IRC 8 1-1997

GUIDELINESFOR

STRENGTHENING OF FLEXIBLEROAD PAVEMENTS USING

BENKELMAN BEAM DEFLECTIONTECHNIQUE

(First Revision)

INDIAN ROADS CONGRESS1997

IRC:81~i997

GUIDELINESFOR

STRENGTHENING OF FLEXIBLEROAD PAVEMENTS USING

BENKELMAN BEAMDEFLECTION TECHNIQUE

(First Revision)

PublishedbyTHE INDJAN ROADS CONGRESS

Jamnagar House,ShahjahanRoad,New Dethi4lOOll

1997

PnceRs. 120/..lP~usPacking& Postage)

IRC:811997

First published: November,1981Reprinted: March, 1991First Revision: July, 1997.Repr~ntedOctoher~20(Xi) (with amendntents

(RightsofPublicationandof iran,’~Lnon arc reserved)

Printedat Dee Kay Printers,New i)elhi(500copies)

IRC:81-1997

MEMBERS OF THE HIGHWAYS SPECIFICATIONS ANDSTANDARDS COMMITTEE

(As on 313.96)

1. Al). Narain* DC (RD),Ministry of SurfaceTransport(Convenor) (Roads Wing), New Delhi

2. S.C. Shanna ChiefEngineer (R) Stds/R, Ministry of(Member-Secretary) Surface Transport (Roads Wing), New Delhi

3. CC. Garg Engineer-in-Chief, Municipal Corporationof Delhi, town Hall, Delhi-I 1(X)(Ws

4. Dr. Ml’. Dhir Director, CSIR (Retd.),A-1/133,SafdarjangEnclave, New Delhi-I 10029

5. RN. Matik Chief Engineer (Mcch.), Ministry of SurfaceTransport (Roads Wing),NEW DELHI

6. CS. Tawartnalani AddI. DirectorCeneral ~S&P),CPWD,Nirman Bhawan, New l)elhi-l 10011

7. I)r. AK. Gupta Professor & Coordinator, Centre ci iransportEngg., University of Roorkee, Roorkee

8. H.P.Jamdar Secretary to the Govt. of Gujaral, R & H Depu.., Block No.14,Sachivalaya Complex, Gandhinagar-382fl10

9. MB. Jayawant Synthetic Asphalts, 103, Pooja Mahul Road,Chembur, Bombay-400074

10, KS. Narayanan Chief Engineer (CCC), Mb. Environment &Forests (Retd.), E-23, Central Govt. Qtrs.,St. Martin Marg, New Delhi-I 10021

II. P.1). Agarwal Chief Engineer (Nil.), UP. PWI), Lucknow-22&X)1

12. Maj. CR. Ramesh Engineer-in-Chief, Public health Engg.,

Ananda Rao Circle, Bangalore-560009

13. Dr. ER. Kadiyali Chief Consultant, Dr. ER. Kadiyali &Associates, S-487, lInd Floor, GreaterKailash-1, New Delhi-I 10048

* ADC(R) being not in position, the meeting was presided by Shri AD. Narain,DG(RD), Govt. of India, MOST

(i)

IRC:81-1997

14. NinanKoshi

15. The Director General,

16. Dr. S. Raghava Chad,

17. VinodKumar

18. P.J. Rao

19. Prof. (IV. Rao

20. Prof. C.G. Swaminathan

21. B. Megu

22. M.K. Saxena

23. Prof. DV. Singh

24. The Director

25. A.Scn

26. RAT Mehta

27. R.L. Koul

28. Prof. C.E.G, Justo

DC(RD), MOST (Retd), 56, Nalanda Apartment,Vikaspuri, New Delhi-I 10018

National Council for Cement & BuildingMaterials, P-21, South Extn. LI, Ring Road,NewDelhi-I 10049

Transport Engg. Section, Deptt. of CivilEngg., Regional Engg. College, Warangal

Director& Head (Civil Engg.). Bureau ofIndian Standards, Manak Bhawan, 9,

Bahadurshah Jafar Marg, New Delhi-I h(XX)2

Dy. l)irector & lhead, Ceotechnical Engg.Division, Central Road Research Institute,Delhi-Mathura Road, New Delhi-I 10020

Prof. ofCivil Engg., I.t.T., HauzKhas,New Delhi-I 10016

‘Badr’i’, 50, Thinivankadam Street,R.A. Purans, Madras-600028

Chief Engineer (Zone-I), Artrnachal Pradesh,PWD, hanagar-791 Ill

Director, National Institute for Training ofHighway Engineers, 174, Jor Bagh,New Dellii-l 10003

Director, Central Road Research Institute,I)elhi-Mathura Road, P.O.CRRI, Okhla,New Delhi-I 10020

Highway Research Station, Guindy,Madrar-600025

Chief Engineer (Civil), Indian RoadsConstruction Corpn. Ltd., 6,Core, 6th floor,Scope Complex, Lodhi Rosd,New Delhi

