................................................................................... 4- 21
4.5.2 Enhancement of Existing Soils on Grade ................................................................ 4- 22
4.5.2.1 Drainage.......................................................................................................... 4- 22
4.5.2.2 Compaction ..................................................................................................... 4- 26
4.5.3 Enhancement Using Soil Modification.................................................................... 4- 28
4.5.3.1 General............................................................................................................ 4- 28
4.5.3.2 Use of Lime for Modification ......................................................................... 4- 29
4.5.3.3 Use of Bituminous Materials for Modification............................................... 4- 30
4.5.3.3.1 General................................................................................................... 4- 30
4.5.3.3.2 Asphalt Materials ................................................................................... 4- 30
4.5.3.3.3 Design Factors ....................................................................................... 4- 30
4.5.3.3.4 Construction........................................................................................... 4- 31
4.5.3.4 Embankment Modification using Chlorides ................................................... 4- 33
4.5.4 Subgrade Enhancement using Soil Stabilization ..................................................... 4- 33
4.5.4.1 General............................................................................................................ 4- 33
4.5.4.2 Portland Cement Stabilization Materials ........................................................ 4- 34
4.5.4.3 Application of P. C. Stabilization to Soils ....................................................... 4- 34
4.5.4.4 Soil Stabilization using Fly Ash ..................................................................... 4- 34
4.5.4.4.1 General................................................................................................... 4- 34
4.5.4.4.2 Laboratory Mixture Design.................................................................... 4- 34
4.5.4.4.3 Construction Procedures and Concerns ................................................. 4- 35
4.5.4.4.4 Concerns when using Fly Ash ............................................................... 4- 38
4.5.4.4.4.1 High Sulfate Ashes ..................................................................... 4- 38
4.5.4.4.4.2 Environmental Concerns............................................................. 4- 39
4.5.4.4.5 Summary................................................................................................ 4- 40
4.5.5 Subgrade Enhancement using Geosynthetics…………………………………. 4- 42
4.5.5.1 General...................................................................................................... 4- 42
4.5.5.2 Types of Geosynthetics............................................................................. 4- 43
4.5.5.2.1 Geotextiles……………………………………………………….. 4- 43
4.5.5.2.2 Geogride........................................................................................ 4- 44
4.5.5.2.3 Geonets………………………………………………………….. 4- 45
4.5.5.2.4 Geomembranes ............................................................................. 4- 45
4.5.5.2.5 Geocells......................................................................................... 4- 46
4.5.5.2.6 Geocomposites.............................................................................. 4- 47
` 4.5.5.3 Applications of Geosynthetics in Minnesota……………………………. 4- 47
4.5.5.3.1 General........................................................................................... 4- 47
4.5.5.3.2 Geosynthetics as a Separation Layer ............................................. 4- 47
4.5.5.3.3 Geogrids used for Reinforcementof a Subgrade............................ 4- 57
4.5.5.3.3.1 General………………………………………………………. 4- 57
4.5.5.3.3.2 Summary of Design and Construction for Geogrids in MN.. 4- 57
4.5.5.4 Factors Effecting Lifespan of Geosynthetics............................................ 4- 60
4.5.5.4.1 Factors Reducing Effective Lifespan…………………………… 4- 60
4.5.5.4.2 Creep Degradation .......................................................................... 4- 61
4.5.5.4.3 Installation Damage ........................................................................ 4- 62
4.5.5.4.4 Chemical and Biological Degradation ............................................ 4- 62
4.5.5.4.5 Polymeric Aging ............................................................................. 4- 62
4.5.5.4.6 Summary of Effects on Lifespan .................................................... 4- 63
4.5.5.5 General Geosynthetics Construction Considerations ............................... 4- 64
4.5.6 Subgrade Enhancement Using Substitution ...................................................... 4- 68
4.5.6.1 General...................................................................................................... 4- 68
4.5.6.2 Substitution with Select Granular ............................................................. 4- 69
4.5.6.3 Substitution with Breaker Run Limestone................................................ 4- 70
4.5.6.4 Use of Lightweight Fills ........................................................................... 4- 70
4.5.6.4.1 Use of Wood Chips for Lightweight Fills………………………… 4- 73
4.5.6.4.2 Use of Shredded Tires for Lightweight Fills………………………... 4- 78
4.5.6.4.2.1 Background and General Design Considerations………………. 4- 78
4.5.6.4.2.2 Summary of Design and Construction Procedures in MN……… 4- 80
4.5.6.4.3 Use of Geofoam for Lightweight Fills……………………………….. 4- 87
4.5.7 Recommendations for When to Use the Various Methods of Subgrade
Enhancement…………………………………………………………………… 4- 91
4.5.7.1 General…………………………………………………………………….. 4- 91
4.5.7.2 Summary of Subgrade Soil Enhancement Procedures…………………….. 4- 92
Chapter 5 PAVEMENT SECTION MATERIALS
5.1 Background..................................................................................................................... .. 5- 1
5.2 Definitions.................................................................................................................... ..... 5- 2
5.2.1 Granular Subbase and Select Granular ( Mn/ DOT Specification 3149- B2)............. 5- 2
5.2.1.1. Granular ........................................................................................................... 5- 2
5.2.1.2. Select Granular................................................................................................. 5- 2
5.2.1.3. Subbase Course ( Mn/ DOT Specification 3138, Class 4.................................. 5- 2
5.2.2. Aggregate Base Course............................................................................................. 5- 2
5.2.2.1 Granular ( Mn/ DOT Specification 3138, Class 3, 5 and 6................................ 5- 2
5.2.2.2 Salvage Materials ( Mn/ DOT Specification 3138, Class 7............................... 5- 3
5.2.3. Stabilized Base Materials.......................................................................................... 5- 3
5.2.3.1. Portland Cement, lime and/ or fly ash .............................................................. 5- 3
5.2.3.2. Asphalt Cement, Emulsions, Cutbacks............................................................ 5- 3
5.2.4. Recycling and Reclaiming ........................................................................................ 5- 3
5.2.4.1. Cold In- Place Recycling .................................................................................. 5- 3
5.2.4.2. Full Depth Reclamation ................................................................................... 5- 3
5.2.5. Hot Mix Asphalt ( HMA) ......................................................................................... 5- 3
5.3 Pavement Design Factors................................................................................................... 5- 4
5.3.1 General...................................................................................................................... 5- 4
5.3.2 Granular Equivalency Factors................................................................................... 5- 4
5.3.3 Resilient Modulus for Pavement Materials............................................................... 5- 4
5.4 Construction of the Pavement Layers ................................................................................ 5- 5
5.4.1 Specifications Review............................................................................................... 5- 5
5.4.1.1 Granular Materials Properties and Gradations................................................. 5- 5
5.4.1.1.1 Granular Subbase ( Specification 3149.2B2)........................................... 5- 5
5.4.1.1.2 Granular Base and Subbase Materials .................................................... 5- 6
5.4.1.1.3 Stabilized Base........................................................................................ 5- 7
5.4.1.1.4 Recycled and Reclaimed Materials......................................................... 5- 7
5.4.1.1.5. Sampling and Testing ............................................................................. 5- 7
5.4.1.2 Construction of Aggregate Base ...................................................................... 5- 8
5.4.1.2.1 Construction Requirements..................................................................... 5- 8
5.4.1.2.1.1 General........................................................................................... 5- 8
5.4.1.2.1.2 Placing and Mixing........................................................................ 5- 8
5.4.1.2.1.3 Spreading ....................................................................................... 5- 9
5.4.1.2.1.4 Compaction .................................................................................... 5- 9
5.4.1.2.1.5 Workmanship and Quality ............................................................. 5- 9
5.4.1.2.1.6 Aggregate in Stockpiles ............................................................... 5- 10
5.4.1.2.1.7 Random Sampling Gradation Acceptance Method...................... 5- 10
5.4.1.2.1.8 Payment........................................................................................ 5- 11
5.4.1.3 Hot Mix Asphalt ( HMA) Mixtures ................................................................ 5- 11
5.4.1.3.1 General.................................................................................................. 5- 11
5.4.1.3.2 MnDOT 2360 Plant- Mixed Asphalt Pavement combined 2360/ 2350..........
( Gyratory / Marshall Design) Specification.............................................. 5- 11
0.1 Description................................................................................................ 5- 12
0.2 Materials ................................................................................................... 5- 13
0.3 Mixture Design ......................................................................................... 5- 17
0.4 Mixture Quality Management................................................................... 5- 18
0.5 Construction Requirements....................................................................... 5- 21
0.6 Pavement Density ..................................................................................... 5- 22
0.7 Thickness and Surface Smoothness Requirements................................... 5- 23
5.4.2 Field Control Procedures to Meet Specifications ................................................... 5- 25
5.4.2.1 General........................................................................................................... 5- 25
5.4.2.2 Granular Subbases and Bases ........................................................................ 5- 25
5.4.2.2.1 General.................................................................................................. 5- 25
5.4.2.2.2 Schedule of Materials Control .............................................................. 5- 26
5.4.2.2.3 Standard Methods of Testing ................................................................ 5- 26
5.4.2.2.4 Methods of Compaction Control for Aggregate Bases......................... 5- 27
5.4.2.2.5 Job Guide for Aggregate Base Construction ........................................ 5- 28
5.4.2.3 Hot Mix Asphalt ( HMA) Construction.......................................................... 5- 29
5.4.2.3.1 General.................................................................................................. 5- 29
5.4.2.3.2 Standard Methods of Testing ................................................................ 5- 30
5.4.2.3.3 Methods of Compaction Control for HMA .......................................... 5- 30
5.4.2.3.4 Job Guide for Plant Mix Bituminous Paving........................................ 5- 31
Chapter 6 Summary and Recommendations
6.1 General……………………………………………………………………………………. 6- 1
6.2 Thickness Design Procedures………………………………………………….................. 6- 1
6.3 Traffic………………………………………………………………………….................. 6- 1
6.4 Subgrade ( Embankment) Soil………………………………………………….. ………... 6- 4
6.4.1 Subgrade Soil Design Parameters…………………………………………….. 6- 4
6.4.2. Construction Specifications and Methods for Subgrade Soils………………... 6- 4
6.4.3 Subgrade Soil Enhancement Procedures in Minnesota……………………...... 6- 5
6.4.4 Recommended Enhancement Procedures for Specific Conditions…………… 6- 6
6.4.5 Documentation of In- Place Projects Using Soil Enhancement……………...... 6- 6
6.5 Pavement Section Materials……………………………………………………………… 6- 6
6.5.1 General……………………………………………………………………...... 6- 6
6.5.2 Specifications and Design Factors……………………………………………. 6- 7
6.5.3 Construction of Granular Bases………………………………………………. 6- 7
6.5.4 Construction of Hot Mix Asphalt Materials…………………………………... 6- 8
References..................................................................................................................... ............ R- 1
Appendix A Use of Investigation 183 and 195 Test Sections As a Long Term....................... A- 1
Performance Comparison with the Minnesota M- E Design Procedure
Appendix B Vehicle Classification Field Guide for Low Volume Roads............................... B- 1
LIST OF TABLES
Table 3.1 Vehicle Classification Percentages – Rural CSAH or County Road....................... 3- 4
Table 3.2 Average ESAL Factors by Vehicle Type ................................................................ 3- 5
Table 3.3 Sample Computation of ESAL Factor ..................................................................... 3- 6
Table 3.4 Growth Factors ........................................................................................................ 3- 7
Table 3.5 Lane Distribution Factors ........................................................................................ 3- 7
Table 3.6 ESAL Calculation Worksheet.................................................................................. 3- 8
Table 4.1 Sampling Rates ........................................................................................................ 4- 3
Table 4.2 AASHTO Soil Classification................................................................................... 4- 5
Table 4.3 AASHTO- Soil Factor Correlation ........................................................................... 4- 5
Table 4.4 General Correlation Table for Strength and Stiffness Tests .................................. 4- 14
Table 4.5 MnPAVE Design Moduli Correlation ................................................................... 4- 18
Table 4.6 Methods of Incorporating Water to Compaction………………………………… 4- 27
Table 4.7 Limitations and Safety Precautions for Asphalt Treatment……………………… 4- 31
Table 4.8 Mn/ DOT Geosynthetic Classifications ( Mn/ DOT Spec 3733.1)………………… 4- 42
Table 4.9 Geosynthetic Property Testing Methods………………………………………….. 4- 64
Table 4.10 Breaker- Run Limestone and Mn/ DOT Class 5 Gradations……………………… 4- 70
Table 4.11 Characteristics of Common Lightweight Fill Materials ( 52)…………………….. 4- 73
Table 4.12 Typical Costs of Wood Chips……………………………………………………. 4- 77
Table 4.13 Advantages/ Disadvantages and Practical Use of Waste Tires ( 52)……………… 4- 78
Table 4.14 Subgrade Soil Enhancement – Granular Soils…………………………………… 4- 93
Table 4.15 Subgrade Soil Enhancement – Semi Plastic Soils……………………………….. 4- 94
Table 4.16 Subgrade Soil Enhancement – Plastic Soils……………………………………... 4- 95
Table 4.17 Subgrade Soil Enhancement Recommendations for Peat and/ or Swamp Areas… 4- 96
Table 5.1 Granular Equivalent ( G. E.) Factors……………………………………………….. 5- 4
Table 5.2 Default Resilient Modulus Values to Use in MnPAVE .......................................... 5- 5
LIST OF FIGURES
Figure 2.1 Flexible Pavement Design Using Soil Factors ....................................................... 2- 2
Figure 2.2 R- Value Design Chart ............................................................................................ 2- 4
Figure 4.1 Stabilometer R- Value Testing Apparatus............................................................... 4- 7
Figure 4.2 Resilient Modulus Testing Apparatus .................................................................... 4- 9
Figure 4.3 Load and Deformation vs. Time for Resilient Modulus Test............................... 4- 10
Figure 4.4 FWD Deflection Basin ......................................................................................... 4- 13
Figure 4.5 MnDOT DCP......................................................................................................... 4- 15
Figure 4.6 Type V Woven Geofabric Connected Using a “ Prayer Seam” with 75- mm ( 3- in.)
