The document outlines pavement design principles, detailing the characteristics and construction of flexible, rigid, and composite pavements. It discusses the importance of subgrade properties and evaluation methods, the factors influencing pavement design, and traffic considerations for ensuring structural integrity. Additionally, it presents the AASHTO design methodology and traffic growth assessments for various road types and load factors.

1. Mohammad Bulbul Hossain
Executive Engineer, RHD
Road Design & Standard Division,
Elenbari, Tejgaon, Dhaka.
PAVEMENT DESIGN

2. DESIGN FLEXIBLE AND RIGID PAVEMENTS
Design principles
pavement components and their role
Design practice for flexible and rigid pavements,

3. Pavement: Types
• Flexible Pavement
- Different layers of compacted aggregates
- ISG, Sub-grade, Base, Binder Course, Surface
• Rigid Pavement
- Portland Cement Concrete placed on a granular sub-base
• Composite Pavement
- One or more HMA courses over PCC Base
3

4. Types of Pavements

5. FLEXIBLE PAVEMENT RIGID PAVEMENT

7. Wheel Load Distribution

8. Flexible Rigid

10. Type of Concrete Pavement
• Jointed Plain Concrete Pavement (JPCP)
• Jointed Reinforced Concrete Pavement
(JRCP)
• Continuously Reinforced Concrete
Pavement (CRCP)
• Prestressed Concrete Pavements (PCP)

11. • Jointed Plain Concrete Pavement
(JPCP)

14. Properties Flexible Rigid
Design
Principle
Empirical method
Based on load distribution
characteristics of the
components
Designed and analyzed by using the elastic
theory
Material Granular material Made of Cement Concrete either plan,
reinforced or prestressed concrete
Flexural
Strength
Low or negligible flexible
strength
Associated with rigidity or flexural strength
or slab action so the load is distributed over
a wide area of subgrade soil.
Normal
Loading
Elastic deformation Acts as beam or cantilever
Excessive
Loading
Local depression Causes Cracks
Stress Transmits vertical and
compressive stresses to the
lower layers
Tensile Stress and Temperature Increases
Design
Practice
Constructed in number of
layers.
Laid in slabs with steel reinforcement.
Temperature No stress is produced Stress is produced
Force of
Friction
Less. Deformation in the
sub grade is not transferred
to the upper layers.
Friction force is High
Opening to
Traffic
Road can be used for traffic
within 24 hours
Road cannot be used until 14 days of curing
Surfacing Rolling of the surfacing is
needed
Rolling of the surfacing in not needed.

15. LOAD DISTRIBUTION

16. Components of Flexible Pavement

17. • Basement soil of road
bed.
• Important for
structural and
pavement life.
• Should not deflect
excessively due to
dynamic loading.
• May be in fill or
embankment.
Function and Significance of Subgrade Properties

18. Cut and Fill Sections

19. Desirable Properties of Soil as
Subgrade Material
• Stability
• Incompressibility
• Permanency of strength
• Minimum changes in volume and stability
under adverse condition of weather and
ground water
• Good drainage
• Ease of compaction

20. Subgrade Performance
• Load bearing capacity:
Affected by degree of compaction, moisture content,
and soil type.
• Moisture content:
Affects subgrade properties like load bearing capacity,
shrinkage and swelling.
Influenced by drainage, groundwater table elevation,
infiltration, or pavement porosity (which can be assisted
by cracks in the pavement).
• Shrinkage and/or swelling:
Shrinkage, swelling and frost heave will tend to deform
and crack any pavement type constructed over them.

21. Subgrade Soil Strength
Assessed in terms of CBR of subgrade
soil for most critical moisture conditions.
• Soil type
• Moisture Content
• Dry Density
• Internal Structure of the soil
• Type and Mode of Stress Application.

