0% found this document useful (0 votes)
87 views94 pages2
India
Uploaded by
Phuc Nguyen QuangCopyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF or read online on Scribd
0% found this document useful (0 votes)
87 views94 pages2
India
Uploaded by
Phuc Nguyen QuangCopyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF or read online on Scribd
/ 94
IRC:37-2018
GUIDELINES FOR
THE DESIGN OF FLEXIBLE PAVEMENTS
(Fourth Revision)
INDIAN ROADS CONGRESS
2018 IRC:37-2018
GUIDELINES FOR
THE DESIGN OF FLEXIBLE PAVEMENTS
(Fourth Revision)
Published by:
INDIAN ROADS CONGRESS
Kama Koti Marg,
Sector-6, R.K. Puram,
New Delhi-t10 022
NOVEMBER, 2018
Price : € 1400/-
(Plus Packing & Posiage) IRe37-2018
First Published
Reprinted
First Revision
Reprinted
Reprinted
‘Second Revision
Reprinted
Reprinted
Reprinted
Reprinted
Reprinted
Reprinted
Reprinted
Reprinted
Reprinted
Third Revision
Reprinted
Reprinted
Reprinted
Fourth Revision
Reprinted,
September, 1970
December, 1976
December, 1984
October, 1890 (Incorporates Amendment No, 1, September 1988)
April, 1995
July, 2004
March, 2002
July, 2004
April, 2005
June, 2008
June, 2007
December, 2007
‘September, 2008,
October, 2008
July, 2014,
December, 2012
June, 2013
May, 2015
October, 2017
November, 2018
‘September, 2019
(All Rights Reserved. No part of this publication shall be reproduced,
translated or transmitted in any form or by any means without the
permission of the Secretary General, Indian Roads Congress)
Printed by I. G. Printers Pvt, Ltd., New Delhi - 110.020
1100 Copies IRC:37-2018
CONTENTS
S.No. Description Page No.
Personnel of the Highways Specifications and Standards Committee. Hi
Abbreviations and Symbols ‘iki
1 Introduction 1
2 Scope 3
3 Design Principles 3
4 Traffic 13
44 General 13
42. Traffic Growth Rate 13
4.3. Design Period 4
4.4. Vehicle Damage Factor 14
4.5 Lateral Distribution of Commercial Traffic over the Carriageway 16
4.8 Computation of Design Traffic 17
Pavement Compositions "7
‘Subgra 18
6.1 General 18
6.2. Selection of Dry Density and Moisture Content for Laboratory Testing
of Subgrade Material 19
6.3. Resilient Modulus of the Subgrade 419
6.4 Effective Modulus/CBR for Design 20
7 ‘Sub-Bases 24
7.1 General 2
7.2 Granular (Unbound) Sub-base Layer 24
7.3. Cementitious (Cement Treated) Sub-base (CTSB) Layer 23
8 Bases 24
8.1 Unbound Base Layer 24
8.2 Cementitious Bases (CTB) 28
8.3. Crack Relief Layer 26
8.4 Bitumen Emulsion/Foamed Bitumen treated Reclaimed Asphalt
Pavement (RAP) Base 7
9 Bituminous Layers a7
9.4 General ea 92. Resilient Modulus of Bituminous Mixes
10 Long-Life Pavements
1" Pavement Design Procedure
41.4. Stops Involved in the Pavement Design
2 Pavement Siructural Design Catalouges
18 Design in Frost Affected Areas
4 Quality Control Tests During Construction
5 References
‘Appendix A: The Principles and Approach followed in these Guidelines
At An Overview
A2 Cracking in Bituminous Layers
A3_ Rutting in Bituminous Pavements
A4_ Structural Analysis of Pavement
AS. Effect of Climate and Environment on Pavement Performance
A6 Mix Design
AT Tests and Design Documentation
AB Performance Monitoring
‘Annex I: Installation and Use of IITPAVE Software
1. Salient Features of ITTPAVE
1.2 Installation of IITPAVE
13. Using IITPAVE for Analysis of Flexible Pavements
‘Annex Il: Worked out Examples for Pavernent Design
II1_ Estimation of Effective Subgrade Modulus/CBR:
IL2_ Design Example to Check the Adequacy of Granular Sub-base Thickness
13 Design of Bituminous Pavement with Granular Base and Sub-base
14 Ilustration of Computation of Cumulative Fatigue Damage in
‘Cement Treated Base (CTB) Layer
IS Design of Bituminous Pavement with Reclaimed Asphalt
Pavement (RAP) material treated with Foamed Bitumen’Biturnen
Emulsion and Cemented Sub-base
|L6 Worked out Design Example: Long-life Pavement
17 Stage Construction
I.8__ Design options for Diversions
‘Annex Ill: Example Calculations for Selected Pavement Compositions
29
32
32
22
82
62
53
56
56
56
58
59
59
60
62
62
63
BBB88
70
R
76
7
79 7
8
19
20
RB RRB
1RC:37.2018
PERSONNEL OF THE HIGHWAYS SPECIFICATIONS,
AND STANDARDS COMMITTEE (HSS)
Singh, BN.
(Convenor)
Balakrishna, ¥.
(Co-Convenor)
Kumar, Sanjeev
(Member-Secretary)
Behera, Bijan Kumar
Bose, Dr. Sunil
‘Chana, Dr. Satish
Gupta, DP.
Jain, RK,
Kapila, KK.
Kukrety, BP,
Kumar, Or. Mahesh
Lal, Chaman
Moana, HLL.
Nashikkar, JT.
Nirmal, S.K.
Pandey, LK.
Paride, Prof. (Dt) M.
Patel, SL
Prasad, R. Jel
Rawat, MS.
Rody, Or. KS. Krishna
Reddy, |.
Reddy, Prof. (Dr) KS.
Sharma, 8.C.
Shrivastava, AK.
Singh, Nirmait
{As on 23.10.2018)
Director Generel (Road Development) & Special Secretary to Get. of
Indi, Mnisty of Road Transport and Highways, New Dethi
‘Additional Director General, Ministy of Road Transport and Highways,
New Delhi
Chief Engineer (R) S, R & T, Ministry of Road Transport & Highways,
New Delhi
Members
Engineer in-Chiet (Cv), Oaisha
Head (Retd,), FPC Division, Central Road Research Institute, New Dalhi
Director, Central Road Research Institute, New Delhi
DG(RD) &AS (Retd,), Ministy of Road Transport and Highways, New Delhi
Chief Engineer (Reta), PWD Haryana
(Chairman & Managing Director, ICT Pvt. Ltd,, New Delhi
‘Associate Director CEG Lid, New Delhi
Engineerin-Chief (Retd.), PWD (B&R) Haryana.
Engineer-in-Chief (Reta), PWD Haryana
Secretary (Retd.), PWO Rajesthan
Secretary (Rett), PWD Maharashtra
‘Secretary General, Indian Roads Congress, New Delhi
‘Additional Director General, Ministy of Road Transport and Highways,
New Deli
Dean, SRIC, Indian Insitute of Technology, Roorkee:
Secretary (Rela), PWD (Roads and Buildings) Gujarat
Engineer-in-Chief (Rel), PWD & Bangalore Mahanegar Pale, Karrataka
Executive Director, AECOM India Pvt. Li.
