FLEXIBLE PAVEMENT DESIGN CMND

TOPIC 5
FLEXIBLE PAVEMENT
DESIGN

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Content

Flexible Pavement Structure
Factors to be Considered in Designing

Flexible Pavement Thickness
Thickness Design Methods

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Pavement types

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Type of Pavement & Load Distribution

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Pavement Types & How They Effect the
Subgrade

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Elements of a flexible pavement:

 Sub-grade – upper layer of natural soil or fill, support load
transmitted from overlaying layers.

 Sub-base – specified material, secondary load spreading
layer, prevent infiltration of sub-grade into pavement,
construction platform for construction traffic, drainage layer

 Road base – specified material, main load spreading layer,
provide pavement with added stiffness and resistance to
fatigue

 Surfacing – uppermost layer, provide safe & comfortable
riding surface, withstand traffic stresses, protect lower layers,
impermeable and flexible, may consist of BC and WC, premix
layer.

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Factors to be Considered in
Designing Flexible Pavement
Thickness

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1. Failure Criteria

 Failure mechanism – 2 categories:
 Permanent deformation- fail if rut (accumulation of

permanent strain)> 20mm
 Crack (fracture under repeated or fluctuating stress)

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Rut

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RUT

 A rut is a depression or groove worn into a road or path
by the travel of wheels or skis.

 Ruts can be formed by wear, as from studded snow tires
common in cold climate areas, or they can form
through the deformation of the asphalt concrete,
pavement or subbase material.

 In modern roads the main cause is heavily loaded
trucks. These heavy loaded trucks imprint their tire
impressions on roads over time, causing ruts.

 Rut is a common pavement distress and is often used in
pavement performance modeling

DCC30103 Highway & Traffic Engineering (Nizam PMM)

2. Traffic Loading

Total applied tire load Tire inflation pressure The higher tire
determines the depth tekanan inflasi influences pressure the less
the quality of material in contact occur
of pavement – to between tire &
ensure the subgrade upper layer of pavement – obvious
pavement in the upper layer.
not over -stressed
a. Tire
loads &
pressures

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Tire loads get closer
together – influence
areas on pavement

begin overlap

Commercial Producing
vehicles have axles combined effect
of the interacting
with twin -tired
wheel assemblies tire loads

b. Axle & wheel
configurations

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Enviroment, Damage is When it reaches
damage cumulative certain value-
pavement over the life
over time of pavement will reached the
end of its useful
c. Load
repetation service life

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Loads on 1 Carry a Lane often
direction different carries heavy
portion of the
different from loading vehicles –
the other. greatest
d. Traffic deformation
distribution

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Ex: heavy buses stop & sit Greater thickness/ better
while loading/unloading quality of pavement
passengers, intersection
materials is required in urban
& uphill gradients. areas compare to rural

Slower speeds & stop areas due to lower average
conditions allow load speeds in urban areas
for a longer period on

pavement.

e. Vehicle
Speed

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Converts wheel to an
loads of various equivalent
magnitudes & number of
standard loads
repetitions based on
damage
f. Equavalent
standard amount
axle (ESA)
Using the ESAL method,
DCC30103 Highway & Traffic Engineering (Nizam PMM) damage from all loads (including
multi-axle loads) are converted

to damage from an equivalent
number of 80kn.

3. Traffic Decaying Power

 Using ESA method, all loads are converted to an equivalent number
of 80 kN single axle loads.

 A load equivalent factor , e, represents the equivalent number of
ESA for the given weight-axle combination.

 Pavement damage ( axle load) .
 The value of n lies in range of 3.2 to 5.6 .
 In practice the value of n = 4 is often used .
 Load equivalency for a particular vehicle ,
 e = Σ [ L/Ls ] 4
 Ls equal to : 80kN @ 8200kg @ 18000lb

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Example 1

The whole weight of a lorry is 260 KN and is channeled through THREE (3)
axles which are 100kN, 90kN and 70kN. Illustrate the arrangement and weight of each
axle in the sketch. Then calculate the equality factor, F.

