pavement design - ii

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Pavement DesignGuest Lecturer

Dr. Sirous Alavi, P.E.

SIERRA TRANSPORTATION ENGINEERS, INC.1005 Terminal Way, Suite 125

Reno, Nevada 89502

Topics

Introduction– Design Factors– Pavement Types

Fundamentals of Pavement Design– AASHTO– Asphalt Institute

Types of Design

State-of-Practice State-of-the-Art

Empirical Mechanistic-Empirical Mechanistic

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Mechanistic-Empirical (M-E) Design

Primary advantage is the consideration of the state of stress

HMABase

Subbase

Subgrade Soil

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Establishes connection between distress and distress mechanism

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Accounts for new materials, traffic loads, and construction proceduresAll design features affecting pavement performance considered Relies more on fundamental engineering mechanicsPrimary focus on pavement performance

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1993 AASHTO Guide Design Variables– Time– Traffic– Reliability– Environment– Serviceability– Structural Number

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AASHTO Design

Time Constraints– Performance Period

Refers to the time that an initial pavement structure will last before rehab

– Analysis PeriodRefers to the period of time that any design strategy must cover

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AASHTO Design

Traffic– Equivalent Single Axle Load (ESAL)

Converts wheel loads of various magnitudes and repetitions to an equivalent number of "standard" or "equivalent" loads based on the amount of damage they do to the pavementF

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AASHTO Design

Equivalent Axle Load Factor (EALF)– Damage per pass to a pavement by the axle

in question relative to the damage per pass of a standard axle load

– Depends of type of pavements, thickness or structural capacity and terminal conditions

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EALF Table for Flexible Pavement, Single Axle & pt of 2.5

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Axle Load (kips)

1 2 3 4 5 6

2 0.004 0.004 0.003 0.002 0.002 0.0024 0.003 0.004 0.004 0.003 0.002 0.0026 0.011 0.017 0.017 0.013 0.010 0.0098 0.032 0.047 0.051 0.041 0.034 0.03110 0.078 0.102 0.118 0.102 0.088 0.08012 0.168 0.198 0.229 0.213 0.189 0.17614 0.328 0.358 0.399 0.388 0.360 0.34216 0.591 0.613 0.646 0.645 0.623 0.606

Pavement Structural Number (SN)

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AASHTO Design

m = number of axle load groupsFi = the EALF for the ith axle load groupni = number of passes of the ith axle load group

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∑=

=m

iiinFESAL

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200X AASHTO Design Guide

No more ESALsTraffic input– Vehicle type (number of axles)– Axle weight

Quantity and quality of raw traffic data similar to that used to compute ESALS– Consistent with FHWA Traffic Monitoring

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Traffic Hierarchical Input Levels

PoorNational Default WIM & AVC, Vehicle Counts3

ModestRegional Default WIM & AVC, Vehicle Counts 2

GoodSite specific WIM & AVC1

Knowledge of ParametersInput ValuesInput

Level

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200X AASHTO Design GuideLoad Spectra– Axle weight frequencies for each

common axle combination (e.g. single axle, tandem axle, tridemaxle, quad axle).

0

100

200

300

400

500

600

700

800

0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000 65000 70000 75000 80000

Axle Load (lbs)

Num

ber

of A

xles

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AASHTO Design

Reliability - Incorporating some degree of certainty into the design process to ensure that various design alternatives will last the Analysis Period

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Functional Classificaiton Urban Rural

Interstate 85 - 99.9 80 - 99.9Arterials 80 - 99 75 - 95

Collectors 80 - 95 75 - 95Local 50 - 80 50 - 80

Recommended Level of Reliability

AASHTO Design

Environmental– Temperature

Stresses induced by thermal actionChanges in creep propertiesEffect of freezing and thawing of subgrade

– RainfallPenetration of surface water into underlying materialsF

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AASHTO Design

Serviceability– Initial serviceability index is function of

pavement type and construction quality– Terminal serviceability index is lowest

index that will be tolerated before rehab, resurfacing, or reconstruction

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AASHTO DesignStructural Number– mi = drainage coefficient for layer i– a1, a2, a3 = layer coefficient representative of

surface, base, and subbase course, respectively– D1, D2, D3 = thickness representative of surface,

base, and subbase course, respectively

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33322211 mDamDaDaSN ++=

SURFACE (AC)

BASE

SUBGRADE

SUBBASE (OPTIONAL)

AASHTO Design Example

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– 20-year flexible pavement analysis period

