A06__Engineering_Calcs_FINAL_36_pages__.pdf

CAHA – 248511 TABLE OF CONTENTS - 1

TABLE OF CONTENTS

NUMBER TITLE NO. OF PAGES

Table of Contents

Equivalent Single Axle Load (ESAL) Calculations

Flexible Pavement Structural Section Calculations

APPENDIX A - NCDOT Pavement Design Procedure AASHTO 1993 Method

NOTE: The state of Connecticut Department of Transportation calculation spreadsheets was used to develop the structural pavement sections for this project. Coefficients and criteria used in the spread sheet used NCDOT Pavement Design Procedure AASHTO 1993 Method. N.C. Department of Transportation, “Materials and Test Unit – Pavement Section, January 4, 2019, attached herewith as Appendix A

= not applicable

= user input

= solution(s)

= accumulated ESALs for the designated functional class

Town(s) Pavement Scope Description Full Depth Reconstruction (20-year)

Nags Head

End Limit Pavement Surface Age

Legend = automatically calculated or linked value (do not edit)

Completed By

Disclaimer: Please use the spreadsheet in a manner that best applies to your project while considering the recommendations provided within this document. No claims of accuracy are made about the answers provided by this tool. CTDOT is not responsible for errors in calculation in this ESAL Calculator.

General Information Project Number

Project Description

PMIS# 248511 (HECO NPS22-0383)

Oregon Inlet Parking Lot

Bart Brooke Reviewed By

Company Name Road Name

Start Limit

Not Known South End of Parking lots Entrance Road Oregon Inlet Parking Lots HECO Engineers, Inc.

Zach Matthews https://portal.ct.gov/DOT/Engineering/Pavement-Design/Design-Guidance

Introduction:

• The ESAL Calculator provides the ability to calculate the W18 value (ESALs over design period) used in the pavement design tool(s).

• This tool is intended to be used in conjunction with the Flexible Pavement Design Tool and/or the Rigid-Composite Design Tool, which should be filled out after completing this spreadsheet. These tools can be found on the CTDOT webpage at the link below:

• This tool follows AASHTO Guide for Design of Pavement Structures (1993) as closely as possible. A physical or digital download copy of the guide may be purchased through the AASHTO bookstore at the following link:

• All variables used in the calculation will be defined on each sheet. Commentary on each step is provided as well.

ESAL Definition:

• An ESAL, or an Equivalent Single Axle Load, is defined as the predicted number of 18-kip equivalent single axle load applications (W18) for a pavement structure over the selected design life. The design life is the period of time for which the pavement design/analysis is to be conducted. In general, the design life refers to the time elapsed as the newly constructed (or rehabilitated) pavement structure deteriorates from its initial to terminal serviceability. Typical design life values are listed in Step 6 on the next sheet.

• To determine the accumulated ESALs, the calculator divides the total traffic volume that is input (ADT = Average Daily Traffic) by the percentage of each vehicle type for the subject roadway. Default percentages have already been provided, but may be changed by the user if more specific or recent information on vehicle type/class percentages is available. Please note that the assumed vehicle type distribution varies for each roadway functional classification. To change these values, unhide the desired sheet by right clicking on the tabs below and following the directions provided.

• The vehicle type percentages are first applied to the ADT with consideration given to the specified growth rate over the design period. These traffic values are then multiplied by defined ESAL factors (sometimes referred to as LEFs, or Load Equivalency Factors) for each class, and are finally summed together. The more damaging the vehicle type is to the pavement structure, the higher the ESAL factor is. This summed value represents the accumulated ESAL value over the design life. Default ESAL factors are provided and typically should not be changed.

Outputs:

• The key output here is the accumulated ESALs, which is the value in Step 8 on the next sheet in the light green cell.

• This value is used in the pavement design equation and should be copied into the corresponding Flexible Pavement Design Tool and/or Rigid-Composite Design Tool, which can be found on the CTDOT Pavement Design Unit webpage at the link above.

Equivalent Single Axle Load (ESAL) Calculator https://store.transportation.org/Item/CollectionDetail?ID=86

Project Number = automatically calculated or linked value (do not edit) Project Description

Town(s) = user input Pavement Scope Description

Completed By = solution(s) Reviewed By

Company Name = accumulated ESALs for the designated functional class Road Name

Pavement Surface Age = not applicable

Value Unit Commentary User Notes AASHTO93 Reference (or Other)

Appendix D

Two-way Traffic? Yes (please click green cell and then choose drop down selection)

I-11, 1.4.1

ADT Year 2023 The year for the ADT should be from the same source where the ADT value was taken. N/A

The year for EOC may not always be known or provided. In this case, reach out to the lead design staff for the latest project schedule. For CTDOT projects please refer to the link to Compass below.

https://ctgovexec.sharepoint.com/projects/Pages/Projects.aspx

232 vpd (vehicles per day)

The Design ADT value is calculated by using a default 2% growth rate from the year of the provided ADT to EOC. Typical practice is to project from the ADT year to EOC and use that number as the initial value for the start of the pavement structure's design life

Appendix D

100 % Lane distribution varies by the number of through lanes, and values lower than 100% may be used for the lane distribution (see chart below). Please use the CTDOT lane distribution values unless noted otherwise.

I-11, 1.4.1 I-9, 2.1.2, Table 2.2

Number of Lanes CTDOT AASHTO

2 lanes (1 per direction) 100% 100%

4 lanes (2 per direction) 90% 80-100%

6+ lanes (3+ per direction) 70% 50-80%

0.0 % (cars)

0.0 % (trucks)

I-43 to I-47, 3.4.2 to 3.6.7 II-6 to II-7, 2.1.1 https://pavementinteractive.org/reference-desk/design/structural-design/perpetual-pavements/

Rural 27,685 ESALs (W18)

Urban FALSE ESALs (W18)

Period of time for which the pavement design/analysis is to be conductedyears

PMIS# 248511 (HECO NPS22-0383)

Design ADT is a calculated value that will be used to determine the accumulated ESALs

Full Depth Reconstruction (20-year) Nags Head https://portal.ct.gov/DOT/PP_SysInfo/Traffic-Monitoring

Available ADT (Average Daily Traffic) is the measured total volume of vehicle traffic on the subject roadway in both directions . The top link, below, contains an interactive AADT map for all roadways in CT that can be used to locate traffic data. The bottom link contains expressway ADT maps for limited access facilities as well as ADT maps for towns.

https://portal.ct.gov/DOT/PP_Bureau/Documents/MapsStep 1: ADT

Oregon Inlet Parking Lots HECO Engineers, Inc.

