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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.


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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.


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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).


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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.


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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.

6le0ible 7a%ement Design 8ethods9 7repared b# Ra:esh +had3a&acem;

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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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Documents

2.4 Road Note 31