pavement analysis

ASSIGNMENT FLEXIBLE PAVEMENT DESIGN ECV 5606 Saeed Badeli

1

INTRODUCTION

Differences Between Concrete and Asphalt Pavement

Historically, pavements have been divided into two broad categories, rigid and flexible.

These classical definitions, in some cases, are an over-simplification. However, the terms

rigid and flexible provide a good description of how the pavements react to loads and the

environment.

The flexible pavement is an asphalt pavement. It generally consists of a relatively thin

wearing surface of asphalt built over a base course and subbase course. Base and subbase

courses are usually gravel or stone. These layers rest upon a compacted subgrade (compacted

soil). In contrast, rigid pavements are made up of portland cement concrete and may or may

not have a base course between the pavement and subgrade.

The essential difference between the two types of pavements, flexible and rigid, is the manner

in which they distribute the load over the subgrade. Rigid pavement, because of concrete’s

rigidity and stiffness, tends to distribute the load over a relatively wide area of subgrade. The

concrete slab itself supplies a major portion of a rigid pavement's structural capacity. Flexible

pavement, inherently built with weaker and less stiff material, does not spread loads as well

as concrete. Therefore flexible pavements usually require more layers and greater thickness

for optimally transmitting load to the subgrade.

The major factor considered in the design of rigid pavements is the structural strength of the

concrete. For this reason, minor variations in subgrade strength have little influence upon the

structural capacity of the pavement. The major factor considered in the design of flexible

pavements is the combined strength of the layers.

One further practical distinction between concrete pavement and asphalt pavement is that

concrete pavement provides opportunities to reinforce, texture, color and otherwise enhance a

pavement, that is not possible with asphalt. These opportunities allow concrete to be made

exceedingly strong, long lasting, safe, quiet, and architecturally beautiful. Concrete

pavements on average outlast asphalt pavements by 10-15 years before needing

rehabilitation.


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Introduction to the Pavement Design Process

Effective pavement design is one of the more important aspects of project

design. The pavement is the portion of the highway which is most obvious

to the motorist. The condition and adequacy of the highway is often judged

by the smoothness or roughness of the pavement. Deficient pavement

conditions can result in increased user costs and travel delays, braking and

fuel consumption, vehicle maintenance repairs and probability of increased

crashes.

The pavement life is substantially affected by the number of heavy load

repetitions applied, such as single, tandem, tridem and quad axle trucks ,

buses, tractor trailers and equipment. A properly designed pavement

structure will take into account the applied loading

. It illustrates the terms used in this Figure bellow in pavement structure is shown-A typical flexible

are not present in every Figure bellow manual that refer to the various layers. All the layers shown in

flexible pavement.

http://www.globalsecurity.org/military/library/policy/army/fm/5-430-00-1/CH5.htm#fig5_1

http://www.globalsecurity.org/military/library/policy/army/fm/5-430-00-1/CH5.htm#fig5_1


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A new 6-lane expressway is proposed to be built from Bandar A to Bandar B. The length of the

expressway is approximately 25 km.

AASHTO Flexible Design Procedure :

The design basis presented in this document is based upon the 1993 American Association of State

Highway and Transportation Officials (AASHTO) Design Guide. The objective is to provide design

parameters for local materials and conditions, and to provide guidance on the use of AASHTO

equations.

For estimating the thickness base on the AASHTO design method procedure we need to

determine the SN ( structural number ) from the design chart for flexible pavement or using

the equation as the above indicate :

In this project we have decided use the chart instead of equation so before using the chart we

need to have some parameters for using it :


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1.reliability that be given in the project ,

Reliability= 85%

2.Standard Deviation that be given ,

Standard Deviation= 0.45

3.ESAL

4.The resilient Modulus for the different roadbed layers

5.Design Serviceability Loss,

∆PSI = PSI terminal – PSI initial = 4.2 – 2.0 = 2.2

By the above information at first we require to have the ESAL ( equivalent Single Axle Load)

Traffic analysis :

Overview

Pavement is designed based on the traffic loadings expected in the highway’s design lane,

the lane expected to experience the greatest number of 18,000 pound equivalent single axle

loads (18K ESALs) over the design period (usually 20 years). The traffic data required to

calculate the ESALS include:

base year ADT

ADT traffic growth rate for the design year

percentage trucks, including dual-rear-tire pickups and buses, for each classification

category

directional distribution for the design period

lane distribution factor for the design period.

