unit 14 ( flexible pavement design )

FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14

FLEXIBLE PAVEMENT DESIGN

OBJECTIVES

General Objective

To know the methods and procedures in designing the flexible pavement for

roads in Malaysia.

Specific Objectives

At the end of the unit you should be able to :-

describe the basic layers of road design

calculate the design using the required formula and figure.

design the basic flexible pavement using JKR method.

UNIT 14UNIT 14


14.0 INTRODUCTION

A typical section through a pavement is shown in the following sketch ( not to

scale )

In some type of construction some layers maybe combined.

14.0.1 Foundation

Surfacing Wearing course

Base course

Road-baseLower

Upper

Sub-base

Capping

Sub-grade

INPUT

FLEXIBLE PAVEMENT DESIGN


Foundation provides uniform support to the pavement through its

life so that maintenance operation is confined to the upper level of the

pavement.

i. Sub-grade – either natural soil or material placed to form

embankment.

ii. Capping – on sub-grade with a low CBR, a capping layer

is required provide working. Platform on which

sub-base construction can proceed with

minimum intersection from wet whether a

minimize effect at weak sub-grade on road

performance.

14.0.2 Sub-base

This layer forms the upper of the pavement foundation and

provides a regulated working platform at a consistent strength on which to

transport, place and compact the bound layers of pavement.

14.0.3 Road Base

Road base is a main structural element that purposes to spread

induced by repeated wheel loads over the foundation and to with stand

internal stresses without excessive deformation.

14.0.4 Surfacing


Surfacing is done in order to provide acceptable running surface of

adequate skid resistance and to reduce water penetration to underlying

layer.

14.1 FACTORS FOR DESIGN

14.1.1 Failure Criterion

The definition from Croney, failure as transformation shape or deflection of 20mm

tire’s lane not speeding that measuring from ground level.

14.1.2 Traffic Loading

Protection of the sub-grade from the loading imposed by traffic is one of

the primary functions of a pavement structure. The designer must provide a

pavement that can withstand a large number of repeated applications of a

variable-magnitude loading. The primary loading factors that are important in

flexible pavement design are

1. Magnitude of axle (and wheel) loads.

2. Volume and composition of axle loads.

3. Tire pressure and contact area.

Slow lane Fast lane

20 mm


The magnitude of maximum loading is commonly controlled by legal load

limits. Traffic survey and loadometer studies are often used to establish the

relative magnitude and occurrence of the various loading to which a pavement

during its design life is a very difficult but obviously important task. Most design

procedures provide for an increase in traffic volume on the basis of experience

by using some estimate growth rate.

14.1.3 Climate or Environment

The climate or environment in which a flexible pavement is to be

established has an important influence on the behavior and performance of the

various materials in the pavement and sub-grade. Probably the two climatic

factors of major significance are temperature and moisture.

The magnitude of temperature and its fluctuation affect the properties of

certain materials. For example, high temperatures cause asphaltic concrete to

lose stability whereas at low temperatures asphaltic concrete becomes very hard

and stiff. Low temperature and temperature fluctuations are also associated with

frost heave and freeze-thaw damage. Granular materials, if not properly graded,

can experience frost heave. Likewise, the sub-grade can exhibit extensive loss in

strength if it becomes frozen. Certain stabilized materials can suffer substantial if

large numbers of freeze-thaw cycles occur in the material.

Moisture also has an important influence on the behavior and performance

of many materials. Sub-grade soils and other paving materials weaken

appreciably when saturated, and certain clayey soils exhibit substantial moisture-

induced volume change.

14.2 FLEXIBLE PAVEMENT DESIGN METHOD


14.2.1 JKR Method

This method is a combination of two methods above 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.

14.2.3.1 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.

14.2.3.2 Road Hierarchy Base Of JKR Classification.

a. Road Classification and its Construction Material.

CLASS TYPES OF CONSTRUCTION

A1 Concrete Surfacing


A2

B

C

D

E

Hard Bituminous Metalled

Hard Waterbound Metalled

Hard Bituminous Sealed

Gravelled Waterbound

Soil Surfacing

b. Category and its road width.

