IR(: 37-1984

GUIDELINES FOR THE DESIGNOF

FLEXIBLE PAVEMENTS(PirsiRcvlsion)

THE INDIAN ROADSCONGRESS1995

lkC: 37-19fl4

GUIDELINES FOR THE DESIGNOF

FLEXIBLE PAVEMENTS

(First Revision)

Publishedby

THE INDIAN ROADS CONGRESS~JamnagarHouse, Shahjahan Road,

New Delhi — 1100111995

Price Rs, 100/-/ Plus Packing& Posta~e)

First publishedReprintedFirst RevisionReprinted

Reprinted

Reprinted

September. 1970December. 1976Decembet 1984October 990 (IncorporatesAmendment No 1. September 1988)

:April, 1995October, 2000

(R(gh&c of Publication and of Thansiwion are Resenia(1

Printed at DeeKay Printers,NewDelhi(1000copies)

CONTENTS

1. Introduction2.Scope 23. Recommended Method of Design 34. Thickness and Composition 15S. Drainage Measures 226. Design in Frost~Affected Areas 257. Worked Examples Illustrating the Design Method 25

Appendices.lppcndix1: Preparation of LaboratoiyTest Specimens 29• Ippendix2: Special Points Relating to Design

of Pavements on Expansive Soils 31

IRC: 37-1984

GUIDELINES FOR THE DESIGN OF FLEXIBLEPAVEMENTS

1. INTRODUCTION

1.1.Thedesignof aflexiblepavementinvolvesthe interplayof severalvariables suchas the wheel loads,traffic, climate,terrainandsubgradecon-ditions. In the existingstateof knowledge,the individual effectof manyofthesefactors is difficult to evaluatemathematicallywith any precision.Hence,a fully acceptable,theoreticalmethodof designhas notemergedasyet, andthe methodsin voguehaveof necessityto be empirical,basedonsuccessfulpastpracticesandexperiences,and somequantitativeevaluationof the subgradesoils,to yield designscapableof withstandinggivencondi-tions of traffic andclimate.

1.2. In Indiaquite diverse practices have beenprevalentin regardtotheprovision of pavementthicknt~ssesso far. Considering theneed~ohaveaunified andreasonably acceptableapproachfor working out the c~i~nforconditionsobtainingin the country, theIndian RoadsCongress, throughitsFlexible PavementDesign Subcommittee(personnelgiven below), set upunder the Specificationsand StandardsCommitteeexaminedthe variouspossiblemethodsandformulatedguidelinesfor generaladoption:

SN.Sirtha Convenor

R.P.Sikka Member-Secretary

B.R. Chopra Member

Dr. C.E.O. JustoD.R. Kohli

Mahalir Prasad

J.S. Marya

N.Sen

Dr. Bh. Subbaraju

Prof.C.G. SwaminathanDr. H.L. Uppal

1.3. Theseguidelineswere approvedby the SpecificationsandStan-dardsCommitteein their meetingheld on the26th and27th February,1970andby theExecutiveCommitteein their meetingheldonthe5th March,1970andlater by the Council in theirmeetingheld at Darjeeingonthe 5th and6thApril, 1970.

A subgrouppersonnelgiven below wasconstituted in 1984to review

I

JRC :37.1984

the guidelinesin light of needto meetthe heavieraxle loadsandkeepinginview thesuggestionmadein thePanelDiscussionduringthe Annual Sessionof the Indian RoadsCongressheld at Nagpurin January1984.

K.K.Sarin Convenor

N. Sivaguru Member-SecretaryDr. M.P. Dhir Member

SB.Kulkami

Dr.C.E.G.Justo

N.Sen

P.K, Lauria

S.A.LaLheef

S.C. Shaima

The guidelinesas revisedby the subgroupwere approvedby theExecutiveCommitteeandlaterby theCouncil in their 111thmeetingheldatTnvandrumon the 15th September1984.

1.4. It is emphasisedthattheguidelinesareto beregardedas tentative~.syet, tothe extentthat theywould requirerevisionfrom time to time in thelight of future experienceanddevelopmentsin this field. Towardsthisend,it is suggestedto all the organisationsintending to use the guidelinesforstrengtheningof existingpavements orthedesignof pavementsof newroadstokeepadetailedtabulatedrecordof thetotal thickness,typeofconstruction,period betweenrenewal coatsand the year to year performanceof theindividual sections ofpavements.

2. SCOPE

2.1.Forthepurposeof thisguide,flexible pavementsareconsideredto includethe usualgranulartype constructionssuchas waterboundmac-adamandotherflexible basesandsub-basesconformingto IRC Standardsorto Sections400and500of the Ministryof SurfaceTransportSpecificationsfor Roadand Bridge Works(SecondRevision),1988.

2.2. The recommendationsprimariiy apply to new constructions.However,for the time being these guidelineswill alsoapply to designofstrengtheningmeasuresfor existing pavementsuntil amore scientific ap-proachto overlaydesignis developedfor Indian conditions.Specialpointsrelevantto strengtheningof existingroadsarehighlightedwherenecessary.

2

IRC :37-1984

An alternative approachto overlaydesign is described inIRC: 81-1981ntativcGuidelinesfor Strengtheningof FlexibleRoadPavements using

Benl~elmanBeamDeflectionTechnique”.

3. RECOMMENDED METhOD OF DKSICN

3.1. General

3.1 . I. The methodof designrecommendedis a modification of the(Thhfornia BearingRatio(CBR) Method indicatedin thepreviousedition. Inthis methodtraffic is definedin termsof the cumulativenumberof standardaxles (816() kg) to be carriedduring the design life of the~road. it is wellrecognisedthatthestructuraldamagecausedby a vehicledependson the axleload it imposeson the~road,andthe equivalent axleload conceptis the bestmethodavailable, fordesignpurposes,to handlethe largespectnim of axleloadsactuallyappliedto apavement.The designcurvesrelatingpavementthickness to the cumulativenumberof standardaxles to be carried fordiifcrcnt sub-gradestrengthvaluesaregiven in Fig. 1. Thesubgradestrengthis assessedin termsof the CBR valueof the subgradesoil asper proceduredescribedin paragraph3.3. The thicknessesdeducedfrom Fig. I are totalthicknessesand consistsof variouscombinationsofbituminous surfacingandgranular baseand sub-basethicknesses.Therecommendedminimum thick-nesses andcompositionsof component layers for newconstructionsaregivenin Thickness Combination Block, Fig.2.Thesemay,however,bemodified ifenvironmental conditions andexperienceso justify. In casesof trafficestimatesexceeding30 million standardaxle (msa) thecurvesmaybe suita-bly extrapolatedliar determiningthe designthickness.