Traffic Data Provided

ADT traffic growth rate for the design year

percentage trucks, including dual-rear-tire pickups and buses, for each classification

category

directional distribution for the design period.

http://onlinemanuals.txdot.gov/txdotmanuals/glo/e.html#i1005434

http://onlinemanuals.txdot.gov/txdotmanuals/glo/e.html#i1005434


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Traffic Data

ADT = 25, 500 vehicles (both direction)

% Trucks = 15*

1ffic growth factor = 12.58

Design period = 10 years

Directional distribution = 60/40

Lane distribution

Slow lane = 65%

Middle lane = 25%

Fast lane = 10%

Lane width = 3.70 m ( 12 ft)

*Detailed information on trucks

Cars, pickups, light vans = two 2000-lb (8.9-kN) single axles ( 40%)

Single-unit truck = 8000-lb (35.6 kN) steering, single axle ( 15%)

= 22,000-lb (97.9-kN) drive, single axle ( 15%)

Tractor semi-trailer truck = 10,000-lb (44.5-kN) steering, single axle (10%)

= 16,000-lb (71.2-kN) drive, tandem axle (10%)

= 44, 000-lb (195.7-kN) trailer, triple axle (10%)

Tandem drive axle on a tractor frame during manufacturing


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Determine ESAL :

ESAL initial = ADT * %T * Gi * N * 365 * Y

ESAL final = ESAL ini * Dd * Ld

Determine N :

In terms of the table 6.4 the EALF can be found so :

Cars, pickups, light vans

2 * 0.00018 = 0.00036

0.00036 * 0.4 = 0.000144

Single-unit truck

0.0343*0.15=0.00514

2.18*0.15=0.327

Tractor semi-trailer truck

0.0877*0.1=0.00877

0.0472*0.1*2 =0.00944

0.723*0.1*3 = 0.2169

N = 0.000144 + 0.00514+0.327+0.00877+0.00944+0.2169

N= 0.567

ESAL initial = 25500 * 0.15 * 12.58 * 0.567 * 365

ESAL initial = 9958364.168

ESAL final = 9958364.168 * 0.6 * 0.65

ESAL final = 3883762.025 psi

ESAL final = 3.9 * 10^6 psi


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Determine MR :

Resilient Modulus (Mr) is a fundamental material property used to characterize unbound

pavement materials. It is a measure of material stiffness and provides a mean to analyze

stiffness of materials under different conditions, such as moisture, density and stress level. It

is also a required input parameter to mechanistic-empirical pavement design method. Mr is

typically determined through laboratory tests by measuring stiffness of a cylinder specimen

subject to a cyclic axle load. Mr is defined as a ratio of applied axle deviator stress and axle

recoverable strain.

Reslient Modulus Experimental Setup

Resilient modulus is determined using the triaxial test. The test applies a repeated axial cyclic

stress of fixed magnitude, load duration and cycle duration to a cylindrical test specimen.

While the specimen is subjected to this dynamic cyclic stress, it is also subjected to a static

confining stress provided by a triaxial pressure chamber. It is essentially a cyclic version of a

triaxial compression test; the cyclic load application is thought to more accurately simulate

actual traffic loading.

In this project we have resilient modulus for 3 different layers this means that we do not need

to find the resilient modulus base on AASHTO design method.

Resilient modulus properties :

)Stone Matrix AsphaltSMA ( =3104 Mpa (450,000 psi)RSMA, M

Base, MR= 241 Mpa (35,000 psi)

Subbase, MR= 93 Mpa (13,500 psi)

Subgrade, MR ( Subgrade Resilient Modulus Varies throughout the project length)

Subgrade, MR= 48 Mpa (7,000 psi)

The Subgrade resilient modulus is the effective resilient modulus.

So we have enough information for determining the Structural Number by using the chart.

http://www.pavementinteractive.org/article/resilient-modulus/triaxial-test


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As the above chart indicates we have 3 different Structural Number by 3 different roadbed

Resilient modulus,

Base resilient modulus = 35000 psi SN 1 = 2.30

Subbase resilient modulus = 13500 SN 2 = 3.30

Subgrade resilient modulus = 7000 SN 3 = 4.00


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Determine the Thickness :

For determining the thickness by AASHTO ,it gives the equation

SN = a1D1 + a2D2m2 + a3D3m3

In which a1 , a2 and a3 are the layer coefficients of the asphalt, base and subbase layers

which be given in this project

D1 , D2 and D3 are the thicknesses of the different layers

,m2 is the drainage coefficient for the base layer and m3 for the subbase layer.