Zach Matthews Bart Brooke vpd (vehicles per day)Available ADT

Rural Local

Step

Step 6: Design Life 20

End of construction (EOC) year for the project

Year for the available ADT data

Please leave this value as "Yes" as the default value for two-way traffic on undivided roadways or if using combined directional data for a divided highway. Otherwise, please select "No" for a one-way road design (ramps, roundabouts, etc.) or if using single direction traffic data for a divided highway (i.e. using northbound data on a N/S expressway). For one-way roads, the ADT will be doubled to account for the default 50% directional distribution assumption of the spreadsheet.

Variable Definition

Double click to expand notes:

• 20 year design life is standard for state roadway design and should be the default value. It can also be used for most town roads and highway ramps. 15 year design life may be used for town roads as well depending on the program and treatment proposed.

Not Known

General Information

Oregon Inlet Parking Lot

Legend

Annual growth rate of all heavy vehicle types over the design period

Lane distribution is the percentage of traffic that will be carried in the design lane proposed in the final project configuration, not the existing lane conditions (check the project final plans and/or coordinate with the designer or traffic engineer if necessary). "Lanes" refers to the through lanes only, not auxiliary lanes (turning, passing, climbing, acceleration/deceleration, etc.)

I-11, 1.4.1 Appendix D https://www.fhwa.dot.gov/policyinformation/pubs/pl18027_traffic_data_pocket_guide.pdf

Double click to expand notes:

• Please note that ADT is general measure of mean daily traffic and may represent a short-term traffic study (i.e. 3-day or 7-day count) while AADT (Average Annual Daily Traffic) represents data for the entire year. Both values are acceptable for use in this calculator; however, it should be recognized that AADT may provide a more precise solution because of a larger traffic data sample size.

• ADT may vary depending on the source of information and the year it was recorded.

• Typically the ADT from the most recent year should be used. However, using a higher available ADT from a different year will yield a more conservative design.

Step 2: Year

EOC Year

Step 3: Design ADT

Step 4: Lane Distribution

Annual growth rate of cars over the design period Please use a default growth rate of 2% for cars and heavy vehicles unless another value is specifically provided or researched.

Percent of ESALs in Design Lane

Step 5: Growth Rates

Step 8: Accumulated ESALs

The accumulated ESALs is calculated automatically within the roadway FC sheets that have been hidden. They can be unhidden by right clicking on the tabs below.

Default percentages have already been provided, but may be changed if more specific information on vehicle type/class percentages is available. Please note that the assumed vehicle type distribution varies for each roadway functional classification.

I-10 to II-13, 1.4 Appendix D

Predicted number of 18-kip equivalent single axle load applications to the roadway over the selected design life. This value should only be used for flexible (asphalt) pavement design calculations. Design ESALs for rigid (concrete) or composite (asphalt on concrete) pavement design will require an adjustment to this value (accumulated ESALs multiplied by a factor of 1.5). See Rigid-Composite Design Tool for implementation https://portal.ct.gov/DOT/PP_SysInfo/Functional-Classification-Maps

A roadway functional class (FC) is the designation of a roadway into systems according to the character of service it provides in relation to the total roadway network. Please note that in this case the "Multi-lane" class is equivalent to an interstate highway. The FC maps for each town in Connecticut are found at the link below:

https://www.fhwa.dot.gov/planning/processes/statewide/related/highway_functional_classifications/fcaua

After determining the roadway FC, the ESAL value will be calculated automatically using the appropriate vehicle distributions. The result will be displayed in green in Step 8 corresponding to a Rural or Urban functional class. The red cell labeled "FALSE" is not applicable.

(please click green cell and then choose drop down selection)

Step 7: Roadway Functional Class

VEHICLE TYPES PERCENTAGES CURRENT GROWTH DESIGN E.S.A.L. DESIGN

TRAFFIC FACTORS TRAFFIC FACTOR E.S.A.L.

MOTORCYCLES 0.100 0 20.00 847 0.0001 0

PASSENGER CARS 82.000 95 20.00 694442 0.0020 1389

FOUR TIRE 14.900 17 20.00 126185 0.0389 4909

HEAVY VEHICLES

BUSES 0.100 0 20.00 847 0.4111 348

SINGLE UNITS

SIX TIRE TRUCKS 0.400 0 20.00 3388 0.2004 679

THREE AXLE TRUCKS 0.400 0 20.00 3388 1.1384 3856

FOUR AXLE TRUCKS 0.100 0 20.00 847 3.4784 2946

SINGLE-TRAILER TRUCKS

FOUR OR LESS AXLES 2.000 2 20.00 16938 0.8005 13559

FIVE AXLES 0.000 0 20.00 0 1.3377 0

SIX OR MORE AXLES 0.000 0 20.00 0 1.2303 0

MULTI-TRAILER TRUCKS

FIVE OR LESS AXLES 0.000 0 20.00 0 3.0655 0

SIX AXLES 0.000 0 20.00 0 2.1102 0

SEVEN OR MORE AXLES 0.000 0 20.00 0 2.1102 0

UNCLASSIFIED 0.000 0 20.00 0 1.4500 0

SUM OF ALL TYPES 100.000 116 27685 ESALs

AVERAGE DAILY TRAFFIC 232

LANE DISTRIBUTION 100

GROWTH RATE OF CARS 0.0 20 20.00

GROWTH RATE OF TRUCKS 0.0 20 20.00 151

Annual G.Rate in % Life (yrs) Growth Factor

G.F. = ( (1+g)^n - 1 ) / g

General Information Project ID PMIS# 248511 (HECO NPS22-0383)

Project Description Oregon Inlet Parking Lot Pavement Scope Description Full Depth Reconstruction (20-year)

Completed By Bart Brooke

• Within road functional class tabs, the light blue cells are used to assign percentages of the Average Daily Traffic by vehicle type (FHWA distribution).

• If you do not have separate information on alternative vehicle type percentages, you may use the default values already provided in the spreadsheet.

• If you do have more information or need to change these values based on better available data, the easiest way is to look at the column to the right of the "percentages". It lists how many vehicles of each type are going in each direction per day. For instance, if 30 buses are traveling (15 each way), you may adjust the % of buses until you see 15 in the appropriate row.

• Note that the most important vehicle classes for pavement design are the trucks (higher ESAL factors) and buses.

• For vehicle type descriptions that are unclear, please see one of the links below - they have a picture by each vehicle class.

= two-way ADT for the applicable segment (value determined in tab)

= lane distribution (value determined in tab)

= growth rates and factors (values determined in tab)

= classification of traffic by vehicle class (sum must be 100%)

= ESAL factors (typically should not be changed)

= automatically calculated or linked value (do not edit) for one row must be compensated for in another. The "Sum of all types" value will be highlighted in red if the values do not add up to 100%.