3.1.2. Notwithstandingthe aforesaidrecommended method, wheredata is riot available to adopt the equivalent axleload concept,the CBRnwthod whichconsiderstraffic in termsof commercialvehiclesperday mayheusedprovidedthedesign trafficisnotmorethan 1500commercial vehiclesper day. TheCBR curves updatedfor 10.2 tonnessingleaxle legal limitpresently in force arc recommendedfor design,Fig. 3. Estimation of thedesign traffic is describedin paragraphs3.2.1., 3.2.2. and 3.2.4., and the

procedurebr determiningtheCBR valueof thesubgradcsoil is describedinparagraph3.3. The thickness of different layers of sub-base, baseandsurfacingcan be determinedby repeateduseof thesecurvesand dulytakinginto accountthe minimum thicknessand compositional requirementsspeci-fied in paragraph 4.As the requirementswith regard to the minimum

3

IRC :37-1984

‘Is

I-‘IsI-J~1I

45~m

zrU

I-

I-.z‘ISI115>

-i

5-05-

CUUULATIVt STANDARD AXt.tS

Fig. 1. Pavementthickjiess designchartNose: 1. Read total pavement thickness from cOnhilMIouS curves

2. Use dotted curves for proportioning sub-base thickness

0Os 02 44 06085 2 4 4 8 10 55 20 301506

4

IRC: 37-1984

THSCSCNESSCOM8~NATIONet~OCKBINOUSI’- ~ TOTAL Th$CXNESSSURPACING —j4 ‘V3RANULAR ‘~ FROM THICKNtSS CIIAR’T

BASE -

GRANULAR -it~~~ ~m~.tSUB Bs*5t

Fig. 2STRUCTURAL SECTION

Cumuld tedstandard

axles,ndleopi (Id)

Minintwnthickness of compo~tentlayerscompacted shickjiess (mm)

Surfacing(X)

Base(Y)

Subbase(Z)

L).5 M 20mm PCj2-Coat SD 150(T--150)

Minimum thickness 100mm onsubgrades of CBR less than 20%

052M

2-SM

2OmmPC/MS 225

I

(T-.225)Minimumthickness 150mmo~ssobgradesof CBR lesa than 20%

20mm1~1MS/SDC+ 50 mmTlS mm BM

250~T--3OW325)

Minim~ thickness150 mmonsubgrsdes of CRR less than 30~

5-10 Ni 25mm SDC/AC#bOtoSOmmDBM

250 (T-335 so 355)--do--

20-30Ni 40mm AC 250 (‘7-390 to 405)

1 + 0010 itS rum DOM - -do..

SD -Surface dressing to the MOST SpecificationIRC/StandardsPC Premix Carpet -do-MS Mix SeatSurfacingto thcMOST SpecificationSDC Semi-dense Carpet -do-AC Asphalsic Concrete -do-H51 BituminousMacadam Binder Course to the MOST SpecificationDIIM Dense Bituminous Macadam Binder c:ow-se~oie : (i) If the CBR of the suhgrade is more than the minimum requirement for the sub-

base, rio subbase is required.(ii) Binder course of thickncss more than 80 mm should be laid in two ayers.

10-ISNi

15-21) Ni

25040mm SDC/AC4 65 to 80 mm DBM

4OmrnAC+ S0t~100mmDBM

(1~--355to 370)--do--

250 (T--370 to 390)--do.-

5

IRC :371984

E

2

zxUSfr

20

U

20lL~

0

2

aw0

CALIFORNIA SEAR~SO RATIOS PERCCNT

3 4

Fig.3~CBR. cunesfor flexible pavement design

6

IRC :37-1984

thicknessandcompositionof various layersspecified in paragraph4 are interms of cumulativenumberof standardaxles,, the following approximatetraffic conversionsmay be usedto decidethe minimum thicknessandcom-position of variousLayers:

Traffic range Adopt minimum layer thicknessand composition applicable to

(i1 Design irsific uplo 150 cs/day Upto 0.5 nssltion(CBR curve ABC) standard axles (tnsa)

(ii) Design traffic iSO 450 cv/d~ 1)-S to 2 msaiCli K curve 0)FOsig,ntraffic 4511-1500 cs/day ‘2 to 4 msa

COR curve El

Traffic

12.1. General

1,2.1] - Feim the. purpose of structural designonly the number ofcommercial vehicles of ladenweight of 13 tonnesa’ more anti their axle-loading will be considered.

1.2. To obtain a realistic.estimateof desi,grttraffic dueconsidera—lion shouldhegiven totheexistingtraffic or thatanticipatedin thecaseof newe.tynstru~c:lions,[X)ssiHechangesin road network andland use. of the areaserve.d the probablegrowth of traffic, anti design life.

Estimateof the inItial daily averagetraffic flow for any road s:houldnormally he basedon 7-day2,4-hourclassified trafficcounts.However, ine.xcepliooalcaseswherethis information is not available 3-daycount couldhe used.In casesof new roadstraffic estimates canbe madeon the basisof

potential land useand traffic on existingrotites in the area.

An estimateof likely growth ratecan beobtainedby studying the pasttrends intraffic growth. If adequate data is notavailable,it is recommended‘that an averagevalueof 7.5 per centmay be adoptedfor ruial routes.

7

ERC :37-1984

3.2.2.Design life

3.2.2.1.It is consideredappropriate that roadsin rural areasshould bedesignedfor alife of 10-15yearsbut provision must bemadein the desigi forprogressivestrengtheningof the road. Arterial roadsshould normally bedesignedfor 15 years life and othersfor 10 years life. Urban roadsmay,however,bedesignedfor a longer life basedon judgememuarid dependingonthe iate of growthof the trafficexpected.

3.2.7.2.Very olten itmaynot bepossibletoprovidethefull thicknessof pavementneededultimately right at thetime of initial construction.Stageconstructiontechniquesshouldberesortedto in suchcasesandthoseformsof constructionchosenthat couldreadily be ~t.rengthenedastraffic increased.The initial stage periodshould not be less than 5 years.

3.2,3.Computation of traffic for useof pavement thicknessdesignchart given in Fig. 1.

3.2.3.1.The designtraffic is consideredin terms of the cumulativenumberof standardaxles(in the lane carryingmaximumtraffic) to becarriedduring thedesign life of the road. Its computationinvolves estimatesof theinitial volume ofcommercialvehicles perday, lateraldistributionof traffic,thegrowth rate,thedesignlife in yearsand thevehicledamagefactor(numberof standard axleper commercialvehicle) to convertcommercialvehiclestostandardaxles.

The following equationmay beusedto makethe requiredcalculation:

N~= F

where rN~=The cumulative number of standardaxlesto be catered

for in the designA= Initial traffic, in the year of completionof construction,

in terms of the numberof commercialvehiclesper dayduty modified to account for lane distributionasexplained in paragraph3.2.3.2.

r= Annual growth rate of commercialtrafficx= Design life in yearsF= Vehicle damagefactor (number ofstandardaxlesper

commercialvehicle) refer to paragraph3.2.3.3.

8

IRC : 37-1984

3.2.3.2.. Distributionof commercialtraffic overthecarriageway:Arealisticassessmentof distribution of commercial traffic by directionandbylane is necessary as it directly affectsthe totalequivalent standardaxle loadapplicationsused in the design.In the absence ofadequateandconclusivedata forIndianconditions, it is recommendedthat for thetime beingthe fol-lowing distributionmay be assumed fordesignuntil morereliabledataonplacement ofcommercialvehicleson the carriagewaylanesareavailable:

(i) 5ingle~laneroads(3.75its width):

Traffic tendsto be morechannelited on singlelane roads than on two lane roads and toallow for this concentration of wheel load repetitions the design shouldbe basedon thetotal numberof commercialvehiclesper day in boshdirectionsmultiplied by two,

(ii) Intermediate width roads(5.5 m width):

‘i’hc dcsignshouldhebasedon thetotal numberof commercial vehicles per dayin bothdirections multiplied by1.5

(iii) Two~lanesingle cas-rtagewayroads:

mcdesignshouldbebasedon 75per centof the total number of commercial vehiclesinboth directions,

(iv) Four~lanesInglecarriageway roads:

The designshouldbe basedon 40 percent ofshesoul number of commercial vehiclesinboth directions.

