IRC 78-2000

STANDARD SPECIFICATIONSAND

CODE OF PRACTICEFOR

ROAD BRIDGES

SECTION :VU

F(ftNDAT[ONS ‘NI) S(BSTRL( ~

(S~eundRevisim)

THE INDIAN ROADS CONGRESS2000

IRC : 78-2000

STANDARD SPECIFICATIONSAND

CODE OF PRACTICEFOR

ROAD BRIDGES

SECTION : VII

FOUNDATIONS AND SUBSTRUCTURE

(SecondRevision)

PublishedbyTHE INDIAN ROADS CONGRESSJamnagarRouse,ShabjahanRoad,

New Dethi-ilOOlI2000

Price Rs.200/-(Plus packing& postage)

IRC: 78-2000

First Published

First Revision

ReprintedReprintedReprintedReprinted

SecondRevision

July 1980 (as Part I)

December,1983 (IncorporatingPartH andamendmentsI, 2 and3 to Part I)

September,1988

October, 1994September,1998September,2000

December,2000

(Rights of Publication and ofTranslationare Reserved)

Printed at Dee Kay Printers,New Delhi-I 10015(1000Copies)

CONTENTS

SECTION VII

Foundations and SubstructureClauseNo, Page

Personnelof Bridges Specifications (i) toand StandardsCommittee (iii)

Background 1

700 Scope 2701 Terminology 2

70L1. Abutment 2701.2. Afflux 3701.3. Balancer ‘ 3701.4. Bearing Capacity 3701,5. Bearing Stress 4701.6. Cofferdam 4701.7. Foundation 5701.8. Pier 5701.9. Piles 5701.10. RetainingWall 6701.11. Substructure 7701.12. Well Foundation 7

702 Notations 7703 DischargeandDepthof Scourfor 9

FoundationDesign

703,1. Design Dischargeof Foundation 9703.2. Mean Depthof Scour 10703.3. Maximum Depthof Scour for Design 11

of Foundation

704 Sub-surfaceExploration 13

704.1. Objectives 13

IRC 78-2000

704.2. Zoneof Influence 147043. Methods of Exploration 14

705 Depth of Foundation 15

705.1. General 15705.2. Open Foundations 15705.3. Well Foundations 16705.4. Pile Foundations 17

706 Loads,Forces,Stability and Stresses 17

706.1. Loads,Forcesand their Combinations 17706.2. Horizontal Forcesat Bearing Level 18706.3. Base Pressure 20

707 Open Foundations 22

707.1. General 22707.2. Design 22707.3. Open Foundationsat SlopedBed Profile 25707.4. Construction 25

708 Well Foundations 27

708.1. General 27708.2. Well Steining 28708.3. Design Considerations 30708.4. Stability of Well Foundations 32708.5. Tilts and Shifts 33708.6. ~Cutting Edge 34708.7. Well Curb 34708.8. Bottom Plug 35708.9. Filling the Well 36708.10. Plug over Filling 36708.11. Well Cap 37708.12. Floating Caissons 37708.13. Sinking of Wells 37708.14. PneumaticSinking of Wells 38708.15. Sinking of Wells by Resortingto Blasting 38

IRC: 78-2000

709 Pile Foundation 38

709.1. General 38709.2. Requirementand Stepsfor 41

Design and Installation709.3. Capacityof Pile 42709.4. StructuralDesign of Piles 47709.5. Designof Pile Cap 48709.6. Important Consideration,Inspection! 49

Precautionsfor DifferentTypes of Piles

710 Substructure 51

710.1. General 51710.2. Piers 52710.3. Wall Piers 54710.4. Abutments 55710.5. Abutment Pier 56710.6. Dirt Walls, Wing Walls andReturn Walls 56710.7. RetainingWalls 58710.8. Pier and Abutment Caps 59710.9. CantileverPier and Abutment Cap 60710.10. Pedestalsbelow Bearing 61

Appendices

1. Guidelinesfor Calculating Silt Factor for Bed Material 63Consistingof Gavelsand Boulders

2. Guidelinesfor Sub-surfaceExploration 643. Procedurefor Stability Calculation 794. Precautionsto be taken during Sinking of Wells 845. Capacityof Pile Basedon Pile Soil Interaction 916. Filling Behind Abutments,Wing and Return Walls 95

IRC: 78-2000

PERSONNEL OF THE BRIDGES SPECIFICATIONSAND STANDARDS COMMITTEE

(As on 19.8.2000)