Design of layer thickness :

D1 = SN1 / a1*m1

D1=2.30/0.44*1

D1=5.227 ≈ 5.50 inch = 13.97 cm

SN* = D1*a1*m1

SN* = 5.50*0.44*1

SN*=2.42 ≥ 2.30 OK√

------------------------------------------------------------------------------------------------------

D2 = (SN2-SN1*)/(a2*m2)

D2=(3.30-2.42)/(0.15*0.75)

D2=7.82 inch ≈ 8.00 inch = 20.32 cm

SN*2 = 8.00*0.75*0.15

SN*2 = 0.90

SN*1 + SN* 2 ≥ SN2

0.90 + 2.42 = 3.32

3.32 ≥ 3.30 OK√

------------------------------------------------------------------------------------------------------

D3 = (SN3 – ( SN* 2 + SN*1 )) / (a3*m3)

D3 = (4.00 – (0.90+2.264)) / (0.75*0.10)


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D3 = 11.147

D3 = 11.50 inch = 29.21 cm

SN* 3 = 11.50*0.75*0.10

SN* 3 = 0.8625

SN*3 + SN*2 + SN*1 ≥ SN3

0.8625+0.90+2.42=4.183 4.00 OK√

So the layer thickness for the asphalt , base and subbase are :

D1=5.50 inch = 13.97 cm

D2=8.00 inch = 20.32 cm

D3=11.50 inch = 29.21 cm


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JKR method based on CBR

California Bearing Ratio (CBR)

The California Bearing Ratio (CBR) test is a simple strength test that compares the

bearing capacity of a material with that of a well-graded crushed stone (thus, a high

quality crushed stone material should have a CBR @ 100%). It is primarily intended for ,

but not limited to, evaluating the strength of cohesive materials having maximum

particle sizes less than 19 mm (0.75 in.) (AASHTO, 2000). It was developed by the

California Division of Highways around 1930 and was subsequently adopted by

numerous states, counties, U.S. federal agencies and internationally. As a result, most

agency and commercial geotechnical laboratories in the U.S. are equipped to perform

CBR tests.

JKR Method

This method is a combination of two methods using a formula and figures from the result of

the testing. A complete guideline for pavement design can be found in “ Arahan Teknik

(Jalan) 5/85”. The thickness of the pavement depends on the CBR value and the Total

Cumulative of Standard Axle ( JBGP ).Some data need to be collected before starting any

design. They are;

i. Design life.

ii. Road hierarchy base of JKR classification.

iii. Average daily traffic volume.

iv. Percentage of commercial vehicle.

v. Yearly rate of traffic growth.

vi. CBR value for sub-grade.

vii. Topography condition.

Design Life

The design life on JKR Design Method is suggested for 10 years. The design life begins from

the road starts in use for traffic until the maintenance is required.


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This manual is to be used for the design of flexible pavements for roads. It comprises of

details for the thickness design,materials specification and the mix design requirements.

For determining the thickness JKR recommend to use the bellow nomograph

So in terms of the above nomograph we require to find the CBR of the subgrade and also

Equivalent Axle Load.


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FHWA Class 9 five-axle tractor semi trailer (18 tires total). A typical tire load is 18.9 kN (4,250 lbs) with an inflation pressure of 689 kPa

100 psi

Traffic Estimation

Vo = ADTT*Dd*Ld*365*Pc/100

ADTT = ADT * T%

ADTT = 25500*0.15

ADTT = 3'825.00

Determine Pc :

In terms of the table 6.4 the EALF can be found so :

Cars, pickups, light vans

2 * 0.00018 = 0.00036

0.00036 * 0.4 = 0.000144

Single-unit truck

0.0343*0.15=0.00514

2.18*0.15=0.327

Tractor semi-trailer truck

0.0877*0.1=0.00877

0.0472*0.1*2 =0.00944

0.723*0.1*3 = 0.2169


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Pc = 0.000144 + 0.00514+0.327+0.00877+0.00944+0.2169

Pc= 0.567

Vo=3825*0.60*0.65*365*0.567

Vo = 308'725.1213

In which Vo is the initial annual commercial traffic for one direction .

The total number of commercial vehicles for one direction Vc is obtained by :

Vc = (Vo*(((1+r)^x) – 1 )) / r

Vc = Vo * Gi

Vc= 308725.1213 * 12.58

Vc = 3883762.026 psi

Vc = 3.9 * 10^6

In this case we have :

The total equivalent standard axles (ESA) can determine as :

ESA = Vc

ESA = 3.90 * 10^6

The maximum hourly traffic volume is calculated as follows :

C = I * R * T

For determining the above equation we should use the table 3.2 , 3.3 and 3.4 on the JKR

Road type = Multilane

I = 2000*3 = 6000

R= 1.00

T= 100 / (100+pc)


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T= 100/(100+15)

T= 0.87

C= 6000 * 1 * 0.87

C= 5220 veh/hour/lane

C reflects 10% of the 24 hours , then the one way daily capacity is as follows:

C= 10 * c

C = 52200 veh/day/lane

V = ( ADT * (1+r)^x) / 2

Gi=12.58

For finding r ,we can use the 6.13,

r=0.05

V= ( 25500 * (1+0.05)^10 ) / 2

V = 20768.41 veh/day/lane

Hence capacity has not been reached after 10 years .