(v) t)ual carriageway roads:

The designof dualtwo-lanecarriagewayroads should be basedon 75 per centof thenumberofcommercialvehiclesin eachdirection.The distributionfactorshall bereducedby 20 per cent for each additionallane,

Er For dual three.lanecarriageway distribution factor-60 percent.

The traffic in each direction may be assumed to be hatf thesum in both directionswhen the lasteronly is known. Where significantdifferencebetween the two streamscan occur,the conditionin the more beavily traffickedlane shouldbe consideredfordesign.

However,if in aparticularsituationabetterestimate ofthe distributionof traffic between thecarriagewaylanes isavailablefrom traffic surveys,thesame should beadopted and the design is basedon the traffic in themostheavily traffickedlane.The designwill normally be applied overthe wholecarriagewaywidth,

9

IRC :37.1984

3.2.3.3. Vehicledamagefactor: The vehicledamagefactor isamulti-plier for converting the number of commercial vehiclesof different axle loadsto Ihenumberof standard axle-load repetitions. Thevehicledamagefactor isarrived at from axle-loadsurveyson typical road sections so asto cOvervariousinfluencing factorssuchas: traffic mix, typeoftransportalion,typeofcommoditiescarried, time of the year,terrain, road conditionanddegreeofenforcement.The AASFIO axle-loadequivalence factorsmay be usedtoconverttheaxlelo:J spectrumtoanequivalentnumberof standardaxles.Fordesigninganew rojiL~pavementor strengtheninganexistingroadpavement,the vehicledamagefactor ~hutsklbe arrived atcarefullyby usingc’ relevantavailabledata.Somesurveysha\ been carriedout in thecountryon NationalHighway sections,The resultscan be taken advantage of,to the extentthatthey maybe relevantin aparticular case.

TABLE I. iNDICATIVE VDF VALUF.S

Initial traffic VDFvaluea(standardaxles of 8.16)intensisS’ in Terrain tonnrs per commercial vehicle)tennsof situnberof eontinercialvehicles/day f Unsurfaced Thin Thick

bituminous bituminoussurfacing surfacing

Lessthan 150 HillyRoIlingPlain

0.51.52.0

0.751.752.25

150.1 500 HillyRoIlingPlain

1.02.02.5

1.252.252.75

More than t5(X) HillyRoIlingPlain

1.252.252.75

1.52.53.0

Where sufficient informationis not available,thetentativeindicativevalues ofvehicledamagefactoras givenin Table 1 may be used. Thesemaybejudiciouslymodifie.d foranyspecialconditionswith regardto traffic mix,typeof transportation,etc.The validity of the valuechosenmay be checkedafter the pavementhasbeenput to use,so that the warrantedcorrectivestepscan be undettaken.

10

tRC : 37-1954

:3,2,4. Computationof traffic for useof CRR designcurvesgiven in Fig. 3

3.2.4.1. The CBR curves(Fig. 3) give the total thicknessof thepavementin terms of the volume of commercial traffic. The traffic isconsideredin unitsof commercialvehiclesperday in bothdirectionsdividedtnto t usecateg~arie~sas indicated in Table~2.

TAstui 2, O.A5SIF1FATI0N

Trslfic

OFTRAFFtC FOR DESIGN

CBR designcurveapplicablecOlTllsscrcIsl vehicles Ix:r dat)

0.15 A15-45 B45-150 C150450 1)450-15(X) 0

The.designcurvesareto be usedwith respectto the numberof corn-mcrcial vehiclesexpectedat theendof designlife. The formulaforpredictingfuture traffic is given by:

AWhere

A = Numberof commercialvehiclesperday for design

P = Numberof commercialvehiclesper dayat lasscount= Annualgrowthrate of commercialtratlic

n r. Nusnberof ycassbetweenthe last countandtheyearof completionofconsitu ction

a Designlife iss years

3.2.4.2.. For Uhvo-laneroadsthe designwill be basedon the numberofcommercial vehiclesper !~avin both directionswhereassingle lane roadsshould be designedfor twtce the traffic in both directions.

3.2.5.Where traffic is increasingrapidly, it is probablethat a single-lane~roadmayrequireupgradingto two-lanestandardswithin ashort periodeven otherwiseandthisaspectshouldbe bornein mindwhendeciding thepavementthickness.

3.3.Subgrade

3.3.1.The subgradewhetherin cut or fill shouldbewell compactedtoutilise its full strengthandto economisetherebyon theoverall Ihicknessofpavemenlrequired.Mostspecificationsprescribeuseof selectedmaterialand

11

IRC :37.1954

stiffer standardsof colnpaction in lhe top 50 cm portion of the roadway(usually 95-1(X) per cent of lhe StandardProctordensity; sometimesevenhigher)andtheseclausesshouldhestrictly enforced.IRC.’36-1970“Recom-mended Practice for the Constructionof Earth EmhankmenLsfor RoadWorks’’ shouldbe followed for guidance.

3.3.2.Fordesign,thesubgradestrengthis assessedin termsof theCBRof thesuhgradesoil atthemostcrittcal moisturecondition!’s likely to occurin-situ.

3.3.3.SincetheOR testis an ad hocpenetrationtest, it is necessarythat the standardtestprocedureshouldbe strictly adheredto.. This is de-scribed in 15:2720 (PartXVI) “Methods of Testfor Soils : LaboratoryDeterminationof CBR”. Thetestmustalwaysbeperformedon remouldedsamplesof soils in the laboratory.Whereverpossible, the test specimensshould he preparedby static compactionbut if not sopossible dynamicrne:hodmay be usedasanalternative.Bothproceduresaredescribedin briefin Appendix1. In-situ testsarenotrecommendedfor designpurposesasit isnot possible to satisfactorilysimulate thecritical conditionsof dry densityandmoisture contentin the field,

3 .3.4..Selectionof dry densityand moisture content for test sped-men: For a given soil, the CBR value,andconsequentlythe design,willdependlargely on the density and moisturecontent of the test sample.Therefore, the test conditionsshould reproduceas closely as possibletheweakestconditionslikely to occur underthe roadafterconstruction.

3.3.4.1.For newroads,thesamplesof soil shouldbe compactedto adry densitycorrespondingto the minimum stateof compactionlikely to be.achievedin practicehavingregardto thecompactionequipmentusedandthecompaction limits specified.By and largeProctor density (conformingtoIS:2720(Part VIl)) could be madeuseof. In the caseof existingroads,however,themouldingdensityshouldcorrespondto the actualdensityof thesuhgradcsoil as determinedin-situ with the help of a sand-jarapparatus‘naccordancewith procedurelaid down in IS : 2720 (PartX.XVIIi).