Answer

Equivalent factor, F :
F = ( 70/80)4 + ( 90/80)4 + ( 100/80)4
= 4.63

Jika semua beban ditanggung oleh 1 gandar sahaja, kira faktor setaraan.

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Kenapa rekabentuk mengambilkira
kenderaan perdagangan ?

 Kerana kuasa pemusnahan kereta penumpang terlalu kecil dan diabaikan
dalam rekabentuk , walaupun jumlahnya banyak.

 Contoh..
 Berat kereta penumpang 8 kN . Dengan itu,
 e = ( 8 / 80 ) 4 = 0.0001 = 1/10 000 gandar piawai.

DCC30103 Highway & Traffic Engineering (Nizam PMM)

4. Environmental Factor

Temperature Rheology
Expansion and

contraction
Sunlight

Environmental

Safety

Moisture Rainfall -
unbound
material

Placing HMA in
wet conditions

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 affect the performance of the pavement materials & cause various
damages.

 Two types of environmental factors;

DCC30103 Highway & Traffic Engineering (Nizam PMM)

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Flexible Pavement Cross –section :

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Objective :

To provide a structure that will be
suitable in a specific environment
and able to sustain the anticipated
traffic loading

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OBJEKTIF REKABENTUK :

Kos pembinaan Pemilihan bahan
adalah minimum yang sesuai

Penentuan Keselamatan
ketebalan yang lalulintas
sesuai setiap lapisan
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Design process

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Pavement Thickness
Design Methods

ATJ 5/85 ATJ 5/85 RN31
(2013)

ATJ 5/85
Pavement Thickness Design

DCC30103 Highway & Traffic Engineering (Nizam PMM)

ATJ 5/85 Design Method (2013 revision)

Data required:

 Type and volume of commercial vehicles
 Design life
 Sub-grade type and strength
 Type and properties of paving materials
 Environment which pavement will be exposed to

DCC30103 Highway & Traffic Engineering (Nizam PMM)

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Traffic

Data

 Number of commercial vehicles during Year 1 of Design
Period, which is the expected year of completion of
construction.

 Vehicle class and axle load distribution.
 Directional and lane distribution factors.
 Traffic growth factors.
 Design period

 10 years for low volume and rural road.
 20 years for high volume and urban road

DCC30103 Highway & Traffic Engineering (Nizam PMM)

 Design traffic (1st year of design period)
 ESALY1 = ADT x 365 x PCV x LEF x L x T ------ (eq. 1)

 ESALY1 = number of ESALs for base year (design lane)
 ADT = Average Daily Traffic
 PCV = Percentage of CV (un-laden weight > 1.5 tons)
 VLF = Vehicle Load Equivalent Factor (including Tire Factor) (Table 1)
 L = Lane Distribution Factor (Table 2)
 T = Terrain Factor (Table 3)

DCC30103 Highway & Traffic Engineering (Nizam PMM)

If traffic distribution by vehicle type is available:
ESALY1 = [ADTcv1 x LEFcv1 + ADTcv2 x LEFcv2 +…+ ADTcv3 x LEFcv3] x 365 x L x T

----- (eq. 2)

Vehicle Basis for Calculating VLF

HPU Class Class LEF TAF Vehicle Load
Designation Factor (VLF)
C <0.01 N/A
 Cars and 0
Taxis

 Small Trucks CV1 0.1 1.0 0.1
and CV2 1.4
CV3 4.5 2.4 1.4 4.0
Vans (2 3.1 (3.2 to 5.2)
Axles) CV4 1.2
MC 2.6 4.2 N/A 4.4
 Large Trucks CV % 2.9 (3.9 to 5.8)
(2 to 4 Axles) 4.1
1.8
 Articulated 1.5 0
Trucks (3 or more
Axles) 3.5