22. Flexible Pavement Design
Basic Principles
• Vertical stress or strain on sub-grade
• Tensile stress or strain on surface
course

23. Factors for design of pavements
• Design wheel load
 Static load on wheels
 Contact Pressure
 Load Repetition
• Subgrade soil
 Thickness of pavement required
 Stress- strain behaviour under load
 Moisture variation
• Climatic factors
• Pavement component materials
• Environment factors
• Traffic Characteristics
• Required Cross sectional elements of the alignment

24. Subgrade Soil
Base/Subbase
Surface

d
SUR
SUB
SUR
Axle
Load

Pavement Responses Under Load

25. Axle Configurations
Single Axle With Single Wheel
(Legal Axle Load = 5.5t)
Single Axle With Dual Wheel
(Legal Axle Load = 10t)
Tandem Axle
(Legal Axle Load = 18t)
Tridem Axle
(Legal Axle Load = 24t)
An axle is a central shaft for a rotating wheel or gear

26. Standard Axle
Single axle with dual wheels carrying a
load of 80 kN (8 tonnes) is defined as
standard axle
80 kN
Standard Axle

27. Evaluation Of Pavement Component
Layers
• Sub-grade
• To Receive Layers of Pavement
Materials Placed over it
• Plate Bearing Test
• CBR Test
• Triaxial Compression Test

28. Evaluation Of Pavement Component Layers
- Sub-base And Base Course
- To Provide Stress Transmitting Medium
- To distribute Wheel Loads
- To Prevent Shear and Consolidation
Deformation
In case of rigid pavements to
- Prevent pumping
- Protect the subgrade against frost action
- Plate Bearing Test
– CBR Test

29. Wearing Course
• High Resistance to Deformation
• High Resistance to Fatigue; ability to withstand high
strains - flexible
• Sufficient Stiffness to Reduce Stresses in the
Underlying Layers
• High Resistance to Environmental Degradation;
durable
• Low Permeability - Water Tight Layer against Ingress
of Surface Water
• Good Workability – Allow Adequate Compaction
• Sufficient Surface Texture – Good Skid Resistance in
Wet Weather

30. Flexible Pavement Design Using CBR
Value Of Sub-grade Soil
 Required data
Design Traffic in terms of
cumulative number of Equivalent standard
axles(CESA)
CBR value of subgarde

31. Traffic Data
Initial data in terms of number of
commercial vehicles per day (CVPD).
Traffic growth rate during design life in %
Design life in number of years.
Distribution of commercial vehicles over the
carriage way

32. Traffic – In Terms Of CESA (8160 Kg)
During Design Life
• Initial Traffic
 In terms of Cumulative Vehicles/day
 Based on 7 days 24 hours Classified Traffic
• Traffic Growth Rate
Establishing Models Based on Anticipated Future
Development or based on past trends
 Growth Rate of LCVs, Bus, 2 Axle, 3 Axle, Multi
axle, HCVs are different

33. Design Life
• National Highways – 20
Years
• Regional Highways – 20
Years
• Zilla Highways – 20 Years

34. Vehicle Damage Factor (VDF)
 Multiplier to Convert No. of
Commercial Vehicles of Different Axle
Loads and Axle Configurations to the
Number of Standard Axle Load
Repetitions indicate VDF Values
 Normally = (Axle Load/8.2)n
n = 4 - 5

35. Single Lane Roads
 Total No. of Commercial Vehicles in both Directions
Two-lane Single Carriageway Roads
 75% of total No. of Commercial Vehicles in both
Directions
Four-lane Single Carriageway Roads
 40% of the total No. of Commercial Vehicles in both
Directions
Dual Carriageway Roads
 75% of the No. of Commercial Vehicles in each
Direction
Distribution Of Traffic

36. Computation of Traffic for Use of Pavement
Thickness Design Chart
365 xA[(1+r)n – 1]
N = --------------------------- x D x F
r
N = Cumulative No. of standard axles to be catered for the
design in terms of msa
D = Lane distribution factor
A = Initial traffic, in the year of completion of construction,
in terms of number of commercial vehicles per day
F = Vehicle Damage Factor
n = Design life in years
r = Annual growth rate of commercial vehicles

37. Subgrade
• Soak the Specimen in Water for FOUR
days and CBR to be Determined.
• Use of Expansive Clays NOT to be Used
as Sub-grade
• Non-expansive Soil to be Preferred.