– Low volume road with limited growth potential

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COPPER POINTCOPPER POINT

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GREEN RANCH

ADO

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MOUNTAIN VISTA

PLUM

AS

PLUMAS

RIDGEVIEW

RID

GEV

I EW

RIDGEVIEW

RID

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NA

MED

UNNAMED

WIND

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– 72-hour vehicle counts were conducted directionally at three locations within the project boundaries using machine traffic counters

– Manual classification counts were conducted at the machine count locations to “calibrate”the machine count data and categorize into the FHWA 13 vehicle classification scheme

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Adjusted Traffic Volumes and Vehicle Classification Year 2005 Through 2010 Road Segment: Ridgeview Drive @ Plumas Street Class 1 Class 2 Class 3 Class 4 Class 5 Class 6 Class 9 Total

EB % 43.64 54.11 0.35 1.60 0.15 0.15 100 Volume 1132.30 1404.00 9.10 41.60 3.90 3.90 2594.8

WB % 43.29 54.11 0.70 1.60 0.15 0.15 100 Volume 1123.20 1404.00 18.20 41.60 3.90 3.90 2594.8 5189.6 Total ADT Road Segment: Ridgeview Drive @ Mountain Vista Way Class 1 Class 2 Class 3 Class 4 Class 5 Class 6 Class 9 Total

EB % 43.44 54.11 0.45 1.60 0.20 0.20 100 Volume 823.65 1026.00 8.55 30.40 3.80 3.80 1896.2

WB % 42.94 54.11 0.95 1.60 0.20 0.20 100 Volume 814.15 1026.00 18.05 30.40 3.80 3.80 1896.2 3792.4 Total ADT

Adjusted Traffic Volumes and Vehicle Classification Year 2011 Through 2025 Road Segment: Ridgeview Drive @ Plumas Street Class 1 Class 2 Class 3 Class 4 Class 5 Class 6 Class 9 Total

EB % 43.94 54.11 0.35 1.60 0.00 0.00 100 Volume 1140.10 1404.00 9.10 41.60 2594.8

WB % 43.59 54.11 0.70 1.60 0.00 0.00 100 Volume 1131.00 1404.00 18.20 41.60 2594.8 5189.6 Total ADT Road Segment: Ridgeview Drive @ Mountain Vista Way Class 1 Class 2 Class 3 Class 4 Class 5 Class 6 Class 9 Total

EB % 43.84 54.11 0.45 1.60 0.00 0.00 100 Volume 831.25 1026.00 8.55 30.40 1896.2

WB % 43.34 54.11 0.95 1.60 0.00 0.00 100 Volume 821.75 1026.00 18.05 30.40 1896.2 3792.4 Total ADT


Compute ESALs using EALFs from AASHTO Tables in Appendix DAssumptions – Typical axle weights for each vehicle class– SN of 3.0 – pt of 2.5

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Plumas Mountain Vista Plumas Mountain Vista Plumas Mountain Vista

2005 0 90 81 33,031 29,487 33,031 29,4872006 1 90 81 33,031 29,487 66,062 58,9732007 2 90 81 33,031 29,487 99,093 88,4602008 3 90 81 33,031 29,487 132,124 117,9472009 4 90 81 33,031 29,487 165,155 147,4332010 5 90 81 33,031 29,487 198,187 176,9202011 6 75 66 27,362 23,963 225,548 200,8822012 7 75 66 27,362 23,963 252,910 224,8452013 8 75 66 27,362 23,963 280,271 248,8072014 9 75 66 27,362 23,963 307,633 272,7702015 10 75 66 27,362 23,963 334,994 296,7322016 11 75 66 27,362 23,963 362,356 320,6952017 12 75 66 27,362 23,963 389,717 344,6572018 13 75 66 27,362 23,963 417,079 368,6202019 14 75 66 27,362 23,963 444,441 392,5822020 15 75 66 27,362 23,963 471,802 416,5452021 16 75 66 27,362 23,963 499,164 440,5072022 17 75 66 27,362 23,963 526,525 464,4702023 18 75 66 27,362 23,963 553,887 488,4322024 19 75 66 27,362 23,963 581,248 512,3952025 20 75 66 27,362 23,963 608,610 536,357

WB Yearly ESALs Cumulative ESALsWB Daily ESALs

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Materials– R-value data was collected at five sample

locations (8, 7, 10, 20, 8) – Resilient Modulus (MR) relationship

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R-value ≤ 20 MR = 1000 + 555 x R-value (psi)