Secretary, Public Works, Ports & Inland Water Transport Department,
Kametaka
Engineer.in-Chief (NH, CRF & Buildings), PWD Hyderabad
Professor, ncian Insilute of Technology, Kharagpur
[DG{RD)& SS (Rett), Ministry of Road Transport and Highways, New Delhi
‘Additional Director General (Retd), Ministry of Road Transpott and
Highways, New Delhi
DG{RO) & SS (Retd,), Ministry of Road Transport and Highways, New Delhi IRC:37-2018
ar
28
Ey
30
3
32
33
a
38
40
Sinha, AV,
“The Chist Engineer
(Basar, Tol)
“The Chit Engineer
(Kumer, Ani)
“The Director (Tech)
(Prochan, 8.6)
‘The General Manager
(aul, Satsh)
“The JICA Expert
(Kitayama, Michiya)
‘The Member (Projects)
(Pandey, RK)
“The Professor
(Chakeobory, Dr Partha)
The Secretary
(esava, $8.)
The Secretary (Roads)
(Joshi, C.P)
‘The Secretary Tech.)
(Tickoo, Bimal) (Retd,)
‘The Special Director
General (Ret)
(Bansal, M.C.)
Venkatesha, M.C.
Wasson, Ashok
saigopal. RK.
Justo, Prof, (Dr) CEG.
\Veereragavan, Prot.
(Dr)A.
President,
Indian Roads Congress
Director General (Road
Development) & Special
Secretary to Gov. of India
‘Secretary Gonoral.
Indian Roads Congress
DG(RD) & SS (Retd,), Ministry of Road Transport and Highways, New Delhi
PWD Arunachal Pradesh
Border Roads Organisation, New Del
"National Rural Infrastructure Development Agency, New Debi
Nationa Highways and Infastucture Development Corporation,
New Delhi
Japan International Cooperation Agency, New Delhi
National Highways Authority of India, New Delhi
Indian Insitute of Technology, Kanpur
Roads and Buidings Department, Gujarat
PWD Maharashira
Roads and Buildings Department, Jammu & Kashmir
‘CP WD, Nirman Bhawan, New Deli
Consultant
‘Member (Tech, (Ret), National Highways Authority of India, New Delhi
Corresponding Members
MO, Struct Geotech Research Laboratories (P) Ltd, Bengaluru
Professor (Rett), Emeritus
Professor, Indian Instute of Technology, Macras
Ex-Officlo Members
(Reddy, Dr. K'S. Krishna), Secretary, Public Works, Ports & Inland
Water Transport Department, Karnataka
{Singh, B.N.), Ministry of Road Transport and Highways, New Delhi
Nirmal, Sanjay Kumar IRC:37-2018
ABBREVIATIONS AND SYMBOLS
‘All the abbreviations and symbols are explained in the guidelines wherever they appeared first
in the document.
AKSHO -
AASHTO. -
ASTM -
AUSTROADS =
BBD :
BC :
BIS :
BM -
CBR 3
crD A
sa
creieT -
cTsB :
cvPD -
Dam :
NHAI :
RAP :
RF :
‘SAMI :
‘spac :
SMA :
SP :
ss2 :
ucs :
‘Some of the abbreviations and symbols are listed below:
‘American Association of State Highway Officials
‘American Association of State Highway and Transportation Officials
‘American Sociely of Testing and Materials
Association of Australian and New Zealand Road Transport and Traffic
Authorities
Benkelman Beam Deflection
Bituminous Concrete
Bureau of Indian Standards
Bituminous Macadam
California Bearing Ratio
Cumulative Fatigue Damage
Cumulative standard axles
Cement Treated Base (includes all types of cement and chemical stabilized
bases)
‘Cement Treated sub base (includes all types of coment and chemical stabilized
sub-bases)
‘Commercial Vehicles Per Day
Dense Bituminous Macadam
Falling Weight Deflectometer
Granular Base
Gross Domestic Product
Gap Graded Mix with Rubberized Bitumen
Granular Sub-base
Indian Roads Congress
Indian Standard
Indirect Tensile Strength
Kilonewton
Layer Coefficient Ratio
Mechanistic Empirical Pavement Design Guide
‘Modulus Improvement Factor
Milimetre
Ministry of Road Transport & Highways
Mega Pascal
National Highways Authority of India
Reclaimed Asphalt Pavement
Reliablity Factor
‘Stress Absorbing Membrane interlayer
‘Somi-Dense Bituminous Concrete
Stone Matrix Asphalt
Special Publication
Slow Setting-2 Emulsion
Unconfined Compressive Strength IRC:37-2018
i
prammooe>
&
i
ZZ zezee
RSet? Uz
PR prne
Vehicle Damage Factor
Water Bound Macadam
Wet Mix Macadam
Degree Celsius
Initial traffic
Radius of circular contact area
‘Adjustment factor for fatigue life of bituminous layer
Lateral distribution factor
Elastic modulus of CTS material
Elastic modulus of cement ireated sub bases
Vehicle Damage Factor (VDF) used in the design traffic estimation equation
Thickness of the granular layer
Latitude
Reslliont modulus of granular layer
Resilient modulus of the bituminous mix
Resilient modulus of subgrade soil
Effective resilient modulus of the layer supporting the granular layer
28-day flexural strength of the cementitious base
= Million standard axles
Microstrain
Number of standard axle load repetitions which the coment treated material
‘can sustain
Design life period, in years
‘Cumulative number of standard axies to be catered for during the design
period of ‘n’ years
Fatigue life of the bituminous layer
Fatigue life of CTB material which is the maximum repetitions of axle load
class 1’ the CTS material can sustain
Expected (during the design fe period) repetitions of axle load of class
Subgrade rutting life
Number of commercial vehicles per day as per last count
Contact pressure
Annual growth rate of commercial vehicles in decimal
‘Temperature at a depth of 20 mm of layer
Air temperature
Percent volume of air voids in the mix.
Percent volume of effective bitumen in the mix
Number of years between the last count and the year of completion of
construction |
Maximum surface defection
Horizontal Tensile Strain
Vertical compressive strain
Radial stress at the location
‘Tangential stress at the location
Vertical compressive stress at the location 1RC:37-2018
GUIDELINES FOR THE DESIGN OF FLEXIBLE PAVEMENTS
4. INTRODUCTION
4.1 The first guidelines for the design of flexible pavements, published in 1970, were
based on (i) subgrade (foundation) strength (California Bearing Ratio) and (i) traffic, in terms.
‘of number of commercial vehicies (having a laden weight of 3 tonnes or more) per day. These
guidelines were revised in 1984 considering the design trafic in terms of cumulative number
of equivalent standard axle load of 80 kN and design charis were provided for design traffic.
volumes up to 30 milion standard axle (msa) repetitions. The 1970 and 1984 versions of the
guidelines were based on empirical (experience based) approach,
4.2 The second revisionwas carried outin 2001 [{Jusing sem-mechanistic (ormechenistic-
empirical) approach based on the results available from R-6(2], R-S6{3} and other research
‘schemes of the Ministry of Road Transport and Highways (MoRTH). The mechanistic-empirical
performance models for subgrade rutting and bottom-up cracking in the bottom bituminous
layer, developed using the rasults of these research schemes, ware used for the design of
flexiole pavements. FPAVE software, developed for R-56 research scheme for the analysis of
linear elastic layered pavement systems, was used for the analysis of pavements and for the
development of thickness design charts. Thickness charts were provided for design trafficlevels,
up to 150 msa.
1.3 The third revision of the guidelines was carried out in 2012{4] to facitate () design
of bituminous pavements for trafic volumes more than 160 msa (i) utlization of new types of
pavement materials such as bituminous mixes with modified binders, foarnlemulsion treated
granuler or Recleimed Asphalt Pavement (RAP) material bases and sub-bases and coment
treated sub-bases and bases and stabilized subgrades and (il) utilization of new constuction
techniquesipraciices. Recommendations were made for the use of harder grade binders te resist
rutting and top-down cracking in the upper bituminous layer and for fatigue resistant bituminous
‘mixes for the bottom bituminous layer. Mechanistic-empirical performance models were given
for rutting in subgrade and bottom-up cracking in bituminous layers for twa different levels (80%
‘and 90%) of reliability, Fatigue criteria were included for cement treated bases also.