3.3.4.2.Thechoiceof moisturecontentof thetestspecimenisnot quiteso simple. The moistureconditionof the suhgradewhich the testsampleisexpectedto simulateis governedby local environmentalfactorssuchas thewater table,precipitation,soil permeability,drainageconditionsandwater-

12

IRC: 37.1984

proofnessof the pavementThe surfacingsprovided in India are relativelythin andpermeablewhichdo not alwayssealthepavenienteffectively againstingressof water. Further,the bermsandvergesaretsually unsurfaced,andnotkept in well-maintained state tothe requisite,cross-fail, which enablesthesurfacewater to readilypercolateinto thesubgradefrom nearthe edges of thepavement,leadingto weak subgrade conditions.

I-fence,it is recommendedthat asageneralpracticethedesignfornewconstructions should bebasedon the strengthof the samplespreparedatoptimummoisture content anddry densitycorrespondingtoProctorcompac-tion and soakedin water for a period of four days prior to testing. If thesubgradesoil is identified asexpansivesoil the moulding densityandmois-turecontentshould beas discussedin Appendix2.

In the case ofexisting roads requiringstrengthening thesoil should bemouldedat the field moisturecontentandfield densityandsoakedfor fourdaysprior to testing.The field moisture contentusedfor moulding shouldbedeterminedpreferablyimmediatelyafter therainy season.However,in caseit is not foundpracticableto determinethefield moisturecontentin therightseason,or thereisdifficulty in mouldingthesamplesatthismoisturecontent,specimensfor test may be preparedsimply atoptimum moisturecontent;thesemustof coursebe. soaked priorto testing.

It is recommendedthat measurementsof field density and moisturecontent,in the caseof designsfor strengtheningof existingroadsshouldbe,as far as possible,carriedout at adistanceof 0.6 to 1 m from the pavementedgebelow thepavement.

3,3,4,3,However,it should berealised that soakingfor four daysmaybe an unrealistically severemoisturecondition in certain cases. Casesfallingin thiscategorywould be:

(i) Subgrades(excluding espansivesoils)of roadswherea comparativelythick bitumi-nous turfacingof impernseable**natureis providedon top, such as a welllaid andsealeddense carpet, and wheresimultaneously(a) water tableis too deep toaffectthesubgradeadversely (i.e.greaterthaat m in sandtand3m in sandyclayt),and(b) well-shapedvergesexitt facilitatingquick drainageof thesurfacewaterto the side drainsand(orpavement baselayeris continued acrosspan/full width of thevergewith thesameobjective.

**trrespectiveoftheirthickness,bitsiminoutconstructionssuch asopengraded premix,

bituminousmacadam, or grouted macadam, havingvoids contentof morethan5 per rent, arenot

to b. deemedasimpermeable.13

mc :37~19S4

(ii) Subgradein areas(esclssdirsgexpanssvesoil areas)where the climates aridthrough-out the year, i.e., theannualtsissfaii is of the order ofSO cmcsrlessand the watertable

rs too deep to affect the subgradc adversely.

In the above..situationsit is anticipatedthatthe. most severemoisturec,:onditonin the field will he far behind that of thesampleattheendof fourd.ayssoaking,resulting,in unduly c.onservativedesigns ifsoakingprocedurewasadoptetiHencetheprocedureof s.oakingfor fourdayscouldbe discardedin such casesand the specimenstested immediately after compactionatmoisture contentsindicated in the next paragraph.

13.4.4. It is recommendedthat fbr the determination ofCBR the soilspecimens of category(i) road should hecompactedatoptimum moisturecontent in the Proctor cotnpactiontest. Investigati.oi.shave revealedthatunder the circumstances.of thes.eroadsthe most adversemoistureconditionof t.he subgra.desoonafter withdrawal ofthemonsoon isin genemidrierthantheoptimum moisturecontent. In a.rid regionsthe normal road camberandsurface.wate.rdrait agemeasureswill usuallysufflce to preventany excessiveaccumulationof water beneaththe pavement.Therefore, it is recommendedthat soil specimensfor category (ii) roadsshould be. preparedat naturalmoisturecontentof thesoil immediatelyafter recessionof the monsoon atsuhgradedepth for finding the CBR value,

3.3.5. l.Jse of testresultsfor designandthe minimumnumberoftests required

33.5.1.Thedesignshouldhe. base.don theCBR valueof the weakestsoil type expected tobe. encounlere.dextensivelyat subgradelevel over agiven sectionof theroad,asrevealedby thesoil surveys.Pavementthicknessmay be modifiedat intervalson newroadsas dictatedby thesoil changesbutgenerallyit will be found inexpedient todosomore frequentlythanonceortwice perkilometre. Frequentchangesin crust thicknessare,a.t any rate,anundesirable featureon resurfacingprqjeccsbecauseof their possible adverseeffect on thelongitudinalprofile of theroad.Hence,these shouldbe resortedto only whenvery necessaryin the interestof structural design.

3.3.5.2. it is possiblethat incertainsoil typesor underabnormalcon-ditionsthemeasuredCBR. valuesmay appeardoubtful andnottruly represen-tative of the stre.ngthof soil. A more complete study of the soil may bewarrantedin suchcasesto arrive at a more reliabledesign.

14

tRC 37-1984

3.3.53. On new worksthc. designevolvedshotilil be revisedat site iffotind necessaryduring the construction phase on account cd’ the fieldcompaction being lowerthanthatanticipated.Normally thiscouldhe gotoverby increasingthethicknessof the. sub-base.in addition, there shouldalsobeprovisionfor theremoval oflocal areasof soft soil.

3.3.5.4. The reproducibility of the CBR results is dependenton anumberof factorsandwide variations invaluescan beexpected.Therefore,in order to avoid errors,at least threesamplesshouldbe lesiedon eachtypeof soil atthe samedensityandmoisturecontent.This will enablea reliableaveragevalue to be obtainedin most cases. Toweedout erratic results,iermissihlemaximumvariationwithin theClIP values fromthreespecimensis indicatedbelow:

Cfl (per cent) ~Upto 10 3Above 10 to 30 5Above 30 to 60 10Above60 Not significant

Wherevariationis morethantheabove,thedesignCBR shouldbe theaverage,of testresultsfrom atleastsix samplesandnot three.

4. TFt1CKNESS ANDCOMPOSITtON

The thicknessdeducedfrom Fig. 1 or Fig. 3 is the total physicalthicknessto be providedandconsistsof granularsub-base,granularbaseandbituminoussurfacing.A practical designof this thicknesscanlx~dctivedfromthe thicknessCombinationBlock given in Fig.2 which specifiesthe mini-mum thicknessof individual pavementlayers in termsof the cumulativenumberof standardaxles to becarried. Examplesillustrating the designmethodare given inparagraph7.

In stage construction, thethicknessof sub-baseshould be provided toultimate pavement sectionfor the full designlife andthe thicknessof roadbaseshouldbebasedon theinitial stageperiodchosen.The sub-baseandbaseare placedand coveredwith a thin bituminous surfacing(20 mm premix..carpet)without any underlying layer of bituminou.s hinder course. Extrapavementthicknessis added when the first stage designtraffic has beenc.arried.Example2 givenin paragraph7 illustratesthe designprocedureforstageconstruction.

15

tRC :37.1984

4.!.Sub-base

4.1.1. Sub-base materialscomprisenatural sand,moorum, gravel,laterite,kankar,brick metal, crushed stone,crushedslag or combinationsthereofor any other material like stabilisedsoil whichremainsstableundersaturated conditions.Ministry of Surface Transport Specificationsforgranularsub-basematerials (Clause401) recommend threegradingsandspecifythatthematerialspassing 425micronsieve whentestedin accordancewith 15:2720(PailV) should haveliquid limit andplasticityindexofnot morethan25 and6 respectively.Theserequirementsshould beenforced.