Overlap and 401 Stitch…………………………………………………………… 4- 50
Figure 4.7 Granular Material Placed on Overlapped Geofabric……………………………... 4- 52
Figure 4.8 Typical Section Using Geofabric……………………………………………….... 4- 53
Figure 4.9 Geofabric Construction Sequence with Belly Dump and Motorgrader…………. 4- 54
Figure 4.10 Geofabric Construction Sequence ( cont.)………………………………………. 4- 55
Figure 4.11 Geofabric Construction ( Transverse Placement)……………………………….. 4- 56
Figure 4.12 Overlapping Layers of Type V Nonwoven Geofabric Separating Granular
Material from Wet, Fine Soil ( 150- mm ( 6- in.) of Class 5 Granualar Material
Protects the Geofabric from the Breaker Run Material………………………… 4- 72
Figure 4.13 Steel- wheeled Roller Applies Compactive Effort to a 225- mm ( 9- in.) Lift
Of Breaker Run Limeston.................................................................................... 4- 72
Figure 4.14 Lumber Mill Sawdust .......................................................................................... 4- 75
Figure 4.15 Bulldozer Spreading Lumber Mill Sawdust ........................................................ 4- 76
Figure 4.16 Wood Chips Placed on Geofabric ....................................................................... 4- 77
Figure 4.17 Tire Shreds........................................................................................................... 4- 81
Figure 4.18 Live- Bottom Truck Delivering Tire Shreds ........................................................ 4- 83
Figure 4.19 Placing Tire Shreds with “ Thumb- Like” Attachment ......................................... 4- 83
Figure 4.20 Tire Shreds Placed on Geofabric......................................................................... 4- 84
Figure 4.21 Geofabric and Fill Being Placed over Tire Shreds.............................................. 4- 84
Figure 4.22 Placing Geofoam ( EPS) Blocks ( 52)................................................................... 4- 89
1 - 1
CHAPTER 1
INTRODUCTION AND SUMMARY
1.1. Introduction
This manual has been developed to present methods of design and construction of Hot Mix
Asphalt ( HMA) pavements in Minnesota. Mn/ DOT and the flexible pavement industry are now
in a time of transition for thickness design and construction procedures. The MnPAVE thickness
design procedure is a mechanistic- empirical computer software program that takes into account
many variables that could not be considered previously. The MnPAVE procedure is based on
work done at the University of Minnesota using an elastic layered system WESLEA developed at
the Corps of Engineers ( 1). The University program called ROADENT used performance
prediction equations for fatigue and subgrade rutting based on material properties and
performance of test sections at MnROAD ( 2). This analysis with some updates has been used to
develop MnPAVE. The performance of some 40- year old test sections has been used to check
the performance prediction equations used in MnPAVE. Appendix A of this report is the report
presenting the results of these comparisons. A big advantage of using a mechanistic- empirical
design procedure is that the properties of various materials can be entered into the software to
check what thicknesses would be predicted to perform well.
Chapter 2 reviews the three HMA thickness design procedures currently used in Minnesota –
the Soil Factor, Stabilometer R- Value and MnPAVE methods. A survey of the city and county
engineers in Minnesota indicated that both the Soil Factor and R- Value are being used
throughout the state ( 3). About two- thirds of the counties use the soil factor and about two- thirds
of the cities use the R- Value.
The Soil Factor Design Procedure is presented in the Mn/ DOT State Aid Manual ( 4). The R-Value
method is presented in the Mn/ DOT Geotechnical and Pavement Design Manual ( 5). The
MnPAVE software Beta Version 5.009 is now available. The draft of a MnPAVE Operating
Manual gives instructions on how to set up and run the software ( 6). Each of the three design
procedures is presented and summarized in Chapter 2.
1 - 2
The loading on a pavement, the traffic, is discussed for each of the three design procedures in
Chapter 3. The two- way Annual Average Daily Traffic ( AADT) and Heavy Commercial Daily
Traffic ( HCADT) predicted for the design year ( usually 20 years in the future) are used for the
Soil Factor Method. The R- Value and MnPAVE Procedures use Equivalent Single Axle Loads
( ESALs) to predict the traffic effect. The ESAL concept equates the effect of these various
weight and configurations of axle loads to the effect of an 80- kN ( 18,000- lb) single axle load.
Eventually, the MnPAVE procedure will use the Load Spectra concept to evaluate traffic. Load
Spectra gives a distribution of axle loads and types predicted to use that road over the design
period ( 6).
The subgrade and embankment evaluation procedures for the three design procedures are
presented in Chapter 4. These are the Soil Factor, R- Value and Resilient Modulus ( Mr)
determined for the soils to be used for a given project. The Soil Factor is based on the AASHTO
Soil Classification and the R- Value can be measured in the laboratory or estimated from the soil
classification. The Resilient Modulus can be estimated from either the R- Value or soil
classification using relationships developed by Siekmeier and Davich ( 7). The resilient modulus
of the soil can be varied throughout the year using variations at MnROAD defined by Ovik, et al
using MnROAD soil stiffness variabilities measured ( 8). This work resulted in the definition of
five ( 5) seasons for a given year in Minnesota. These are early spring, spring, summer, fall and
winter.
The strength ( stiffness) and variability of a given subgrade soil are very dependent on the
construction procedures used for selecting, mixing, placing and compacting the soils. The
procedures start with a good survey of what soils exist at the construction site and knowledge of
how these materials will react under construction, environment and loading conditions. The
construction procedures start with a good set of specifications. Mn/ DOT Specifications 2105,
2111 and 2123 from the 2000 Mn/ DOT Specifications for Construction book are recommended
for the construction of subgrades in Minnesota ( 9). These specifications are summarized in
Chapter 4.
Methods for carrying out the specifications from the Mn/ DOT Grading and Base Manual
( 10) and the Geotechnical and Pavement Design Manual ( 5) are summarized.
General Design Considerations and notes from the Inspector’s Job Guide for Construction
( 11) published by the Office of Construction, Technical Certification Section is also presented to
1 - 3
help show what procedures and documentation are recommended to result in successful
construction of a subgrade. Various methods of subgrade enhancement are presented in Section
4.5.; Enhancement of in- place soils using proper design of drainage and good compaction,
modification using lime, bituminous materials and chlorides, stabilization using fly ash., and use
of geosynthetics for separation and reinforcement. General design considerations along with
factors affecting of geosynthetic lifespan are also presented.
Substitution using various higher quality granular and lightweight materials is presented
in Section 4.5.6. The granular materials are Select Granular and Breaker Run Limestone. Design
and construction procedures along with specifications are presented. Design and construction of
lightweight fills using Wood Chips, Shredded Tires and Geofoam are also covered.
Summaries using each of the materials and procedures are presented for design and
construction control. Specifications for materials and procedures to use in Minnesota along with
contacts for further information are presented.
Based on a review of the literature, questionnaires and interviews with Mn/ DOT and
county engineers and review of specific projects recommendations are made for when and how
the various procedures should be used. The parameters used for the recommendations are “ Grade
above Water Table” and “ Moisture Conditions”. There are essentially no conditions
recommended for soil enhancement for granular soils. Methods of Modification, Stabilization,
Separation and Reinforcement are recommended for various conditions in the tables.
Table 4.17 lists the conditions including “ Thickness of Peat” for which the various
lightweight fills are recommended.
A database has been developed to document installations using the procedures listed.
Projects were located during visits to the cities and counties during the summer, 2002. Sixty five
projects have been identified. It recommended that the projects identified be reviewed about
every three years and the location and parameters for additional projects be added to the
database. In this way actual performance of the various methods of subgrade enhancement can
be documented.
A subsequent study will look at the various methods of modification, stabilization and
reinforcement as they can be used with the MnPAVE mechanistic- empirical design procedure.
The methods of evaluating the various layers of a pavement section are presented in
Chapter 5. The materials discussed are Select Granular, Granular Subbases and Bases,
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Salvaged/ Recycled Aggregates and Hot- Mix Asphalt Mixtures. The specifications used to define
and construct these materials are MnDOT 3149, 3138, 2360/ 2350 respectively ( 9). The design
parameters, which are recommended for each of the materials for each thickness design
procedure, are presented.
Field control procedures needed to meet the specifications are also presented in Chapter 5.
The Inspector’s Job Guide for Construction ( 11) sections for base and HMA construction are
summarized to present items that will help field personnel to give them checklists to properly
construct the pavement layers. Again, in order to realize the performance predicted by the
respective design procedures both in terms of strength ( stiffness) and durability the specifications
must be followed carefully.
The remainder of Chapter 1 is a summary of Chapters 2, 3, 4, and 5. The chapters cover the
following items: Chapter 2, the three design procedures, Chapter 3, the Traffic Factors
definitions and determination, Chapter 4, Subgrade Design and Construction, and Chapter 5,
Pavement Layer Design and Construction.
1.2. Minnesota Thickness Design
1.2.1. Soil Factor Design Procedure
The Soil Factor Design is shown in Figure 2.1. It is published in the MnDOT State Aid
Manual ( 4). The chart uses seven categories of traffic based on the projected 20- year two-way
Annual Average Daily Traffic ( AADT) and Heavy Commercial Daily Traffic
( HCADT). The procedures for predicting AADT and HCADT are presented in Sections 3.2
and 3.3. General flow maps are available for the entire state; however, it is recommended that
a District Traffic Engineer or the Office of Transportation Data and Analysis be contacted to
make the 20- year design predictions. These values will be dependent on future development
planned for the area.
