CEE 3604 Transportation Engineering Pavement Design128.173.204.63/courses/cee3604/cee3604_pub/Transportation_pave… · Transportation Engineering (A.A. Trani) AASHTO Design Procedure

Transportation Engineering (A.A. Trani)

CEE 3604 Transportation Engineering

Pavement Design

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Pavement Design

• The level of service of roads depends not only onnumber of lanes and safety features of the road butalso on the quality of pavements

• Pavement design techniques:

• Flexible and Rigid pavements

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Read Florida DOT Pavement Design Document


Definition of Flexible Pavement Layers

• A typical pavement is made up of multiplelayers

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source: Florida DOT Flexible Pavement Design Manual


Definitions• Friction course

• Provides a skid-resistancesurface

• Structural course

• Distributes the traffic loadsto the base course

• Base course

• Supports the structuralcourse and distribute loads tothe stabilization (subgrade)layer

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Types of Pavements

• Flexible pavements

• Rigid pavements

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Source: Encyclopedia Britannica


Flexible Pavements

• Multi-Layered system (3-4 layers)

• Design life is usually 10-20 years

• Unit cost ($2-$3 per square foot according toRO Anderson Engineers, 2017)

• Higher maintenance cost

• Relatively low flexural strength (highdeformation of the sub-grade)

• Better ride quality (no expansion joints)

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Rigid Pavements

• Normally 2-3 layers

• Design life 30-40 years

• Unit cost ($6-$8 per square foot according toRO Anderson Engineers, 2017)

• Lower maintenance cost

• Relatively high flexural strength (lessdeformation of sub-grade)

• Lower ride quality (due to expansion joints)

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Example: Original Airport Pavement for Dulles International Airport (circa 1962)

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Source: Fuselier, Grubs and McQueen, ASCE 2008 Transportation Engineering (A.A. Trani)


Example: New Specification for Airport Pavement at Dulles International Airport (circa 2005)

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18 inches of PCC6 inch Cement Treated Base layer12 inch subgrade Soil (Cement Stabilized)


Why Do some Pavements Have to Be So Complex?

• To support large transportation vehicles (like very large aircraft)

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Airbus A380-800 maximum takeoff mass is around 570 metric tons


AASHTO Equation

• An equation that relates the pavementstructural performance and various operationalfactors such as the vehicle loadings, strength ofroadbed soils and pavement structure

• The American Association of State Highway Officials(AASHTO)

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AASHTO Design Equation Variables

• Accumulated 18-kip Equivalent Single Axle LoadsESAL or ESALD

• Traffic load information used in pavement design

• Traffic levels for ESAL

• Resilient Modulus (MR)

• A measurement of the stiffness of the roadbedsoil

• Reliability (%R)

• Standard Normal Deviate (ZR)

• Reliability (%R) value converted into logarithmicform for calculations purposes

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AASHTO Equation Design Constants

• Standard deviation (So)

• Accounts for variability in traffic load and construction (So = 0.45 typical)

• Current Serviceability Index (PSI)

• A rating of 0 to 5 is used with 5 being the best and 0 being the worst

• Initial Serviceability (PI)

• Terminal Serviceability (PT)

• Change in Serviceability (dPSI)

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AASHTO Design Procedure

• Required Structural Number (SNR)

• “a weighted thickness in inches calculated from traffic load information and roadbed soil stiffness, representing the required strength of the pavement structure”

• The objective of the AASHTO design method is to calculate the value of SNR

• SNR represents the strength of the pavement required to carry the traffic loads down to the road soil layer with adequate serviceability throughout the life cycle of the pavement

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AASHTO Design Equation

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AASHTO Design Procedure (per Florida DOT Manual)

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Design Periods (Florida DOT Design Manual)

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Design Procedure Required Structural Number

• Step 1 - the 18-kip Equivalent Single Axle Loads 18-kip (ESAL's) are obtained from the District Planning Office

• Step 2 - the Resilient Modulus (MR) used to characterize the strength of the roadbed soil is obtained from actual laboratory testing

• Step 3 - A safety factor is applied using a Reliability (%R) value from Table 5.2. Recommended values range from 75 to 99%. A Standard Deviation (SO) of 0.45 is used in the calculation. The Standard Normal Deviate (ZR) is dependent on the Reliability (%R)

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Design Procedure• Most DOTs have produced tables with acceptable values

of SNR for given inputs to the AASHTO Equation (see the Florida manual DOT)