Functional Class Tabs: Legend

Vehicle Classification Guidance http://onlinemanuals.txdot.gov/txdotmanuals/tda/fhwa_vehicle_classification_figures.htm https://www.fhwa.dot.gov/policyinformation/tmguide/tmg_2013/vehicle-types.cfm

• Please check that the vehicle type percentages add to 100%. Any changes to % made

= unsolved target cell/inadequate pavement structure

Oregon Inlet Parking Lot

PMIS# 248511 (HECO NPS22-0383)

= user input

Legend

Links to Pavement Interactive (free pavement information resource):

https://pavementinteractive.org/reference-desk/design/structural-design/1993-aashto-flexible-pavement-structural-design/ https://pavementinteractive.org/apps/calculators/1993-aashto-flexible-pavement-structural-design/

= automatically calculated/linked value (do not edit)

= solution(s)

= solved target cell/adequate pavement structure

Disclaimer: Please use the spreadsheet(s) in a manner that best applies to your project while considering the recommendations provided within this document. No claims of accuracy are made about the answers provided by this tool. CTDOT is not responsible for errors in calculation in this Flexible Pavement Design Tool.

Reviewed By

South End of Parking lots Entrance Road Oregon Inlet Parking Lots HECO Engineers, Inc.

Zach Matthews Bart Brooke Full Depth Reconstruction (20-year) Nags Head https://pavexpress.com/

Company Name Road Name

Town(s) Pavement Scope Description

Start Limit

Link to PAVEXpress (an alternate pavement design tool):

End Limit

General Information Project Number

Project Description

Not KnownPavement Surface Age

Completed By

• All variables used in the calculation will be defined on each sheet. Commentary on each step is provided as well.

https://portal.ct.gov/DOT/Engineering/Pavement-Design/Pavement-Design-Unit https://store.transportation.org/Item/CollectionDetail?ID=86

Introduction:

• The Flexible Pavement Design Tool is intended to help engineers and designers complete a flexible pavement design primarily for use on CTDOT projects, or other projects where the CTDOT is involved. This may be used for non-DOT related projects as the information contained within represents good pavement design practice in general.

• This tool is also intended to be used in conjunction with CTDOT's ESAL Calculator, which should be completed prior to using this tool as it provides a critical input to design a flexible pavement. The ESAL Calculator can be found on the CTDOT Pavement Design Unit webpage at the link below:

• Additionally, this tool is only intended for flexible (asphalt) designs, and is not to be used for design of rigid (concrete) or composite (asphalt on concrete) pavement structures. Procedures vary significantly for a pavement structure composed entirely or partially of concrete pavement. Please refer to the Rigid-Composite Design Tool at the link above as needed.

• This tool follows AASHTO Guide for Design of Pavement Structures (1993) as closely as possible. A physical or digital download copy of the guide may be purchased through the AASHTO bookstore at the following link:

Flexible Pavement Design Concepts:

Structural Adequacy

• The purpose of using the Flexible Pavement Design Tool is to design a structurally adequate roadway, meaning it is capable of supporting vehicle traffic over a certain period of time.

Structural Number (SN)

• For a pavement structure to be structurally adequate, the proposed combination of asphalt and granular material types/depths must be able to withstand traffic loadings over the selected design life. In equivalent engineering terminology, the Provided SN must be greater than the Required SN. These terms are defined in more detail in the next sheet.

ESAL (Equivalent Single Axle Load)

• This value is defined and calculated using the ESAL Calculator, which can be found at the link above. Generally, the ESAL Calculator should be completed first, as it is one of the main inputs in this Flexible Pavement Design Tool.

Flexible Pavement Design Methodologies:

1. New Construction/Reconstruction ("New Flexible Pavement Design") = all layers of a pavement structure are being completely replaced or are being constructed as new, including all asphalt (HMA or PMA) and granular base (Subbase or Processed Aggregate Base) layers

2. Rehabilitation of an Existing Pavement ("Rehab Flexible Pavement Design") = some portion of an existing flexible pavement structure is being replaced (typically the surface layers, by means of milling) with new asphalt, while existing layers below will remain in place, both contributing to the provided structural number (SN) for the design

Other Common Project Types:

Widening

• Consider a flexible pavement project consisting of a mill and pave treatment within the travel lanes of the roadway and full-depth pavement widening of the shoulders. A new flexible pavement design can be used for the widened shoulders, where there is currently no existing pavement structure. Additionally, the rehabilitation flexible pavement design can be used for the travel lanes that will be milled and paved. If the existing travel lanes are composed of concrete pavement base to remain, the Rigid-Composite Design Tool should be used for these areas instead.

Preservation

• Pavement preservation projects are not designed to add structure, but are designed to extend the life of the pavement.

Therefore, it is not necessary to perform a flexible pavement design – only an evaluation of condition showing that the pavement is structurally adequate and can support the proposed preservation treatment is necessary. Example preservation treatments for flexible pavements include crack sealing, fog seals, chip seals, thin overlays, ultra-thin bonded overlays, microsurfacing, in-place recycling, etc.

Flexible Pavement Design Tool

Project Number Project Description

Town(s) Pavement Scope Description

Completed By Reviewed By

Company Name Road Name

Pavement Surface Age

Step Parameter Variable Value Unit Commentary User Notes Initial Serviceability Po 4.2 Default value for flexible pavements I-6 to I-9, 1.2 to 1.3

II-10 to II-11, 2.2.1 II-31 and II-34, 3.1.1 to 3.1.3

Terminal Serviceability Pt 2.0 Use a value of 2.5 for all functional classifications, except collectors (urban/rural, major or minor) and local roads which may use a value of 2.0

I-6 to I-9, 1.2 to 1.3 II-10, 2.2.1 II-31 and II-34, 3.1.1 to 3.1.3

Change in Present Serviceability Index (PSI) ΔPSI 2.20 Value is calculated automatically I-6 to I-9, 1.2 to 1.3 II-10 to II-11, 2.2.1 II-31 and II-34, 3.1.1 to 3.1.3

Reliability Level R 90 % Use a value of 95% for Interstates/Expressways (limited access), and use 90% for all other lower functional classifications (unlimited access) as defined in the ESAL Calculator I-60 to I-64, 4.2.3 to 4.5, Table 4.1 II-9, 2.1.3, Table 2.2

II-31 and II-34, 3.1.1 to 3.1.3

Standard Normal Deviate ZR -1.28 Value is calculated automatically I-5, 1.2 I-60 to I-64, 4.2.3 to 4.5, Table 4.1

II-8, 2.1.3

II-31, 3.1.1

Overall Standard Deviation S 0.45 Default value selected (AASHTO allows 0.40 to 0.50 for flexible pavement design) I-5, 1.2

II-9, 2.1.3 II-10, 2.2.1

Step 2: Traffic Analysis Accumulated ESALs W18 27,685 ESALs Double click to expand notes:

