flexible pavement design
DESCRIPTION
flexTRANSCRIPT
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
FLEXIBLE PAVEMENT DESIGN
OBJECTIVESGeneral 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 14
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 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 courseBase course
Road-baseLower
Upper
Sub-base
Capping
Sub-grade
INPUT
FLEXIBLE PAVEMENT DESIGN
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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 DESIGN14.1.1 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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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 CONSTRUCTIONA1 Concrete Surfacing
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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 ROADW (m)
RESAVER (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.
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
Inflow control degree – half. Distance – quite far. Geometry design level – high.
Inflow control degree – fully. Distance – far. Geometry design level – high
Notes :R – RuralU – 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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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;
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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 TWhere;
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.
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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 =
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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 (%) =
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
1.
a. Failure Criterion
b. Traffic Loading
c. Climate or Environment
d. Moisture
2. -
FEEDBACK ON ACTIVITY 14
Answer
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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
FLEXIBLE PAVEMENT DESIGNHighway Engineering C3010 / UNIT 14
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