1.1Drainage Coefficient for SB layer, m3

1.1Drainage Coefficient for Base layer, m2

1.0Drainage Coefficient for AC layer, m1

0.08Layer Coefficient for Subbase (Borrow), a3

0.14Layer Coefficient for Gravel Base, a2

0.39Layer Coefficient for New Plant Mix Surface (AC), a1

350Modulus of Elasticity for New AC (ksi)2.5Terminal Serviceability, Pt

4.2Initial Serviceability, P0

6.9Subgrade Resilient Modulus, MR (ksi)10.60Subgrade R-value0.45Standard Deviation (New Construction), So

80%Reliability, R (%)610,000Traffic (ESALs), W18

20Design Life, years

AverageParameter

SN ≈ 3.1

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AASHTO Design

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1.31.1in 1014.0in 0.439.0

22211

=××+×=

+=

SNSN

mDaDaSN

SURFACE (AC)

BASE

SUBGRADE

Assume D values for surface and base– Asphalt is 4 inches– Base is 10 inches

Calculate SN - Is it acceptable?

Topics

Introduction– Design Factors– Pavement Types

Fundamentals of Pavement Design– AASHTO– Asphalt Institute

Asphalt Institute (AI) Design

Determine minimum thickness of asphalt layer that will adequately withstand the stresses that develop for two strain criteria– Vertical compressive strain at surface of

subgrade– Horizontal tensile strain at bottom of asphalt

layer

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SUBGRADE

Stress distribution within different layers of the pavement structure

General form of stress reduction

P0

P1

P1

Wheel load


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SUBGRADE

Wheel load

TensionCompression


Design Criteria– Fatigue

Nf = allowable number of load repetitions|E*| = dynamic modulus∈t = horizontal tensile strain at the bottom of the asphalt layerAssumes asphalt volume of 11% and air void volume of 5%

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Nf = 0.0796(∈t)-3.291 |E*|-0.854

20% Fatigue

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Design Criteria– Permanent Deformation

Nd = allowable number of load repetitions∈c = vertical compressive strain on the surface of the subgrade

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Nd = 1.365 x 10-9 (∈c)-4.477

0.5 inch


Five main steps1. Select or determine input data2. Select surface and base materials3. Determine minimum thickness required4. Evaluate feasibility of staged construction

and prepare plan, if necessary5. Carry out economic analyses

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COPPER POINTCOPPER POINT

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PO

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GREEN RANCH

ADO

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MOUNTAIN VISTA

PLUM

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PLUMAS

RIDGEVIEW

RID

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RIDGEVIEW

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Asphalt Institute (AI) Design Example

Select or determine input data– Traffic

Characteristics– ESALs similar to

AASHTO

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Gross Axle Load (kips)

SingleAxles

Tandem Axles

Tridem Axles

1 0.000022 0.000184 0.00209 0.00036 0.01043 0.001 0.000308 0.0343 0.003 0.001

10 0.0877 0.007 0.00212 0.189 0.014 0.00314 0.360 0.027 0.00616 0.623 0.047 0.011

WB Daily ESALs WB Yearly ESALs Cumulative ESALs

Plumas 2 Plumas 2 Plumas 2

2005 0 118 43,110 43,1102006 1 118 43,110 86,2212007 2 118 43,110 129,3312008 3 118 43,110 172,4412009 4 118 43,110 215,5522010 5 118 43,110 258,6622011 6 72 26,197 284,8592012 7 72 26,197 311,0572013 8 72 26,197 337,2542014 9 72 26,197 363,4512015 10 72 26,197 389,6492016 11 72 26,197 415,8462017 12 72 26,197 442,0432018 13 72 26,197 468,2412019 14 72 26,197 494,4382020 15 72 26,197 520,6352021 16 72 26,197 546,8332022 17 72 26,197 573,0302023 18 72 26,197 599,2272024 19 72 26,197 625,4252025 20 72 26,197 651,622


Select or determine input data– R-value data was collected at five sample

locations (8, 7, 10, 20, 8) – Resilient Modulus (MR) relationship

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MR = 1155 + 555 x R-value (psi)

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Select surface and base materials– Asphalt concrete surface or emulsified

asphalt surface– Asphalt concrete base, emulsified

asphalt base, or untreated aggregate base

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Determine minimum thickness required– Obtained by computer program – Entering the appropriate table or chart

Assume 10 inch untreated aggregate baseSubgrade MR of 7 psiDesign ESAL of 655,000

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6.5 inch

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Evaluate feasibility of staged construction and prepare plan, if necessary– Used when adequate funds are not

available to construct the pavement to the “required” depth

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Carry out economic analyses– Evaluate alternative designs based on

the type of pavement, type of materials used, whether or not staged construction is used, etc.

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Questions

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pavement design - ii

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