The sub-base materialshould have minimumCBR of 20percentforcumulativetraffic upto 2 million standardaxles (msa)and30 percent fortraffic exceeding2 msa,However,wherethe sub-baserequiredis 300 mmthick or moreapartof thismaybe substitutedin the lowerportionby mate-rialwith aminimumCBRof 10 percentsubjecttoaminimumlayerthicknessof 150mm of eithermaterial,

For very low trafficked rural roadsthe CBR requirementmay berelaxedto 15 per cent.

Thematerialshould betestedat thedrydensityandmoisturecontentexpectedin the field. Where soaking conditions apply for design, theminimum strengthof the sub-base materialshould be determinedaftersoakingthetestspecimenin water forfour days.Wheretheproposedsub-basematerial containsanappreciableamountof particlescoarserthan20 mm,itssuitability canbeesti.mated frompastexperienceor by conductingtheCBRteston thefractionof materialpassing20mmsievein accordancewith Clause401.2.2.of theMOST Specification.

4.1.2.Where provisionofasub-baseis foundnecessary,the thicknessshould not be lessthan100mm for cumulative traffic upto0.5 msaand 150mm for traffic exceeding0.5 msa

4.1.3.WheretheCBRof thesubgradeis lessthan 2 percentacappinglayer of 150mm thicknessof material with a minimum CBR of 10 per centis to be providedin additionto the sub-base required forCBRof 2 percent.

4.1.4.If the CBR of thesubgradeis morethan the minimum require-

ment for the sub-base.,no sub-baseis required.

16

tRC:37-1984

4,1,5,In areas affectedby frost, careshould betakento avoid using

frost susceptiblematerialsin thesub-base,

4.2.. Base

4.2.1. Thicknesses deducedfrom thedesigncharts are appropriatetoavenlentswith unbound granularbaseswhich compriseconventionalwater.eund macadam, wet mix macadamand any other equivalent granular:onstruction.

4.2.2.Basematerials must be of good quality so asto withstand highstressconcentrationswhich develop immediatelyunderthe wearing surface.For thisreasonit is recommendedthatnormallyno materialwith CI3R valuelessthan100percentshouldbeusedin baseconstruction.Since bases willbeaffectedby watertheir strengthshould bedeterminedon soakedspecimens.Whereasubstantialpart of the proposedbasematerial consistsof particleslargerthan20 mm size,theCBR test will not beapplicable andtheir strengthwifl have to beestimatedfrom experience.Standardconventionalconstruc-tions of adequatethicknessover a properly designed sub-basewill beassumedto satisfythe CBR requirementsof 100per cent.

4.2.3.The recommendedminimumthicknessof granularroad-baseintermsof cumulative numbersof standard axleto be carriedis givenin Fig. 2.A minimumof 15 cm thick mad-baseis considerednecessaryevenfor lightlytrafficked roads.

4.2,4. Whenabitumenboundstructurallayer is provided in additionto theminimumbituminoussurfacingsspecifiedin Fig. 2, areductionin thepavement thicknessfrom that deducedfrom Fig. 1 or Fig. 3 may bepennissible. It is recommendedthat pending further experiencean equiva-lency factor of 1.5 for bituminousmacadamand 2 for dense bituminousmacadammight beutiuisedin designto equatethe thicknessof the bitumenbound-layer(provided. in addition to the minimum bituminous surfacingshownin Fig. 2) to that of conventionalwater bound macadamconstruction.Built-up spray grout to the MOST Specification, will however, be regardedasequivalentto conventionalgranularconstruction.

It is emphasisedthat the aboveequivalencyfactorsareonly asugges-tion which has to be corroboratedandmodifiedin the light of further studyand future field performance.

17

IRC 371984

42.5. When semi-rigidmaterialssuch as leancementconcrete,leancement-flyashconcreteare used in flexible constniclions, this method ofdesign is not strictly applicable.However, in the absenceof an establishedprocedurefor the designof composite structures, the thicknessof leancementconcrete-base/sub-basemay be designedfor the presents~ith this methedusinganequivalencyfactor of 15. The thicknessof the serni’rigid layersoobtaIned shallbe checked for adequacyby calculating us ultimateloadcarryingcapacityusingMeyerhofequationsaspertheproceduredescribedinFRC:74-1979 ‘Tentative Guidelines for IRan CementConcrete and Lea.nCemcnt~FlyashConcreteas aPavementBaseor Sub-base.

42& For roadscarrying light to medium traffic soil-cement bases

(havingan average,crushingstrengthof 20 kg/cm2 at7 days age)ma) heusedwhen suitable granularmaterial is not availableor where the useof soil-cementis moreeconomicalandconvenient,

4.3. Bituminous Surfacings

4,3,1.The surfacingconsistsof a wearing courseor a binder courscplus a wearingcoursedependingup.n the traffic to be carried, The mostcommonty used wearing courses comprisesurfacedressing,op..n-gradedpremix carpet,mix seal surfacing,semi-densecarpetanda.sphalticconcrete.For binder coursesthe MOST Specification prescribes bituminousmacadam constructionsof 50 mm and75 mm thickness,The mix has lowbindercontentandhigh voidsand isthusnot imperviousto water,Furthe.rtheeffect of high voids is reducedstiffnessand increasedstressconcentrations.Fromfatigue considerationsthe detrimentaleffectof voidsis more.apparentat low temperatures.On theotherhandduringprolongedhot spells the aver-agepavementtemperaturesare very highandconsequently sucha mix willoperateover a very low stiffness range. Hence,the use of bituminousmacadam binder coursesto the MOST Specificationmay desirably berestrictedtoroadsdesignedto carry upto5 msa.Densebituminousmacadambindercourses arerecommendedfor roadsdesignedtocarry morethan S msa.A properly designeddensebituminousmacadam mixor a ‘recipe mix’ mayhe adopted.

4.12.Recommendedsurfacing materialsand thickness in termsof thecumulative standard axlesto be carriedduring the designlife are givenin

18

[FtC: 37~1984

Fig. 2.The suggestedsurfacingsareadesirableminimum from functional andstructuralrequirementsand should not be assignedhigher equivalency inrelation to other component layers in proportioning the overall structuralthicknessof the pavement.

4.3.3. Choice of appropriate type of bituminouswearingcourseforflexible pavementsbecomesnecessaryin severalcasessuch as newpave-ments,renewal and pavementrehabilitation.The typeof wearingcoursewilldepend onseveralfactors like designtraffic over the service life, the type ofbas~’bindercourseprovided, the fact whether the pavementis to bebuilt upin stages, rainfallandother relatedfactors. Therecommendedtypeandthicknessof wearingcourseunderdifferentsituationsareindicated in Table3. Structural sectionunderFig. 2may be readin conjunctionwith this table.These havebeendevelopedfrom presentknowledgeandmay be modifiedif the environmentalconditionsandexperiencesojustify.

4.3A. For heavy snow precipitation areaswhere snow clearanceoperationsmay be mechanised,as well at locations like bus-stops androundaboutsconsiderationought tobe given to the provision of denseasph-altic concretein single or multiple courses,so asto renderthe surfacemorestable and waterproof.

