This document summarizes a report on the design of flexible pavements in India. It provides an introduction to pavement types and describes the structural layers of flexible pavements. It outlines the empirical California Bearing Ratio method used previously in India and discusses the 2001 introduction of the Mechanistic-Empirical method in the IRC 37-2001 guidelines. The guidelines were updated in 2012 to include more options for flexible pavement designs using various materials. Continued research is needed to further refine the guidelines and optimize pavement structure and performance in a sustainable way.

1. Summer training Report on
Design of Flexible
Pavements
PRESENTED BY:
Amresh Kumar

2. Content
• Introduction
• About Pavement
• Flexible Pavement
• Types of Flexible Pavement
• Structural Analysis
• FLEXIBLE PAVEMENT DESIGN IN INDIA –
IRC:37–2001
• Tentative Guidelines – A way ahead
• CONCLUSION

3. Introduction
• In India, new flexible pavements during twentieth century were
designed by California Bearing Ratio method, an empirical
method, based on subgrade strength measured in terms of CBR
value which was, with the advent of twenty first century, taken
over by Mechanistic-Empirical methods. Continued improvement
in traffic characterization, material characterization and quality,
mix designs, pavement design approaches and construction
methodologies, performance prediction models and laboratory
testing procedures, and maintenance approaches will call for a
review of the present state of-the art pavement design approaches.
In this paper, a review of the flexible pavement design in India till
2012 is briefly outlined along with some suggestions/future steps
to be taken up to further refine the current flexible pavement
design method in view of current developments in order to
optimize the pavement structure and its performance, and to
evolve a sustainable pavement structure.

4. About Pavement
• Broadly, there are three types of pavements; flexible
pavements, rigid pavements and composite pavements.
In this paper, discussion is limited to flexible pavements
only. In flexible pavements, wheel loads stresses are
transferred by grain-to-grain contact of the aggregate
through the granular structure which acts like a flexible
sheet due to less flexural strength. The wheel load acting
on the pavement will be distributed to a wider area, and
the stresses decreases with the depth. Taking advantage
of this distinct stress distribution characteristic, flexible
pavement normally has many layers in which material
quality deceases from top to bottom.
•

5. Flexible Pavement
• Structure
– Surface course
– Base course
– Subbase course
– Subgrade

6. Types of Flexible Pavement
Dense-graded
Open-graded Gap-graded

7. Structural Analysis
To design a pavement we need to know:
• Subgrade Strength or bearing capacity
Measured by the CBR test. Typically CBR 2-3 for clays and
15% or greater for sandy soils. Used directly in the empirical
design procedure
• Pavement Material Characteristics; and
Need to know what materials are available. Generally used Type 2.1 for top 150mm
with Type 2.3 below. For deep pavements, may also have a deep layer of CBR15
material
• Design Traffic Loading
No. of equivalent standard axles that traverse the design lane over the pavement
design life

8. FLEXIBLE PAVEMENT DESIGN IN INDIA –
IRC:37–2001
• To overcome limitations and empiricism in pavement
design as discussed in paragraphs 1.1, 2 and 3, attempts
were made under the patronage of Ministry of Road
Transport and Highways (MORT&H), Government of
India via Research Schemes R-6, R-19 and R-56 which
gave birth to IRC:37–2001 and thus, laid down the
foundation for Mechanistic-Empirical Pavement Design
Method (MEPDM) for flexible pavement designs in
India and open a new chapter in the history of
pavement designs with ample scopes for further
improvements and refinements in future.

9. Tentative Guidelines – A way ahead
• This guidelines can be used for the design of a flexible pavement
on any highway (excluding low volume roads), in which
bituminous surfacing is provided over (a) granular base and
granular subbase, (b) a cementitious base and cemented subbase
with a crack relief layer of aggregate interlayer over cementitious
base layer, (c) a cementitious base and cementitious subbase with
SAMI layer between bituminous and base layer, (d) Reclaimed
Asphalt Pavement (RAP) with or without addition of fresh
aggregates treated with foamed bitumen/bitumen emulsion, and €
bituminous base and granular subbase using the concept of long
life deep strength bituminous pavements. Last four options are
new additions over 2001 revision. There
is no change in pavement design approach or in modeling of the
pavement structure.

10. CONCLUSION
With the advent of twenty first century, IRC:37–2001 introduced the
Mechanistic Empirical Method instead of empirical methods used
during last century to design the flexible pavements in India which
provides the capability to a designer to determine the required layer
thicknesses so that the pavement would last for selected design life
without exceeding predetermined distress levels. IRC:37–2012
includes more options of flexible pavements and evolve optimum
pavement design with sub-standard or recyclable materials also. It
also introduced the design of perpetual pavements which need to be
elaborated along with inclusion of the design procedure for other
thick bituminous pavements.
.

11. Continued improvement in traffic characterization, material quality
and characterization, mix designs, pavement construction
methodologies and maintenance approaches, performance
prediction models, and laboratory/field testing procedures etc.
necessitates further refinement of the IRC pavement design
guidelines which, however, need allinclusive, extensive, integrated
and long term result-oriented research works and field efforts
financed with annual dedicated budget which should be undertaken
without any further delay. It is, however, safely stated that the
refinements in current pavement design method as suggested in this
paper or else will definitely result into reduction of pavement
thickness and better pavement management practices which simply
translates an annual saving of more than ` 1000 crores per year in
view of current pace of highway development programs in the
country.