Chief Engineer fI’&T), Minion of Surface‘Iransport (Roads Wing), New E)elhi

Chief Engineer (Plsnnning), Ministry ofSurface Transport (Roads Wing), New Delhi

Prof.of Civil Engg., Faculty of Engg. -

Civil, Bangalore University, Bangalore

(ii)

IRC:81 -1997

34. AK. Mishra

35. H.S. lihatia

36. R.K. Jam

37. President,Indian Roads Congress

38. DG(RD) & lion, Treasurer,Indian Roads Congress

39. Secretary,Indian Roads Congress

118164, Vasant Kunj, New Delhi- 110030

Chief Engineer (L) Std./R Ministry of SurfaceTransport (Roads Wing), New Delhi-I 10001

D.G.W., LI-in-Chief’s Branch, Army Hqrs.,Kashmir Ilouse, Dl-lQ P0, New Delhi-I 10011

Prof. & Head, Deptt. of Transport Planning,School of Planning & Architecture, 4,Block-B, indraprastha Estate, New Delhi

Chief Engineer, Dy. Director General/DSDte. General Border Roads, Kashmir House,DIIQ P0, New Delhi-I 10011

Director (Technical), Oil CoordinationCommittee,2nd Floor, Core-8, Scope Complex,7, institutional Area, Lc,dhi Road,New Dclhi-110003

ChiefConsultant, Engineers & ManagementAssociates, 3/5, Kalkaji Extn., New Delhi

Project Director, ADB Project, Kothi No.1,Nirman Kunj, Sector-16A, Faridahad

MS. Guram,Chief Engineer, Punjab PWD,B&R Branch, Patiala

A.D. Narain

S.C. Sharma

29. OP. God

30. MR. Kachhwaha

31. Maj. (len. CT. Chad

32. Prof. N. Ranganathan

33. RN. Srivastava

- Ex-Officio

- Ex-Officio

1. L.N. Narendra Singh

2. R.S. Shukla

- Iix-Officio

CORRESPONDING MEMBERS

13-36, Plot 86, Kakateeya Apartments.Patparganj, Delhi-I 10092

13-190, Sector 55, Noida-201301

(iii)

IRC:81-1997

CONTENTS

PageNo.

I. Inlroductiotl I

2. Scope 3

3. BasicPrinciplesof DeflectionMethod 3

4. Procedurefor Deflection Survey 3

5. Traffic 13

6. Analysisof Datatbr Overlay Design 17

7. Designof Overlay 17

IRC:81-1997

GUIDELINES FOR STRENGTHENING OFFLEXIBLE ROAD PAVEMENTS USING

BENKELMAN BEAM DEFLECTIONTECHNIQUE

I. INTRODUCTION

A.C. Benkclman devised the simple deflection beamin 1953 formeasurementof pavementsurfacedeflectionon theWASHOTest Road. It is widelyusedall overtheWorld forevaluationof the requirementsof strengtheningof flexiblepavemenLs.Deflection beam has been in use in India for morethan two decadesby different organizations. To lay down a uniform procedure for the design offlexible overlays using the BenkelmanBeam deflection technique, tentativeguidelineswere publishedby the Indian Roads Congressunderthetitle “TentativeGuidelinesforStrengtheningof Flexible Road PavementsUsing BenkelmanBeamDeflection Technique” IRC:81-1981.

Thetentativeguidelines(IRC:81-1981)hasbeeninusesincethen andbasedon their applicationinpracticefordesignof overlaysfor flexible pavements,a lot ofusefuldatahavebeencollected and valuableexperiencegained. A researchstudyentitled “Developmentof MethodssuchasBenkelmanBeamDeflection Method forEvaluation of Structural Capacity of Existing Flexible Pavementsand also forEstimationandDesignof Overlaysfor Strengtheningof anyWeakPavement”wasalsoundertakento collect data on pavementdeflection values beforeandafteroverlaying and various other parameterslike temperature,subgradcsoil type andmoisture and their influenceon pavementdeflection andservicebehaviour. Basedon the findings of this study and the experiencegainedovertheyearswith the useof deflection method and other studiescarried out in the country, the FlexiblePavementCommitteepreparedreviseddraftguidelineswhich were discussedby theHighwaysSpecificationsandStandardsCommittee during themeetingheldon 12thMay, 1994.The HSS Committeereferred this draft backto thenewly constitutedFlexible PavementCommittee for in depthstudy.

1

IRC:81-1997

The abovecommittee in its meeting held on 24th May, 1994 set up aSubgroup withthe following members for carrying out the revision of thepresentIRC:8l- 1981.

The subgroup heldsix meetingsanddiscussedat length various aspects ofthe guidelinesin view of the changing loading conditions as well the findings of theResearch Project R-6 of MOST. Dr. Sunil Bose and Shri Nirmal Jit Singh were alsoinvited toauendthe subgroupmeetings.Thedraft preparedby the subgroupwasapprovedby the Flexible Pavement Committee inits meetingheld on i 3th February,1996(personnelgivenbelow).