4,3.5. As a rule the laying of a permanent wearingsurfaceshouldnotbe delayedif closecontrol over materials andmethodsof construction hasbeenexercised.But whenapavementis beingbuilt in stages,or when closecontrol during constructionis not possible,a temporarysurfacingsuchassingle coat surfacedressing mightbe providedat the outsetso asto allowfurther consolidation of the underlying structure to take placeunder trafficand defectiveareasto show up which could be rectifiedat the time of finalsurfacing,whichshouldfollow assoonaspossible.In no.casetraffic shall beallowedon the bituminousmacadambindercoursedirectly.

43.6. When the wearing surfaceconsistsof thin surfacedressingoropen-gradedpremix carpet of upto 2.5 cm thickness, the thickness ofsurfacingshouldnot becountedtowards the total thicknessof thepavementas the surfacingwill then be purely for wearingandwill not be addingtostructuralcapacity of the pavement.

19

IRC 37-1984

1, Granularbaseincluding waterhoundmacadam/wetmists macadam

(i) Two coat surfacedressing

(ii) 20mmpremixcarpet(P.C.)plus liquidsealcoat

(iii) 20mmPC.plussand sealcoat

(iv) Mix seal surfacing(20mm) Type ‘A’or ‘B’.

2. luihup spraygrout(BUSG) Base

(i) 20mm P.C. plusliquid seal coat

(ii) 20mmP.C.plussandsealcoat

(iii) Mix sealsurfacing(200mm)Type’A’or ‘B’

MandH �l0.0 �800

LandM �10,0 5800

L,MandH 510.0 �800

TABLE 3-SHOWING THE RECOMMENDEDTYPE AND flBCKNF.SS OF BITUMINOUS WEARINGCOURSES FOR FLEXIBLE PAVEMENTS UNDER DIFFERENTSITUATIONS

5, Type of base/binder Type of Bituminous Annual rainfall 1~sign Correspo-No, course (toplayer wearing course Low(L) less traffic for nding**

with adequate than1500 mm; servicelife traffic inpavement thickness Medium (M) ofthe termsoffor the cumulativestandardaxles(CSA)

15(10-3000mmandHigh (H)

pavement((5A in

commercialvehicles!

shownin Cot. 5.) more than millions) day31100 mm.

1 2 3 4 5 6

LandM �0.50 540

L,MandH 510.0 5800

LandM �l0.0 �800

L,M andH 510.0 �800

3. Bitumen PenetrationMacadamBase

4. CmshedCementConcreteBase

5. Bituminous Macadambase/binder course

SameasatSI. No.2above,

SameasatSI. No. 2above.

(i) Semidensebituminous concrete(Seani densecarpet)(a) 25 mm(1,) 40mm

(ii) 20mmPremixcarpetwith liquidsealcoat

(iii) Mix sealsurfacing(20mm)Type ‘A’or ‘B’

‘~1

L,MandH �15.0 �1200

20

[RC: 37-1984

6. DenseBituminous Bituminous concreteMacadam (DBM) (Asphalt Concrete)

(i) 25mm )L,MandH ~15.0 51200

(ii)4Omm

Notes:

~‘~‘ From the designtraffic in CSA in Cot, 5, thepresenttraffic in termsof commercialvehicles/dayin Col,6hasbeencalculatedfor thecaseof 2-Lane road, designLife 10years, constructionperiod 2 years, VDF= 2.5,growth rate = 7$ per cent,and lanedistribution=75 per cent

In applying the recommendationscontained in the Table, ‘the following points shouldbespeciallykept In view:

(I) The pavement should bestructurallyadequateandstablefor thedesigntraffic.

(ii) As a general nale, the pavement should bedesignedfor a servicelife ofat least10years.in caseswherea pavementIsdecidedto be developed instagea,the iiurfaclngshouldcorrespondto that for thedesignstage.

(ill) Asfar as possible,wearingcourseamenable tolayingwith paver-finishershould beadoptedover paver-finishedbase/bindercourse.

(iv) Expensivesurfacingslike bituminousconcrete shouldnotbe provided dIrectly overgranular basesor built-up spray grout/penetration macadam.

(v) Built-up spray grout, w1~ereprovided, should notbe in morethan one1ayer~

(vi) The renewal wearingcourseshould be relatedto thedesigntraffic and shouldbeofthe type not inferior to that of theexisting one.

(vii) The designtraffic should be in tarsusof cumulativestandard axles(CSA) over theservice lifecalculatedin accordancewith the method givenIra [FtC : 37-1984.

21

IRC :37-1984

S. URAINACE MEASURES

5.1. The performanceof a pavementcan be seriouslyaffected ifadequatedrainagemeasuresto preventaccumulationof moisture in thepaverent structurearenot taken. Someofthemeasuresto guardagainstpeerdrainageconditionsare:maintenanceof transversesectionin good shajetoreasonablecrosslail so as to facilitate quick run-off of surfacewater~antiprovisionof appropriate surfaceand sub-surfacedrains where necessary.Drainagemeasuresareespeciallyimportantwhen the roadis in cutting orbutht onlow permeabilitysoilsor situatedin aheavy rainfall/snowprecipi ia-lion area.

5.2. On newroadsthe aim shouldbe. to constructthe pavementas farabove,the watertable. as economicallypracticable. Thedifferencebe vee.nthe fOrmationlevel and the level of water table/high flood level should,however., notbe lessthan0.6.1m. In water loggedareas9wherethe suhgradeiswi thin the zoneof capillary saturation,considerationshouldbe given to thenstaliattonof suitablecapillarycutoffs** at appropriate level underneaththe...

pavement.

5.1 When the traditional granular construction is provided on a.relatively low pc.rmeability subgrade,the granularsub-baseshould ix. cx-tende.dovertheentireformationwidth (Fig.4) in orderto drainthepavementstructuralsection.Care should beexercisedto ensurethat ils exposedend.sdonot getcovered bytheembank~.mentsoil. The trench typesectionshouldnotbe adoptedin any caseas it would lead to the entrapmentof water in thepavementstructure~.

Drainageof the pavementstructuralsection can be greatly improvedby providingahighp.rmeabiliiydrainagelayer(opengraded material)whichc.anbe substitutedon a centimetrefor centimetre basisfor the granularsub-base,

Aggregatesmeetingthe following criteria are regardedas very gooddrainagematerials:

D55<4D15D2)2,5mm

[RC::341970“Reccmmendationsfor RoadConstrictionin WaterloggrdArear’~

22

IRC :37-1984

meansthesizeof thesievethatallows85 percentby weightof thematerial to passthroughit. Similar is themeaningOfDai andD2

The drainagelayer when placed on soft erodibie soils should beunderlainby alayerof filter material to preventthe intrusionof soil fines intothe drainagelayer (Fig. 4).

5.4. \Vhere large inflows are to be taken care of, an adequatelydesigned sub-surfacedrainagesyste.mconsistingof an open gradeddrainagelayerwith collectorandoutlet pipesshouldbe provided.The system shouldbe designedon .a. rationalbasisusing seepage principlesto estimatetheinflowquantities andthe..: outflow conductivity of thedrainagesystem.It should beensure.dthattheoutflow capabilitiesaithesystemareatleastequalto thetotalinflow sothat no free. water ac.cumulate.sin the pavementstructuralsection.Sub-surfacedrainsshouldconform to therequirements prescribedin Clause309.1of the MOST Specificationfor RoadandBridge Works.