The soil is defined using the soil factor, which is dependent on the AASHTO
Classification of the material represented on the particular project. Section 4.2 reviews
methods for determining the appropriate soil that represents the embankment conditions on
the project. The soil classification system is presented in Section 4.3.2.1. and the relationship
between the soil class and soil factor is given in Section 4.3.4.2.
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The thickness for the Soil Factor design is given in terms of the Granular Equivalent
defined in Section 5.3.2.2. Granular Equivalency factors are assigned to materials based on
the specification that they pass. For instance a Specification 3139 class 5 or 6 material has an
equivalency factor of 1.0. A Class 4 material has a factor of 0.75 because it has a less
restrictive gradation band. The relevant specifications for the other pavement materials are
listed in Figure 2.1. Minimum bituminous and total granular equivalent are also shown for
each traffic category. The thicknesses shown in Figure 2.1 represent a reduction in subbase
thickness for granular type soils ( soil factor less than 100%) and an increase in thickness for
soil factors greater than 100% ( heavy clay and some silty soils).
The soil factor recommended thicknesses have changed somewhat throughout the years
because of changes in traffic levels and construction procedures.
The construction specifications and procedures presented in Chapters 4 and 5 for the soil
and pavement section materials respectively must be followed to realize the design life
predicted by the design procedures.
1.2.2. R- Value Procedure
Figure 2.2 is the R- Value design chart currently used by MnDOT for design of HMA
pavement sections. The chart is in Reference 5. The embankment soil R- Value is determined
by a standard laboratory test procedure that is run in the MnDOT Maplewood Laboratory.
The procedure is outlined and discussed in Section 4.3.2.2.
The R- Value can also be predicted from the AASHTO Classification of the soil as shown
in Table 4.5, which is in Section 4.3.4.3.
The traffic for the R- Value procedure is defined in terms of Equivalent 80- kN ( 18,000- lb)
axle loads ( ESALs). ESALs represent the effect of various axle loads and configurations on
the performance of a pavement. Methods for estimating ESALs for a given location are
presented in Section 3.4. ESALs are calculated from the total traffic predicted in a design
lane ( Section 3.4.1), the vehicle type distribution ( Section 3.4.2.) and the average effect of
each vehicle type in terms of ESALs per passage of that vehicle ( Section 3.4.3.). Methods of
taking into account predicted growth are given in Section 3.4.4. A spreadsheet to make the
calculations is presented in Section 3.4.6.
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The thickness for the R- Value procedure is given in terms of Granular Equivalent
thickness using the same concepts as for the Soil Factor Design. The G. E. factors are listed in
Section 5.3.2.2.
The three thicknesses obtained from Figure 2.2 are the total G. E., the bituminous plus
base thickness G. E. and the minimum bituminous G. E.
An alternate R- Value Design in terms of full depth HMA is presented in Figure 5- 3.7 of
Reference 5. MnDOT no longer uses this “ full depth” design chart unless a 1- m ( 30- in.) layer
of select granular material is used under the surface layer. Some cities and counties use full
depth design where there is limited vertical clearance or there is a severe aggregate shortage.
If this procedure is used for design it is very important that the subgrade be compacted well
and uniformly to adequately support construction equipment and the design traffic for the
pavement.
1.2.3. MnPAVE Procedure
The Beta Version 5.009 of MnPAVE is now available ( 6). MnPAVE is a mechanistic-empirical
based procedure, which uses relationships from MnROAD to predict the
performance of a pavement. Elastic layer theory is used to calculate the critical strains in the
system, which are correlated with fatigue cracking and development of rutting. In order to
calculate strains, the resilient modulus of each layer including the subgrade must be
determined and used along with the thicknesses of the pavement layers. The design then
involves the determination of the thickness required to keep the strain low enough to
withstand the calculated repetitions.
MnPAVE is set up so that the year can be divided into five seasons defined in Section
2.4.4.2. These can be adjusted for special situations. This makes MnPAVE much more
versatile than the others.
Currently, MnPAVE uses ESALs as input for traffic. The ESALs are calculated using the
procedure presented in Section 3.4 just as for the R- Value procedure. For the mechanistic
calculations the traffic is defined using Load Spectra, which represents the distribution of
loads on various axle configurations.
The subgrade is defined using the Resilient Modulus ( Mr) as it is predicted to vary
throughout the year. The resilient modulus can be determined in the laboratory with a
repeated load triaxial test using the test conditions given in Section 4.3.2.3. However,
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laboratory triaxial testing has only been performed on a limited number Minnesota soils. The
correlations given in Table 4.5 should be used to estimate the resilient modulus either from
the R- Value or the AASHTO Classification. These correlations result in five moduli
representing the five seasons defined at MnROAD.
The resilient moduli of the pavement layers are determined based on the specifications
that the granular material or mixture passes. The moduli listed in Table 5.2 in Section 5.3.3.
were measured from in- place testing at MnROAD. The high values for each layer in the
winter represent frozen conditions and the other moduli represent the variations measured
with the Falling Weight Deflectometer ( FWD).
Section 2.4 summarizes the draft of an operating manual being developed for MnPAVE
( 6). The manual includes the Setup, Startup, Input and Output for the software. The results
will give the operator the predicted life based on the design parameters assumed for a given
pavement.
1.2.4. Procedure( s) to Use in 2001- 03?
The three design procedures available in Minnesota have been summarized in Chapter 2.
More complete descriptions of Soil Factor and R- Value procedures are given in References 4
and 5 respectively. These procedures have been used around Minnesota for the past 25 plus
years on roads with all levels of traffic. The MnPAVE software is now being developed ( 6).
The MnPAVE program makes it possible to account for many factors that could not be
directly considered previously. The potential for improved design with MnPAVE is very
great. However, it needs to be used for various design situations to develop confidence in the
performance prediction equations. Designs with different types of materials such as stabilized
or reinforced subgrades or bases should be tried to see what is predicted from MnPAVE
compared to performance observed in the field. When new procedures or materials are used
the resulting pavement section should be simulated with the MnPAVE model.
It is recommended that if a pavement is being designed with either the Soil Factor or R-Value
procedures that a corresponding design be done with MnPAVE. A comparison
between the two designs should be made. We ask that the Minnesota Road and Research
Section be informed of the results of these comparisons. A form summarizing the
comparisons of the designs should be completed so that the experience with MnPAVE
relative to the current designs can be documented.
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MnPAVE is very versatile and will become more useful as more people gain experience
with it. Also, in the next year ( we hope) the 2002 AASHTO Design Guide will be available.
This program will need calibration for each state. As the engineers in Minnesota gain
experience with MnPAVE they will be able to calibrate AASHTO 2002 to Minnesota
climate, materials and traffic conditions effectively.
1.3. Traffic Estimates
The methods recommended for estimating traffic for the three design procedures have been
summarized in Section 1.2. Chapter 3 presents the procedures, tables, procedures, and software
available to make the estimates.
The Soil Factor Design requires an estimate of AADT and HCADT predicted for 20 years
into the future, or whatever the design life is for the given roadway. To estimate current and
future HCADT it is necessary to know the vehicle type distribution. The distribution can be
estimated from a state HCADT map or measured on specific roadways using the procedure
presented in Section 3.4.2. b. For many relatively low volume roads the value from the statewide
map may be appropriate; however, in any special situations such as access routes for agriculture
or manufacturing, a better estimate can be made using the field measurement procedure.
The R- Value and MnPAVE procedures currently use ESALs for traffic load evaluation.
ESAL estimates require an estimate of AADT, vehicle type distribution, ESAL factors ( the
average effect of a given type of vehicle in terms of ESALs), a calculation or estimate of growth,
and design lane distribution. Methods for predicting these factors and using them for predicting
ESALs over the design life are presented in Section 3.4.
The MnPAVE design procedure uses the concept of Load Spectra to predict the life of a
given pavement section. Load Spectra is a prediction is a measure of the load distribution within
each axle configuration. The Load Spectra will be used for mechanistic design for the 2002
AASHTO Design Guide ( 12). MnDOT is working on procedures to help predict load spectra on
Minnesota roadways.
1.4. Subgrade ( Embankment) Soil
1.4.1. Background
The subgrade or embankment soil on which a pavement is built is the most important part
of the pavement structure because:
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• It is the layer on which the remainder of the structure is supported and helps resist the
destructive effects of traffic and weather.
• It acts as a construction platform for building subsequent pavement layers.
• If there are embankment performance problems due to lack of strength or uniformity,
the entire pavement section will have to be removed and replaced to correct the
problem( s).
It is, therefore, imperative that the embankment be built as strong, durable and uniform
and also economically as possible. The most economical embankment is one that will
perform well for many years.
In Chapter 4 methods are presented to help achieve adequate STIFFNESS, STRENGTH
and UNIFORMITY for a given embankment soil. This starts with a good soil survey at the
location so that proper design and construction procedures can be designed into the project.
Section 4.2, which is a summary of a more complete procedure for conducting a soil survey
in Reference 5, presents some criteria for how to conduct a survey at a given location.
Section 4.3 presents the design factors used to evaluate the soil on a project to determine
the appropriate thickness design for the three Minnesota procedures. These procedures have
also been summarized in Section 1.2. Section 4.3.3. presents the Falling Weight
Deflectometer ( FWD) and Dynamic Cone Penetrometer ( DCP) as methods to determine the
stiffness or strength of the soils, subbase and base materials in place. The advantage of using
field measurements is that the variability of the in- place materials can be determined.
Variability will eventually be an input for the MnPAVE design procedure.
1.4.2. Drainage
Section 4.4 includes a discussion of the importance of drainage for a pavement section
and most importantly the embankment soil. Specific design considerations to achieve
adequate drainage are given in Reference 5. The most important design feature is to keep the
final grade at least 1.7 m ( 5 ft) above the water table. This can be accomplished by either
raising the grade or lowering the water table by dewatering.
Lateral drains can also be used in the pavement section. However, for them to work
properly it is necessary to construct a drainable base and/ or subbase [ less than 7% passing the
0.075- mm ( No. 200) sieve]. Proper drainage will not only help maintain the strength of the
pavement section, but will also minimize the effect of frost heave.
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1.4.3. Subgrade ( Embankment) Soil Construction
1.4.3.1. General
To obtain the design values discussed above for the embankment soils in the field,
proper construction practices must be followed. These start with specifications that will
help assure good construction. In Chapter 4 the specifications that pertain to embankment
soil construction, general construction design considerations and some field checklists are
presented as suggestions on how best to build the embankment soil.
1.4.3.2. Specifications
MnDOT has three specifications that pertain to the construction of embankments.
These are Specifications 2105, 2111, and 2123 ( 9). Specification 2105 is defined as a
“ Quality” specification for which two types of density control can be used. These are
“ Ordinary” and “ Specified” compaction. The methods are similar because the
specification states that compaction must be accomplished to the satisfaction of the
Engineer. For ordinary compaction an experienced Engineer or Inspector must be on the
project to make sure adequate compaction is achieved. For “ specified” compaction the
judgment of the Engineer is aided with the determination of a measured density. The
density must be measured using an agreed upon test procedure and using the
representative moisture- density test for the soil being constructed. Of these two
alternatives in Specification 2105 the specified density is recommended.
Specification 2111 presents the test rolling method for density control. An
experienced Inspector can determine where soft spots occur in the constructed subgrade
and make sure measures are taken to correct these. This method of compaction control is
recommended over Specification 2105 because more ( almost total) coverage of the
embankment grade construction is possible.
Specification 2123 lists the equipment and characteristics of the equipment required to
carry out Specifications 2105 and 2111.
1.4.3.3. General Design Considerations
Based on the soil type and project conditions the structural design and appropriate
specifications certain procedures need to be set up and followed to result in good soil
construction. The goal is to provide a strong and uniform embankment for the pavement
structure. Many of the procedures presented depend on the type of soil encountered on
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the project. As the project is started variations in the soils may be encountered and
therefore the field Engineer and Inspector must be aware of the effect of these possible
changes. The following considerations are presented in Section 4.5.3.