I-5, 1.2 I-10 to I-13, 1.4

I-54 to I-55, 4.1.3 II-31 to II-35, 3.1.1 to 3.1.4

Step 3: Soil Analysis Subgrade Resilient Modulus M[r] 11,152 psi Double click for M[r] values:

11152-psi I-6, 1.2 and I-13 to I-15, 1.5 II-12 to II-15, 2.3.1

II-31 to II-35, 3.1.1 to 3.1.4 III-91 to III-97, 5.3.4 to 5.4.5

Layer Coefficient, a[i] Thickness Unit

Surface Mix (TYPE S 9.5 B) 0.44 1.00 inch

Base Mix (TYPE S 9.5 B) 0.30 1.50 inch

Processed Aggregate Base (P.A.B.) 0.14 2.00 inch

Subbase 0.14 4.00 inch

8.50 inch

Solved target cell =

Unsolved target cell =

1.73 This value is calculated by multiplying each pavement layer's thickness by the corresponding layer coefficient. The Provided SN is the sum of these values.

I-6, 1.2 III-95 to III-96 III-101, 5.4.5

1.62 This value is calculated automatically after Step 5 II-31 to II-32 III-95 to III-96 III-101, 5.4.5

0.11 A suggested factor of safety for this value is approximately 0.5. The larger this value, the more conservative the design.

Yes If the output reads "Invalid", please refer to Step 5 and solve the Target Cell as instructed

Safety Factor 1.1

Reliability

Difference between initial and terminal design serviceability index

AASHTO93 Reference (or Other)

0.00

Variable Definition

Step 1: General Information

Definitive material property used to characterize roadbed soil for pavement design and is a measure of the elastic property of soil recognizing certain nonlinear characteristics

Predicted number of 18-kip equivalent single axle load applications over the design life.

The design life is the period of time for which the pavement design/analysis is to be conducted (determined with the ESAL Calculator linked on the previous sheet).

Combined standard error of the traffic prediction and performance prediction

Standard normal deviate corresponding to a level of reliability, R

Not Known Oregon Inlet Parking Lots HECO Engineers, Inc.

Zach Matthews

General Information

PMIS# 248511 (HECO NPS22-0383)

Full Depth Reconstruction (20-year) Nags Head Oregon Inlet Parking Lot

Bart Brooke

If the pavement structure is adequate given the design life, the output is "Yes". If it is not adequate, the output is "No".

This value represents the difference between the SN provided by the pavement design and the SN required for all future traffic on the pavement structure

The Required SN represents the structural number required to carry the future traffic according to inputs such as accumulated ESALs, subgrade resilient modulus, etc.

The Provided SN expresses the predicted structural strength of the roadway provided by the proposed pavement structure

Please solve the target cell by clicking on the "Data" tab > under the "Analyze" category > click "Solver" and then click "Solve" in order to determine the pavement structure adequacy.

The cell should be green and read "0.00" when successfully solved. If values have been changed, the cell will turn red and should be solved again.

Step 6: Pavement Structure Adequacy

Step 5: Solve Design Equation

Required Structural Number (SN)

Difference between provided and required SN

Adequate?

Provided Structural Number (SN)

Target Cell https://support.microsoft.com/en-us/office/load-the-solver-add-in-in-excel

If the "Solver" Add-in is not loaded in Excel, please use the link below:

Legend

= user input

= automatically calculated/linked value (do not edit)

Terminal design serviceability index

Initial design serviceability index

Total Pavement Structure Thickness:

Step 4: Proposed Pavement Structure - Layer Thicknesses

Thickness: Identifying and defining pavement layer thicknesses will provide the load-carrying capacity corresponding to the design SN, or in this spreadsheet the "Provided

SN"

Layer Coefficient, a[i]: The layer coefficient is a measure of the relative ability of the material to function as a structural component of the pavement

Double click to expand notes:

Thickness: Please insert the depth of each layer being constructed within the proposed pavement structure in the cells on the left

• A minimum total pavement structure depth of 18" - 20" (asphalt and granular base layers combined) is recommended for the purpose of mitigating potential damage from frost action.

This is approximately half the frost depth in CT (~ 40").

• For pavement structures with a single mix type, it is recommended to split the depth https://portal.ct.gov/DOT/Engineering/Pavement-Design/Pavement-Design-Unit

II-17 to II-22, 2.3.5 II-35 to II-37, 3.1.4 and 3.1.5 III-95 to III-105, 5.4.5, Table 5.2

MTG Pavement Design Catalog (see for typical pavement structures):

= unsolved target cell/inadequate pavement structure

= solved target cell/adequate pavement structure

= solution(s)

APPENDIX A

NCDOT Pavement Design Procedure AASHTO 1993 Method

NCDOT

PAVEMENT DESIGN PROCEDURE

AASHTO 1993 METHOD

N. C. Department of Transportation

Materials and Tests Unit – Pavement Section January 4, 2019

TABLE OF CONTENTS

INTRODUCTION

PAVEMENT DESIGN EQUATIONS

TRAFFIC ESALS

TERMINAL SERVICEABILITY INDEX

RELIABILITY

LAYER COEFFICIENTS

LOADING LEVELS (SUPERPAVE MIX DESIGNS)

UNIT WEIGHTS; APPLICATION RATES

ASPHALT CEMENT PERCENTAGES

PAVEMENT LAYER DEPTHS

MINIMUM DEPTHS FOR PAVEMENT DESIGNS

PAVEMENT DESIGNS FOR DETOURS

THIN-DEPTH PAVED SHOULDER DESIGN

BRIDGE REPLACEMENT PAVEMENT DESIGNS

RECOMMENED LOW VOUME PAVEMENT DESIGNS

REHABILITATION DESIGNS

PAVEMENT DRAINAGE

UNIT COSTS

APPROVED LIFE CYCLE COST ANALYSIS

PAVEMENT TYPE SELECTION

PRELIMINARY PAVEMENT DESIGNS

FINAL PAVEMENT DESIGNS

PAVEMENT REVIEW COMMITTEE

FINAL PAVEMENT DESIGN LETTER

ROADWAY DESIGN PAVED SHOULDER POLICY

QUICK CHECK LIST – FLEXIBLE DESIGNS

INTRODUCTION

The pavement design guidelines included herein are to be used for the design of all new and rehabilitated projects in

North Carolina. This procedure will be updated as necessary to include new developments in design and analysis procedures and will be distributed to Division Engineers and Pavement Review Committee members.

PAVEMENT DESIGN EQUATIONS

The AASHTO design equations as presented in the AASHTO Interim Guide for Design of Pavement Structures, 1993 are to be used for the design of both flexible and rigid pavements.