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Layer Calculations

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Pavement Design Layer Calculations

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SNc = a1D1+ a2D2 + a3D3+ a4D4

where:SNc= Total calculated strength of all pavement layers (inches or millimiters)a1 = first pavement layer coefficient (dim)D1 = first pavement layer thickness (inches or millimiters)a2,a3 and a4 are coefficients for other layersD2,D3 and D4 are thicknesses forother layers


Layer Coefficients (per Florida DOT Manual)

• “Layer coefficients ( ) have been developed which represent the relative strength of different pavement in materials”

• “The values for these materials are given in Table5.4” of the Florida Pavement Design Manual

• The coefficients presented in this table are basedon the best available data. Future adjustments willbe made to these values by manual revisions shouldresearch or other information dictate”

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a1,a2,a3 and a4


Layer Coefficients (Table 5.4)

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Design Examples (Florida DOT Design Manual)

• Page 47 of Florida DOT Flexible Pavement design Manual

• Go to page 64 in the DOT Flexible Pavement Design Manual

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Design Example # 1 (AASHTO Method)

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Design Example # 1 (Florida DOT Design Manual)

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Asphalt Concrete Friction Course Selection Chart (Table 4.1)

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Design Example (Initial Step)

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32source: Florida DOT Flexible Pavement Design Manual


Design Example Solution

33source: Florida DOT Flexible Pavement Design Manual


Example of FC-5 Material

Source: Jim Musselman , Florida Department of Transportation

Permeable 3/4 inch layerTexture and aggregates to improve friction and avoid hydroplaning

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For example problem


Structural Numbers for Base Layer

Source: Florida Department of Transportation

36a

Note that using optionalbase group 10 with astructural course of 5''provides an SN number of 4.09 (versus 4.05 required)

atrani

Highlight

atrani

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For example problem



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Typical Cost of Mix Asphalt

Source: Yin and West, 2018 - https://eng.auburn.edu/research/centers/ncat/files/technical-reports/rep18-03.pdf

SMA = Stone Matrix AsphaltSuperpave = Superior Performing Asphalt Pavement

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Virginia Pavement Data

SMA Pavements Superpave Pavements

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Example of Pavement Design Software

40c

• Uses National Cooperative Highway research Program (NCHRP) Mechanistic-Empirical method

• Calculates pavement responses (stresses, strains, and deflections)

• Includes traffic, climate, and materials parameters

• Hot-mix asphalt (HMA) and Portland Cement Concrete (PCC) pavements

https://www.aashtoware.org/wp-content/uploads/2018/10/Pavement-ME-Design-Brochure-FY-2019.pdf


Minnesota DOT Software

https://www.dot.state.mn.us/materials/pvmtdesign/software.html

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Airport Pavements

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Note: At rest, ~ 95% of the aircraft weight is on the main landing gear


Sample Airport Pavement Charts

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Aircraft manufacturersprovide ready-made charts

for quick verification

http://www.boeing.com/commercial/airports

Boeing 777-300ER Taking Off at ChicagoO’Hare Airport



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Boeing 777-300ERDimensions in

Airport Design Document

http://www.boeing.com/commercial/airports

Boeing 777-300ER Taking Off at ChicagoO’Hare Airport



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Flexible PavementDesign Chart

U.S. Army Corps of Engineers

Design Method (S-77-1):

Source: 777-200LR / -300ER / -Freighter

Airplane Characteristics for Airport Planning



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U.S. Army Corps of Engineers

Design Method (S-77-1):



California Bearing Ratio (CBR)

Flexible Pavement Thickness (inches)

Weight onMain Landing

Gear

Annual Departures


California Bearing Ratio (CBR)

• A measure of the load-bearing capacity (or strength) of natural soil

• Strength of soil compared to crushed California limestone (assumed to have a CBR value of 100)

• CBR is a standard described in ASTM Standard D1883-05 (for laboratory samples)

• D4429 (for soils in the field)

• AASHTO T193

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Check out information in : http://www.pavementinteractive.org/california-bearing-ratio/



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Portland Cement Association

Design Method





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Portland Cement Association

Design Method



Allo

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Pave

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StrengthModulus

(lb/cu.inch)

Weight onMain Landing

Gear

CEE 3604 Transportation Engineering Pavement Design128.173.204.63/courses/cee3604/cee3604_pub/Transportation_pave… · Transportation Engineering (A.A. Trani) AASHTO Design Procedure

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