CATEGORY WIDTH OF ROAD

W (m)

RESAVE

R (cm)

01

02

03

04

05

06

4.5

5.0

6.0

7.0

7.5

3.5 per lane

20.0

30.0

30.0

40.0

40.0

40.0 or more

Notes : 01 – 03 – Village Roads.

04 – 06 – Urban Roads.

14.2.3.3 Classification by JKR Standard

Road hierarchy Description

The lowest of hierarchy and geometry design level. Traffic for one way.

This road hierarchy is same like type. Geometry design

level is lowest from type. The lowest hierarchy for single

carriageway.

This road is design for local traffic. Geometry design level – low and non inflow traffic control.

Another road is allowed to intersect in the same level. Geometry design level is intermediate. Allowed maximum velocity – intermediate.


Inflow control degree – half. Distance – quite far. Geometry design level – high.

Inflow control degree – fully. Distance – far. Geometry design level – high

Notes :

R – Rural

U – Urban

14.2.3.3 Traffic Estimation

To design using this method, commercial vehicles without loading

weight more than 1500 kg are to be taken.

The formula is include:

Vo = PLH

Where :

Vo = Total of Yearly Commercial Vehicle for one

direction.( JBKP )

PLH = Average Daily

Traffic Ratio for two directions.

Pc = Commercial Vehicle Percentage.

To determine the Total of Yearly Commercial Vehicle ( JBKP ) for

the one direction for ever lasting Design Life, we have to apply

following formula;

x


Vc =

Where;

Vc = JBKP at one direction for ‘x’ year.

r = Rate of Traffic Growth.

x = Road pavement Design Life ( in year’s unit )

To determine the Total Cumulative of Standard Axle ( JBGP ) for

traffic mixture, equivalent axle load concept is used.

JBGP = JBKP x equivalent factor

Where ;

JBKP = Vc

Equivalent Factor = use the data in Table 10.7 = e

Thus,

JBKP = Vc x e

Using the JKR Method, the traffic volume checklist is used by

comparing the maximum traffic volume. The formula is;

Vx = V1 ( 1 + r )X

Where;


Vx = The total traffic volume (commercial and non

commercial) at the end of pavement design life

of one direction after ‘x’ year.

V1 = The Daily Traffic Volume of one direction

r = Rate of Yearly Traffic Growth.

x = Life design (in year’s unit)

c = I x R x T

Where;

c = Maxima Traffic Loading per hour for one way.

I = Absolute Traffic Loading per hour - ( Refer

Table 10.8 )

R = Road Decreasing Factor – ( Refer

Table 10.9 )

T = Traffic Decreasing Factor – ( Refer Table

10.10 )

In JKR Standard, Traffic Loading for an hour is assumed that equal

with 10 % daily loading, as:

C = 10 x c

Where;

C = Daily Traffic Loading ( 24 hours traffic loading

at one direction)

c = Traffic Loading per hour.


With comparison ‘C’ value and ‘Vx’, we can conclude that;

a). C > Vx - Road still obtain to support the Traffic Volume

at the end of the life design for ‘x’ years.

b). C < Vx - Road cannot obtain to support the Traffic

volume at the end of the life design for ‘x’

years.

For (b) condition, this formula are used,

C = V ( 1 + r )n

Where;

C = Daily Traffic Loading for one way ( 24 hours )

V = Daily Traffic Volume for one way that

assumed loaded for road.

r = Rate of Yearly Traffic Growth.

n = Life Design.

14.2.3.4 CBR-Sub-grade Value

n =


To determine the CBR value, 1.0 m sub-grade soil must be taken

from the hard rock level. To get CBR for sub-grade design, this

formula must be applied.

Where;

NGC1, NGC2 , = CBR value for layer 1,2 ….

h1, h2 = soil deepness from form level for

sample 1,2 ….

14.2.3.5 Pavement Thickness Design

Figure 10.8 shows the Nomograph Thickness Design that is used

to design pavement thickness. An early process of design, the

CBR (Sub-grade) and JBGP value must be determined first. To use

the Nomograph, the following steps are normally applied.