4.4 The fourth (current) revision has been done based on the feedback received on the
performance of bituminous pavements in general and that of bituminous layers in partcuiar.
Different provisions mado in tha third revision of the guidelines have been fine-tuned based
on the feedback. Some of the salient features of the fourth revision are: (a) recommendation
of better performing bituminous mixes and binders for surface and base/binder courses (b)
guidelines for selection of appropriate elastic moduli for bituminous mixes used in the surface
and other courses (c) recommendation of minimum thicknesses of granular and cement treated
sub-bases and bases and bituminous layers from functional requirements (d) generalization of
the procedure forthe estimation ofthe effecive resilient modulus/CBR of subgrade (e) provision
forthe use of gao-synthetics and (1 rationalization of the design approach for stage constriction.
4.5 The draft of the basic document was prepared by Late Prof. BB. Pandey of IIT
Kharagpur based on the feedback received during the open house discussion on IRC:37-2012
1 IRC37-2018
hheld at the National Highways Authority of India (NHAl) headquarters on @" April, 2016 and
‘Subsequent comments received fram different practicing professionals, experts and the members
of the H-2 committee on the field performance of bituminous pavements and on other design
‘and practical issues. The draft was further edited and modified by a sub-committee consisting of
‘ShriA.V, Sinha, Shri R.K. Pandey and Shri Bidur Kant Jha. The draft was deliberated in various
meetings of Flexible Pavement, Airfield & Runways Committee (H-2) and was approved in its
‘meeting held on 23% September, 2018. The Highways Specifications and Standards Committee
(HSS) in its meeting held on 23% October, 2018 approved the document and authorized the
Convenor to modify the document subject to written comments received and comments offered
during the meeting. Executive Committee of IRC approved the document in its meeting held on
27" October, 2018. Thereafter, meeting was convened by the Convenor, H-2 Committee along
with members of drafting Sub-group on 17* November, 2018 at New Delhi to incorporate
compliance of the comments in the document. This modified draft was further deliberated and
‘approved in a meeting convened by HSS Convenor & DG (RD) & SS, MoRTH on 19" November,
2018 wherein Secretary General, IRC and member of Sub-group were also present. The Council
in ts meeting held on 22% November, 2018 at Nagpur considered and approved the document
for printing and releasing,
The composition of H-2 Committee is given below:
Reddy, Prof. (Dr.) K. Sudhakar... Convenor
Nirmal, Sanjay Kumar cecum Co-Convenor
‘Shukla, Manoj Kumar ‘Member-Secretary
‘Members
Basu, SB. Lal, Chaman
Bongirwar, PL. Murthy, D.V, Sridhar
Bose, Dr, Sunil Panda, Prof. (Dr.) Mahabir
Director (Tech.), NRRDA Pandey, LK.
Garg, Sanjay Pandey, Prof. (Dr)B.8. (Expired in Oct, 2018)
Ghai, Indesit Pandey, RK.
Jain, NS. Rep. of DGBR.
Jain, RK. ‘Sharma, S.C.
Jha, Bidur Kant Sinha, AV.
Krishna, Prabhat Sitaramanjaneyulu, K.
Kumar, Prof. (Or) Praveen Tyagi, BR,
Corresponding Members
Justo, Prof. (Or) CEG. Seehra, Dr. SS.
Rao, Prof, (Dr) SK. \Veoraragavan, Prof. (Dr) A IRC:37.2018
Ex-Officio Members
President, (Reddy, Dr. K.S. Krishna), Secretary, Fublle
Indian Roads Congress Works, Ports & Iniand Water Transport
Department, Kamaiaka
Director General (Singh, B.N.), Ministry of Road Transport &
(Road Development) & Special Highways,
Secretary to Govt. of India
Secretary General, Nirmal, Sanjay Kumar
Indian Roads Congress
2. SCOPE
24 The Guidelines shall apply o the design of new flexible pavements and reconstruction
‘of damaged pavements for roads with a design trafic of two milion standard axle (msa) load
repetitions or more. For the roads with a design trafic of ess than 2 msa, IRC:SP:72{5] stall be
adopted for pavement design. For rehabiltaton of in-service pavements, overlay design shall
be done as per Faling Weight Deflectometer (FWD) method (IRC:115)6] or Benkelman 3eam
Deflection (BBD) test method (IRC:81)(7
2.2 Users of the guidelines are expected to use their skills, experience and engineering
judgment and take into consideration the local climatic conditions, cost and availabilty of
materials, their durability and past pavement performance in theirrespective regions for selecting
‘a suitable pavement composition,
2.3 Theguidelines may require revision from time to time in the ight of fulure performance
data and technological developments. Towards this end, itis suggested that all the organizations
intending to use the guidelines should keep @ detailed record of the year of construction,
‘subgrade CBR, soll characteristics, pavement composition and specifications, traffic, pavernent
performance, overlay history, climatic conditions, etc., and provide feedback to the Indian Roads
‘Congress for further revision.
3. DESIGN PRINCIPLES.
3.1. While various sections of these guidelines describe the design procedures in detall,
these are supplemented by a discussion on the ‘principle and approach to design’ given in
the Appendix-A to this document, which needs to be considered as an integral part of the
Guidelines, The Annexes (Ito Ill) given to this document intend to elaborate the finer points of
design and support the recommendations by different worked out design examples to help the
Users in familiarizing themselves with different provisions of the guidelines and for arriving at a
‘safe, economical and performing design.
‘The philosophy of pavement design involves designing pavements for satisfactory functional
‘and structural performance of the pavement duting its intended service life period. Roughness
‘caused by variation in surface profle, cracking of layers bound by bituminous or cementitious
3 1RC:37-2018
‘materials, rutting (permanent or plastic deformation) of unbound/unmodified or partially modified
subgrade, granular layers and bituninous layers are the primary indicators of the functional
fend structural performance of pavements. Performance of the pavement is explained by
performance models which are either (a) purely empirical (only based on past experience) or (b)
‘mechanistio-empiical, in which the distresses/performance are explained in terms of mechanistic
parameters such as stresses, strains and deflections calculated using a specific theory and as
pper a specified procedure. Most ofthe current pavement design methods follow the machanistic~
‘empirical approach for the design of bituminous pavernents. In these methods, for each of the
selected structural distresses, a critical mechanistic parameter is identified and controlled to an
accsptable (limiting) value in the design process. The limiting values of these critical mechanistic
parameters are obtained from the performance models.
3.2 The mechanistic-empirical design approach, which was used in the second and
third revisions of IRC:37, is retained in the current revision as well for the design of flexible
pavements. The theory selected for the analysis of pavements is ‘linear elastic layered theory’ in
which the pavement is modeled as a mult-layer system. The botiom most layer (foundation or
subgrade) is considered to be semi-infinite, and all the upper layers are assumed to be infinite
Inthe horizontal extent and finite in thickness. Elastic modulus, Poisson's ratio and thickness of
teach layer are the pavement inputs required for calculation of stresses, strains and deflections
produced by a load applied at the surface of the pavement. IITPAVE software, which is an
Updated version of FPAVE developed for MoRTH Research Scheme R-56 “Analytical design of
Flexible Pavement'[3], has been used for the analysis of pavements.
