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Road Note 31/ Catalogue Method A Guide to the Structural Design of Bitumen Surfaced Roads in Tro
tropical Countries.
ORN !" is based principall# on research conducted in countries $orld b# the O%erseas Centre& Transport Research 'aborator# (TR')& *the O%erseas De%elopment Administration (ODA).
Road Note !" $as ,rst published in 1962and re%ised in 1966& 1977
No$ O%erseas Road Note (ORN) !"& "!& th/dition.
th edition of the Road Note !" has dra$n on the e0perienc
collaborating organi1ations in o%er !2 Tropical and Sub-tropical Countr
th edition e0tends the designs of pre%ious editions to cater for tramillion equivalent tandard a!le and ta3es account of the %ariabproperties and construction control& the uncertaint# in tra4c forecastsclimate and high a0le loads and the o%erall statistical %aria
performance. 6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh+had3a& acem
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"eign #roce
3 Main $tep to be follo$ed in designing a ne$ road pa%em
These are9
(i) estimating the amount of tra4c and the cumulati%ee>ui%alent standard a0les that $ill use the road o%er design life?
(ii) assessingthe strength of the subgrade soil o%er $hich the
built?
(iii) selectingthe most economical combination of pa%ement la#er thic3nesses that $ill pro%ide satisfactor# ser%ice o%life of the pa%ement using structural catalogues. (It is usuato assume that an appropriate level of maintenance is also
6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh+had3a& acem
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#avement %a&er
6le0ible 7a%em
ent Design 8ethods97repared b# Ra:esh +had3a& acem
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Surfacing:
This is the uppermost la#er of the pa%ement and $ill norof a bituminous surface dressing or a la#er of premi0e
material. @here premi0ed materials are laid in t$o la#e3no$n as the $earing course and the base course (or bin
Roadbase:
This is the main load-spreading la#er of the pa%emnormall# consist of crushed stone or gra%el& or of gdecomposed roc3& sands and sand-cla#s stabilised $ith or bitumen.
6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh+had3a& acem
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Sub-base:
This is the secondar# load-spreading la#er underl#ing the roa
t $ill normall# consist of a material of lo$er >ualit# than tharoad base such as unprocessed natural gra%el& gra%el-sansand-cla#.
This la#er also ser%es as a separating la#er pre%enting conthe roadbase b# the subgrade material and& under $et condan important role to pla# in protecting the subgrade fromconstruction tra4c.
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Capping layer (selected or improved subgrade):
@here %er# $ea3 soils are encountered& a capping la#er necessar#.
This ma# consist of better >ualit# subgrade material imelse$here or e0isting subgrade material impro%ed b# mchemical stabilisation.
Subgrade:
This is the upper la#er of the natural soil $hich ma# belocal material or ma# be soil e0ca%ated else$here and plac
n either case it is compacted during construction to
strength. 6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh+had3a& acem;
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'rafc
The deterioration of pa%ed roads caused b# trafrom both the magnitude of the indi%idual $heel
the number of times these loads are applied.
6or pa%ement design purposes it is necessar# t
not onl# the total number of %ehicles that $ill usbut also the $heel loads (or& for con%enience& the aof these %ehicles.
The loads im osed b ri%ate cars do not 6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh +had3a&
acem;
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6or the purposes of structural design& cars and s%ehicles can be ignored and onl# the total num
a0le loading of the hea%# %ehiclesthat $ill use theits design life need to be considered.
n this conte0t& hea%# %ehicles are de,ned as thosunladen $eight of !222 3g or more.
6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh+had3a& acem
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"eign %i(e
6or most road pro:ects an economic anal#sis period of bet;2 #ears from the date of opening is appropriate.
Design life does not mean that at the end of the period the pbe completel# $orn out and in need of reconstruction? itto$ards the end of the period the pa%ement $ill need to be so that it can continue to carr# tra4c satisfactoril# for a furth
Condition sur%e#s of bituminous pa%ements should be carronce a #earas part of the inspection procedures for mainten
6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh +had3a&acem
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)timating 'rafc *lo+
n order to determine the total tra4c o%er the design life of,rst step is to estimate baseline tra4c Eo$s.
The estimate should be the (Annual) A%erage Dail# currentl# using the route.
The ADT is de,ned as the total annual tra4c summdirections and di%ided b# !=.
t is usuall# obtained b# recording actual tra4c Eo$s o
period from $hich the ADT is then estimated.
6or long pro:ects& large di5erences in tra4c along the roadnecessar# to estimate the Eo$ at se%eral locations.
t should be noted that for structural design purposes the tin one direction is re>uired and for this reason care is al$
$hen interpreting ADT ,gures.;
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,!le %oading - ,!le )quivalenc&
The damage that %ehicles do to a road depends %er# stroa0le loads of the %ehicles.
6or pa%ement design purposes the damaging po$er of a0leto a FstandardF a0le of ."= tonnes using e>ui%alence factorsbeen deri%ed from empirical studies.
n order to determine the cumulati%e a0le load dampa%ement $ill sustain during its design life& it is necessar#the total number of hea%# %ehicles that $ill use the roaperiod in terms of the cumulati%e number of e>ui%alent sta(esa).
6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh+had3a& acem
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A0le load sur%e#s must be carried out to determinload distribution of a sample of the hea%# %ehicle
road.
Data collected from these sur%e#s are used to camean number of e>ui%alent standard a0les for a t#pin each class.
These %alues are then used in con:unction $ith tra4to determine the predicted cumulati%e e>ui%alena0les that the road $ill carr# o%er its design life.
6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh+had3a& acem
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"etermination o( Cumulative)quivalent $tandard ,!le
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6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh+had3a& acem
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Numerical )!ample
In a certain section of single lane road, it is inconstruct the road pavement. The trac survthat the road caters present ADT of !" cvannual growth rate of trac is $%. The pavemedesigned for ' years period and epected c
period is " years from the last date of trac c$.* percentile +- value of the su&grade soil i
&e *%. Design the pavement section as per -oa/uideline.
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Solution:
Cumulati%e no. of std. a0les at the end of design period
N . .
Here,7 "!; c%pd
r H 2.2
0 ; #ears
n "2 #earsNo$&
N .
. 076 ! 106 ea
6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh
+had3a& acem;
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According to Road Note ! "uideline,
6or& N . 076 ! 106 ea 'rafc Cla . '3
and
6or& CR . $u4grade $trength Cla . $3
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No+ (rom the "eignChart 1
Granular Sub base ;;mm Granular Road Base
;22 mm Surface Course Surface Dressing (SD)
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