Flexible Pavement Designs

1993 Flexible Design Equation log(W18) = Z𝑅 ∗ 𝑆𝑜 + 9.36 ∗ log(SN + 1) − 0.20 + log [

∆𝑃𝑆𝐼

4.2 − 1.5

0.40 +

(𝑆𝑁 + 1)5.19

+ 2.32 ∗ log(𝑀𝑅) − 8.07

W18 = predicted number of 18-kip equivalent single axle load applications

ZR = standard normal deviate

So = combined standard error of the traffic prediction and performance prediction

ΔPSI = difference between the initial design serviceability index, po, and the design terminal service index, pt

MR = resilient modulus (psi)

SN = structural number required of the total pavement thickness. Design SN must be within 0.10 of this SN Required.

The following inputs are used for flexible pavement design:

Design period = 30 years*

*A 20 year design is to be used on secondary roads with the ADT is less than 20,000 and no LCCA is needed.

po = 4.20 pt = see Terminal Serviceability (pg. 4)

So = 0.45

ZR = see Reliability (pg. 5)

MR = if no resilient modulus is available use following equation to convert CBR values

𝑀𝑅 = 2555 ∗ (𝐶𝐵𝑅 𝑉𝐴𝐿𝑈𝐸)0.64

Rigid Pavement Designs

1993 Rigid Design Equation log(W18) = Z𝑅 ∗ 𝑆𝑜 + 7.35 ∗ log(D + 1) − 0.06 + log [

∆𝑃𝑆𝐼

4.5 − 1.5

1 +

1.624 ∗ 107

(𝐷 + 1)8.46

+ (4.22 − 032 ∗ 𝑝𝑡)

∗ log[ 𝑆𝑐

′ ∗ 𝐶𝑑 ∗ (𝐷0.75 − 1.132)

215.63 ∗ 𝐽 [𝐷0.75 − 18.42

(𝐸𝑐/𝑘)0.25]

W18 = predicted number of 18-kip equivalent single axle load(ESALS) applications

ZR = standard normal deviate

So = combined standard error of the traffic prediction and performance prediction

D = thickness (inches) of pavement slab

ΔPSI = difference between the initial design serviceability index, po, and the design terminal service index, pt

S’c = modulus of rupture (psi) for Portland cement concrete used on a specific project

J = load transfer coefficient used to adjust for load transfer characteristics of a specific design

Cd = drainage coefficient

Ec = modulus of elasticity (psi) for Portland cement concrete

K = modulus of subgrade reaction.

The following inputs are used for concrete pavement design:

Design period = 30 years po = 4.50 pt = see Terminal Serviceability (pg. 4)

So = 0.30

ZR = see Reliability (pg. 5)

J = 2.8 (tied PCC shoulders) or 3.2 (asphalt or RCC shoulders) If outside lanes are widened to 13’ a value of 2.8 can be used with any shoulders.

E = 3,500,000 psi

K = 400 psi/in (drainage layer on stabilized subgrade) or 200 psi/in (ABC)

Cd = 1.0

S’c = 650 (psi)

TRAFFIC ESALS

The following traffic information is required for all pavement designs:

Initial ADT Percent Duals

Projected ADT Percent TTST

If the traffic forecast is more than 2 years old check to see if updated traffic information is available from the Traffic

Forecasting Unit. The projected ADT is normally for a 20-year period, although 30-year projections are needed for pavement design and life cycle cost analyses. Unless the Traffic Forecast Unit provides 30-year projections, the 20-year growth rate should be used to project traffic counts to the 30-year mark. The minimum growth rate used for designs is 2.0%, unless the Traffic Forecast Unit provides a lower rate. Traffic loadings are expressed in terms of 18 kip equivalent single axle loads (ESALs) in the AASHTO design equations. Truck weight studies are used to determine "average" loadings for two different truck classifications - Duals and TTST. The term "Duals" represents single unit single axle trucks whereas the term "TTST" represents various combinations of multiple unit and multiple axle trucks. Loadings from automobiles are considered to be negligible. Design values of 2% Duals and

TTST 1% are considered minimums. Equations for growth rates and ESALS are listed below.

%𝐺𝑟𝑜𝑤𝑡ℎ = (10^ log10(

𝐴𝐷𝑇𝐹𝑢𝑡𝑢𝑟𝑒

𝐴𝐷𝑇𝐼𝑛𝑖𝑡𝑖𝑎𝑙

(𝑌𝑒𝑎𝑟𝐹𝑢𝑡𝑢𝑟𝑒−𝑌𝑒𝑎𝑟𝐼𝑛𝑖𝑡𝑖𝑎𝑙 )∗365.25

∗ 365.25 − 365.25) ∗ 100

𝐴𝐷𝑇𝐶 = 𝐴𝐷𝑇𝐼𝑛𝑖𝑡𝑖𝑎𝑙 ∗ (1 +

%𝐺𝑟𝑜𝑤𝑡ℎ

100 ∗ 365.25 )^((𝑌𝑒𝑎𝑟𝐶𝑜𝑛𝑠𝑡𝑟𝑢𝑡𝑖𝑜𝑛−𝑌𝑒𝑎𝑟𝐼𝑛𝑡𝑖𝑎𝑙)∗365.25)

𝐸𝑆𝐴𝐿𝑆𝑇𝑜𝑡𝑎𝑙 =

((1+

%𝐺𝑟𝑜𝑤𝑡ℎ

100∗365.25

)(365.25∗𝑁𝐷)−1)∗(𝐴𝐷𝑇𝐶∗

%𝑇𝑇𝑆𝑇

∗𝑇𝑇𝑆𝑇𝐹+𝐴𝐷𝑇𝐶∗

%𝐷𝑢𝑎𝑙𝑠

∗𝐷𝑢𝑎𝑙𝐹)∗

%𝐷𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛

∗𝐿𝐷

ln(1+ %𝐺𝑟𝑜𝑤𝑡ℎ

100∗365.25

ND=Design Number of Years TTSTF= TTST Loading Factor

ADTC = Average Annual Daily Traffic in the year of construction. DualF = Duals Factor

Lane Distribution Factors (LD)

No. of Lanes

In One direction

Lane Distribution

Factor

1 1.0

2 0.9

3 or more 0.8

A lane distribution factor of 0.50 will be used for the design of inside (median) lane widening of existing facilities with

2 or more lanes per direction.