3.3 The vertical compressive strain on top of the subgrade is considered in these
guidelines to be the critical mechanistic parameter for controlling subgrade rutting, Horizontal
tensile strain at the bottom of the bottom bituminous layer is taken as the causative mechanistic
parameter which has to be limited to contral bottom-up cracking in bituminous layers. Similary,
‘to ensure that the Cement Treated Bases (CTB) do not fall by faligue cracking, tensile strain and
tensile stress al the bottom of the CTB are considered to be the critical parameters to control
3.4 Rutting within bituminous layers caused by accumulated plastic (permanent)
deformation in these layers due to repeated application of trafic loads is another major distress
Which ocours in bituminous pavements. High pavement temperatures and heavy loads can cause
early development of unacceptable levels of rut depth in bituminous mixes as the stifhess of
the bituminous mix reduces at higher temperatures and the proportion of plastic (imrecoverable}
deformation out of the total deformation will be larger under higher temperature and heavier
loading conditions. Moisture damage of mixes and brittle cracking resulting from excessive
‘age hardening of bitumen in the upper layers are the other major concems to be taken into
consideration. These distresses are considered by integrating the mix design into the structural
design by incorporating the mix volumetric parameters into the performance models and by
making suitable recommendations about the choice of binder and mix to be used in different
layers.
3.5 For the satisfactory performance of bituminous pavements and to ensure that
the magnitudes of cistresses are within acceptable levels during the service life period, the
{uidolinee recommend that the pavement sections he selecied in such a way that they satisfy
the limiting stresses and strains prescribed by the performance models adopted in the guidelines
4 IRC:37-2018
for subgrade rutting, bottom-up cracking of bituminous layer and fatigue cracking of cement
treated bases. Additional measures have been suggested inthe guidelines by way of integrating
the mix design parameters that have a significant bearing onthe performance of pavements into
the design process. It may be noted that the design of the bituminous mix was integrated into
te structural design process even in the second revision (2001 version) of IRC:37 as the strain
values used inthe fatigue andiruting performance models are computed using the elastic adult
bf bituminous mixes and other layer materials. Also, the elastic modulus ofthe bituminous layer
‘appears in the faligue performance criterion. Suitable recommendations have also been made in
the guidelines for) fatigue cracking and moisture damage resistant mixes forthe bottom (base)
bituminous layer (i) rut and moisture damage resistant bituminous mixes for the intermediate
{einder) biuminous layer (f provided) and li) rut, moisture damage, fatigue cracking and age
resistant surface course and (iv) drainage layer for removal of excess moisture from the interior
of the pavernent.
36 Performance Criteria
The following performance criteria are used in these guidelines for the design of bituminous
pavements.
3.6.1 Subgrade rutting criteria
An average rut depth of 20 mm or more, measured along the wheel paths, is considered in hese
guidelines as ortical or failure rutting condition, The equivalent number of standard axle lozd (80
kN) repetitions that can be served by the pavement, before the critical average rut depth of 20,
mm or more occurs, is given by equations 3.1 and 8.2 respectively for 80 % and 90 % rellabilty
levels. The rutting performance model developed initially based on the MoRTH R-6 Reszarch
‘Scheme(2] performance data was subsequently developed into two separate models fer two
different reliabilty levels based on the additional performance data collected for MoRTH R-58
Research Scheme[3}
Ng= 4.1656 x 10% [VeJ!®7 (or 80 % reliability) (4)
Ng=1.4100x 10 [Hie}" (for 90 % rlititty) (32)
Where,
N= subgrade rutting life (cumulative equivalent number of 80 KN standard axle
loads that can be served by the pavement before the critical rut depth of 20 mm
(or more occurs)
c,= vertical compressive strain at the top of the subgrade calculated using linear
clastic layered theory by applying standard axle load at the surface of the
selected pavement system
IITPAVE software is used in these guidelines for the analysis of pavements. For the computation
of stresses, strains and deflections in the pavement, thicknesses and elastic properties (elastic
modulus and Poisson's ratio) of diferent layers are the main inputs. Detailed instructions for
installation and use of IITPAVE software, which is provided along with these guidelines, are
‘given in Annex |. Guidelines forthe selection of the elastic modulus and Poisson's ratio values
of different pavement layers are given in different sections of the guidelines. For the calculation
5 IRO:37-2018
of vertical compressive strain on top ofthe subgrade, horizontal tansile strain at the bottom of the
bottom bituminous layer and the horizontal tensile strain atthe bottom of cement treated base
{CTB) layer, the analysis is done fora standard axle load of 80 KN (single axle with dual wheels.
‘Only one set of dual wheels, each wheel cerrying 20 kN load with the centre to centre spacing
‘of 310 mm between the two whee!s, applied atthe pavement surface shall be considered forthe
‘analysis. The shape of the contact area of the tyre is assumed in the analysis o be circular. The
uniform vertical contact stress shall be considered as 0.56 MPa. However, when fatigue damage
anaiysis of Cement Treated Bases (CTB) is caried out, (using Equations 3.5 to 3.7) he contact
pressure used for analysis shell be 0.80 MPa. The layer interface condition was assumed to be
fully bound. The materials are assumed to be isotropic.
3.6.2 Fatigue cracking criteria for bituminous layer
“The occurrence of fatigue cracking (appearing as inter connected cracks), whose total area
In the section of the road under consideration is 20 % or more than the paved surface area
of the section, Is considered to be the critical or failure condition. The equivalent number of
standard axle (80 kN) load repetitions that can be served by the pavement, before the critical
Condition of the cracked surface area of 20 % or more occurs, is given by equations 3.3 and
34 respectively for 80 % and 90 % reliability evels. The fatigue performance models given by
equations 3.3 and 3.4 were developed under MoRTH R-56 scheme[3] utilizing primarily the R-6
scheme (Benkelman Beam Studies) performance data(2] supplemented by the data available
from R-19 (Pavement Performance Studies)[8] and R-56 schemes{3}.
606440+10 [1/¢}2[11M,,J°2 (for 80 % reliability) @3)
5161-C+10% [1/e (1M, (for 90 % reliability) 64)
Where
C= 10, and wal Ye
|
V, = per cent volume of air void in the mix used in the bottom bituminous layer
Vy, = percent valume af effective bitumen in the mix used in the bottom biturninous
layer
IN, _ =fatigue life of biturninous layer (cumulative equivalent number of 8O KN standard
aie loads that can be served by the pavement before the crtical cracked area
0f 20 % or more of paved surface area occurs)
& _ =maximum horizontal tensile strain at the bottom of the bottom bituminous layer
(OBM) calculated using linear elastic layered theory by applying standard axle
Toad at the surtace ofthe selected pavement system
resilient modulus (MPa) ofthe bituminous mix used in the bottom bituminous
layer, selected as per the recommendations made in these guidelines.
‘The factor'C'is an adjustment factor used to accountfor the effectof variation in the mix volumetric
parameters (elective binder volume and air vord content) on te fatigue lif of bkumInous mixes
[Bland was incorporated in the fatigue models to integrate the mix design considerations into the
fatigue performance model.
Moy IRo:37.2018
‘Apopular approach used for enhancing the fatigue life of bituminous layers is to make the bottom
‘most bituminous mixes richer in bitument 10], Larger binder volume in the mixxmeans an inoreased
thickness of the binder film in the mix and an increase in the proportion of bitumen over any
‘ross-section of the layer normal to the direction of tensile strain. Besides having longer fatigue
lives, larger binder volumes wil also be beneficial in making the mix more moisture damage
resistant due to thicker binder lms which also reduce the ageing of the binder. Considering that
the bottom bituminous layer wil be subjected to significantly lower stresses and lower summer
temperatures compared to the upper layers, the chance of rutting of the lower layer will be less.