Determine the subgrade CBR:

The CBR can be found by the resilient modulus of subgrade soil which is :

Subgrade, MR= 48 Mpa (7,000 psi)

In terms of the subgrade resilient modulus we have :

CBR = 48 / 10

CBR = 4.80


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From the above nomograph, the chart shows that for ESA of 8.30*10^6

,the required TA is 24.70 cm

Determine the Structural Layer Coefficient :

For estimating this number for each layers we can use the Table 3.5


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a1=1.00

a2=0.32

a3=0.23


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Design of Layer Thickness :

In terms of the table 3.8 ,the minimum thickness of bituminous layer in this case will be 15.0

cm.

TA = a1D1 + a2D2 + a3D3

1st Trial :

Nominate

D1=15.00 cm

D2=16.00 cm

D3=18.00 cm

Then

TA = 1.00*15.00 + 0.32*16 + 0.23*18

TA = 24.26 ≤ T

Second Trial

D1=15 cm

D2=18 cm

D3=18 cm

T 24. ≈ T

So the Final thickness of Asphalt, Base and Subbase layers are :

D1 = 15 cm

D2 = 18 cm

D3 = 18 cm


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Cost considerations :

Cost of Materials and construction (includes transportation cost)

Crusher-run Base = RM 22.00 tonne

Sand Subbase = RM 15.00 per tonne

Stone Mastic Asphalt = RM 330.00 per tonne

Cost of construction RM 15.50 per sq meter

cubic meters * density = tonnes


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Determining the total cost by using the AASHTO thickness :

The above table is indicated that the sum of cost will be more than 97 million RM which is

effected from the Stone Matric Asphalt layer which is more than 68 million RM.

Layer

Cost of

Material

(RM/ton)

Required

Density

(ton/m³)

No.

of

Lane

Lane

Width

(m)

Road

Length

(m)

Thickness

(m)

Construction

cost (m²)

Project Cost

(RM)

SMA 330.00 2.35 6 3.7 25000 0.1397 15.50 68'729'729

Base 22.00 2.25 6 3.7 25000 0.2032 15.50 14'184'912

Subbase 15.00 2.3 6 3.7 25000 0.2921 15.50 14'195'485

Total =

97'110'126

RM


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Determining the total cost by using the JKR method and thickness :

The above table is indicated that the sum of cost will be more than 98 million RM which is

affected from the Stone Matric Asphalt layer which is more than 73million RM.

Layer

Cost of

Material

(RM/ton)

Required

Density

(ton/m³)

No.

of

Lane

Lane

Width

(m)

Road

Length

(m)

Thickness

(m)

Construction

cost (m²)

Project Cost

(RM)

SMA 330.00 2.35 6 3.7 25000 0.15 15.50 73'162'875

Base 22.00 2.25 6 3.7 25000 0.18 15.50 13'547'550

Subbase 15.00 2.3 6 3.7 25000 0.18 15.50 12'049'050

Total =

98'759'475

RM


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RECOMMENDATIONS :

The above tables is indicated the different cost for constructing the roadway.

The first table shows that the cost of AASHTO method is more than 108 million RM with

0.1651 m asphalt layer thickness.

The second table shows that the cost of using the JKR method of design is more than 101

million RM with 0.158 m asphalt layer thickness.

The JKR method gives a higher cost than the AASHTO .

The layer thickness of AASHTO method is thinner compare to the JKR method.

So the AASHTO method in this case is cost-effectiveness than the JKR method so the

authorities should use the AASHTO method . Many project in the U.S.A and many other

countries design by AASHTO method.

The most important factor that effects the cost is the asphalt thickness

We require to have a minimum thickness of asphalt layer for have a cost-effective design so

try to use the minimum thickness and finding the base and subbase based on the minimum

thickness of asphalt layer.

Maximize crushed stone thickness and sand subbase thickness – minimize AC thickness Can

also stabilize base to use less HMA

Use gravel only for fill or frost

pavement analysis

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design of flexible pavements

overview pavement

pavement life

design of rigid pavements

design chart

designed pavement structure

deficient pavement conditions

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