.5 5. Drainageof existing pavementof ‘Trench type’ stxtion on lowpermeabilitysub-gradescanbe.improvedby providingacontinuous drainagelayerof 10-15 cm thicknessunder theshouldersat the suhgradelevel or byproviding acombinationof longitudinalandlateraldrains, the latterspacedat.5 to 6 tm intervals. The drains are cut through theshouldersupto thesubgradelevel andhackfilledwith coarsedrainagematerial.

5.6.Very often, water enters thebase,sub-baseor the sub-gradeat thejunction of the verges and the bituminoussurfacing.. To counteracttheharmful effectsof thiswater, it is recommendedthattheshoulders shouldbewell-shaped and,if possible, constructedof impermeablematerial..With the.sameintent it is suggestedthatasfaraspracticable,andin anycase.on majorthrough roads,the base should beconstructed 30-45cm wider than thereiuiredbituminoussurfacingso that.therun-offwaterdispersesharmlesslywell clearoff the maincarriageway.

.5.7. Shouldersshould beaccordedspecialattentionduringsubsequentma.tenanceoperationstoo.They should be dressedperiodicallysothat theyalwaysconform to the requisitecrossfal.iandarenot higherthanthelevel .ofthe carriagewayatany time.

23

IRC :37-1984

~ITUI~INOUS SURFACING

GRANULAR 8AS~

SUB-8ASE

(a) ROAD ON FILL(NO SUB- St~FAc~DRAIN~

t.AYtR ~ ~J~SASE I WNt~~,OUI~O I

(bI ROAD IN CUTIKO SUB- SURFa~DRA~N5I

r $fl’U~9~NOUSSUPFAC 1MGlr~,u~uLAReA.s~

T EX’rENOUNOCP ll,op~~OUTLET PIPE SHOULDERS ~ LA’ItR OP $JB-BASEC%U-ICTOR PIPI ...~ REQUIRED

t’FILTER MATERIALIWNIRE PIOUrRID I

(cI DRAIN~6GESYSTEM WITH SUB-SURFACE DRAINS

Fig 4. Dratnage of pavementson impermeablesubgrades~Not to scale)

24

tRC : 37-1984

6. DESIGN IN FROST-AFFECTED AREAS

6.1. In areassusceptibleto frost action, the designwill haveto berelatedto actual depthof penetrationand severity of the frost. At thesuhgradelevel,fine grainedclayeyandsilty scilsaremoresusceptibletoiceformation,hut freezingconditionscouldalsodevelopwithin the pavementstructureifwaterhadachanceof ingressfrom above.

6.2. One remedy against frostattack is to increase the depth ofconstructionto correspondto the depthof frost penetration,but thismay notalways be economicallypracticable.As ageneralrule, it would be inadvis-able to povidetotal thicknesslessthan45 cm evenwhentheCBR valueofthesubgradewarrantedasmaller thickness.In additionthematerialsusedforbuilding up the crust should be frost resistant.

6.3.Another precaution against frost attack is that watershouldnot beallowed to collect at the subgradelevel which may happenon accountofinfiltration throughthe pavementsurfaceor verges ordueto capillary risefrom ahigh watertable, Whereas capillaryrise canbe preventedby subsoildrainagemeasure.sandcutoffs, infiltering watercan be checked onlybyprovidinga suitablewearing surface.

7. WORKED EXAMPLES ILLUSTRATING THE DESIGN METHOD

ExampleI.. Designor pavementfor the ttslI designlife that Is withoutconsldertngstage

construction

DATA:

(i) Two lane single carriageway(ii) Initial traffic in theyear of

completion of construction

(iii) Growth rate per annum

(iv) Design life(v) Vehicle damagefactor

(vi) DesignCBRof subgradesoil

Dt.sIcNC&.cutsnoNs

(i) tnitial traffic in designlane

Initial traffic a Distribution

factor as perpera3.2.3.2.

= 1000CV/day

Sumof both directions

= 7.5 per cent

= t5yeara

= 2.5 (standard axles

per commercialvehicle)

= 4percern

= 1000 a 0.75

= 750CV/day

25

IRC i7~1984

(b~ calcolsecumulativenumber

of standard axles tobe catered = 18 msafor in the design

(Equation given in para 3 3.1.)

(iii) Total pavementthicknessfor

CBRr=4percent, = 680mm

Traffic = 18 maa (Fig.l)

(iv) Pavement Composition:

FromFig.. 2, ThicknessCombination Block

(a) Bituminous surfacing : 130mm

consistingof 40mm AC wearing course +

90mm DBM binder course

(b) Roadbase : 250mm WBM(c) Su&base : 300mmgranular material of CBR not lest than 30

per cent in the top 150mm portion andof CBR not

less than 10 per cent in the lower portion (pars.

4.1.1.)

Example: 2: : Designofpavement providingfor stageconstruction

DATA:

(i) Data as for Example I

(ñ) I>.sign thepavementfor an initial stage periodof 5 years andrpecifythe strengthening

layer to be addedafter the initial stagetraffic has been carried.

DEStON CALCtJt.A11ONS

(i) initial uaffic itt design = 750 CV/day

lane (Example 1)

(ii) Cumulative number of = 18 msa

standard axles tobe carried

over the designlife of 15

years (Example 1)

(iii) Calculate cumulative number

of standard asksto be carried

over the initial stageperiodof5 years(Equation givr’n in pans3.2.2.) = 4 msa

26

ERC :37-1984

(iv) Total thicknessfor 15 years

life (Example1)

(v) Sub-base thicknessfor the

fulllifeofl5yeaes(As

worked out in Example 1)

(vi) Designthicknessfor

S years life,CBR= 4 per cent,

Traific = 4 msa (Fig, I)

(vii) Pavementcomposition for

the initial stageperiodof

5 years:

= 680mm

= 300mm

= 550mm

(a) Bituminous surfacing

(b) Road base(ror 4 rosa from Fig. 2)

(c) Sub-base(Provide thicknessrequired for the full design

life of IS years,

pars4)

Total:

thickness required-thickness

provided initiatly=680.550=l3thnm.‘l’he existing surfaceshouldbe

rectified to permissible

tolerance prior tolayingof

the strengthening course

E.xansple3:Designor strengtheningmeasures

DArk

Checkwith respect to the

total thickne~sasper step(vi)

(viii) Extra thicknessto be added

after the initial stage traffic

hasbeen carried.Ultimate

= 20 mm PC wearingc.ossrse

= 2SOmmWBM

= 300mmgranularmaterialof CBR

not tessthan 30 per cent inthe top

150mm portion andofCBR notlessthan10%us the lowerportion

550 mm

= O.K.