‘The recent version of the Asphalt Institute manual for mix design{10] recommends design of the
bitumen rich mixes (or rich bottom mixes) at 2 to 2.5 per cent air voids and to compact the rich
bottom layer to less than 4 per cent in-place air voids. The recommendations made in these
guidelines about the volumetric parameters and the in-place air voids to be achieved are given
in para 92.
3.8.3 Fatigue performance models for Cement Treated Base (CTB)
3.6.3.1 In thecase of pavements with CTE layer, fatigue performance check for the CTBlayer
should be carried out as per equation 3.5 (based on cumulative standard axle load repetitions
estimated using vehicle damage factors), and as per equations 3.6 and 3.7 (cumulative
fatigue damage analysis) using axle load spectrum data. it may be noted that ‘cement treated’
refers to stabilization by different types of cementitious materials such as cement, lime, fy=
ash, or a combination thereof. The terms, ‘cement treated’ and ‘cementitious’, have been used.
interchangeably in these guidelines. Equation 3.5 is based on the Australian experience[ 11)
‘whereas equation 3.6 is as per the recommendations of the Mechanistic-Empirical Pavement
Design Guide[12]. Pavement analysis shall be carried out using IITPAVE with a contact stress.
of 0.8 MPa on the pavement surface to determine the tensile strain (et) value at the bottom of
the CTB layer. The number of standard axle loads derived from equation 3.6 by substituting the
‘computed tensile strain value along with other inputs shall not be less than the design trafic.
“fel
“ (5)
Where,
RF = relabilly factor for cementitious materials for failure against fatigue
= 1 for Expressways, National Highways, Sate Highways and Urban Roads and
for other categories of roads if the design trafic is more than 10 msa
= 2 for all other cases.
N= number of standard axle load repetitions which the CTB can sustain
E = elastic modulus of CTB material (MPa)
£, tensile strain atthe bottom ofthe CTB layer (microstain),
3.6.3.2 Cumulative fatigue damage analysis
The CTB layer is subjected to cumulative fatigue damage by the application of axle loads of
different categories and different magnitudes applied over the design life period. The fatigue life
7 IROS7-2018
N, of the CTB material when subjected to a specific number of applications (n) of axle load of
class '! during the design period, is given by equation 3.6. Delails of different types of axles, axle
load specirum, repetitions of each load group expected during the design life period, shall be
obtained from the analysis of the axle load survey data,
For the purpose of analysis, each tanciem axle repetition may be considered as two repetitions of
a single axle carrying 50 % of the tandem axle weight as axles separated by a distance of 1.30
m ormore do not have a significant overlapping of siresses. Similarly, one application of a tridem
axle may be considered as three single axles, each weighing one third the weight of the tridem
‘axle, For example, if @ tridem axle carries a load of 45 tonnes, it may be taken to be equivalent
to three passes of a 15 tonne single axle,
For analyzing the pavernent for cumulative fatigue damage of the CTB layer, contact stress shall
be taken as 0.80 MPa instoad of 0.56 MPa.
0972-(6,0Mug)
0912-(6\ew) (3.6)
aga (3.6)
where,
Ny Fatigue life of CTB material which is the maximum repetitions of axle load
class 'T the CT material can sustain
a tensile stress at the bottom of CTB layer for the given axle load class.
M, = 28-day flexural strength of the cementitious base
Cig = Stes Ratio
‘The Cumulative Fatigue Damage (CFD) caused by diferent repetitions of axle loads of diferent
categories and different magnitudes expected to be applied on the pavement during its design
period is estimated using equation 3.7.
CFD = (nN) co)
Where,
1, =expected (during the design life period) repetitions of axle load of class
= fague Ife or maximum number of oad repetitions the CTE layer would sustain
i only axle load of clase T were to be applied
IF the estimated CFD is less than 1.0, the design is considered to be acceptable. If the value of
‘CFD is more than 1.0, the pavernent section has to be revised
3.7 Reliability
These Guidelines recommend 90% reliablity performance equations for subgrade ruting
(equation 3.2) and fatigue cracking of bottom bituminous layer (equation 3.4) for all important
roads such as Expressways, National Highways, State Highways and Urban Roads. For ather
categories of roads, 90 % reliability is recommended for design traffic of 20 msa or more and 80
per cent reliability for design trafic ess than 20 msa. 1RC:37.2018
3.8 Analysis of Flexible Pavements
For computing the stresses, sIraine and deflections, the pavement has been considered in these
guidelines as a linear elastic layered systam. IITPAVE software, developed for analysis of near
elastic layered systems, has been used in these guidelines for analysis and design of paverrents.
Dolails of the IITPAVE software, which is supplied with this document, are given in Annex. As
mentioned previously in these guidelines, the vertical compressive strain on top of subgrade and
the horizontal tensile strain atthe bottom of the bituminous layer are considered to be the citical
mechanistic parameters which need to be controled for ensuring satisfactory performance of
flexible pavements in terms of subgrade rutting and bottom-up cracking of bituminous layers.
‘Similaty, the horizontal tensile stress and horizontal tensile strain at the bottom of the CTE layer
_are considered to be critical for the performance of the CTB bases. Figs. 3.1 to3.6 show diffrent
flexible pavement compositions for which the locations at which different critical mechanistic
parameters should be calculated are shown. The critical locations are indicated as dots in the
figure. Table 3.1 presents the standard conditions recommended in these guidelines for the
pavement analysis.
‘Theoretical calculations suggest that the tensile strain near the surface close to the edge of the
‘wheel can be sufficiently large to initiate longitudinal surface cracking followed by transverse
‘racking much before the flexural cracking of the bottorn layer occurs, ifthe mix tensile strength
is not adequate at higher temperatures(13] [14]
‘Table 3.1 Standard Conditions for Pavement Analysis using ITPAVE
Analysis Conditions
‘Material response model | Linear elastic model
Layer interface condition | Fully bonded (all layers)
No. of Wheels Dual whee!
Wheel loads: 20 kN on each single wheel (two wheels)
(Contact siress for critical] 0.56 MPa for tensile strain in bituminous layer and vertical
parameter analysis ‘compressive strain on subgrade; 0.80 MPa for Cement treated
base
Critical Mechanistic Parameters
Bituminous layer Tensile strain at the bottom
(Cement treated base __| Tensile stress and tensile strain at the bottom
[Subgrade Compressive strain at the top
‘Note: (a) Only the absolute values of strains/stresses (without the + or ~ sign) should be used
in the performance equations (b) For pavements with strong bases andior thin bituminous,
layers, its possible thatthe strain atthe bottom of the bituminous layer may be compressive
instead of tensile. IRC:37-2018
ual wheel
‘Tensile strain at the bottom
of bituminous ayer Tensile stn near surface
Rut Resistant Layer
Fatigue Resistant Layer
Subgrade
Fig. 3.1 A Pavement Section with Bituminous Layer(s), Granular Base and GSB Showing the
Locations of Critical Strains.