 Buses
(2 or 3 Axles)

 Motorcycles

 Commercial
Traffic (Mixed)

Table 1:Load Equivalence Factor (LEF) based on Traffic Categories

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Number of Lanes (in ONE Lane Distribution Factor, L
direction)
1.0
One 0.9
Two 0.7
Three or more

TABLE 2 : Lane Distribution Factors

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Type of Terrain Terrain factor, T
Flat 1.0
1.1
Rolling 1.3
Mountainous/steep

Table 3 :Terrain Factors

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 Design Traffic (Number of ESALs) for the Design Period

 ESALDES = ESALY1 x [(1 + r)n – 1)]/r ----- (eq. 3a)

 ESALDES = design traffic for the design lane in one direction
 r = annual traffic growth rate factor for design period

 n = number of years in design period

OR

 ESALDES = ESALY1 x TGF ----- (eq. 3b)

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Design Period Annual Growth Rate (%)
(Years) 234567

5 5.20 5.31 5.42 5.53 5.64 5.75
10 10.95 11.46 12.01 12.58 13.18 13.82
15 17.29 18.60 20.02 21.58 23.28 25.13
20 24.30 26.87 29.78 33.06 36.79 41.00
25 32.03 36.46 41.65 47.73 54.86 63.25
30 40.57 47.58 56.08 66.44 79.06 94.46

TABLE 4: Total Growth Factors (TGF)

DCC30103 Highway & Traffic Engineering (Nizam PMM)

 For the purpose of this Manual, predicted traffic expressed as number of
ESALs over the design period is classified into the following traffic categories
(Table 5).

Traffic Design Traffic Probability (Percentile) Applied to
Category (ESAL x 106) Properties of Sub-Grade Materials

 T1 ≤ 1.0 ≥ 60%
 T2 1.1 to 2.0 ≥ 70%
 T3 2.1 to 10.0 ≥ 85%
 T4 10.1 to 30.0 ≥ 85%
 T5 ≥ 85%
> 30.0

TABLE 5: Traffic Categories used in this Manual (ESAL = 80 kN)

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Sub Grade Properties

Min 5% CBR for T1- T3
If not, at least 0.3 meter of SG shall be replaced or

stabilized to ensure the minimum value is met.
Large volume traffic T4 and T5, min CBR 12%

DCC30103 Highway & Traffic Engineering (Nizam PMM)

Sub-Grade Elastic Modulus (MPa)
Category
CBR (%) Range Design Input Value
 SG 1 5 to 12
 SG 2 12.1 to 20 50 to 120 60
 SG 3 20.1 to 30.0 80 to 140 120
 SG 4 > 30.0 100 to 160 140

120 to 180 180

TABLE 6: Classes of Sub-Grade Strength (based on CBR) used as Input in the Pavement Catalogue of this Manual

DCC30103 Highway & Traffic Engineering (Nizam PMM)

 Determine Sub grade Strength
 Design Input Value = Mean – (Normal Deviate x

Standard Deviation)

60% Probability: Mean - 0.253 x STD
70% Probability: Mean - 0.525 x STD
85% Probability: Mean - 1.000 x STD

DCC30103 Highway & Traffic Engineering (Nizam PMM)

3 types of pavement :

 Conventional flexible pavement with granular base.
 Deep-strength flexible (composite) pavement with

bituminous surface course(s) and a base stabilized with
Portland cement, bituminous emulsion, or a combination
of both.
 Full-depth asphalt pavement with bituminous base
course

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T1 : < 1 million ESALs

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T2 : 1- 2 million ESALs

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T3: 2 -10 million ESALs

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T4 : 10 – 30 million ESALs

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T5 : > 30 million ESALs

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T5 : > 30 million ESALs ( Polymer Modified
Asphalt)

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DCC30103 Highway & Traffic Engineering (Nizam PMM)

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