Line A value is fixed to 3% and line B is the required JBGP. Draw a

straight crossed line. Then determine C values i.e the thickness

Equivalent, (TA).

a. Insert CBR design value at the line A and draw a line by using

previous C value until crossing line D, Determine D value i.e the

Equivalent Thickness Interval (TA’), if all the entire pavement is

constructed from the wearing course or road base.

NGC (%) =


To determine the thickness of each pavement layer, table 10.11

and table 10.12 is used with the following formula below i.e to

determine D1, D2 and D3 value of the surface layers, base and road

sub-base.

Where,

a1, a2, a3 = Determine from the table 10.11 based on the

types of pavement requirement at the certain

layers.

= Layer Structure Coefficient.

D1, D2, D3 = Approximate thickness design of the certain

layer ( minimum thickness value according to

table 10.12 )

SN = a1D1 + a2D2 + a3D3


TEST YOUR UNDERSTANDING BEFORE YOU CONTINUE WITH THE NEXT

INPUT

1. State the factors of design that will give impact on to the designing of

flexible pavement.

2. What is the meaning of in road hierarchy outlined by JKR standard.

ACTIVITY 14

Question


1.

a. Failure Criterion

b. Traffic Loading

c. Climate or Environment

d. Moisture

2. -

FEEDBACK ON ACTIVITY 14

Answer


This road hierarchy is same like type. Geometry design level is

lowest from type. The lowest hierarchy for single carriageway. R is

for Rural and U is for urban,

A road with hierarchy of 05 has a surface width of 7.0 m and road reserve of

40.0m is to be built as a main road in a residential area. It has a initial average

daily traffic of 7000cv/day in both directions. The rate of traffic growth is 7%.

Percentage of commercial vehicle is 25%. Design a flexible pavement for the

road which needs a design life of 10 years. The CBR for sub-grade of the road is

5%. ( Employ the JKR Malaysia Design Method ).

Note:

Question


Requirement of pavement layers:

i. Wearing Course = Asphalt Concrete.

ii. Road-Base Course = Broken Aggregate.

iii. Sub-Base Course = Broken Aggregate.

Vo = PLH

Vo = 6800

= 310250

Answer


Vc =

Vc =

= 4286552.98

JBGP = JBKP X EQUAVALENT FACTOR

JBKP = Vc x e

JBKP = 4.29 x 106 x3.0

= 12.87 x 10 6

Vx = V1 ( 1 + r )x

Vx = 6800/2( 1 + 0.07 )10

Vx = 6689

x

10


c = I x R x T

I = Absolute Traffic Loading per hour - ( Refer

Table 10.8 )

= 2000/2

= 1000

R = Road Decreasing Factor – ( Refer

Table 10.9 )

= 1.0

T = Traffic Decreasing Factor – ( Refer Table

10.10 )

= 100/(100 + 25 )

= 0.8

c = I x R x T

= 1000 x 1.00 x 0.8

= 800 vec/hr/lane

C = 100c

= 100(800 vec/hr/lane )

= 8000 vec/day/lane


From Nomograph Diagram;

D = 43 cm

From table10.11 and table 10.12

a1 = 1.00

a2 = 0.32

a3 = 0.25

From table 10.12

Wearing Course = 4 + 5

= 9 cm

Base Course = 10 cm

Sub Base = 10 cm granular

SN = a1D1 + a2D2 + a3D3

SN = 1D1 + 0.32D2 + 0.25D3

= 43 cm


Try and Error

1. D1 = 9

D2 = 10

D3 = 10

SN = 1(9) + 0.32(10) + 0.25(10)

= 14.7 cm < 43 cm

2. D1 = 20

D2 = 40

D3 = 50

SN = 1(20) + 0.32(40) + 0.25(50)

= 46 cm > 43 cm

3. D1 = 18

D2 = 40

D3 = 50

SN = 1(18) + 0.32(40) + 0.25(50)

= 43.3 cm < 43 cm OK

unit 14 ( flexible pavement design )

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