‘Tensile strain atthe bottom
of bituminous layer
Bituminous Laverts)
‘Tensile train/stress at the
bottom of CTE
Granular Crack Relief Layer
Sh tl cTB
Vertical Stain |
‘on subgrade \ . crea
Subsrade
: t
ey
Fig. 32.A Pavement Section with Bituminous Layer(s), Granular Crack Relief Layer, CTB, and
‘CTSB Showing the Locstions of Critical sirains/Stresses
10 iRc37.2018
‘Tensile strain at the bottom Dual wheel
of bituminous layer “Tensile strain near surface
Bituminous Layer(s)
C—O
“Tensile strain/strest ar ! SAMI
bottom of CTR ! on
Fig. 3.3 A Pavement Section with Bituminous Layer(s), SAMI Crack Relief Layer,
TB, and CTSB Showing the Locations of Critical Strains/Stresses
Tensile stain atthe bottom Dual wheel
of bituminous layer
Tensile strain noar surface
Bituminous Laver(s)
Eulsion/foam bitumen stabilised
stabilised RAP/vingin agaregate
Vertical Swain |_|
on subarade y cTsB
Subgmde
Fig. 3.4 A Pavement Section with Bituminous Layer(s), Emulsion/Foam Bitumen Stabilised RAP/
Virgin Aggregate Layer and CTSB Showing the Locations of Critical Strains
" IRC:37-2018
Dual wheel
Tensile strain at dhe bottom
of bituminous layer Tensile strain near sutface
Bituminous Layer(s)
‘Tensile straiwstress atthe i
bottem of CTB '
inistess atthe Sg
Granular Crack Relief Layer
crB
a
‘Vertical Stain, |
‘on subgrade } od
Subgrade
Fig, 3.5 A Pavement Section with Bituminous Layers), Granular Crack Rellef Layer,
‘CTB, and GSB Showing the Locations of Critical Strains/Stresses
Tensile strain atthe botom, | Dust whee
of bituminous layer “Tensile strain near surface
Subgrade
Fig. 2.6 A Pavement Section with Bituminous Layer(s), Granular Base (WMM) and
‘CTSB Showing the Locations of Critical Strains
12 1RO:37-2018
4. TRAFFIC
4a General
‘This section covers the guidelines forthe estimation of design traffic for new roads. The guidelines
‘consider that the structural damage to the pavement i.e, fatigue cracking in the bound layers
‘and rutting in the subgrade is caused by the applied traffic loads. The relative structural damage
‘caused {o the pavement by different types of axles carrying different axle loads is considered
using Vehicle Damage Factors (VDF) in the estimation of design trafic.
AAA The design traffic is estimated in these guidelines in terms of equivalent number
of cumulative standard axles (80 KN single axle with dual wheels). For estimating the factors
required to convert the commercial traffic volumes into equivalent repetitions of the standard
axe, itis necessary to measure the axle load spectrum relevant for the strotch of road under
consideration, Axle load spectrum data are especially required for the design of pavements
having layers treatedistablised using cementitious materials such as cement, lime, fly ash, etc.,
for estimating the cumulative fatigue damage expected to be caused to the cement treated base
by different axle load groups. The following inputs are required for estimating the design traffic.
{in terms of cumulative standard axle load repetitions) for the selected road for a given design
period.
(initial trafic (two-way) on the road after construction in terms of the number
of commercial vehicles (having the laden weight of 3 tonnes or more) per day
(evpd)
(i) average trafic growth rate(s) during the design life period
(il) design Ife in number of years
(iv) spectrum of axle loads
{¥) factors for estimation of the lateral distribution of commercial trafic over the
carriageway
41.2 Only the commercial vehicles having gross vehicle weight of 3 tonnes or more are
considered for the structural design of pavements.
41.3. Estimation of the present day average traffic should be based on the seven-day
24-hour trafic volume count made in accordance with IRC:9[15]
42 Traffic Growth Rate
4.24 For estimating the cumulative trafic expected to use the pavement over the design
period, it is necessary to estimate the rate(s) at which the commercial traffic will grow ovar the
design period. The growth rates may be estimated as per IRC:108[16]). Typical data required for
estimation of the growth rates(r) are:
()_pasttrends of traffic growth and
(i) demand elasticity of traffic with respect to macro-economic parameters (Ike the
gross domestic product and state domestic product) and the demand expected
6000 110 per cent (subject to a minimum of 900 cvpd)
15 IRC37-2018
445 Axle load spectrum
For the analysis of the axle load spectrum and for calculation of VDFs, the axle load data may be
Classified into multiple classes with class intervals of 10 kN, 20 kN and 30 KN for single, tandem
and tridem axles respectively
448 For small projects, in the absence of weigh pad, the axle loads of typical commercial
vehicles plying on the road may be estimated approximately from the type of goods carried.
Where information on the axle loads is not available and the proportion of heavy vehicles using
the road Is small, the indicative values of Vehicle Damage Factor given in Table 4.2 can be
used. These indicative VDF values have been worked out based on typical axle load spectrums
and taking into consideration the legal axle load limits notified in the Gazette of India dated
16" July, 2018.
‘Table 4.2 Indicative VOF values.
Tnitial (Two-Way) Traffic Volume in Terms of, Terrain
‘Commercial Vehicles Per Day
Rolling/Plain Hilly
0-160, 17, 06
150-1500, 39 17
More than 1500 50 28
45 Lateral Distribution of Commercial Traffic over the Carrlageway
454 Lateral distribution
Lateral cistibution of commercial trafic on the carriageway is required for estimating the design
traffic (equivalent standard axle load applications) to be considered for the structural design of
pavement. The following lateral distribution factors may be considered for roads with different
types of the carriageway:
4.5.1.1 Single-ane roads
‘Traffic tends to be more channelized on single-lane roads than on two-lane roads and to allow
for this concentration of whee! load repetitions, the design should be based on the total number
(sum) of commercial vehicles in both directions.
4.5.1.2 Intermediate lane roads of width 5.50 m
‘The design traffic should be based on 75 per cent of the two-way commercial trafic
4.5.1.3 Tworlane two-way roads
‘The design should be based on 50 per cent of the total number of commercial vehicles in both
the directions.
45.1.4 Fourlane single carriageway roads
40 per cant of the total number (sum) of commercial vehicles in both directions should be
considered for design.
16 IRC:37.2018
45:15 Dual camageway roads
design of dual two-lane carriageway roads should be based on 75 per cent of the number
of commercial vehicles in each direction. For dual three-lane carriageway and dual fourlane
carriageway, the distribution factors shall be 60 per cent and 45 per cent respectively.
46 Computation of Design Traffic
4.6.1 The design traffic, in terms of the cumulative number of standard axles to be carried
during the design period of the road, should be estimated using equation 4.5,
gs = SEO Ng eo (45)
Now = cumulative number of standard axles to be catered for during the dasign
period of ‘n’ years
‘A. = Initial trafic (commercial vehicles per day) in the year of competion
of construction (directional traffic volume to be considered for divided
carriageways where as for other categories of the carriageway, twoway
traffic volume may be considered for applying the lateral distribution factors)
D = lateral distribution factor (as explained in para 4.5)
F = vehicle damage factor (VDF)
n= design period, in years
+ =annual grow rate of commercial vehicles in decimel (eg. or 6 pe’ cent
‘annual growth rata, «= 0.06). Variation of the rate of growth over diferent
periods ofthe design period, if avaliable, may be considered for estimating
the design trafic
‘The trafic inthe year of completion of construction may be estimated using equation 4.6.
Po +n} (4s)
Where,
Pp jumber of commercial vehicles per day as per last count.
x = number of years between the last count and the year of completon of
‘construction.
46.2 Forsingle carriageway (undivided) roads, the pavement may be designed for design
traffic estimated based on the larger of the two VDF values ablained for the two directions. For
divided carriageways, different pavement designs can be adopted for the two directions of trafic.
depending on the directional distribution of trafic and the corresponding directional VDF values
in the two directions.
5. PAVEMENT COMPOSITIONS.
‘Afexible pavement considered in these guidelines essentially consists of three functional layers.