Prof. CC. SwaminathanEngineer-in-Chief Branch,AHQ(Lt.Col. V.K. Ganju)Chief Engineer (R) S&R, MOST(SC; Sharma)V.K. Soodt)r.M.S. SrinivasanProf. C.E.G. JustoR.K. JamRep. of Directorate General Border Roads

I.C.GoelCS.SanwalDr. L.R. KadiyaliProf. 5K. RaoV.K. AroraProf. V.5. BatnDr,M.P.Dhir1.Koti PadmakarD.P. Gupta

Ex-Offlelo Members

President, IRC (M.S. Guram)

Secretary, IRC (S.C. Sharma)

DG(RD) & Honorary Tteasurer,IRC (A.D. Narain)

CorrespondingMembers

Prof OP. Bhatia

The guidelines were approvedby the Highways SpecificationsandStandards Cotnmittee inits meetingheld on 19th March,1996and by the ExecutiveCommitteein its meeting on 17thApril, 1996. The guidelineswerefinally approvedby theCouncil in its meetingheld atDarjeelingon 24th May,1996.

Shri S.C. SharmaProf. S.S. lain

Prof. A.K. GuptaProf. 13.13. PandeyProf. C.E.G. Justo

Members

ConvenorMember-Secretary

Prof. OP. BhatiaShri 1.R. Arya

Prof. AK. GuptaProf. S.S. Jam

Convertor

Member-Secretary

Members

Hariom Prak ash SIt am~aMM. livani

R.S.ShuklaProf. P.1). Marathe

2

IRC:81-1997

2. SCOPE

2.1. These guidelines aremeantfor evaluatingthestrengtheningrequirementofexistingflexible roadpavementsusingtheBenkelmanBeam DeflectionTechnique.The recommendationsarebasedon the findings of MOSTResearchstudy(R-6)andwork doneat variousacademicandresearchinstitutionsin thecountryaswell as thefield experiencegainedoverthe yearsin additiontothe findingsfrom abroadwhicharerelevantto Indianconditions.

2.2. Theguidelinesmay requirerevision from time to time in thelight of futureexperienceanddevelopmentsin the field. Towardsthis end, it is suggestedto all theorganisationsintending to use the guidelinesto keepa detailedtabulatedrecordofperiodical deflection measurements(both beforeandafterstrengthening),typeandthicknessof overlayprovided,performance,traffic, climatic conditions,etc.

3. BASiC PRINCIPLES OF DEFLECTIONMETHOD

3.1. Performanceof flexible pavementsis closelyrelatedto theelastic deflectionof pavementunderthewheelloads.Thedeformation or elastic deflection under agivenload dependsupon suhgradesoil type, its moisture contentandcompaction,the thickness and quality of thepavementcourses,drainageconditions,pavementsurfacetemperatureetc.

3.2. Pavementdeflectionis measuredby theBenkelmanBeamwhich consistsofa slenderbeam3.66in longpivotedat a distanceof 2,44 m from thetip (seeFig.!).By suitablyplacing theprobebetween the dual whee•••is of a loadedtruck, it ispossibleto measurethe reboundand residualdeflecüonsof thepavementstructure.While the rebound deflectionis the one related to pavement performance,theresidualdeflectionmay he due to non- recoverable deflection of the pavementorbecauseof the influenceof the deflectionbowl on the front legsof thebeam.Rebounddeflection is usedlbr overlaydesign.Para4.3discussesthe method of deflectionmeasurementandAnnexure-1givesthemeasuremepiprocedure.

4. PROCEDUREFOR DEFLECTION SURVEY

4.1. General

The deflection survey essentiallyconsistsof two operations:(i)conditionsurvey for collecting the basicinformationof the roadstructureandbasedon this,thedemarcationof the road into sections of more or less equalperformance;and (ii)actualdeflectionmeasurements.

3

IRC:81 -1997

4.2.1. This phase of operation, which shall precedethe actual deflectionmeasurement, consists primarily of visual observations supplemented by simplemeasurementsfor rut-depthusinga 3 metrestraight edge. Basedon these,theroadlength shallbeclassified into sectionsof equalperformancein accordancewith thecriteriagivenin Table1.

Table I. Criteria for Classiticationof PavementSections

Classification Pavement condition

Good No cracking,rutting lessthan 10mm

Fair No cracking or crackingconfinedto singlecrack in the wheeltrackwith rutting between 10 mmand20mm

Poor Extensivecracking and/or rutting greater than 20 mm.Sections with cracking exceeding 20percentshall betreated as failed.

FIg. 1. Benkelman Beam

4.2. PavementCondition Survey

4

IRC:81-1997

4.2.2. As it is inexpedient to modify the overlaydesignat frequentintervals,itwill bepreferableif the lengthofeachsection is kept at a minimum of1 km exceptin the case of localised failure or other situations requiring closer examination whereminimum length of section may be suitablyfixed.

4.2.:.. The datacollectedduring the condition survey shall berecordedas per theProforma given in Table 2. In casethe pavementshows severedistress or signsof prematurefailure further investigationswould be necessary to ascertainthecausesand design remedial nicasures.