38. Sub-base
• Material – Natural Sand, Moorum, Gravel,
Laterite, Kankar, Brick Metal, Crushed
Stone, Crushed Slag, Crushed Concrete
• GSB- Close Graded / Coarse Graded
• Parameters – Gradation, LL, PI, CBR
• Stability and Drainage Requirements

39. Sub-base
• Min. CBR 20 % - Traffic up-to 2 msa
• Min. CBR 30 %- Traffic > 2 msa
• If GSB is Costly, Adopt WBM, WMM
• Should Extend for the FULL Width of
the Formation
• Min. Thickness – 150 mm - <10 msa
• Min. Thickness – 200 mm - >10 msa

40. Base Course
• Unbound Granular Bases – WBM /
WMM or any other Granular
Construction

41. 41
ROAD DESIGN
PAVEMENT
DESIGN
GEOMETRIC
DESIGN
PAVEMENT
DESIGN GUIDE
FOR RHD
Gemetric Design Standard
Manual 2005

42. Constructions and
Maintenance
Considerations
Environmental
Considerations
Subgrade
Evaluation
Pavement
Materials
Design Traffic
Pavement Design
Comparison of
Designs
Implement Design
And Collect feed back
Validation and
Refinement of
Design procedure
Pavement Design System

43. Design Method
 AASHTO Pavement Design Manual
 Overseas Road Note 31
 Road Note 29
The basic design philosophy of AASHTO design is designing
a pavement based on a specific total traffic volume at desired
PSI (initial) and minimum or terminal level of serviceability
desired at the end of the performance period/designed life.

44. Pavement Analysis
• Method of Equivalent Thickness
– Assumption: homogeneous mass
– Simplest
• Layered Elastic Analysis
– Assumptions: homogeneous, isotropic, linear-
elastic
– Most popular
– Software: CIRCLY, BISAR, WESLEA,
KENLAYER, DAMA, EVERSTRESS, ELSYM5
etc

45. Asphalt Institute (AI)
• 1964 – revised design methodology based on
AASHO road test, British road test, and other
local test sections

46. Concrete Pavement Design:
Road Note 29

47. VEHICLE DAMAGE FACTOR
ESA for axle load Wi(in tones) = (Wi/8.2)4
Where ESA stands for Equivalent Standard Axle
Standard Axle Load = 8.2 tones.
SL.No. Axle Load (Ton) ESA
1 8.20 1.00
2 12.30 5.06
3 16.40 16

48. Vehicle Category Equivalent Factor
Large Truck (dual axle) 4.8
Medium Truck(single axle) 4.62
Small Truck 1.0
Large Bus 1.0
Minibus 0.5
VEHICLE DAMAGING FACTOR

49. Cumulative ESA = ((1+r)n – 1)/r
where r = annual traffic growth rate
n = design life in years
For National Roads r = 10%, and n = 20 years;
For Regional Roads r = 7% and n = 20 years
Road Type ESA Factor
National Road 57.3
Regional Road 41.0

50. Vehicle
Type
Traffic/day
(0.5*two way
flow
(a)
ESA factor(vehicle
damaging factor
(b)
ESA per
day
(a)*(b)
Annual ESA
(a)*(b)*365
Heavy
Truck
20 4.8 96 35,040
Medium
Truck
150 4.62 693 252,945
Light Truck 50 1.00 50 18,250
Large Bus 100 1.00 100 36,500
TOTAL 342,735
ESA CALCULATION EXAMPLE
Cumulative Design ESA = ((1+r)n – 1)/r
Design ESA = 342,735*41 = 14 millions
ESA = ((1+7/100)20 -1)/(7/100)=41.00

51. AASHTO DESIGN METHOD
Cumulative ESA
Structural Number
Reduction Servic Index
Subgrade Resilent
Standard Normal
Deviate
Variance

52. Thank You