‘above the subgrade. These are: sub-base, base and bituminous layers. Detailed discussion
fon subgrade and each of the pavement layers is presented in the subsequent sections of the
17 IRo37-2018
uidelines. The sub-base and base layers may be (a) granular, (b) cement treated or (c) a
combination of granular and cement treated materials, Base layer can also be a foam bitumen
‘or emulsion treated granularfReciaimed Asphalt Pavernent (RAP) materialicombination of RAP
and aggregate layer. When CTE is used, a crack relief layer is to be mandatory provided,
either as an aggregate interlayer or as a siress absorbing membrane inter-layer (SAMI). The
bituminous layer comprises two diferent types of materials, categorized as bituminous base and
surfacing. Ifthe base bituminous layer is constructed in two layers, these are generally termed
‘as binder and base bituminous layers. Unless specified otherwise, each functional layer can be
Constructed in one or more layers. The same elastic properties (elastciresiient modulus and
Poisson's ratio) may be considered forall the sub-layers of a functional layer for the analysis of
the pavement using linear elastic layered theory (IITPAVE software). Granular sub-base layers
{fiter and drainage layers) and granular base layer are considered (unless specified otherwise)
as a single layer in the analysis of the pavement. Similarly, bituminous base (binder and base)
‘and surfacing course are considered as a single layer. Aggregate (granular) crack relief layer
shal be considered as a separate layer in the analysis. The SAMI crack relief treatment (if used)
over the GTB layer shall not be considered in the structural analysis
6, SUBGRADE
61 General
‘On new roads, the alm should be to construct the pavement as far above the water table as
economically practicable. The difference between the bottom of subgrade level and the level of
water tablemigh flood level should, generally, not be less than 1.0 m or 0.6 m in case of existing
roads which have no history of being overtopped. In water logged areas, where the subgrade
{s within the zone of capillary saturation, consideration should be given to the installation of
suitable capillary cut-off as per |RC:34 at appropriate level underneath the pavement,
The top 500 mm ofthe prepared foundation layer immediately below the pavement, designated
2s subgrade, can be made up of in-situ material, select sol, or stabilized soll forming the
foundation forthe pavernent. I should be well compacted to derive optimal strength and to limit
the ruiting caused due to additional densification ofthe layer during the service if. It shall be
compacted to attain a minimum of $7 per cent ofthe laboratory maximum dry density obtained
corresponding to heavy compaction as per 1S:2720 Part-8{17] for Expressways, National
Highways, State Highways, Major District Roads and other heavy trafcked roads. When the
subgrade is formed using a material whichis stronger than the upper 600 mm of embankment
soll or when the subgrade itself Is prepared in two separate layers with significantly ifferent
strengths, the effective combined contribution ofthe subgrade and the embankment layers has
to be considered for design. The principle to be used for the estimation ofthe effective strength
or mechanical property is discussed in para 6.4. As previously mentioned in these guidelines,
the elasticltesilient moduli of cifferent pavement layers are the main inputs forthe analysis and
design of pavernents. Since the measurement of resent modulus of soll requires sophisticated
equipment, the same is generally estimated from the California Bearing Ratio (CBR) value of the
material. The following sections present the details ofthe compaction effor and moisture content
to be used for preparing the specimens in te laboratory for evaluating the CBR value or resilient
modulus value of the soll
18 IRO:97-2018
62 election of Dry Densily and Moisture Content for Laboratory Testing of
‘subgrade Material
6.21 The laboratory test conditions should represent the field conditions as closely as
possible, Compaction in the fleld is done at a minimum of 97 per cent of the laboratory maximum
density obtained at optimum moisture content, n the field, the subgrade undergoes moisture
variation depending on different local conditions such as water table depth, precipitation, soil
permeability, drainage conditions and the extent to which the pavement is impermeatie to
‘moisture. In high rainfall areas, lateral infltrtion through the unpaved shoulder, median, porous
and cracked surface may have a significant effect on the subgrade moisture condition. The
California Bearing Ratio (CBR) of the subgrade soll, for the design of new pavements and
reconstruction, should be determined as per IS:2720 Part-16|18] at the most critical moisture
condition ikely fo occur at the site. The test should be performed on remoulded samples of soils in
the laboratory. The pavement thickness should be based on 4-day soaked CBR value of the soil,
remoukied at placement density (minimum 97 % of maximum Proctor compaction test density)
and optimum moisture content ascertained irom the compaction curve. In areas with less than
+1000 mm rainfall, four-day soaking may be too severe a condition for a subgrade well protected
with thick bituminous layer and the strength of the subgrade soll may be underestimated. Ifdata
|s available about the seasonal variation of moisture, the moulding moisture content for the CBR
test can be selected based on the field data. The test specimens should be prepared by static
‘compaction to obtain the target density.
6.2.2 Frequency of tests and design value
IF the type of soil used in different stretches of the subgrade varies along the length cf the
pavement, the CBR value of each type of soll should be the average of at least three specimens,
prepared using that soil. 90° percentile subgrade CBR value should be adopted for the design
Of high volume roads such as Expressways, National Highways, State Highways and Urban
Roads. For other categories of roads, the design can be done based on the 80" percentile CBR
value if the design traffic is less than 20 msa and based on 90th percentile CBR if the design
traffic Is 20 msa or more,
63 Resilient Modulus of the Subgrade
Resilient modulus, which Is measured taking into account only the elastic (or resilient) component
Of the deformation (or strain) of the specimen in a repeated load test is considered to bs the
‘appropriate Input for linear elastic theory selected in these guidelines for the analysis of flexible
pavements. The resilient modulus of solls can be determined in the laboratory by conducting
the repeated tri-axial test as per the procedure detailed in AASHTO 7307-9919]. Since these
‘equipment are usually expensive, the following relationships may be used to estimate the reslient
‘modulus of subgrade soll (MRS) from its CBR value[20, 21],
Mp «== 10.04 CBR for CBR<5% (61)
My = 17.6+(CBRY™ for CBR> 5% (2)
Where,
M, = Resilient modulus of subgrade soil (in MPa).
CBR = California bearing ratio of subgrade soil (%)
Poisson's ratio value or subgrade soil may be taken as 0.96.
19 IRC:37-2018
64 Effective Modulus/CBR for Design
64.1 Sometimes, there can be a significant diference between the CBR values ofthe soils,
used in the subgrade and in the embankment layer below the subgrade. Alternatively, the 500,
‘mm thick subgrade may be laid in two layers, each layer material having different CBR valve, In
such cases, the design should be based on the effective modulus/CBR value of a single layer
‘subgrade which is equivalent to the combination of the subgrade layer(s) and embankment layer.
‘The effective modulus/CBR vaiue may be determined as per the following procedure which is &
‘generalization of the approach presented earlier in an Indian Roads Congress publication{22}
(Using IITPAVE software, determine the maximum surface defiection
(8) due to a single wheel load of 40,000 N and a contact pressure of
0.56 MPa for a two or three layer elastic system comprising of a single (or
two sub-layers} of the 500 mm thick subgrade layer over th semi-infinite
embankment layer. The elastic modull of subgrade and embankment soils!
layers may be estimated from equations 6.1 and 6.2 using their laboratory
CBR values. Poisson's ratio (p) value may be taken as 0.35 for all the
layers.
(i) Using the maximum surface deflection (6) computed in step (I) above,
estimate the resilient modulus Mg, of the equivalent single layer using
equation 63.
204 — pipe
Mp = 20a eee (63)
Pp =contact pressure = 0.56 MPa
of circular contact area, which can be calculated using the load
‘applied (40,000 N) and the contact pressure ‘p’ (0.56 MPa) = 150.8 mm
py =Poisson’s ratio
I is the effective resilient modulus (M,,) value and not the CBR that is used in the design.