4.3. DeflectionMeasurements

4.3.1. Ineachroadsectionof uniform performance(see para4.2) minimum oftenpoints shouldbe marked atequal distance in each lane of traffic for making thedeflection observations in the outer wheel path. Theinterval betweenthe pointsshould notbemore than 50 m.Onroadshaving morethanonelane,the pointsmarkedon adjacent lanes shouldbe staggered.In the transversedirection, the measurementpoints shouldbe&)cm from thepavementedge ifthelane width islessthan3.5mand9() em when the lane width is more than 3.5 m. For divided four lanehighway,themeasurement pointsshouldbe 1.5 m from thepavementedge.

4,3 Variability of deflections in a given section should be considered fordetecting spots whereextra deflection measurements have to bemade.For thispurpose,highestandlowest valuesin a group of ten should be compared withmeanvalue. If the highest or lowest values differfrom themeanby morethan one- thirdof meanthen extradeflectionmeasurementsshouldbe made at25 m on eithersideof rxnnt where high orlow values areobserved.

4.3.3. For measuring pavement deflection the C.G.R.A.procedure(vide detailsgiven in Annexure-I)which is basedon testingunderstatic load may be adopted.In this method, a standard truck having a sear axleweighing 8170kg fitted with dualtyre inflated to a pressure of 5.60kg/cm is usedfor loadingthe pavement.Duringactual tests, the total load and the tyre pressure are maintained within a toleranceof+/- 1 per cent and ÷/-5 percent respectively.

4.3.4. Before.starting the deflection measurements,the BenkelmanBeam shouldbe calibrated toensurethat thedial gaugeand beamare working correctly. This canhe doneby using the simpleproceduredescribedbelow:

The beam is placed and levelledon a hard level ground.A number ofmetallic blocks of different thickness (measured accuratelywith a precision

5

II.aSIISz

IRC

:8l-1997

Table2

iii.0In

IIIIIII1ii

III

6

IRC:81-1997

micrometer)withperfectly plane facesare placedunderthe probe andthe dial gaugereading recorded eachtime. If thebeamis in order, the dial gaugeon the beamshouldread onehalf the thiclnessof the metallic block on which the probewas placed.Otherwise, the dial gauge should be checkedarid replaced if necessary.If the dialgaugeis functioningcorreciiy,thebeampivot shouldbecheckedfor free andsmoothoperation,secondlythestrikingplate beneaththedialgaugespindleshouldbecheckedtoensurethat it i~tightly secured andhasnotbecomegroovedby thedial gaugestylus.

4...5. Dcflections measuredby the BenkclmanBeam arc influenced by thepavementtemperature.Fordesignpurposes,therefore,all deflection values shouldbe related to a common temperature. Measurementsmadewhenthe pavementtemperatureisdifferent thanstandardtemperaturewould needto becorrected.Thestandardtemperatureand the procedureforcorrectionarediscussedin para4.4.

4.3.6. Pavementdeflectionsare also affected by seasonalvariations in climate.For the purposeof applying theseguidelines, it is intended that the pavementdeflectionsshouldpertainto theperiodwhen thesubgradeis at its weakestcondition.In India,this periodoccursduring the recessionof monsoon.It is, therefore,desirableto conduct deflection measurementsduring this period. Where the same~snotfeasible,acorrectionfactorshouldbe applied,vide para4.5.

4.3.7. The deflection measurements.,pavementtemperature,subgradesoil &deflection, and other informationcollectedduring thedeflection study should berecordedin theproforrnagiven inTable3.

4.4. CorrectIonforTemperatureVariations

4.4.1. Thestiffnessofbituminouslayerschangeswith temperatureof thebinderandconsequentlythe surfacedeflectionsof a givenpavementwill vary dependingonthe temperature of the constituentbituminous layers. For purposesof desiga,therefore, it is necessarythat the measureddeflectionsbecorrectedto a commonstandardtemperature.For areasin thccountryhavinga’tropicarclimate, thestandardtemperature is recommended to be 35°C (also see para4.4.4.). Correction fortemperatureisnotapplicable in the caseof roadswith thin bituminoussurfacings(suchas premix carpetor surfacedressingover a non-bituminousbase)sincetheseare usuallyunaffectedby changesin temperatures.But temperaturecorrectionwillherequiredt~rpavementshavinga substantialthicknessof bituminousconstruction(i.e. mInimum40m). Correctionneednothowever,beappliedin the latter case if theroad is subjectto severecrackingor the bituminouslayer is substantiallystripped.

7

IRC:Sl-l997

4.4.2. Available infctmation shows that the deflection-pavement temperaturerelationship islinear.abovea temperatureof 30°C.Forconveniencein the applicationof the temperaturecorrection, it is reeommendedthat the deflectionmeasurementsshould be taken when thepavementtemperature iswithin the rangeof 30°C- 35°C,preferably when the temperature is uniform uLd is near the standard temperature of35”C. Accordingly, as far as possible deflection measurements should be madeduring morning and evening hourson summer months.