= 4OmmAC

90mm DBM

130mm

On thebasisofthe assessmentoftheexisting conditionofa certainNH section,adecisionhas

been takento strengthen it. Designa suitable overlayto carty 10 msa in the neatfive yearsafter

construction. The existing pavement is of 380 mm granular thickness with thin bituminous

surfacing. Subgrade CBRis 5 per cent

27

1RC :37.1984

DmstoNCALQtI .AT1ONS:

(i) Deduce lifeof existing structure

as a new asement

From thicknessdesign curve for CR

S per cent in Fig. 1 read life (rosa)corresponding to380 mm thickness

Future traffic to be carried(ii)

(iii) Design traffic fur determining

overall thickness (i)+ (ii)

(iv) 1~os.alpavementthicknessfor

C13R = 5 percent

Traffic = IC.5 rosa (Fig. 1)

(v) Overlay thickness required

(Total designthickness-

liaitting-thiekness)

(vi) Overlaycomposition

Providing surfacing

corresponding to10 rosa,Fig. 2

Total:

= 180mm

= 25mmAC+80mmDBM

+ 75 mmWBM

180mm

= 0.Smaa

= lOmsa

= 10.5 rosa

= 560mm

28

IRC :37-1984

AppendirI

PREPARATiON OF LABORATORY TEST SPECIMENS

GENERAL

1. Whereverpossible,thetestspecimensshouldbepreparedby staticcompaction,but if not possible,dynamicmethodmay be usedas an alterna-tive,

STATIC COMPACTION

2. Theweight of wet soil atthe required moisturecontent10 give theintendeddensity when occupyingthe standardtest mould is calculatedasfollows

Volume of mould = 2209 ccWeight of dry soil = 2209 dgmWeight of wet soil = 100+m ~2209d gm

Where d = requireddry densityin gm/cem = requiredmoisturecontent (per cent)

3. The soil is brokeninto lttmps, any stoneslarger than20 mm beingdiscarded.S ufficient quantity of the soil is mixed with water to give therequired moisturecontent. The correct weightof wet soil is placed in theniould. Alier initial tampingwith asteel rod,afilter paperis placedon topofthe soil, followed by (he 5 cm displacerdisc, andthe specimencornpn:~ssedin thecompressionmachineunlil the 101) of thedisplaceris flush with thetopof the.collar, The loadis’ heldforabout30 secondsandthen released.In somesoil typeswhereacertainamountof rebound occursit mayhe necessary tore~apply load to force the displacerdi.se slightly below the top of the moLl,ld sothat on rebound the rtghtvolume is obtained.

t)YNAMIC i’OMPACTION

4. ‘The soil ismi~ed with waterto give the reqtiired tnoisturc content,andthen compactedinto the mould in 3 layersus...ing astandardsoil rammer.~to m onp tc lion thi sotl is trimmed Ilttsh wtttt thetop ol thc rnoaltl with thi

29

IRC :37’t984

help ofametal straightedge.Themould is weighedfull and empty to enabledeterminationof wetbulk density,andfrom it, knowingthemoisturecontent,the dry density to be calculated.

5. Farther specimens,at the samemoisture content,are thenpreparedtodifferentdry densitiesby varyingthenumberofblowsappliedtoeachlayer‘of soil so that the amountof compactionthatwill [‘ill the mould uniformlywith calculatedweightof wet soil (videpara2 above)is known.

30

Appendix2

SPECIAL POINTSRELATING TO DESIGN OF PAVEMENTSON EXPANSIVE SOILS

Potentially expansivesoils such as black cotton soils are mont-,ntorillonite claysandare characterisedby their extreme hardnessanddeepcrackswhendry andwith tendencyforheavingduring theprocessof wetting.Roadbcdsmadeup of such soilswhensubjectedto changesin moisturecon-tentsdueto seasonalwetting anddrying or due to any otherreasonundergovolumetric changesleading topavementdistortion, crackingandgeneralunevenness.In semi-aridclimatic conditionswith pronouncedshort wet andlong dry periods,significantfluctuationsin the subgrademoistureconditionsoccurwhich aggravatethe problemof swelling andshrinkage.Duerecogni-tion of theseproblemsat the designstage itselfis requiredso that countermeasurescould be devisedandincorporatedin the pavementstructure.Aproper designincorporatingthe following measuresmay considerablymini-mise theproblemsassociated withexpansivesoils:

1. SUBGRADE MOISTURE, DENSITY AND DESIGN CBR

The amountof volume changethatoccurswhen an expansivesoil road

bedis exposedto additonalmoisturedependson thefollowing:(a) thedry densityof thecompactedsoil(Li) themoisturecontent(c) structureof soil andmethodof compaction

Expansivesoilsswell very little when compactedat low densitiesandhigh moisturebut swell greatlywhencompactedathigh densitiesandlowmoisture.Hence,where theprobabilityof moisturevariationin the subgradeis high, it is expedientto compact thesoil slightly wetof thefield optimummoisturecontentdeterminedon thebasisof afield trial, Experierceshowsthat generally it is not practicable to compact expansivesoils at OMCdeterminedby LaboratoryProctorTestIt is, therefore, necessaryto studyitsfield moisttire-densityrelationshipthroughcompactingthesoilat differentmoisture contentsandunderthesamenumber of roller passes.A minimumdensity correspondingto 95 per centof the standardproctor density shouldbe attained in the field,

31

IRC 37-t984

DESIGNCBR

The pavement thickness should be based on a 4-dat soakedCERvalue of the soil remoulded at placementdensity and moisture contentascertainedfrom the field compactioncurve.

2. BUFFER LAYER

There is a definite gain in placing the pavement on a non-expansivecohesivesoil cushion of 0.6-1,0m thickness~,It prevents ingress of water inthe underlyingexpansive soillayer, eounteractsswellingandsecondly evenifthe underlying expansivesoilheaves,the movement will be moreuniformandconsequentlymore tolerable, However, where provision of non-expan-sive buffer layer is not economically feasible, a blanket courseof suitablematerial and thicknessasdiscussedin para 3 below must be provided.

3.BLANKET COURSE

A blanket courseof atleast225 mm thicknessandcomposedof eoarse/mediumsandor non-plastic moorumhavingP1 lessthan 5 should beprovidedon the expansivesoil subgradeasa sub-baseto serveasaneffectiveintrusionbarrier. The blanket courseshould extendover the entire formation width,

Alternatively, lime-stabilised black cotton sub-baseextending overthe entire formation width may be provided togetherwith measuresfbrefficient drainage of the pavementsection.

4. DRAINAGE

Improvementof drainagecan significantly reduce ‘the magnitude ofseasonalheaves,Specialattention should,therefore, be given to provision ofgooddrainage measuresas also discussedunder Section 5 (Drainage Meas-ures). The desirablerequirements are:

(a)Provisionmust be made for the lateral drainageof the pavementstructuntl section,The granular subbase/baseshould accordinglybe extendedacrossthe shoulders,referto pam 5.3 of Section5(DrainageMeasures).

(b)Normalcamberof 1:40 for the black top surfaceandacrossslope

32

1RC: 37-1984

of 1:20 for the bermsshould be provided to shedoff surface run-offquickly.

(c) No standingwatershouldbeallowedoneithersideof theroadem-bankment,

(d) A minimum height of I m betweenthe subgradelevel andthehighest water level should be ensured.

5. BITUMtNOUS SURFACING

Desirably40 mm thick bituminoussurfacingshould be providedtoprevent ingress of water through surface.

6,SHOULDERS

Shouldersshould be madeup of impervious material soasnot to allowwater topermeateinto thebody of the pavemenLLime stabilised black cottonsoil shoulderof 15-20cm thicknessmay servethe purposeeconomically.

33