• Excavation and Embankment Construction: 1. The finished grade must be kept at
least 1.7 m ( 5 ft) above the water table. 2. The finished grade should be at least
the depth of frost penetration to minimize frost heave and 3. The existing soils or
materials and their preparation including subgrade correction embankment
placement and protection of the completed embankment need to be considered.
• Soils Evaluation: Soils must be evaluated based on whether they are, 1. Suitable
or unsuitable, 2. Excavated soils, 3. Salvaged Materials, 4. Borrow,
• Soils Preparation: Proper preparation of the soils for good uniformity involves
reworking and enhancing the existing materials and eliminating pockets of high
moisture and unstable soils. Soil preparation must also include proper compaction
using test rolling or specified densities, and possible lime treatment for moisture
control.
• Subgrade Correction: Subcuts must be made in areas with pockets of high
moisture, unstable materials or other non- uniform conditions. Subcuts must be
used especially where there are silty type soils, which are particularly frost
susceptible. Subcuts can vary from 0.3 m to 1.3 m ( 1 ft to 4 ft). Tapers must be
provided with the subcuts.
• Placement of Embankment and Backfill Materials: As embankment materials are
placed the same soil must be used for each layer. Specific design considerations to
accomplish uniformity are listed in Section 4.5.3.6.
• Compaction: Compaction must be performed to MnDOT Specification 2105
and/ or 2111 using the equipment specified in Specification 2123. These are Proof-
Rolling, Specified Density and Quality/ Ordinary Compaction. The situations
where one method is appropriate relative to the others are listed in Section 4.5.3.7.
1.4.3.4. Construction Notes and Procedures
The MnDOT Office of Construction, Technical Certification Section has published an
“ Inspector’s Job Guide for Construction” ( 11). This Guide gives the inspector a checklist
that will help get a project started and document the parameters forms and procedures
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that need to be considered based on the specifications to be used. One of the items that
will help keep a project under control is for the Inspector to keep a good diary. This will
help all people involved make sure that work is progressing at an appropriate rate and
that the inspection work is being accomplished.
1.4.3.5. Subgrade Enhancement
Various methods of subgrade enhancement are presented in Section 4.5.
• Enhancement of in- place soils using proper design of drainage and good
compaction are summarized in Sections 4.5.2.
• Modification using lime, bituminous materials and chlorides ( Sections 4.5.3.2.,
4.5.3.3. and 4.5.3.4.)
• Stabilization using Fly Ash ( Section 4.5.4.).
• Use of Geosynthetics
o Separation ( Section 4.5.5.3.2.)
o Reinforcement ( Section 4.5.5.3.)
General design considerations along with factors affecting of geosynthetic
lifespan are presented in Section 4.5.5.4.
• Substitution using higher quality granular and lightweight materials is presented
in Section 4.5.6.
o Higher quality granular materials presented are Select Granular ( Section
4.5.6.2. and Breaker Run Limestone ( Section 4.5.6.3.). Design and
construction procedures along with specifications are presented.
o Design and construction of lightweight fills using Wood Chips, Shredded
Tires and Geofoam are covered in Sections 4.5.6.4.1., 4.5.6.4.2., and
4.5.6.4.3., respectively.
Summaries using each of the materials and procedures recommendations are
summarized for design and construction control. Specifications for materials and
procedures to use in Minnesota along with contacts for further information are presented.
Based on a review of the literature, questionnaires and interviews with Mn/ DOT
and county engineers and review of specific projects recommendations are made for
when and how the various procedures should be used. Recommendations are presented in
Tables 4.14, 4.15, and 4.16 for Granular, Semi- plastic and Plastic soils respectively. The
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parameters used for the recommendations are “ Grade above Water Table” and “ Moisture
Conditions”. There are essentially no conditions recommended for soil enhancement for
granular soils. Methods of Modification, Stabilization, Separation and Reinforcement are
recommended for various conditions in the tables.
Table 4.17 lists the conditions and including “ Thickness of Peat” for which the
various lightweight fills are recommended.
A database has been developed to document installations using the procedures
listed. Projects were located during visits to the cities and counties during the Summer,
2002. Sixty five projects have been identified. It recommended that:
• The projects identified should be reviewed every three years or more often.
• The location and parameters for additional projects should be added to the
database.
In this way actual performance of the various methods of subgrade enhancement
can be documented.
1.5. Pavement Section Materials
1.5.1. General
Pavement section materials are all materials that are added above the subgrade soil to
more effectively withstand the loads caused by the traffic. The materials must be stronger
and more durable closer to the surface. All pavement section materials must be non- frost
susceptible. Chapter 5 presents many different materials that are now used in pavement
sections in Minnesota. There are others that are and will be tried in the future. With the
MnPAVE program it will be possible to simulate the new materials as input for the software
and make predictions of how the material will perform in a pavement.
Chapter 5 follows the same format as Chapter 4 for subgrade design and construction.
Definitions of the various materials are first presented. The materials range from Select
Granular to a high type Hot Mix Asphalt mixture.
The specifications that define each of these materials are listed in Section 5.4.1. The
granular equivalency factors for the Soil Factor and R- Value design procedures are based on
the specification that the material passes.
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Section 5.3 summarizes how the specifications relate to the granular equivalent thickness
factors. The moduli for the pavement layers that can be input for the MnPAVE software are
also presented in Section 5.3.3. The pavement moduli are varied by season just as those of
the subgrade soil. As the MnPAVE procedure and its input are developed further it will be
possible to assign different moduli to various materials that pass a particular specification.
For instance, a Specification 3138, Class 5 material with 10% passing the 0.075- mm ( No.
200) sieve may have a different set of moduli than one with 5% passing the same sieve.
Other variations in gradation and particle angularity may also result in different moduli.
When a reliable laboratory test is finalized these moduli can be measured and then checked
with back- calculated moduli from the falling weight deflectometer or other non- destructive
field tests.
The design factor inputs for the two HMA mixes used by MnDOT are presented in
Section 1.2.
1.5.2. Pavement Layer Construction
1.5.2.1. General
To obtain the design values discussed above for the granular, stabilized and HMA
pavement materials in the field, proper construction practices must be followed. These
start with specifications which when followed to assure good construction. Field control
procedures to help meet the specifications are then presented in Section 5.4.2. This
includes a summary of the Inspector’s Job Guide for Construction ( 11). MnDOT has also
published a “ Materials Control Schedule” in the Grading and Base Manual ( 10), which
summarizes the testing frequency and quantities of materials needed to conform to the
respective specifications.
1.5.2.2. Specifications
In Section 5.4.1. the specifications pertaining to the construction of the pavement
layers are summarized. These include:
• Select Granular ( MnDOT Spec. 3149.2B2) Section 5.4.1.1.1.
• Granular Base and Subbase Materials Gradations ( MnDOT Spec. 3138) Section
5.4.1.1.2.
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• Salvaged/ Recycled Materials Gradations ( MnDOT Spec 3138, Class 7) Section
5.4.1.1.3.
• Aggregate Base/ Subbase Construction ( MnDOT Spec. 2211) Section 5.4.1.2.
• HMA Combined Mix Design ( MnDOT Spec. 2350) Section 5.4.1.3.1.
The specifications are summarized in the indicated sections.
The specifications for Hot Mix Asphalt mixtures cover the materials, mixture design
and construction of the mixtures. Currently, MnDOT uses the 2360/ 2350 specifications
mixture designs. The 2350 mix design uses the gyratory or Marshall hammer for
compaction for developing the Job Mix Formula and construction control. Both of the
procedures use volumetrics including Voids in the Mineral Aggregate ( VMA) and total
air voids. Before the 2350 specification was adopted VMA was used in the design phase
of the mixture, but not checked in the field. Some mixtures were experiencing “ VMA
collapse” in the field ( 13); therefore, the current specifications require that VMA be
controlled in the final mixture. Ride ( smoothness) requirements have also been added to
the 2360/ 2350 specifications. Both incentives and disincentives are included for control
of ride quality.
MnDOT also has Specifications 2331 and 2340 included in the 2000 Specification
Book ( 9). Some of these mixtures are still being produced. The field control procedures
for these mixtures also need to be followed carefully, especially for adequate compaction.
Currently, MnDOT uses the mixes only for Superpave ( 2360) for all new construction
and mid and long life (> 5 years) overlays.
1.5.2.3. Field Control Procedures to Meet Specifications
1.5.2.3.1. General
Section 5.4.2. summarizes procedures presented in the MnDOT Grading and
Base, Geotechnical and Bituminous Manuals ( 10)( 5)( 14). Checklists for field
personnel from the Field Notes for Construction Engineers and Inspectors are also
presented ( 11). Recommendations are made indicating which method is best for field
control. Field control procedures for cold in- place recycling and full depth
reclamation have not been finalized.
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1.5.2.3.2. Granular Bases
The construction of granular bases and subbases involves the following
procedures:
• Manufacture of the material from a gravel pit or quarry
• Storage of the materials
• Transport to the grade
• Placement
• Compaction
The material is initially tested for general quality and gradation and uniformity of
these characteristics. Segregation must be minimized during the entire construction
process.
The current Schedule of Materials Control must be followed for each project.
It is important that the Contractor use exactly the same procedures and the State
when doing Quality Control and Quality Assurance companion testing is being done.
MnDOT specifications define three methods that can be used for compaction
control:
• Specified Density
• Dynamic Cone Penetrometer ( DCP)
• Quality ( Ordinary) Compaction
The specified density is measured using the 150- mm ( 6- in.) Sand Cone Method
( ASTM D 1556- 90. Random sampling procedures should be followed to establish
density test locations.
The DCP is a quick and easier test to run than the sand cone. It also gives a direct
measure of stiffness. The DCP needs to be run using the prescribed procedure
carefully and within 24 hours of compaction so that crusting does not occur.
Quality ( Ordinary) Compaction should only be used if the equipment is not
available to do either Specified or DCP testing. If quality compaction is used the
Inspector and Engineer must be experienced in the construction of granular base and
embankment materials. The compaction operation must be observed continuously. It
generally is only appropriate for small areas where a limited amount of granular
material is being placed.
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The Field Notes for Construction Engineers and Inspectors ( 11) includes a section
for inspection of granular base construction. This checklist will help the field
personnel carry out the specifications well. Just as for the construction of
embankment soils one of the most important items to maintain is a good diary which
includes such things as hours, location, lift thickness, test results, quantity, yield and
other events including weather which may have an effect on the work.
1.5.2.3.3. Hot Mix Asphalt Mixtures
The current Schedule of Materials Control should be reviewed and used for
setting up the field control for each HMA construction project. That document will
establish:
• The specification applicable for the project
• The minimum required field acceptance testing rate
• Form number to use
• Minimum required sampling rate for laboratory testing
• Sample size required for laboratory testing
The construction of an HMA pavement layer includes the following operations:
Plant Operations
• Materials delivery or manufacture and storage ( asphalt and aggregate)
• Materials proportioning and mixing
• HMA storage and/ or transfer to trucks
• Delivery to the construction project
Paving Operations
• Laydown
• Compaction
Each of these steps requires some Quality Control ( QC) testing by the Contractor
and the Quality Assurance ( QA) testing by the Agency as spelled out in the
Specification. The testing will help assure that the material is uniform ( not
segregated) is placed to specification density and that a surface is provided which
passes the ride specifications.
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It is very important that the same standard procedures be used for both QC and
QA testing. The testing must also be done by certified technicians for both the
Contractor and the Agency.
Section 5.4.2.3.3. includes a discussion on Methods of Compaction Control for
HMA. Compaction is the most important part of construction of an HMA mixture.
Inadequate compaction will result in a shorter life because of accelerated
deterioration due to higher air voids resulting in more permeability and lower
strength.