Table 3. Profonnafor Recording PavementDeflectionData

Nameof Road: Date andtimeorobaen’ation

Section:

No, oftrafficlanes:

Climatic conditions (hot/humid/cold)Air temperature,“CAnnual rainrall, mm. :Whethertemperaturecorrectionis : Yes/noto he appliedWhether correction forseasonalvariationis to beapplied : Yes/No

.~‘

,

S.No. t,ocationof test pointand

Pavementtemperature,C(’

Typeof Moisture DialgaugereadingSoil & content tnitiai Intermediate FinalP1

ReboundDeflection

(mm)

identificationof lane

1 2 3 4 5 6 7 8 9

Note: l’hevaluesof pavementsurfacetemperaturewill be measured ateveryhctur during the deflectionstudy

4.4.3. Correction for temperaturevariation ~n deflection valuesmeasured atpavement temperatureother than 35°Cshould’be0.01 mm for each degreecentigrade changefrom the standard temperature of35°C.The correction will bepositive for pavementtemperature lowerthan 35°Cand negativefor pavementtemperature higherthan 35°C. For example, if the deflection is measured at apavementtemperatureof37°C,the correction factorwill be0.02mm(=2 x .01) whichshould besubtractedfrom the measured deflection toobtain the corrected valuecorresponding to standardpavementtemperatureof 35°C.

4.4.4. Incolderareas,and areas of altitudegreaterthan l000m where the averageclay temperature isless than 20°Cfor more than4 months in a year,the standardtemperature of35°Cwill notapply. In the absenceof adequate data aboutdeflection- performance relationship,it is recommendedthat thedeflectionmeasurementsin suchareas be made whentheambienttemperatureis greaterthan20°Cand that no correction for temperature needbeapplied.

8

IRC:81-l997

4.4.5. In cases where temperaturecorrection is to be applied, the pavementtemperature should be measured during the deflection survey. The measurementshould be madeat a depth of 40 mmusing a suitable short-stem mercury or a digitalcontact thermometer. For this purpose, a hole of about 45 mm deep and about 10mm diametershould be drilled in the pavementand filled with glycerol andtemperature can then be recorded after about 5 minutes.

4.5. Correction for SeasonalVariation

4.5.1. Since the pavementdeflection is dependentupon changein the climaticseasonof the year, it is alwaysdesirableto takedeflectionmeasurementsduring theseasonwhen the pavementis in its weakestcondition. Since, in India, this periodoccurssoonaftermonscx)n,deflectionmeasurementsshouldbeconfinedto thisperiodas ft~r as possible. Whendeflections are measured during the dry months, they willrequire a correction factor which is defined as the ratio of themaximum deflectionimmediatelyaliermonsoonto thai of theminimumdeflectionin thedry months.

4.5.2. Correctionfor seasonalvariationshalldependon type of suhgradesoil, itsfield moisture content (at the timeof deflectionsurvey)andaverageannualrainfallin the area. For this purpose, suhgrade.soilshavebeendivided into threebroadcategories,namely sandy/gravelly,clayey with low plasticity(P1 � 15) and claycywith high plasticity (P1 > 15). Similarly, rainfall has beendivided into twocategories, namely low rainfall (annualrainfall� 1300mm)andhighrainfall (annualrainfall >1 3(X) mm). Moisture correctionfactors (or seasonalcorrection factors)shall be~obtainedfrom Figs.2 to 7 forgiven field moisture content,typeof subgradesoil and annualrainfall.

4 The soil samplefor determinationof suhgradetype and its field moisturecontent shall be scooped from belowthepavementasshowninFig. 8.Forthispurposea testpit at the shoulder(adjacent10 pavementedge)shallbedug to a depthupto 15cm below the subgrade level in every kilometerdepending on the uniformity ofsuhgrade soil, topographyof theareaand roadprofile. A soil sampleof weightnotlessthan 100gmshouldhe collectedusinganaugerfrom thesubgradeunderneaththedellectionobservationpoints i.e. 0,6 m and0.9m from thepavementedgefor singleand two lane pavementsrespectivelyat a depth of 50 mm to 100 mm below thesubgradelevel asshown in Fig.S. Thesuhgradesoil shallbe testedas perIS-2720 -

for type of subgradesoil,plasticity indexand field moisturecontent. The test pitshall be madegood immedialely after taking soil sampleand studyof pavementcomposition.

9

36

1 32

25

2 24.