Truck Loading Factors

Flexible Pavement

18 kip ESALs

DUALS TTST

Rural Freeway & Interstates 0.30 1.15

Rural Other 0.30 0.95

Urban Freeway & Interstates 0.30 0.85

Urban Other 0.25 0.80

Rigid Pavement

18 kip ESALs

DUALS TTST

Rural Freeway & Interstates 0.30 1.60

Rural Other 0.35 1.30

Urban Freeway & Interstates 0.35 1.20

Urban Other 0.25 1.10

Rural – Any area that is mostly long distance trucks. (Typically this is outside city limits)

Urban – Any area that is mostly delivery area trucks. (Typically this is inside city limits or industrial area)

% Direction

A Direction spilt of 50% is typically used in all designs. Even if a different peak hour direction is given on the plans, we assume that traffic throughout the day will equal 50% in each direction.

TERMINAL SERVICEABILITY INDEX

The terminal serviceability index (pt) represents the serviceability of a pavement at the end of the design period. The

Present Serviceability Rating (PSR) is based on a rating scale that designates the condition of the pavement at any instant of time. This rating is the average rating of a panel of individuals who rate the pavement on a scale from 0 to

5.0. A rating of 5.0 indicates a "perfect" pavement, whereas a rating of 0 indicates an "impassable" pavement.

Selection of pt is based on the lowest serviceability that will be tolerated before surfacing or reconstruction becomes necessary. A pavement with a terminal serviceability of 2.5 is considered the lowest acceptable rating for a major highway. A terminal serviceability index (pt) of 2.75 will be used for roadways where the 20-year traffic projection exceeds 40,000 ADT with a high heavy truck volume. A terminal serviceability index of 3.0 will be used for design of all roadways where the 20-year traffic projection equals or exceeds 80,000 ADT with a high heavy truck volume.

A terminal serviceability index of 2.5 will be used for the design of all other roadways.

20 Year ADT Terminal Serviceability Index

80,000 or Larger 3.00

40,000 or Larger 2.75

Lowest Acceptable 2.50

Reliability

Design reliability is defined as the probability that a pavement section will perform satisfactorily over the design period. It must account for uncertainties in traffic loading, environmental conditions, and construction materials. The

AASHTO design method accounts for these uncertainties by incorporating a reliability level R to provide a factor of safety into the pavement design and thereby increase the probability that the pavement will perform as intended over its design life. The reliability level is not included directly in the AASHTO design equations. Rather, it is used to determine the standard normal deviate ZR. The levels of reliability recommended by NCDOT for various classes of roads are listed below.

Road Types Reliability ZR

Interstate and Freeways*: 95 -1.645

Primary: 90 -1.282

Secondary with >20,000AADT: 90 -1.282

Secondary: with <20,000AADT 85 -1.036

*All Freeways should have 95% Reliability, even if they are a Primary or Secondary Road.

LAYER COEFFICIENTS

Layer coefficients used in building a new pavement structure to the required structural number (SN) are as follows:

Superpave Mix designs:

(per inch)

Asphalt Concrete Surface Course, Type S9.5X 0.44

Asphalt Concrete Intermediate Course, Type I19.0C 0.44

Asphalt Concrete Base Course, Type B25.0C 0.30

Other Materials:

Permeable Asphalt Drainage Course (PADC) 0.14

Aggregate Base Course (ABC) 0.14

Cement Treated Base Course (CTBC) 0.23

Cracked and Seated Concrete 0.28*

Rubblized Concrete 0.28*

Full Depth Reclaimed Asphalt 0.20*

(for layer)

200 mm (8") Lime Stabilized Subgrade 1.0

-or-

175 mm (7") Cement Stabilized Subgrade 1.0

* Monitoring of existing projects may result in changes to layer coefficients for crack and seat and rubblization.

LAYER COEFFICIENTS FOR EXISTING PAVEMENT

When calculating the structural number for existing pavements, the layer coefficients should be decreased to determine the effective strength provide of the existing pavement. The amount of reduction is based on the surface condition of the existing pavement. Suggested layer coefficients are given in the 1993 AASHTO Design Guide on

Table 5.2.

LOADING LEVELS (Superpave Mix Designs)

The letter designation at the end of Superpave mix designs indicates the level of loading expected in a 20 year design period. When designing for shorter durations, the selection of loading level should be based on the 20 year accumulation of ESAL's.

The selection of asphalt binder grade for Superpave mixes is dependent on loading level. For surface mixtures, the

PG grade increases as a function of loading level.

Superpave loading designations and binder grade requirements are as follows.

Mix Type Loading Range

(20 Year Million ESAL's)

Asphalt Binder Grade

Surface

S9.5B Less than 3.0 PG64-22

S9.5C 3 to 30 PG64-22

S9.5D Over 30 PG76-22

Intermediate

I19.0C All PG64-22

Base

B25.0C All PG64-22

UNIT WEIGHTS; APPLICATION RATES

Wt

Pavement Item lbs/sy-in.

S9.5B 110

S9.5C, S9.5D 112

I19.0C 114

B25.0C 114

PADC 90

ABC 150 Lbs./CF

CTBC (3.5% Cement) 150 Lbs./CF

Asphalt Cement Percentages

Superpave Mix Designs:

Asphalt Concrete Surface Course, Type S9.5B 6.7%

Asphalt Concrete Surface Course, Type S9.5C 6.0%

Asphalt Concrete Surface Course, Type S9.5D 5.7%

Asphalt Concrete Intermediate Course, Type I19.0C 4.8%

Asphalt Concrete Base Course, Type B25.0C 4.5%

Other Materials:

Permeable asphalt drainage course, Type P-57 2.5%

Permeable asphalt drainage course, Type P-78 3.0%

OGAFC, Type FC-1 6.1%

Non-strip Additive................. 10 lbs per ton of asphalt cement

Prime Coat............................ to be used on all pavements with aggregate bases where surface mix is placed directly on ABC at a rate of 0.35 gal. / sy

Asphalt Curing Seal........ for CTBC, Soil cement, and lime treated soil at a rate of

0.15 gal. / sy

PAVEMENT LAYER DEPTHS

Max layer depths: Inches

S9.5X = 3.0

I19.0C = 4.0

B25.0C = no restrictions

ABC = normally limited to 12, recommended depths are typically 6*, 8, 10, and 12 inches.

*Typically Secondary Roads.

CTBC = 8 for plant mixed; for road mixed 8 with top 7 mixed.

Single lift depths: Inches

S9.5B = 1.0 to 1.5

S9.5C,D = 1.5* to 2.0

*1.0” may be used in wedging only

I19.0C = 2.5 to 4.0

B25.0C = 3.0* to 5.5

*For B25.0C placed on unstabilized subgrade, the minimum lift thickness is 4.0.

ABC = 6* to 10

*8” Preferred minimum on unstabilized subgrade for primary & greater roadways.

CTBC = 8

FDR = 12

Any deviations from these depths will be noted on the pavement design letter.

To "build" a structural number, as much of the structural number as possible will be put into the surface and intermediate layers. In other words, the depths of these two layers will be maximized.