Three methods of compaction control are provided for in Specifications
2360/ 2350 ( Gyratory/ Marshall Design):
• Specified Density Method ( 2360.6- B2). The Bulk Specific Gravity of a field
sample is compared to compaction obtained from the same material prior to
compaction and compacted with a Marshall Hammer or gyratory compactor.
The Maximum Theoretical Density is also determined to check the field
compaction with the specified levels listed in Tables 2360.6 B- 2 respectively.
The frequency of and variations permitted between QC and QA testing are
also listed.
• Ordinary Compaction. For Ordinary Compaction a control strip of at least 330
m3 ( 395 yd2) of the same material, on the same subgrade and base conditions
shall be compacted to determine a proper roller pattern to achieve maximum
density. A growth curve of density with roller passes must be used to
determine when maximum density has been obtained. If materials or
conditions change a new control strip must be constructed. A given control
strip can only be used 10 days of construction.
The Specified Density Method should be used unless otherwise indicated.
Ordinary Compaction without a control strip should only be used for very
small areas or thin lifts less than 39 mm ( 1.5 in.). For these areas the HMA should
be compacted until there is no appreciable increase in density with each pass of the
roller as defined by an experienced Engineer or Inspector.
The type and characteristics of the roller( s) to be used for Ordinary Compaction
are presented in the Specifications.
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The Inspector’s Job Guide for Construction ( 11) includes sections on both the
inspection of plant and paving operations.
The Guide assumes that the Inspector will not just be a data or sample taker. The
Inspector should be aware of the whole operation to make sure that a consistent,
uniform quality mixture is produced and constructed.
1.6. Summary and Recommendations.
Chapter 6 presents the summary and recommendations given in the manual. These deal with
the thickness design procedure( s) to use now since the MnPAVE procedure is not documented
fully across Minnesota especially for low volume roads. It is now recommended that either the
Soil Factor or R- Value procedure be used and then the same roadway be designed using
MnPAVE. Comparisons should be made and reported to the MnDOT Research Section. A form
has been developed to report the comparisons.
Traffic is evaluated using 20- year projections of AADT and HCADT for the Soil Factor
design procedure. Equivalent Standard Axle Loads ( ESALs) are used for both the R- Value and
MnPAVE design procedures. ESAL predictions over a 20- year design period require an estimate
of AADT, vehicle type distribution, average effect of the various types of vehicles in terms of
ESALs, a growth factor and lane distribution factor for the roadway. Tables and procedures are
presented in Chapter 3 for determining these values both with estimates and using a field
procedure for measuring vehicle type distribution.
The subgrade or embankment is the most important part of a pavement structure. Chapter
presents the methods of evaluating the subgrade strength or stiffness for the three design
procedures. To realize the design parameters obtained for a given soil good construction
practices must be followed. Good construction starts with good specifications that define how the
material is to be constructed and paid for. The MnDOT specifications that are used for subgrade
construction are Nos. 2105, 2111 and 2123. Chapter 4 includes summaries of these specifications
and the field procedures that will most effectively help carry them out. The importance of well-trained
knowledgeable personnel is emphasized.
Chapter 5 presents how the materials used for the pavement section are evaluated for the
three design procedures. The granular equivalent factors are used for the Soil Factor and the R-Value.
The factors are dependent on the specifications which either a granular material or an
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asphalt mixture pass. The GE factors are presented in Chapter 5 and summarized in Chapter 6.
The resilient moduli that are used for the MnPAVE procedure have been related to the other
specification granular and hot mix asphalt materials. Eventually laboratory and non- destructive
field tests ( the FWD and DCP) will be used to relate the laboratory tests to the field values. One
big advantage of the mechanistic- empirical design ( MnPAVE) is that seasonal variations in
resilient modulus for a material in the pavement section for a given year and from year to year
can eventually be documented.
MnDOT combined 2360 and 2350 ( Gyratory/ Marshall Design) specifications are
recommended for HMA construction on low volume roads in Minnesota. These specifications
feature the use of volumetrics for field control and quality management ( QM) of the team of the
Contractor and the Agency. The Contractor is responsible for Quality Control QC) and the
Agency, Quality Assurance ( QA). The specifications include requirements for material quality,
mixture design, mixture variability, density ( voids), Voids in the Mineral Aggregate ( VMA),
moisture susceptibility, field density and smoothness of the finished surface. Construction
procedures and a checklist for field engineers and inspectors are presented.
One of the major goals of the presentation of design and construction of the subgrade and
pavement section materials is to obtain uniformity, which helps a great deal in the achievement
of good performance.
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CHAPTER 2
THICKNESS DESIGN PROCEDURES
2.1. Background and Introduction
There are three flexible pavement thickness design procedures now used in Minnesota. In
addition some pavements, especially at the local level, are designed by experience based on what
has worked in the past. The three formal thickness design procedures are the Soil Factor Design
found in the MnDOT State Aid Manual ( 4), the Stabilometer R- Value Design found in the
MnDOT Geotechnical and Design Manual ( 5) and MnPAVE, which is the mechanistic- empirical
design procedure currently under development. The Soil Factor Procedure was developed in the
1950’ s and has been modified somewhat since then. MnDOT adopted the R- Value Procedure in
the early 1970’ s. The MnPAVE Procedure is in software form and is being tested against the
other procedures. The Beta version is now available ( 6). In this Chapter the procedures are
presented along with the factors needed for thickness determination.
The traffic factor for each of the procedures is presented in Chapter 3. The embankment
( subgrade) factors for design and construction specifications and recommended procedures are
given in Chapter 4. The thickness of the pavement section is defined using the Granular
Equivalent for the Soil Factor and R- value design procedures. The Resilient Modulus ( Mr) and
the thickness of the layers define the structure for the MnPAVE Procedure. The required
specifications and recommended construction procedures to attain the respective pavement
section factors are presented in Chapter 5.
2.2. Soil Factor Design
Since 1954 some pavements in Minnesota have been designed using a table similar to Figure
2.1. This is the 2001 version from the State Aid Manual which uses English and metric units ( 4).
The chart uses seven traffic categories based on 20- year projected two- way AADT and HCADT
and eight embankment types using the AASHTO classification system. Thickness in terms of
Granular Equivalent ( G. E.) is determined for each level of traffic and soil type. Each design also
has a specified maximum spring axle load.
The traffic factors are Average Daily Traffic ( ADT) and Heavy Commercial Average Daily
Traffic ( HCADT). The ADT and HCADT are both two- way values. The ADT includes all
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vehicles and the HCADT is defined as all trucks with six or more tires; thus HCADT does not
include cars, small pickup and panel- type trucks. The ADT and HCADT normally used for
design are values predicted for 20 years into the future. Local conditions must be considered and
the projected value may either be increased or decreased based on the projected future use of the
road. More specific methods of determining design values are presented in Chapter 3.
As noted in Figure 2.1 a soil factor of 100% represents an A- 6 or A- 4 soil. Stronger soils
have soil factors less than 100% and weaker soils greater than 100%. The soil factor percentage
represents the percent increase or decrease in the thickness of the subbase ( D3). There are ranges
of percentages shown for A- 1, A- 2, A- 4 and A- 7 soils. Therefore, it is possible to use some
judgment relative to the capabilities of the soils after evaluating drainage and other design
S. F. Minimum
Bit. G. E. Total G. E. S. F. Minimum
Bit. G. E. Total G. E. S. F. Minimum Bit. G. E. Total G. E.
50 3.0 ( 75) 7.25 ( 180) 50 7.0 ( 175) 14.00 ( 350) 50 8.0 ( 200) 20.30 ( 510)
75 3.0 ( 75) 9.38 ( 235) 75 7.0 ( 175) 17.50 ( 440) 75 8.0 ( 200) 26.40 ( 660)
100 3.0 ( 75) 11.50 ( 290) 100 7.0 ( 175) 21.00 ( 525) 100 8.0 ( 200) 32.50 ( 815)
110 3.0 ( 75) 12.40 ( 310) 110 7.0 ( 175) 22.40 ( 560) 110 8.0 ( 200) 35.00 ( 875)
120 3.0 ( 75) 13.20 ( 330) 120 7.0 ( 175) 23.80 ( 595) 120 8.0 ( 200) 37.40 ( 935)
130 3.0 ( 75) 14.00 ( 350) 130 7.0 ( 175) 25.20 ( 630) 130 8.0 ( 200) 39.80 ( 995)
Minimum Minimum
Bit. G. E. Bit. G. E. Superpave Hot Mix Spec. 2360 2.25
50 3.0 ( 75) 9.00 ( 225) 50 7.0 ( 175) 16.00 ( 400) Plant Mix Asp Pave Spec 2350 2.25/ 2.25/ 2.00
75 3.0 ( 75) 12.00 ( 300) 75 7.0 ( 175) 20.50 ( 515) Plant- Mix Bit. Type 41,61 2.25
100 3.0 ( 75) 15.00 ( 375) 100 7.0 ( 175) 25.00 ( 625) Plant- Mix Bit. Type 31 2
110 3.0 ( 75) 16.20 ( 405) 110 7.0 ( 175) 26.80 ( 670) Aggregate Base ( Class 5 & 6) 3138 1
120 3.0 ( 75) 17.40 ( 435) 120 7.0 ( 175) 28.60 ( 715) Aggregate Base ( Class 3 & 4) 3138 0.75
130 3.0 ( 75) 18.60 ( 465) 130 7.0 ( 175) 30.40 ( 760) Select Granular Spec 3149.2B 0.5
AASHTO SOIL
CLASS
SOIL FACTOR
( S. F.) %
ASSUMED
R- VALUE
Minimum Minimum A- 1 50 - 75 70 - 75
Bit. G. E. Bit. G. E. A- 2 50 - 75 30 - 70
50 7.0 ( 175) 10.25 ( 255) 50 8.0 ( 200) 18.50 ( 465) A- 3 50 70
75 7.0 ( 175) 13.90 ( 350) 75 8.0 ( 200) 23.70 ( 595) A- 4 100- 130 20
100 7.0 ( 175) 17.50 ( 440) 100 8.0 ( 200) 29.00 ( 725) A- 5 130 + -
110 7.0 ( 175) 19.00 ( 475) 110 8.0 ( 200) 31.10 ( 780) A- 6 100 12
120 7.0 ( 175) 20.50 ( 515) 120 8.0 ( 200) 33.20 ( 830) A- 7- 5 120 12
130 7.0 ( 175) 22.00 ( 550) 130 8.0 ( 200) 35.30 ( 885) A- 7- 6 130 10
NOTE: If 10 ton ( 9.1 t) design is to be used, see Road Design Manual 7- 3.
For full depth bituminous pavements, see Road Design Manual 7- 3.
* Granular Equivalent Factor per MnDOT Technical Memorandum 98- 02- MRR- 01.
S. F. Total G. E.
9 TON @ LESS THAN 150 HCADT 9 TON - 600 @ 1100 HCADT
S. F. Total G. E.
S. F. Total G. E. S. F. Total G. E.
9 TON - MORE THAN 1100 HCADT
7 TON @ 400 - 1000 ADT 9 TON - 300- 600 HCADT
MATERIAL TYPE OF
MATERIAL G. E. FACTOR*
7 TON @ LESS THAN 400 ADT 9 TON - 150- 300 HCADT
FLEXIBLE PAVEMENT DESIGN USING SOIL FACTORS
Required Gravel Equivalency ( G. E.) for various Soil Factors ( S. F.)
For new construction or reconstruction use projected ADT. For resurfacing or reconditioning use present ADT.
All units of G. E. are in inches with millimeters ( mm) in parenthesis.
Figure 2.1 Flexible Pavement Design Using Soil Factors
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considerations. Chapter 4 includes a discussion on the selection of these and other design
parameters for the embankment soils.