1 20

1 2

M2IS1UCE CONILN1, S

FIg. 2. MoIsture correction factor for Sandy/Gravellysoil subgrade for low rainfall areas(Annual rain#allS 1300mm)

HLDtJ~JTh

1~5516160 LDN~1Nl N

105

IRC:81-1997

1 54

I 40

2 I 32

1 25

211

NN

Is,

Fig. 3. Moisture correction factor for Sandy/Gravellysubgradefor high rainfall areas(Annual rainfall > 1300 mm)

10

IRC:81-1997

I I II I JI[]IJIIDhTI1TT~4 b 10 12 4 16 ~8 .W .22

M0I~TURtCONTENT 1~)

Fig. 4. Moisturecorrect.Ionfactor for elayeysubgradewith low plastIcity (Pt < 15) for low rainfallareas(Annual rainfall 5 1300 mm)

I i I~b.5 10 12 14 15 15 20 22

MOISTURE CONTSNT, ~

Fig.5. Moisturecorrectionfactor for clayeysubgradewith low plastklty (P1 < 15) for high rainfallareas(Annual rainfall >1300mm)

Ii

2,2

2.0

IC0

18IC0U

16Sr06,)

1.4C0

2 .2

1.0

22

2,0

1.6

15

IC01)C

IC

0C)

SIIC0U

SI

:2

100

IRC:81 1997

2.2

2.0 —SI

0

18

IC0

U

Sr 16Sr0U

SI

1.4LI

0

MOISTURE CONTENT. S

Fig. 6. Moisture correctionfactor for clayey subgradewith high plasticity (N> 15)for low rainfallareas(Annual rainfall 5 1300 mm)

Sr0

.5

0U

Sr 1,Sr0U

Sr

3

100

MOISTURE CONTENT, S

Fig. 7. Moisturecorrectionfactorfor clayeysubgradewith high plasticity (Pt> 15) for highrainfall areas (Annual rainfall > 1300mm)

12

IRC:81 -1997

4.5.4. The annual rainfall data has to be obtainedfor that’particulararea. Thedeflection valuescorrectedfor temperatureshall be multiplied by the appropriatevaluesof seasonalcorrectionfactorsto obtain correctedvaluesof deflection.

5. TRAFFIC

Traffic in terms of million standardaxle shall be consideredfor thedesignof overlay.If sufficientdataareavailableatthestretchwith respectto thewheelload distribution of commercial vehiclesor the vehicle damage factor and theirtransverseplacement,thecumulativestandardaxlesmaybeworkedOut based on actualdata,otherwisedesigntraffic maybecalculatedasperthe proceduregiven in IRC:37and pam5.4below.

5.1. General

For purposesof the design, only the numberof commercialvehicles ofladen weight of 3 tonnesor more and their axle loading will be considered. Thetraffic isconsideredin bothdirections in thecaseof two laneroadandin thedirectionof heaviertraffic in thecaseof multi lanedivided highways.

To obtain a realistic estimateof design traffic dueconsiderationshouldbe givento theexisting traffic,possiblechanges in road network and land useofthe areaserved,theprobablegrowthof traffic anddesignlife.

~lNOUS LAYERS,—PIT TO BE CUT ON S~DE

/ OF’ PAVEMENT UPTO 50cm— if BELOW SUB BASE LEVEL

20

FIg. 8. Determination olfield moIsture content usingauger

13

IRC:S 1-1997

Estimate of the initial daily averagetraffic flow Ibr any road shoult.normally be based on 7-day 24-hoursclassifiedtraffic counts. However, inexceptionalcaseswherethis information isnotavailable3-daycountcouldbeused.

5.2. Tralflc growth rate

An estimateof likely growth rate can be obtainedas follows:

a) By studying the pasttrendin traffic growth.b) Elasticityof transportdemand.c) If adequatedata is not available, it is recommended that an average

value of 7.5 percentmay be adoptedfor roadsin rural routes.

5.3. Designlife

It is recommended that the design life for strengtheningof major roadsshould be atleast10 years. Lessimportantroadsmay, however,he designedfor ashorterdesignperiodbutnot lossthan 5 yearsin any case.

5.4. Computationof designtraffic

5.4.1, The design traffic is consideredin tenns of the cumulative number ofstandardaxlesto be carried during the design life of the road. Its eoniputationinvolves estimatesof the initial volume of commercial vehiclesper day, lateraldistribution of traffic, thegrowthrate,thedesignlife inyearsand thevehicledamagefactor (numberof standardaxle per commercialvehicle) to convertcommercialvehiclesto standardaxles.

The following equation may he usedto maketherequiredcalculation

365 x A l(1+rf - IIxF .. (1)

where,N, = The cumulative number of standard axles to he catered fOr tO the designA = Initial traffic, in the year of completionof constmctirsi, in tcmls of the number of

commercial vehicles ~xr day duly modified to aecsslnt for lane distritiutisas asexplained in paragraph 5.4.2.

= Annual growth rate of commercial vehiclesa = Design life in yearsF = Vehicle damage factor (numher of standard axles ~r commercial vehicle) refer to

paragraph 5.4.3.

14

IRC:8 1-1997

5.4.2. DistributIon of commercial traffic over thecarriageway

A realistic assessment of distributionof commercialtraffic by directionandhy lane is necessary as it directly affectsthetotal equivalent standardaxle load‘applicationsused in the design. It is recommendedthat for the time being thefollowing distribution may be assumedfor design until more reliable data onplacementof commercialvehicleson thecarriagewaylanesareavailable. However,if in a particular situation a betterestimateof thedistributionof traffic betweenthecarriagewaylanesis available from iraffic surveys~~,thesameshouldbeadoptedand the design is basedon the traffic in themostheavilytrafficke.dlane.Thedesignwill normallybe appliedoverthe wholecarriagewaywidth.