However, if required, the CBR value can be reported using equations 6.2 and 6.3. A worked out
example for the estimation of the effective resilient modulus/CBR is given in Annex-l.
In case the borrow material is placed over a rocky foundation, the effective CBR may be larger
than the CBR of the borrow material. However, only the CBR of the borrow material shall be
adopted for the pavement design. Additionally, proper safeguards should be taken against the
development of pore water pressure between the rocky foundation and the borrow material.
If the embankment consists of multiple layers of materials having different CBR values, mult-
layer analysis can be carried out using IITPAVE software and the effective resilient modulus can
be estimated using the concept discussed above.
6.42 _Forthe purpose of design, the resiiont modulus (Mj), thus estimated, shall be limited
to @ maximum value of 100 MPa
6.4.3 The effective eubgrade CER ehould be more than 5 % for roads estimated to carry
‘more than 450 Commercial Vehicles Per Day (CVPD) (two-way) in the year of construction,
20 IRo:37-2018
7. SUB-BASES
A Goneral
“The sub-base layer serves three functions: (I) to provide a strong support for the compaction of
the granular base (WMM/W8M) layer (il) to protect the subgrade from overstressing and Gi
‘serve as drainage and fiter layers, The sub-base layers can be made of granular material which
‘can be unbound or chemically stabilized with additives such as cement, ime, flyash and other
‘cementitious stabilizers. The thickness of the sub-base, whether bound or unbound, should eet
these functional requirements, To meet these requirements, minimum sub-base thicknesses
have been specified in the following paragraphs.
7.2 Granular (Unbound) Sub-Base Layer
724 Sub-base materials may consist of natural sand, moorum, gravel, laterite, kenkar,
btick metal, crushed stone, crushed slag, reclaimed crushed concreta/rectaimed asphalt
pavement, river bed material or combinations thereof meeting the prescribed grading and
physical requirements. When the granular sub-base material consists of a combination of diffrent
materials, mixing should be cone mechanically by elther using a suitable mixer or adopting the
‘micin-place method, Granular sub-base (GSB) should confotm to the MoRTH Specifications for
Road and Bridge Works{23}.
Ifthe thickness of the sub-base layer provided in the design permits, the sub-base layer shallhave
{wo sub layers; drainage layer and the filler layer. The upper layer of the sub-base functions as a
drainage layer to drain away the water that enters through surface cracks. The lower layer of the
‘sub-base should function as the flterseparation layer to prevent intrusion of subgrade sol into
the pavement. The aggregate gradations recommended for the drainage layer are granular sub-
base gradations Ill and IV of MoRTH Specifications|23}. The gradations |, Il, V and Vi specified
for GSB by MoRTH[23] are recommended for fiter/separation layer.
If the design thickness of the granular sub-base is less than or equal to 200 mm, both drainage
and fiter layers cannot be provided separately (considering the rinimum thickness requirements
‘given in 7.2.2). For such cases, a single dralnage-curn‘iler layer with GSB gradation V or VI of
MoRTH Specifications may be provided,
‘The fiter and drainage layers should be designed as per IRC:SP:42{24) and IRC:SP:50(25}
It is necessary to extend both drainage and fier layers to full width up to the slope of the
fembankment to have efficient drainage. Commercially available synthetic geo-composite, grid
lock geo-cel! with perforated vertical faces filed with aggregates meeting the requirement as
specified In IRC:SP:59[26] can also be used to function as both fteriseparation and drainage
layers. Its strengthening effect can be considered in the pavement design in accordance with
the provisions of IRC:SP:59,
When GSB layer is also provided below the median in continuation with that of the pavement,
‘a non-woven geo-synthetic may be provided over the GSB in the median part so that the fines
percolating through the median do not enter into the GSB and choke it
7.2.2. Minimum thioknosses of granular sub-base layers
Irrespective of the design trafic volume, the following minimum thicknesses of granular sub-
2 IRC37-2018
base layers may be provided.
(The minimum thickness of drainage as well as fiter layer shall be 100 mm (Le..
minimum thickness of each of these two layers is 100 mm).
(i)_The minimum thickness of the single fiter-cum-dralnage layer shall be 150 mm
from functional requirement.
(ii) The minimum thickness of any compacted granular layer should preferably be at
least 2.5 times the nominal maximum size of aggregates subject to a minimum
cf 100 mm,
(iv) The total thickness of the granular sub-base layer should be adequate to cary
the construction trafic that may ply on the GSB. This thickness requirement
may be worked out to satisfy the subgrade rutting limiting strain criterion given
by equation 3.1 oF 3.2 (as applicable for the classification of highway and design
traffic). The design traffic for this purpose can be worked out based on the
expected number of operations of dumpers and other construction vehicles on
the GSB layer to carry material for the construction of granular or cement treated
base layer. The indicative values of construction trafic loading and the procedure
iven in the worked out example in Annex can be used for the estimation of
the construction traffic operating over the granular sub-base if more accurate
and practical estimation cannot be done.
(¥) The sub-base thickness should be checked for the design trafic worked out
{as per the above mentioned procedure or 10,000 standard axle repetitions,
whichever is more
(vi) The two-layer system (subgrade and GSB) should be analyzed by placing @
standard load overit (cual whee! set of 20,000 N each acting at 0.56 MPa contact
pressure) and computing (using IITPAVE) the maximum subgrade vertical
‘comoressive strain. The GSB thickness should be varied until the computed
strain is less than or equal to the limiting subgrade vertical compressive strain,
Given by equations 3.1 or 3.2 (as applicable).
The worked out example given in AnnexcIlilustrates the estimation of GSB thickness from
construction traffic consideration.
7.2.3. Resiliont modulus of GSB layer
‘The elasticresilient modulus value of the granular layer is dependent on the resilient modulus
value of the foundation or supporting layer on which it rests and the thickness of the granular
layer. A weaker support does not permit higher modulus of the upper granular layer because of
the larger deflections caused by loads result in de-compaction in the lower part ofthe granular
layer. Equation 7.1[20] may be used for the estimation of the modulus of the granular layer from,
its thickness and the modulus value of the supporting layer.
Macnan = 0.2(H)"%* Masencrr ay
Where,
n thickness o granular layer mmm
Moray = Fesiliont modulus of the granular layer (MPa)
Masupeoar = (effective) resilient modulus of the supporting layer (MPa)
2 IRC:37-2018
‘As stated previously in these guidelines, the granular base and granular sub-base are consicered
225 a single layer for the purpose of analysis and a single modulus value is assigned to the
‘combined layer. Thus, when the pavement has the combinaton of granular base and granularsub-
base, the modulus of the single (combined) granular layer may be estimated using equation 7.1
taking the Mygayy a8 the modulus of the combined granular layer atid Mesiproqr 28 the effective
modulus of the subgrade. However, when a cement treated or emulsionffoam bitumen treated
base layer is used over the granular sub-base, both the layers have to be considered separately
in the analysis and separate modulus values have to be assigned for the GSB and the treated
base layers, Equation 7.1 can be used to estimate the modulus of the granular sub-base taking
Myeuyy 88 the modulus of the granular sub-base layer and Mysmoar 35 the effective modulus of
tne subgrade,
For the granular layers reinforced using geo-synthetic materials, IRC:SP.59{26] suggests Layer
Coefficient Ratios (LCR) and Modulus Improvement Factors (MIF) which can be used to estinate
the improvement inthe modulus value ofthe granular layer due to geo-synthetic reinforcement.
These values are to be obtained from detailed fleld and laboratory investigations as discussed
in IRC:SP:59. IRC:SP:59 suggests the estimation of the moduli values of the un-reinforoed