The strength and stiffness of the soil supporting the pavement are very dependent on the
density and moisture conditions of the constructed soil. Uniformity is also important to
minimize differential heave during freeze up. The construction specifications and procedures
presented in Chapter 4 must be followed to attain the strength and stiffnesses inferred in the
given soil factors.
The Granular Equivalent ( G. E.) defines a pavement section by equating the thickness of each
aggregate or HMA layer to an equivalent thickness of granular base material. Equation 2.1 is
used to calculate the Granular Equivalent. In Minnesota this is a Specification 3139 material,
Class 5 or 6 ( 9). The relevant specifications for the other pavement materials are listed in Figure
2.1. Minimum bituminous and total granular equivalents are also shown for each traffic category.
The total Granular Equivalent is defined using Equation 2.1.
G. E. = a1D1 + a2D2 + a3D3 + … ( 2.1)
Where: D1 = thickness of asphalt mix surface, in. ( mm)
D2 = thickness of granular base course, in. ( mm)
D3 = thickness of granular subbase course, in. ( mm)
a1, a2, and a3 = G. E. Factors listed in Figure 2.1.
The required design thicknesses are listed in two categories ( minimum bituminous G. E. and
total G. E.). The maximum granular base thickness can be calculated by subtracting the minimum
bituminous G. E. from the total G. E. Other design combinations of bituminous and granular
materials can be determined using the G. E. factors.
The respective specifications and construction procedures necessary to attain the material
characteristics defined for the soil factor design are presented in Section 5.3.2.
2.3. Stabilometer R– Value Design
The Stabilometer R- Value is the current design procedure used by MnDOT to determine the
design thickness of an HMA surfaced pavement. This procedure is based on research done in the
1960’ s using results from the AASHO Road Test. The basis of the design is limiting spring
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deflections by increasing the strength ( stiffness) of the soil or by increasing the strength
( stiffness) of the pavement layers for a given level of traffic.
Figure 2.2 is the R- Value design chart from the MnDOT Design and Geotechnical and
Pavement Design Manual ( 5). The embankment R- Value can be measured with a standard
laboratory test ( ASTM D- 2844) or estimated from the soil type or classification. The R- Value
laboratory procedure used in Minnesota is presented in Chapter 4. An exudation pressure of
1655kPa ( 240 psi) is used for determining a design R- Value in Minnesota. Predictions of R-Value
from soil classification are also presented in Table 4.5.
The traffic is evaluated in terms of 80- kN ( 18,000- lb) equivalent standard axle loads
( ESAL’s). For a particular road being designed the ESAL’s are estimated for a design lane in one
direction. Calculated ESAL’s will be different for flexible and rigid pavements for the same
traffic mix. Chapter 3 presents methods for estimating design ESAL’s for flexible pavements in
Minnesota.
Figure 2.2 R- Value Design Chart
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The thickness is defined in terms of Granular Equivalent in inches. Granular equivalent
factors ( a1, a 2, and a 3) for the R- Value design are listed in Section 5.3.2. Equation 2- 1 is used to
calculate the total granular equivalent in the same way as for the soil factor design. In addition to
the lines for specific R- Values showing the required GE for a given number of ESAL’s, lines on
the R- Value design chart represent:
1. The minimum bituminous thickness GE and
2. Bituminous plus base thickness GE.
The actual thicknesses represented can be calculated using the appropriate G. E. factors.
Examples of designs using the R- Value design chart with minimum thicknesses of
surface and base, plus other combinations are given in Reference 5.
2.4. MnPAVE Design
2.4.1. General
The Minnesota Department of Transportation and the University of Minnesota have
developed a mechanistic- empirical ( M- E) design method for flexible pavements. The
procedure has been developed as a software package ( MnPAVE) because of the great
quantities of data and analyses used for the design. A Beta Version of the software is now
available. It is still being fine- tuned somewhat.
MnPAVE predicts the structural performance of pavement sections using calculated
strains in a simulated elastic layered system. To use the elastic layered system moduli and the
thickness of each pavement layer must be determined for the pavement. Up to five ( 5) layers
can be used for the calculations of:
• The tensile strain in the bottom of the surface layer and
• The compressive strain on the top of the subgrade, which is assumed to be infinite in
depth.
Various combinations of material properties ( moduli) are used to simulate the seasons
throughout the year. Currently, five seasons are used ( winter, early spring, late spring,
summer and fall). MnPAVE calculates the percent of damage that occurs in each season,
maximum stress, strain and displacement at the critical locations, the allowable axle load
repetitions and reliability percentages. The life in years is then predicted using the predicted
traffic in ESAL’s or load spectra.
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Fatigue cracking has been correlated with the tensile strain in the HMA surface layer and
embankment rutting has been correlated with the compressive strain on the embankment. The
performance equations are derived from the development of fatigue cracking and rut depth
on the MnROAD test sections. Moduli of the layers have been measured throughout the year
using backcalculated Falling Weight Deflectometer ( FWD) data or estimated from the
Dynamic Cone Penetrometer ( DCP) or other standard tests.
The performance equations were also checked using the performance of a number of 40-
year old test sections from Investigation 183 ( 15). The research to develop the information to
check the performance of these sections was done as part of this project and reported in
Appendix A of this report.
Variability can also be incorporated into MnPAVE. Variations in the following
parameters contribute to the overall variation of the pavement section.
• Layer Moduli
− HMA Surface
− Granular base and subbase
− Subgrade Soil
• Layer Thicknesses
• Load Predictions
− Vehicle class predictions
− Vehicle weight estimates
− Total number of vehicles
The variability of these parameters is used with the predictions equations to calculate the
reliability of the performance predictions. A Monte Carlo simulation is used to calculate the
reliability of the performance predictions ( 16). With this type of analysis it is possible to
relate the variability of the thickness, material properties and traffic predictions to required
thickness. More uniform construction can therefore be translated into thickness saved or
increased life predictions.
MnPAVE requires that the materials be described by their stiffness ( modulus) for the
seasons defined. This requires that the modulus be defined for these seasons either directly or
backcalculated using the FWD or DCP. Correlations with other standard tests as shown in
Table 4.5 can also be used.
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At this time MnPAVE should be used in conjunction with one or both of the current
methods. In this way a city or county can develop confidence in the results of the MnPAVE
design. Without the MnPAVE software it has not been possible to take into account the many
variables that affect the performance of a pavement section.
MnPAVE has the following features:
• Three design levels based on input data quality
• Material properties adjusted seasonally
• Traffic quantified using either ESAL’s or load spectra
• English or System International ( S. I.) Units
• HMA modulus temperature adjustment equations that can be modified
• Reliability estimates using Monte Carlo simulations
2.4.2. Set Up
MnPAVE is designed for Windows 95/ 98/ NT operating systems and requires 2 MB of
hard drive space and a 200 MHz processor or higher.
Installation can be accomplished using the following procedure:
1. Create a new folder on the hard drive called “ MnPAVE”
2. Copy the *. exe file from the floppy disk to the MnPAVE folder.
3. Run the program.
2.4.3. Start Up
2.4.3.1. Control Panel
The “ Control Panel” is the first window to appear when MnPAVE is started. The
control panel includes areas for input data which includes “ Climate, Structure and
Traffic” A button to display “ Output” also appears on the window. The input must be
entered in order beginning with “ Climate” and ending with “ Traffic”, because the
seasonal factors used in “ Structure” depend on Climate and some of the ESAL
calculations in Traffic depend on Structure. Changes can be made in these input windows
at any time. However, for a given design check, all inputs must be completed before
“ Output” can be selected.
2.4.3.2. General Operation
MnPAVE uses the pull- down menu and window selection structures common to most
software packages. The pull- down menu at the top of the screen includes, “ File, Edit,
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Record, View, Window and Help.” The Output will provide damage factors for asphalt
fatigue, rutting and the percent of damage for each season. It also displays the maximum
stress, strain and displacements at the critical locations, the allowable load repetitions and
reliability percentages.
2.4.4. Inputs
2.4.4.1. General
MnPAVE can be operated using either S. I. or the English system of units, sometimes
called Customary units. The system of units can be selected separately for the Climate,
Structure and Traffic data. However, is recommended to use the same System for a given
design application.
The data for each of the input parameters, Climate, Structure and Traffic are defined
using three design levels, “ Basic, Intermediate or Advanced”.
• The Basic Level requires the least amount of data and is intended for many low
volume roads. It may also be used for preliminary design for higher volume roads.
• The Intermediate Level requires more specific information for a given project
and is similar to the information required for that of the Soil Factor or R- Value
design procedures.
• The Advanced Level requires detailed traffic and material property information
and is intended for high volume trunk and interstate highways. It is possible for
the designer to use a different design level for each type of input data.
For this manual only input for the Basic Level and Intermediate Level are
considered. At this time the procedures for obtaining and using the data for the
Advanced Level have not been developed. However, the actual moduli and other values
that are used for the stress and strain calculations are shown in the Advanced Level
window.
2.4.4.2. Climate Inputs ( Seasonal Design)
The material properties used for the design levels are adjusted for seasonal changes in
temperature and moisture. For example, typically the HMA modulus will be lower during
the warm summer season and higher during the cooler seasons. Also, the modulus of an
aggregate base will be lower during the wet spring periods. These variables cannot be
taken into account with the Soil Factor and R- Value Design Procedures.
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For the current version of MnPAVE the year is divided into five seasons, which
reflect the major periods influencing pavement behavior as observed at MnROAD. The
seasons are “ Early Spring, Late Spring, Summer, Fall ( standard), and Winter”.
• Early Spring is defined as the period when the aggregate base or subbase is
thawed, but the subgrade is still frozen.
• Late Spring is the period when the aggregate base has drained, but the subgrade
is thawed, saturated and weak.
• During Summer the aggregate base has fully recovered its strength and the
subgrade has only partially regained its strength.
• By Fall, both aggregate base and the subgrade have recovered their strength.
Fall is considered the standard season for estimating stiffness ( modulus)
variations throughout the year.
• Winter is the season for which all the pavement layers are frozen.
The duration of the seasons will vary somewhat for different locations around the
State and from year to year. A study by Ovik, et al ( 8) using moduli calculated at
MnROAD indicated that the season durations were respectively, 4, 7, 13, 13, and 15
weeks for Early Spring, Late Spring, Summer, Fall, and Winter respectively. These must
always total 52 weeks and could be redistributed as more specific data are obtained for
other locations. For the Advanced Level of Climatic data in MnPAVE any combination
of duration and material properties during the various defined periods of the year could
be used.
To estimate the seasonal modulus for the HMA the temperature at one- third the depth
can be entered directly or estimated using seasonal average daily air temperatures and
predictive equation developed by Witczak ( 17).
2.4.4.3. Structural Inputs
The structural inputs required for the MnPAVE software include the number,
thickness and elastic properties ( moduli) of each layer. The number and thicknesses are
the design values being tried for that trial.
The moduli can be directly input if laboratory testing of the materials have been
measured. If the project- specific materials have been tested, this would be considered an
“ advanced” determination of the moduli.
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If the correlations shown in Chapter 4 for subgrade materials or Chapter 5 for the
pavement section materials are used, then these would be considered Basic or
Intermediate Levels of Input.
Layer 1, the surface layer can be either HMA or “ Other”. The “ Other” option is used
to allow the designer to use materials that have moduli value outside the HMA range
allowed by MnPAVE.
The lower layers may include “ Aggregate Base, Subbase, Engineered Soil,
Undisturbed Soil, Groundwater and Bedrock”.
The Aggregate Base and Subbase are to be constructed stiff enough to enhance
HMA compaction as well as provide long term support for the HMA and help protect the
subgrade.
The Engineered Soil is located directly below the base and/ or subbase. This is the
layer of soil that is excavated, blended, shaped and compacted to result in the most
efficient use of that material. The construction specifications and procedures outlined in
Chapter 4 must be followed to achieve the properties predicted for these materials.