(i) Single-laneroads(3.75m width)

Traffic tends to be morechannelisedon singlelaneroadsthan on twolaneroadsand to allow for this concentrationof wheelloadrepetitions,thedesignshouldbebasedon thetotal numberof commercialvehiclesper day in bothdirectionsmultiplied by two.

(ii) Two-lanesinglecarriagewayroads

The design should be basedon 75 percentof thetotal number ofcommercialvehiclesin bothdirections.

(iii) Four-lanesinglecarriagewayroads

The design should be based on 40 percentof the total numberofcommercialvehiclesin bothdirections.

(iv) Dual carriagewayroads

The design of dual two lanecarriagewayroadsshouldbe basedon75 per centof thenumberofcommercialvehiclesin eachdirection.Thedistribution fadershall be reducedby 20 per centfor eachadditionallane.

Ex: For dual three-lane carriageway distribution factor - 60 per cent

The traffic in each direction may be assumed to be half the sum in bothdireclions when the Iatteronlyis known.Wheresignificant difference between the

15

IRC:81-l997

two streamscanoccur,the condition in the moreheavilytrafficked laneshouldbeconsideredfor design. However,if on a particularsituationa betterestimateof thedistribution of traffic betweenthe carriagewaylanes is available from trafficsurveys,thesameshouldbe adoptedandthedesignis basedon thetraffic in the mostheavily traffic lane. The designwill normallybeappliedoverthewholecarriagewaywidth.

5.4.3. VehIcle damagefactor

Thevehicledamagefactor(VDF) is a multiplier for converting thenumberof commercialvehiclesof differentaxleloadsto the numberof standardaxle-loadrepetitions.The vehicledamagefactor is arrived at from axle-load surveysontypical roadsectionsso as to cover various influencingfactorssuchas traffic mix,type of iransportation,type of commoditiescarried,time of the year,terrain,roadconditionanddegreeof enforcement.The AASHO axle load equivalence,factorsmay be usedfor converting the axle load spectrum to an equivalentnumberofstandardaxles.Fordesigninga strengtheninglayeron an existingroadpavement,thevehicledamagefactorshouldbearrived atcarefully by using therelevantavailabledataor carryingoutspecific axle load surveys dependingupon importanceof theproject. Some surveyshave beencarriedout in thecountryon National Highways,State Highways and MDR’s which reveal excessiveoverloadngof commercialvehicles.Thedesignershouldtakethe exactvalue of VDF afterconductingtheaxleloadsurveyparticularly in the caseof majorprojects.Wheresufficient informationon axle load is notavailable,the tentativeindicative valuesof vehicledamagefactorasgiven in Table4 may he used.

Table4. lndlcatl~eVDF Values

Initial traffic intensity intemis ofnumber ofcommercial vehicles per

Terrain

Rolling/Plain Hillyday (Traffic range)

•0-150 1.5 0.5

150.15(X) 3.5 1.5

more than 1500 4.5 2.5

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IRC:81-1997

6. ANALYSiS OF D-ATA FOR OVERLAY DESIGN

~.l. CharacteristicDeflection

6.1.1. Overlay design for a given section is basednoton individualdeflectionvaluesbuton astatisticalanalysisof all the measurementsin the sectioncorrectedfor temperatureand seasonal variations. This involvescalculation of meandeflection, standard deviation and characteristic deflection. The characteristicdeflection for designpurposesshallbe takenasgiven in equations(4) and(5). Theformulaeto beusedin thecalculationareasfollows:

—Mean Deflection, X = — .. (2)

StandardDeviation, _________ ..

Characteristic Deflection, fl -

(1) Dr= ~+2r‘for major arterialroads(like NH & SH)

(ii)Dc= it + afor all otherroads

where X = Individual deflection, men= Mean defiection,mm

n = Number o deflection meaturemenraa = Standard deviation, mm

Dc = Characteristicdeflection, mm

Theseshallbe recordedin theProformasuggestedinTable5.

7. DFSIGN OF OVERLAY

7.1. The design curves relating characteristic pavementdeflection to thecumulative number of standardaxlesto be carriedoverthedesignlife is given inFig.9.

7.2. The characteristicdeflection (Dc) value to beusedfor design purposeswill bethesameasgiven in equations(4) and(5). This will bedeterminedaspertheproceduregiven in Para6.1.

