Structural Design of Pavement
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STRUCTURAL DESIGN OF
FLEXIBLE PAVEMENT
HIGHWAY ENGINEERING
SAB2832
FLEXIBLE PAVEMENT
CHE ROS ISMAIL (fka, utm)
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STRUCTURAL DESIGN OF
FLEXIBLE PAVEMENTby
CHE ROS ISMAIL (fka, utm)
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Structural design of flexible
pavement
1. Introduction
2. Elements of a Flexible Pavement Structure
3. Factors to be Considered in the Design
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3. Factors to be Considered in the Design
4. Methods of Design for New Pavements
5. Malaysian Design Methods
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Introduction
Aim: to design a structure that will ensure that the
transmitted stresses are sufficiently reduced and do
not exceed the capacity of the underlying subgrade
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Flexible pavement structure
Elements of a flexible pavement:
1. Sub-grade – upper layer of natural soil or fill, support load transmitted from overlaying layers.
2. Sub-base – specified material, secondary load spreading layer, prevent infiltration of sub-grade into pavement, construction platform for construction traffic, drainage layer
3. Road base – specified material, main load spreading layer,
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3. Road base – specified material, main load spreading layer, provide pavement with added stiffness and resistance to fatigue
4. 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.
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Load Distribution
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Factors to be Considered in The
Design
1. Failure mechanism – permanent deformation and cracking rut(accumulation of permanent strain – water ponding) crack(fracture failure under repeated or fluctuating stress – fatigue failure in the bituminous layer)
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2. Traffic loading – pavement design must account for cumulative traffic loading during design life
a. Tire loads & pressure – contact load and area
b. Axle & wheel configuration – no of contact points
c. Load repetition – cumulative
d. Traffic distribution – lane, direction
e. Speed – loading period (slow, climbing)
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Present serviceability index
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Rut
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Factors to be Considered in The
Design
f. ESA – convert wheel loads to standard loads
std load = 80 kN, 8160 kg, or 18000 lb
load equivalency factor, e = (L/Ls)n
consider only commercial vehicles
CV (BTM > 1.5 ton, 3 ton for RN31)
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CV (BTM > 1.5 ton, 3 ton for RN31)
3. Environmental – temperature (asfalt – brittle/soft) and
moisture (safety of users and pavement)
80 kN ESALs80 kN ESALs
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Commercial vehicle
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Commercial vehicle
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Methods of Design for New
Pavements
Objective – to determine the number, material composition, and thickness of different layers that will be suitable in a specific environment and able to sustain the anticipated traffic loading
Three methods:
1. Precedent – rule-of-thumb, std thickness for particular road
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1. Precedent – rule-of-thumb, std thickness for particular road classification
2. Empirical – soil classification or strength using experience, experimentation, or both
3. Theoretical/semi – mechanistic, based on mechanical model, relate pavement parameters (stress, strains, deflections) to physical causes (loads, material properties) using mathematical model
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Methods of Design for New
Pavements
Advantages of mechanistic-empirical:
a. Can be use for new construction and rehabilitation
b. Accomodate various load types
c. More reliable performance prediction (use material
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c. More reliable performance prediction (use material
properties)
d. Accomodate environmental and aging effects on materials
Steps in design process
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Design Process
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Malaysian Design Methods
Adopt design method based on AASHTO Guide, and catalogue of
structure method
1. Arahan Teknik Jalan 5/85 – based on AASHO road test,
developed using multi-layered elastic theory. Suitable for
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developed using multi-layered elastic theory. Suitable for
major roads with heavy and medium traffic
2. Overseas Road Note 31 – based on research in tropical and
sub-tropical countries. Design to cater traffic up to 30MSA
in one direction
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pavement thickness design
ATJ 5/85
Data required:
1. Design period, n – suggests 10 years
2. Class of roads
3. Initial Average Daily Traffic - ADT
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3. Initial Average Daily Traffic - ADT
4. Percentage of Commercial Vehicle - Pc
5. Average annual traffic growth - r
6. Sub-grade strength - CBR
7. Terrain condition
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pavement thickness design
ATJ 5/85Design Procedure:
1. Calculate Vo = ADT x (1/2) x 365 x (Pc/100)
2. Calculate Vc= Vo [(1 + r)n - 1] / r
3. Calculate cumulative ESA, ESA = Vc x e (Table 3.1 or e = 2.52)
4. Check daily capacity (Table 3.2, 3.3, 3.4)
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4. Check daily capacity (Table 3.2, 3.3, 3.4)
5. Determine sub-grade CBR
6. Obtain equivalent thickness, TA’ from nomograph
7. Calculate thickness for each layer (Table 3.5, 3.6, 3.7)
TA’ = SN = a1D1 + a2 D2 + ... + anDn
8. Sketch the designed thickness
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Equivalence Factor
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Maximum Hourly capacity
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Reduction Factor
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Terrain Factor
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Layer Coefficient
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Standard and Construction
thickness
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Minimum thickness of
bituminous layer
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Nomograph
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pavement thickness design
ATJ 5/85In case of varying CBR for 1m depth of sub-grade, mean CBR is
determined as follows:
CBRm = [(h1CBR11/3 + h2CBR2
1/3 + … + hnCBRn1/3) / (1000)]3
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where:
CBRm = mean CBR for that location
CBR1, CBR2, … CBRn = CBR of soil strata
h1, h2, … hn = thickness of soil strata (mm)
h1 + h2 + … + hn = 1000 mm
Example:
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pavement thickness design
ATJ 5/85Design Example:
JKR 05, carriageway width = 7.5m, shoulder = 2.0m
ADT = 6600
Pc = 15 %
r = 7 %
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r = 7 %
Sub-grade CBR = 5 %
Rolling Terrain
Material:
Surfacing = AC
Road base = wet mix Macadam
Sub-base = sand
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pavement thickness design
Road Note 31
• Designed for tropical and sub-tropical countries to carry up to
30M CSA
• Heavy vehicle > 3 ton
• Equivalence: e = (L/Ls)4.5
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• Equivalence: e = (L/Ls)
Design procedure:
1. Estimate CSA for design life >>> T (Table 3.8)
2. Assess sub-grade strength >>> S (Table 3.9, 3.10)
3. Select combination of material and thickness from structure
catalogues based on T and S
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pavement thickness design
Road Note 31
Emphasis on 5 aspects:
1. Influence of tropical climate on moisture conditions in road
sub-grades
2. Severe conditions imposed on exposed bituminous surfacing
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2. Severe conditions imposed on exposed bituminous surfacing
by tropical climates
3. Interrelationship between design and maintenance
4. High axle load and tyre pressures
5. Influence of tropical climate on the nature of the soils and
rocks used in the road building
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Traffic Classes
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Sub-grade Classes
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Estimation of Sub-grade
Classes
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Material Definition
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Granular base, surface dressing
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Granular base, structured surface
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pavement thickness design
Road Note 31
Design Example 1:
ADT = 250/day.dir, Pc = 55 %, r = 5 %, CBR = 7 %
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Design Example 2:
CSA = 12M, PI > 45, WT = 3m below formation
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QUESTIONS?
• Thank You
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