The Undisturbed Soil is the material in- place that existed along the road alignment
prior to construction. The modulus of the undisturbed soil is assumed to be one half of
that of the same soil if it has been “ engineered”.
The Bedrock and Groundwater layers must be included if either occurs within 2 m
( 6 ft) of the surface. MnPAVE uses a constant modulus of 350 MPa ( 50,000 psi) for both
the bedrock and soil below the groundwater table because both materials behave rigidly
under dynamic loads. The ditch bottom is usually assumed to be the depth of the water
table. Poisson’s Ratio is assumed to be 0.15 for bedrock and 0.5 for the groundwater
table. The bottom layer of the pavement structure is to be of infinite depth.
After the basic structure has been defined, a trial thickness for each pavement layer
is entered into the boxes next to the “ Materials”. The variability of thickness allowed in
the respective specifications should be considered for prediction of variability of the
design life. Several different materials and thicknesses can be input to develop a variety
of preliminary pavement design structures.
For the Intermediate Design Level the structure is entered in the “ Edit Structure”
section of the window. The number of layers is selected by the “ Material” and
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“ Thickness”. At the Intermediate Level a single design value of the modulus for each
unbound material is used to estimate the seasonal moduli. These are listed in Table 5- 2
and are backcalculated values from FWD tests at MnROAD. The HMA moduli are also
listed in Chapter 5.
The laboratory moduli for each material can either be entered directly or the “ design”
modulus can be estimated using correlations presented in Chapters 4 or 5. Currently, it is
not possible to directly measure the moduli with a laboratory test. However, correlations
with modulus have been made with the laboratory R- Value, or soil classification as
shown in Table 4.2. The moduli determined from the correlations will appear on the
Advanced Level screen.
Damage equations are used by MnPAVE to convert the calculated strain values from
each loading into the number of allowable load applications. The allowable load
applications are compared to the estimated traffic to calculate the damage factor and/ or
design life. The coefficients in and the format of the damage equations will be changed
periodically as more performance information becomes available.
2.4.4.4. Traffic Inputs
The traffic input is quantified by selecting either “ ESAL” or “ Load Spectra” above
the “ Traffic” button on the Control Panel. At this time only ESAL’s can be used for the
Traffic Input. The definition of ESAL’s and methods for predicting and calculating
ESAL’s are presented in Chapter 3.
For the Basic Design Level the designer can obtain an estimate of ESAL’s by
entering Average Annual Daily Traffic ( AADT), Direction Factor, Lane Factor, and
Annual Growth Rate and then can select from a number of typical Vehicle Type
Distributions that have been obtained from around Minnesota.
For the Intermediate Design Level the AADT, Direction Factor, and Annual Growth
Rate are entered along with a Vehicle Type Distribution determined for that specific
location. This value may be obtained from a road with similar traffic, or be a measured
distribution using the procedure presented in Chapter 3.
The Advanced Design Level allows the designer to enter the number of axles
expected in each load class in addition to tire pressure for some special design situations.
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At this time this sophistication is not recommended except for very special design
situations.
It is necessary to enter information into each of the Input Windows ( Climate,
Structure and Traffic) to obtain an estimate of the life and/ or damage factors for that
design.
2.4.5. Outputs
The Output can be viewed either in a “ Seasons” or “ Reliability” format. Seasons output
includes Damage Factors which are the inverse of the number of times the predicted traffic
volume can be supported by the pavement before failing due to either fatigue cracking or
rutting. The input traffic divided by the Fatigue Damage Factor gives the number of
ESAL’s the pavement is able to withstand before developing fatigue failure. Fatigue failure is
defined as 20% of the total lane cracked. The Rutting Damage Factor gives the same type
of prediction for a rutting failure criteria based on a 12- mm ( 0.5- in.) rut depth. A damage
factor of 1.00 over 20 years would be the goal for most designs.
MnPAVE provides an option for the quick recalculation of damage factors as different
layer thicknesses are considered. The layer thicknesses can be altered individually or as a
group until Damage Factors of 1.0 are obtained for both rutting and fatigue cracking.
2.5. Which Procedure Should be Used in 2001- 02?
Three design procedures have been presented and summarized in this chapter. These are the
Soil Factor, Stabilometer R- Value and the Mechanistic- Empirical ( MnPAVE) designs. The Soil
Factor and R- Value procedures are published in the MnDOT manuals ( 4)( 5). They have been
used for the past 25 plus years for the design of many low, medium and high volume roads. The
MnPAVE procedure has been developed initially at the University of Minnesota and now is
being put into useable form by MnDOT.
At this time it is recommended that either the Soil Factor or the R- Value Design continue to
be used and that the resulting design be checked with the MnPAVE Design. The MnPAVE
design takes into account many variables that the other two procedures cannot. For instance the
variation of material properties for different seasons can be input to determine which is the most
critical season and what effect heavier or limited loads will be. Tire pressure, different types of
stabilization or other construction techniques can also be simulated.
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If all of the parameters necessary to use the MnPAVE procedure are not available then the
values can either be assumed for estimated from the correlations given in the respective chapters.
MnPAVE is versatile and will be improved as more people use the software and compare
performance predictions from the software program with field experience and designs
determined from the currently used procedures. Also, in the next year ( or so) nationally, the
AASHTO 2002 Design Guide will be available ( 12). The experience with MnPAVE will make it
possible for MnDOT and other agencies in Minnesota to calibrate the AASHTO 2002 Procedure
to Minnesota climate, materials, and traffic conditions more easily.
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CHAPTER 3
TRAFFIC PREDICTIONS
3.1. Background and Definitions
For design, rehabilitation and maintenance of pavement structures traffic characterization
plays a crucial role. Estimation of the amount and type of traffic that the roadway will be
expected to carry over the design life will affect the types of materials chosen for the pavement,
the thickness design of the pavement structure and the predicted pavement performance. Traffic
analysis is also an essential part of project feasibility studies, project selection, project path
analysis and sizing of facilities. Therefore, it is critical that the traffic be accurately
characterized so that engineers may optimize designs for the expected traffic.
Most pavement design procedures either rely on estimates of heavy commercial average
daily traffic ( HCADT) or equivalent single axle loads ( ESAL’s) for traffic loading
characterization. This chapter outlines the best practices regarding calculation of these two
traffic parameters. Prior to describing the various aspects of traffic characterization, it is
important to define a number of terms often used in traffic data collection and analysis:
1. Average Annual Daily Traffic ( AADT): The estimate of daily two- way traffic on a road
segment representing the total traffic on the segment that occurs in one year divided by
365. It is important to note that AADT is a volume that may never actually occur, but
represents the average daily traffic on that segment throughout the year.
2. Average Daily Traffic ( ADT): A 24- hour two- way traffic volume that must be qualified
by stating a time period ( e. g., average summer weekday).
3. Automated Traffic Recorder ( ATR): A permanent device that continually collects and
stores traffic data.
4. Axle Load: The total load transmitted by all wheels in a single, tandem or tridem axle
configuration. A single axle is defined as one axle with two sets of dual tires; a super-single
is one axle with two single tires. A tandem axle has two axles spaced less than 1.7
m ( 5 ft) apart with two sets of dual tires on each axle. A tridem axle has three axles
spaced less than 1.7 m ( 5ft) apart each with two sets of dual tires on each side. Both
tandem and tridem axles can have single tires if they are wide enough to decrease the
load to 200 kg ( 450 lb) per 25 mm ( 1 in.).
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5. Average Daily Load ( ADL): The estimate of a daily load on a roadway segment
calculated from the daily vehicle types multiplied by their appropriate ESAL factors.
6. Annual Design Lane ESAL: The estimate of total ESAL damage a roadway segment will
experience in one year.
7. Equivalent Single Axle Load ( ESAL): The relative amount of damage imparted to a
pavement structure by the passage of a standard single axle load, with dual tires. The
ESAL standard is typically an 80- kN ( 18,000- lb) single axle and all other axle
configurations and weights are equilibrated to the standard.
8. ESAL Factor: The average effect of a given vehicle type on a pavement, in terms of
Equivalent Standard Axle Loads ( ESAL’s).
9. Heavy Commercial Traffic: All vehicles two or more axles and a minimum of six tires.
10. Heavy Commercial Annual Average Daily Traffic ( HCADT): The estimate of heavy
commercial daily two- way traffic on a road segment representing the total traffic on the
segment that occurs in one year divided by 365. It is important to note that HCADT is a
volume that may never actually occur, but represents the average heavy commercial daily
traffic on that segment of road
11. Weigh- In- Motion ( WIM): A permanent device that continually collects and stores axle
weight data. This device also collects the total number of vehicles, axle spacing, length,
speed and vehicle type data.
12. Vehicle Classification: The classification of traffic by vehicle type ( i. e., cars, pickups, 3-
axle semis, etc.)
3.2. Determination of AADT
For the Soil Factor Pavement Thickness Design Procedure described in Chapter 2 design ( 20-
year projected, usually) AADT is one of the parameters used to categorize traffic. The design
AADT can be calculated using the current value and increasing it by a growth factor depending
on the projected use of that roadway. MnDOT maintains AADT flow maps for the County State
Aid Highway ( CSAH) system. These maps, which are up- dated about every two years are
available on CDROM and may be obtained by contacting either the Traffic Forecast and
Analysis Section or the District Traffic Engineer of MnDOT.
AADT can also be measured by conducting a vehicle count at the location of, or similar
location to the proposed roadway.
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3.3. Determination of HCADT
The other factor used to categorize traffic for the Soil Factor Pavement Thickness Design
Procedure is the two- way Heavy Commercial Traffic ( HCADT). The design HCADT is the
value projected for the last year of the design life, which is usually 20 years. The current
HCADT can be determined by:
• Estimating HCAADT from Mn/ DOT flow maps maintained throughout Minnesota.. The
HCAADT flow maps for trunk highways in each county are available on the Mn/ DOT
Traffic and Data Analysis web site and may be obtained by contacting the MnDOT
Traffic Forecast and Analysis Section. Thedefault HCAADT value found in the Mn/ DOT
Geotechnical and Pavement Design Manual ( 5) and in Table 3.1 is 5.9 percent.
• Conduct a vehicle- type distribution study as outlined in Appendix 3.1. The current
HCADT can be measured and the projected design value can be calculated. Again, the
HCADT includes all vehicles having six or more tires, which includes all vehicles except
passenger cars and pickup trucks.
3.4. ESAL Calculations
The number of Equivalent Standard Axle Loads ( ESAL’s) is used to define the traffic
effect for the R- Value ( 5) and MnPAVE Design Procedures ( 6). The following parameters must
be determined to calculate predicted ESAL’s. The ESAL concept equates the damage of the
measured number of various axle loads to an 80- kN ( 18,000- lb) axle load. The following steps
outline the data collection procedure and the ESAL calculation. Determine:
3.4.1. AADT for project location. ( Section 3.2)
3.4.2. Vehicle Type Distribution for the location.
3.4.3. ESAL factors by vehicle type.
3.4.4. Traffic growth factor( s).
3.4.5. Design lane traffic percentage.
3.4.6. Calculate ESALs.
3.4.1. Estimate AADT
The determination of AADT is presented in Section 3.2.
3.4.2. Vehicle Type Distribution
Vehicle type distribution is very important in calculating ESAL’s because the axle load
weights and configurations greatly affect the damage effect on the pavement. The most
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practical method of estimating the load effect is to determine the current vehicle type
distribution and project that into the future. Two methods are available to predict current
vehicle type distribution for a given roadway:
• Use statewide average distribution for an estimate. The statewide average for Rural
CSAH and county roads for eight vehicle types are listed in Table 3.1.
• Measure the distribution at a given location using the dual hose technique developed
by MnDOT.