17

IRC

:8l-l9

97

Ta

ble

5

I

21pi

~ii~

,,

I

L~‘II

‘lItIDU18

HItI

a

400

300

I:E

0

>C)

~ 2000LI0

:30cE:3

00

Fig. 9. OverlayThicknessDesignCurves

IRC:8l-1997

Chorocter~stkDeflection. mm

19

IRC:81-1997

7.3. The designtraffic in termsof cumulativestandardnumberof axleswill becomputedasper the proceduredescribedin Para5.

7.4. The thicknessdeduced from Fig.9 is the overlaythicknessin terms ofbituminous macadamconstruction. In caseothercompositionsare to be laid forstrengthening,theequivalentoverlay thicknessto be provided may be determinedusingappropriateequivalencyfactorsas suggestedbelow:

cm of Bituminousmacadam = 1.5 cm of WI3M/Wet Mix Macadarn/BUSG

I cntof Bituminous macadam = 0.7 cm ofDBM/AC/SDC

7.5. From structural considerations,the recommendedminimum bituminousoverlay thickness isSOmm bituminousmacadamwith an additional’surfacingcourseof 50 mm DBM or.40mmbituminousconcrete.

7.6. Wherestructuraldeficiencyis not indicated from deflectionvalues, thinsurfacing may be providedto improvetheriding quality asrequired.

7.7. Thetypeof materialtobeusedin o’~’erlay construction will dependon severalfactorssuchasthe importanceof the road, thedesign traffic, the thicknessandcondition of existingbituminous surfacing, constructionconvenienceandrelativeeconomics. For heavily trafficked roads,it will be desirableto provide bituminousoverlays. The thicknessof wearingcourseshouldbein conformitywith IRC:37.

7.8. Before implementingtheoverlay,theexistingsurfaceshallbecorrectedandbroughtto properprofile by filling the cracks,pot holes, rutsandundulations.Nopart of the overlay design thicknessshall be used for correctingthe surfaceirregularities.

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IRC:81-1997

Annexure-I

STATIC LOAD DEFLECTION TEST PROCEDURE

(C.G.R.A. METHOD)

SCOPE

Thismethodof testcoversaprocedurefor thedeterminationof the rebound

deflectionof pavementunderstatic loadof therearaxle ofa standardtruck.EQUIPMENT

The equipment shall includc~

(1) Benkelman ilearn

(a) Length of probe arm from pivot to probe point 244 cm

(b) Length ofmeasurement arm from pivot to dial 122cm

(c) Distance from pivot to front legs 25 cm

(d) Distance from pivot to rear legs 166cm

(e) Lateral spacing of front support legs 33 cm

(2) A 5 tonne truck is reenmmcndcd as the reaction.The vehicle shall have 8170 kg rear axleload equaUy distributed over the two wheels, equipped with dual tyres. Spacing betweenthe tyre watts shouldbe 30-40 mm. The tyres shall be lOx 20, 12 ply inflated to apressure of 5.60 kg/cm

2. The use of tyres with tubes and rib treads is recommended.

(3) Tyre pressure measuring gauge

(4) Thermometer (0-100°C)with 10 division

(5) A mandral for making 4.5 cm deep hole in the pavement for temperature measurement,The dsameter of the hole at the surface shalt he 1.25 cm and at bottom 1 cm.

Procedure

(I) The point on the pavement to be tested is selected and marked, For highways, the pointshould be located 60cm from the pavement edge if the lane width is less than 3.5 m and9(1 cm from the pavement edge for wider lanes. For dividcd four lane highway, themeasurement points should he 1.5 in from the pavement edge.

21

IRC:81-l997

(2) The dual wheels ofthe truck are centered above the selected point.

(3) The probe of the Benketman be.am is inserted between the duals and placed on theselected point,

(4) The tocking pin is removed from the beam and the legs are adjusted so that the plungerof the beam is in contact with the stem of the dial gauge. i’he beam pivot arms are checkedfor free movement.

(5) The dial gauge is set at approximately I em. The initial reading is recorded when therate of defomsation of the pavement is equal or less than 0.025 nun per minute.

(6~ The truck is slowly driven a distance of270cm and stopped.

(7) An intermediate reading is recorded when the rate of recovery of the pavement isequal to or less than 0.025 mm per minute.

(8) The truck is driven forward a further 9 m.

(9) The final reading is recorded when the rate of recovery of pavement is equal to or lessthan 0.025 mm per minute.

(10) Pavement temperature (see para 4.4.) is recorded atleast once every hour insertingthermometer in the standard hssle and filling up the hole with glycerol.

(II) The tyre pressure is checked at two or three hour intervals during the day and adjusted tothe standard, if necessary.

CALCULATIONS

(I) Subtract the final dial reading frsmns the initial dial reading. Also subtract theintermediate reading from the initial reading.

(2) If the differential readings obtained compare within 0.025 mm the actual pavementdeflection is twice the final differensial reading.

(3) If the differential readings obtained do not compare to 0.025 mm, twice the finaldifferential dial reading represents apparent pavement denectiun.

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IRC:81-1997

(4) Apparent deflections are corrected by means of the following fonnula

XT=XA-+-2.9l Y

in which Xi = ‘l’nse pavensent deflection

XA = Apparent pavement deflection

= Vertical mssvement of the front legs i.e. twice the difference between

the final and intermediate dial readings.

(5) The rebound deflection (%) (i.e. en!. 9 of Table 3) shall be the tssice of the Xi value,