For normal mixes this total depth is 5-5.5 in, and for heavy duty designs the total depth is 6 in. 7 in. of surface and intermediate depth is typically required on interstate designs.

For curb and gutter and expressway gutter sections, the total surface and intermediate depth will be increased to 7 in. to match curb depth. For shoulder berm gutter sections, the total surface and intermediate depth will be set to match gutter depth.

Two lifts of surface mix is standard for almost all designs. 1.25” or 1.5” of S9.5B and 1.5” of S9.5C/S9.5D are the typical lift depths. An asphalt base, ABC base, or CTBC base is required on all flexible pavement designs. Normally 8 in of ABC is used as the starting depth for aggregate base.

Prime Coat is required to be used where surface mixes is placed directly on top of ABC.

MINIMUM DEPTHS FOR PAVEMENT DESIGNS

Minimum Structure Depths that are Recommended for NCDOT Designs

Interstate & Freeways

Primary and Secondary

>20,000ADT

Primary

<20,000ADT

Secondary

<20,000ADT

Full Depth Asphalt 11.0" Asphalt 9.5" Asphalt 7.0" Asphalt 6.5" Asphalt

ABC

7.0" Asphalt and

8" ABC

5.5" Asphalt and

8.0" ABC

3.0" Asphalt and

8.0" ABC

2.5" Asphalt and

6.0" ABC

CTBC

7.0" Asphalt and

8.0" CTBC

5.5" Asphalt and

8.0" CTBC

3.0" Asphalt and

8.0" CTBC

2.5" Asphalt and

8.0" CTBC

Concrete 9.0” Concrete 3.0” of PADC

1.25” of S9.5B**

8.0” Concrete 3.0” of PADC

1.25” of S9.5B**

7.0” Concrete 3.0” of PADC

1.25” of S9.5B**

5.0-6.0” Concrete* and

4.0” ABC

*5.0” is the minimum on residential subdivision streets only.

*5.5” is the minimum on collector roadways.

*6.0” is the minimum on Poor to Fair subgrade type (A-4 to A-7)

** For pavements with <2000 average daily trucks 6” ABC can be used rather than the PADC and

S9.5B

PAVEMENT DESIGNS FOR DETOURS

Pavement designs for detours and other temporary pavements will usually be constructed of aggregate base course

(ABC) and minimal asphalt depths to reduce construction waste. ABC recovered from detour structures will be re-used in the project or stockpiled to be used by Division Maintenance Forces. Typical design periods are from 6 months to 2 years as provided by Project Design Engineer. Pavement designs prepared for design periods of less than 6 months should be carefully reviewed since required structural numbers may be unreasonably low. For any detour that is expected to carry truck traffic, the minimum asphalt layer shall be 2 inches. Surface mix is required to be the top layer is any flexible design including detours and temporary pavements.

Note: The selection of loading level for SuperPave mixes will be based on the theoretical 20 year accumulation of

ESAL’s even when the design life used for the pavement structure is for a short duration, with the exception of D mix types, which will be replaced with a C mix.

THIN-DEPTH PAVED SHOULDER DESIGN

For paved shoulders that will not be constructed with full depth of travel lane pavement thickness (see Roadway

Design Paved Shoulder Policy), 2 % of the design lane traffic loads will be used for design.

BRIDGE REPLACEMENT PAVEMENT DESIGNS

Due to the small amount of roadway work involved in most of these projects, final pavement designs for bridge replacement projects are typically made without a soils investigation or review committee input. On bridge replacement projects with roadway work less than 1,200 ft in length, a full depth asphalt design is normally recommended. For lengths in excess of 1,200 ft, an aggregate base course (ABC) will be provided if feasible. All of these designs are to be based on a 20 or 30 year design period, based on ADT. If there is an exception, the reason(s) for the exception should be documented on the final pavement design issued to the Roadway Design or

Design Services Project Engineer. Overlay designs on existing pavement should consist of one to two lifts of surface and based on the condition of the existing roadway. Recommended bridge replacement pavement designs are listed on next page, as low volume designs.

RECOMMENED LOW VOUME PAVEMENT DESIGNS

This table is an easy method to determine designs typically used for low volume pavements, based on required SN (Page 1). Minimum pavement depths based on road types (page 10) still are required, regardless of this table.

****CHECK DESIGN MEETS MINIUM DEPTHS FOR PAVEMENT DESIGNS (PAGE 10)****

Without Curb and Gutter Designs:

(Determine if load level is B, C, or D by using the 20 year ESALS - Page 7)

Table A-1 Recommended Pavement Design - (Full Depth)

Required Structural Number

Surface Inter. Base Structural Number Provided

B LEVEL DESIGNS (Use when 20 year ESALS are <0.3 Million)

<2.37 2.5” S9.5B 4.0” B25.0C 2.30

2.38 - 2.52 2.5” S9.5B 4.5” B25.0C 2.45

2.53 - 2.67 2.5” S9.5B 5.0” B25.0C 2.60

2.68 - 2.82 2.5” S9.5B 5.5” B25.0C 2.75

2.83 - 3.47 2.5” S9.5B 2.5” I19.0C 4.0” B25.0C 3.40

B, C, & D LEVEL DESIGNS (Use when 20 year ESALS are >0.3 Million)

<2.59 3.0” S9.5X 4.5” B25.0C 2.52

2.60 - 2.74 3.0” S9.5X 4.5” B25.0C 2.67

2.75 - 2.89 3.0” S9.5X 5.0” B25.0C 2.82

2.90 - 3.04 3.0” S9.5X 5.5” B25.0C 2.97

3.05 - 3.69 3.0” S9.5X 2.5” I19.0C 4.0” B25.0C 3.62

3.70 - 3.84 3.0” S9.5X 2.5” I19.0C 4.5” B25.0C 3.77

3.85 - 3.99 3.0” S9.5X 2.5” I19.0C 5.0” B25.0C 3.92

4.00 - 4.14 3.0” S9.5X 2.5” I19.0C 5.5” B25.0C 4.07

(Determine if load level is B, C, or D by using the 20 year ESALS - Page 7)

Table A-2 Recommended Pavement Design (ABC)

Required Structural Number

Surface Inter. Base Structural Number Provided

B LEVEL DESIGNS (Use when 20 year ESALS are <0.3 Million)

<2.01 2.5” S9.5B * 6” ABC 1.94

2.02 - 2.29 2.5” S9.5B* 8” ABC 2.22

2.30 - 2.57 2.5” S9.5B* 10” ABC 2.50

2.58 - 3.11 2.5” S9.5B 2.5” I19.0C 6” ABC 3.04

3.12 - 3.39 2.5” S9.5B 2.5” I19.0C 8” ABC 3.32

3.40 - 3.67 2.5” S9.5B 2.5” I19.0C 10” ABC 3.60

B, C, & D LEVEL DESIGNS (Use when 20 year ESALS are >0.3 Million)