Because the distribution presented in Table 3.1 represents a statewide average distribution
from the 1994 Geotechnical and Pavement Manual ( 5) it may not be directly applicable for a
given location and type of road. A comparison between the assumed and measured
distributions made in 1998 and 1999 on roads in three counties indicated that significant
errors could be made by using the assumed distribution. The complete study is presented in
Reference 18.
Table 3.1. Vehicle Classification Percentages – Rural CSAH or County Road
Vehicle Type Percentage in Traffic Stream
Cars and Pickups 94.1
2 Axle, 6 Tire - Single Unit 2.6
3+ Axle - Single Unit 1.7
3 Axle Semi 0.0
4 Axle Semi 0.1
5+ Axle Semi 0.5
Bus/ Truck Trailers 1.0
Twin Trailers 0.0
Ref: Mn/ DOT - Geotechnical and Pavement Manual, 1994 ( 5)
A better approach, given the deficiencies of Table 3.1, is to conduct a vehicle
classification field study on the actual roadway, or similar roadway being evaluated. In
doing so, many of the errors introduced by assuming a vehicle type distribution can be
eliminated. Appendix B contains a field guide for conducting such a field study.
3.4.3. Determination of ESAL Factors by Vehicle Type
Each of the vehicle types specified above will impart a different amount of damage per
vehicle, expressed in terms of ESAL factors. While the ESAL factors are dependent upon the
type and thickness of the pavement, the default values listed in Table 3.2 may be used. A range
of ESAL factors for various traffic conditions can be found in Appendix H. 2 of the MnDOT
Geotechnical and Pavement Design Manual ( 5).
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Table 3.2. Average ESAL Factors by Vehicle Type
Vehicle Type ESAL Factor
Cars and Pickups .0007
2 Axle, 6 Tire - Single Unit .25
3+ Axle - Single Unit .58
3 Axle Semi .39
4 Axle Semi .51
5+ Axle Semi 1.13
Bus/ Truck Trailers .57
Twin Trailers 2.40
Ref: Mn/ DOT - Geotechnical and Pavement Manual, 1994 ( 5).
In cases where axle weight data for a particular vehicle are available and the size and cost
of the project warrant better traffic information, it is possible to calculate the ESAL factors
for particular vehicles. In fact, the values shown in Table 3.2 were obtained through a
method similar to that described in the 1993 AASHTO Guide ( 19) and requires axle weight
data, an estimate of the structural number ( SN) of the pavement and an estimated terminal
serviceability level ( pt). Reference 19 recommends the following:
SN = 5.0
p t
= 2.5
Table 3.3 illustrates the method to calculate an ESAL factor for a hypothetical 5- axle
truck with corresponding weight data from a study including 165 vehicles. The load
equivalency factors were obtained from Reference 19 and are dependent upon SN and pt.
The equation at the bottom of the table demonstrates that an average ESAL factor ( 2.078) is
calculated by dividing the total equivalent axle loads ( ESAL’s) by the total number of
vehicles weighed. In this case the ESAL factor for these 5- axle trucks, which is somewhat
higher than the value shown in Table 3.2. If a distribution of axle weights can be determined
for a given truck type the blank Table 3.3 in the appendix can be used to calculate the
appropriate ESAL factor.
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Table 3.3. Sample Computation of ESAL Factor
Axle Load, kips Traffic Equivalency
Factor Number of Axles 18 Kip
ESAL’s
Singles
3- 5 0.002 x 1 = 0.002
5- 7 0.01 x 5 = 0.05
7- 9 0.034 x 15 = 0.51
9- 11 0.088 x 57 = 5.016
11- 13 0.189 x 63 = 11.907
13- 15 0.36 x 17 = 6.12
23- 25 3.03 x 3 = 9.09
Tandems
27- 29 0.495 x 50 = 24.75
29- 31 0.658 x 72 = 47.376
31- 33 0.857 x 85 = 72.845
33- 35 1.09 x 120 = 130.8
35- 37 1.38 x 25 = 34.5
Total 18 kip
ESAL’s = 342.966
ESAL Vehicle Factor = Total 18 kip ESAL’s = 342.966 = 2.078
Number of Trucks Weighed 165
3.4.4. Determination of Growth Factor
The growth factor is key in determining how traffic volume will change over the life of
the pavement. Two methods are available for calculating anticipated growth.
• A method is presented in the MnDOT Geotechnical and Pavement Design Manual
( 5). This method is illustrated with ESAL calculation spreadsheet ( Table 3.6). This
method assumes the volume of traffic will increase based on the AADT history. It is
assumed the weight of trucks will increase by about 12% over 20 years based on
historical increases.
• A growth factor table is presented in Reference 19. Table 3.4 lists these factors for 10
and 20- year lives with growth rates of 1, 2, and 4%. Growth rates are rarely greater
than 4%.
These factors when multiplied by the current year estimated ESAL’s yields the total
ESAL’s predicted for the given roadway.
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Table 3.4. Growth Factors
Assumed Growth
Rate, %
Design Life,
Years
1 2 3
10 10.46 10.95 12.01
20 22.02 24.30 29.78
3.4.5. Design Lane Distribution
The “ Design” ESAL’s for a given roadway are the number calculated for the lane that is
expected to have the greatest loading. Lane distribution depends on the total number of lanes
and traffic characteristics based on road usage. If trucks are loaded in one direction and not
the other the loading distribution will be skewed.
Table 3.5 is a list of distribution factors assuming uniform directional traffic for 1, 2 and
3 lanes in each direction. Special attention must be made for turning lanes and other
variations.
Table 3.5. Lane Distribution Factors
Lane Distribution Factor
Number of Lanes
in One Direction
Single- Direction
Traffic Data
Two-
Direction
Traffic Data
1 1 0.5
2 0.9 0.45
3 0.7 0.35
3.4.6. ESAL Calculation Spreadsheet
Once all the data have been determined as specified above, the ESALs may be
determined. Mn/ DOT uses a spreadsheet program, MNESALS ( 20). It is strongly
recommended that the program be used for all ESAL calculations. The MNESAL2003
Program is available from the Traffic Forecast and Analysis Section of Mn/ DOT. However, to
demonstrate the essence of the program and how the above data are used, Table 3.6 illustrates
an example ESAL calculation.
The second column in Table 3.6 shows the total AADT in the base year and the AADT
by vehicle type. For example, cars and pickups comprise 80.47 percent of the traffic stream
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( 1207/ 1500). The fifth column also shows AADT, but it has been increased by
approximately 40 percent for all vehicle types to account for an increase in traffic volume
over the life of the pavement. The base and design year average daily loads are simply
calculated by multiplying the ESAL factors by the AADT and summing all the vehicle
classifications together.
Table 3.6. ESAL Calculation Worksheet
Vehicle Classes
Base Year
AADT
( two- way)
ESAL
Factors Base Year
ADL
Design Year
AADT
( two- way)
Design Year ADL
Cars and Pickups 1207 x .0007 = .8 1690 1.2
2 Axle, 6 Tire -
Single Unit 98 x .25 = 24.5 137 34.2
3+ Axle -
Single Unit 34 x .58 = 19.7 48 27.8
3 Axle Semi 6 x .39 = 2.3 8 3.1
4 Axle Semi 8 x .51 = 4.1 11 5.6
5+ Axle Semi 120 x 1.13 = 135.6 168 189.8
Bus/ Truck
Trailers 25 x .57 = 14.2 35 20.0
Twin Trailers 2 x 2.40 = 4.8 3 7.2
Total 1500 206 2100 288.9
The worksheet in Table 3.6 only yields the ADL in the base and design years. Additional
calculations must be done to determine the design ESALs. The following steps must be
completed to determine the total ESALs over the design life and take into account the growth
of ESAL’s from the initial year.
1. Determine average ADL over life.
Average ADL = ( Base ADL + Design ADL) / 2 =
( 206 + 288.9) / 2 = 247 ( rounded)
2. Determine total ESALs over life.
Total ESALs = Days in N years ( assume N = 20 for this example) * Average ADL =
20* 365* 247 = 1,803,100
3. Apply design lane factor to calculate total ESALs in design lane. ( Table 3.4)
Total ESALs in Design Lane = Total ESALs * Design Lane Factor ( assume 4- lane in this example) =
1,803,100 * .45 = 811,951
4. Build in a 12% safety factor for the possibility of increased loads during the design.
Adjusted ESALs = 12% increase factor * Total ESALs in Design Lane =
1.12* 811,951 = 909,385
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5. Round off to the nearest thousand for design.
ESALs = 909,000
3.5. Summary and Conclusions
In this chapter the traffic factors needed to design an asphalt pavement have been defined and
procedures have been presented for estimating the traffic factors used from the three current
Minnesota Design Procedures.
For pavement thickness design the traffic factor should consider
1. The total volume of traffic,
2. The distribution of axle weights and types,
3. The distribution of vehicles and axle weights and types by lane
and
4. The traffic growth at the given location.
The three Minnesota design procedures are the Soil Factor, the R- Value and the Mechanistic-
Empirical ( MnPAVE).
The Soil Factor Procedure uses the design year AADT and HCADT to categorize traffic as
shown in Chapter 2. The methods for determining these factors are presented in Sections 3- 2 and
3- 3.
The R- value and MnPAVE procedures both use the summation of ESAL’s over the design
period for the facility. The estimation of ESAL’s requires the following parameters, which are
presented in Section 3.4:
• AADT Section 3.4.1
• Vehicle Type Distribution Section 3.4.2
assumed ( Table 3.1)
measured ( Appendix 3.1)
• ESAL Vehicle Factors Section 3.4.3.
average for local roads( Table 3.2)
sample calculations ( Table 3.3)
• Growth Factors Section 3.4.4. ( Table 3.4)
• Design Lane Distribution Section 3.4.5. ( Table 3.5)
• Sample ESAL Calculations Section 3.4.6. ( Table 3.6)
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A more comprehensive procedure for estimating ESAL’s is available in a software package
MNESAL2003 ( 20). MNESAL2003 considers the current and past characteristics of the traffic
and predicts future trends from the recent past. MNESAL’s is available from the MnDOT Office
of Transportation Data and Analysis or the District Traffic Engineer.
It is recommended that county and city engineers estimate ESAL factors and Vehicle Type
distributions for typical roads in their jurisdiction. Annual ESAL calculations can then be made
for the traffic distributions experienced at specific locations.
A study was made to determine the effect of using statewide average vehicle type
distributions for city and county roads rather than measuring the distribution using the procedure
presented in Appendix B. Based on the comparisons of thicknesses determined with assumed
distributions versus measured distributions at specific locations. Based on the thickness
variations represented by the differences in traffic prediction the following recommendations are
made:
1. For the Soil Factor Design:
a. If the AADT is 1500 or less the minimum design can be used without considering
HCAADT and therefore not vehicle type distribution. If it is known that the heavy
commercial traffic is very high because of a specific industry then provisions should be
made.
b. The vehicle type distribution should be measured for a specific project if the AADT is
greater than 1500.
2. For the R- Value design procedure:
a. There is essentially no relationship between AADT and ESALs. Therefore, either
assumed or measured distributions can be used for a given project. Statewide averages are
generally not appropriate.
b. Distributions at a given location can be estimated with the help of a Mn/ DOT traffic
engineer or using the procedure presented in Appendix B. The measurements should be carried
out for a minimum of one week in the summer and one week in the fall.
3. When vehicle type distributions are measured or estimated the results should be reported
to the Mn/ DOT Office of Transportation and Data Analysis at Mn/ DOT Mailstop 450 or e-mailing
the information to
Melissa, thomatz@ dot. state. mn. us
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The coding for a given county or city should be used so that the data from around Minnesota
can be coordinated to establish realistic distributions for various areas of the State.
In this way the information can be used to develop a database of vehicle type distributions
throughout Minnesota.
4. Design calculations should continue to be made so that better relationships can be
established between designs from “ assumed” versus “ measured” distributions.
5. Weigh- in- motion data should continue to be collected