<2.23 3.0” S9.5X 6” ABC 2.16

2.24 - 2.51 3.0” S9.5X 8” ABC 2.44

2.52 – 2.79 3.0” S9.5X 10” ABC 2.72

2.80 - 3.33 3.0” S9.5X 2.5” I19.0C 6” ABC 3.26

3.34 - 3.61 3.0” S9.5X 2.5” I19.0C 8” ABC 3.54

3.62 - 3.89 3.0” S9.5X 2.5” I19.0C 10” ABC 3.82

* Prime coat required

Curb and Gutter Designs:

(Determine if load level is B, C, or D by using the 20 year ESALS - Page 7)

Table B-1 Recommended Pavement Design - (Full Depth)

Required Structural Number

Surface Inter. Base Structural Number Provided

<4.35 3.0” S9.5X 4.0” I19.0C 4.0” B25.0C 4.28

4.36 - 4.50 3.0” S9.5X 4.0” I19.0C 4.5” B25.0C 4.43

(Determine if load level is B, C, or D by using the 20 year ESALS - Page 7)

Table B-2 Recommended Pavement Design (ABC)

Required Structural Number

Surface Inter. Base Structural Number Provided

<3.99 3.0” S9.5X 4.0” I19.0C 6” ABC 3.92

4.00 - 4.27 3.0” S9.5X 4.0” I19.0C 8” ABC 4.20

4.28 - 4.55 3.0” S9.5X 4.0” I19.0C 10” ABC 4.48

REHABILITATION DESIGNS

Emphasis for rehabilitation designs is to be placed on structural evaluation of the existing pavement. In addition to the normal investigation of these projects by the Geotechnical Unit, all pavement designs presented before the

Pavement Review Committee will require the following information:

1. Cores of existing pavement structure - to determine thickness of layers, assign structural layer coefficients, and conduct laboratory tests as needed (typically one core for every five FWD test locations).

2. Temperature and FWD deflection data at least every 500 ft. in outside wheel path of outside lane to include all core locations. If project is less than one mile in length, deflections are to be taken every 200 ft.

3. Dynamic Cone Penetrometer (DCP) evaluations to a minimum depth of 24 in. (through stone base, if present, and into subgrade at core locations) as permitted by traffic control and safety considerations.

For rehabilitation designs requiring asphalt overlays, the design period will be 10 years. DCP, FWD, and lab test data in addition to Geotechnical recommendations will be used to determine the existing soil support conditions.

Present and 10 year projected traffic figures are to be used to determine the number of 18 kip axle loads during the design period and the required SN. With this information, three overlay thickness determinations may be prepared as follows:

Design 1 - Condition Survey Method

The existing SN of the pavement is determined from the condition survey and core data. The overlay thickness is determined from:

Overlay SN = Required SN - Existing SN

The existing SN will be determined by the pavement design engineer by assigning layer coefficients to the pavement layers after examination of cores. DCP data will be utilized to determine the depth and layer coefficient for aggregate base. Chapter 5 of the AASHTO Guide provides general guidelines for assignment of layer coefficients based upon pavement surface distress. The layer SN is obtained by multiplying the layer thickness by its assigned layer coefficient. The Existing SN is the sum of all layer

SN's in the pavement structure. The Required SN is the SN needed to support the 10 year projected traffic, with the difference in these two structural numbers being the structural deficiency or overlay requirement.

Design 2 - Effective Structural Number

The effective structural number of the pavement structure will be determined from FWD data as outlined in the Chapter 5 rewrite of the 1986 AASHTO Design Guide.

Effective SN = 0.0045*D*(Ep)^(1/3)

D = total depth of pavement structure (in.)

(total pavement depth above subgrade)

Ep = effective modulus of pavement layer (psi)

(from temperature corrected deflection data)

Overlay SN = Required SN - Effective SN

Design 3 - Effective Modulus

The number of 18 kip axle loads during the 10 year design period is calculated and the target deflection is determined from one of the following equations:

Dt = 10^((log(9.3*109/Wt18)/3.34)) (ABC) or, Dt = 10^((log(5.6*1011/Wt18)/4.6)) (Full depth asphalt)

Dt = target FWD deflection (mils) (desired deflection limit), Wt18 = number of 18 kip single axle load applications during the 10 year design period

Deflection under the load plate is temperature corrected (currently requires air, pavement surface temperature, and thickness of asphalt). The overall modulus of the entire pavement structure is determined from the temperature corrected deflection by using the Boussinesq equation for a one layer structure:

Modulus = 2*1000*P*(1-µ2)/(ã* r *D0)

P = FWD load (lbs) µ = Poisson's ratio r = radius of loaded area (in.)

ã = 3.14159...

D0 = Temperature corrected deflection under load plate (mils)

For the FWD with a 5.905" (150 mm ) radius load plate and Poisson's ratio = 0.35 for the single layer, this equation reduces to:

Modulus (psi) = 94.596*P ÷ D0

Now, by using Odemark's transformation for a 2 layer system, one can determine overlay thickness by calculating the depth of 500,000 psi (3500 MPa) surfacing required to reduce the load plate deflection to the target deflection. In this analysis, the following equation is solved for D:

Dt = 851,360*(D1+D2)

Dt = target deflection (mils)

D1 = 1/(Modulus*(1+((D/r)*((Ep/Modulus)^(1/3)))^2)^0.5)

D2 = (1-(1/((1+(D/r)^2)^0.5)))/Ep r = FWD load plate radius = 5.9055 in. (150 mm).

Ep = 500,000 psi (overlay modulus)

D = overlay thickness (in.)

Modulus = overall pavement modulus (one layer modulus representing entire pavement structure and subgrade) (psi)

All three design procedures may be evaluated by the Pavement Analysis Engineer for each project before providing a design recommendation. Design method 3 is preferred due to larger statistical sample over full project length. In order to accommodate clearance limitations under structures the design thickness may be reduced by utilizing additives in the asphalt mix.

PAVEMENT DRAINAGE

Drainage Sublayers

Rigid pavements will be constructed utilizing a Permeable Asphalt Drainage Layer (PADC) and an asphalt separating layer under the concrete layer in order to provide uniform support and positive drainage, when Average

Daily Truck Traffic (ADTT) > 2000 trucks per day.

Shoulder Drains

Shoulder drains will be used continuously when permeable asphalt drainage layers are used. Shoulder drains will be considered for all projects with average daily traffic (ADT) of 15,000 and heavy truck percent greater than 5%. For projects with average daily traffic of 40,000 and heavy truck percent greater than 15%, shoulder drains are highly recommended.