I. Prafulla Kumar*(Convenor)

2. N.K. Sinha(Co-Convenor)

3. TheChiefEngineer(E3)S&R (Member-Secretary)

4. K.N.Agarwal

5, CR. Ahmchandani

6. [).S. Batra

7. S.S. Chakraborty

8. CV. Kand

9. D.K. Kanhere

10. KrishanKant

Ninan Koshi

l2. Dr. R. Kapoor

l3. Vijay Kumar

4. NV. Merani

15. M.K. Mukherjec

16. AD. Narain

17. M.V,B.Rao

DG(RD) & Addi. Secretary. Ministry of Road Transport &Highways,TransportBhawan, NewDelhi-1l000l

Member(Technical),National Highways Authority of India.1, EasternAvenue,Maharani Bagh, New Delhi-I 10065

(V. Velayutham), Ministry of RoadTransport & Highways.Transport Bhawan, New Delhi-I 1000!

MEMBERS

ChiefEngineer,PWDZoneIV, PWD, MSO Building, I.P. Estate,New Delhi-i 10002

Chairman & Managing Director, STUP Consultants Ltd.,1004-5, Raheja Chambers. 2l3, NarimanPoint.Mumhai-40002I

Consulting Engineer, Sir Owen WilliamsInnovestrnentLid..lnnovestmentHouse, 1072, Sector-37,Noida-201303

Managing Director, Consulting Engg. Services(I) Ltd.. 57.Nehru Place, New Delhi-I10019

Consultant, E-2/l36, Mahavir Nagar,Bhopal.462016

Chief Engineer,Block No. A-8, Building No. 12, Haji AllOlficers’ Qtrs., Mahalaxmi,Mumbai-400034

ChiefGeneralManager.National Highways Authorityof India,I, Eastern Avenue, Maharani Bagh, New Delhi-I10065DG(RD)& Addl. Secy., MOST(ReId.).56, NalandaApartments.

Vikaspuri, NewDelhi-I 10018

Director, UnitechIndia Ltd., Gurgaon

Managing Director,UP State BridgeCorporationLtd., SetuBhavan,16. Madan Mohan MalviyaMarg, Lucknow-226001

PrincipalSecy.,MaharashtraPWD(Retd.),A-47/1344,AdarshNagar,Worli, Mumbai-400025

40/182,CR. Park, New Delhi-I 10019

DO (RD) & AddI. Secy., MOST (Retd.), B-186, Sector26,NOIDA-201301

Head, Bridge Division, Central Road Research Institute,P.O.CRRI, New Delhi-I 10020

*ADG(B) being not in position. The meeting was presided byShri PrafullaKumar, [)(i(RD) andAddI. Secretary to theGovt. of India, M/o. RT&H.

(i)

IRC 78-20008. Dr. TN. Subba Rao

19. D. Sreerama Murthy

20. A. Ramakrishna

21. S.A.Reddi

22. RamaniSarmah

2.3. N.C,Saxena

24. G. Sharan

25. S.R.Tambe

26. Dr. MG. Tamhankar

27 Mahesh Tandon

28. PB. Vijay

29. The Chief Engineer (NH)

30. The Principal Secy, tothe Govt. of Gujarat

3]. The Chief Engineer (NH)

32. The Chief Engineer (NH)

33. The Chief Engineer (NH)

34. The Chief Engineer (R)’S&R T&T

35. The Engineer-in-Chief

36. The Director

37. The Dy. L~irectorGeneral

Chainnan, Construma Consultancy (P) Ltd., 2nd Floor, PinkyPlaza, Mumbai-400052

Chief Engineer (Retd.), H.No,8-3- 1158, Gulrnarg Enclave, FlatNo. 203, Snnagar Colony, Hyderabad

President (Operations) & Dy. Managing Director, Larsen &Toubro Ltd., ECC Constn. Group, Mount Ponnarnallee Road,Mannapakkam,P.O. Box No. 979, Chennai-600089

Dy. Managing Director, Gammon India Ltd., Gammon House,Prabhadevi, Mumbai-400025

Secretary to the Govt. ofMeghalaya, Public Works Department,Lower Lachumiere, Shillong-793001

Executive Director, Intercontinental Consultants & TechnocratsPvt. Ltd., A-Il, Green Park, New Delhi-I 10016

Chief Engineer, Ministry of Road Transport & Highways,Transport Hhavan, New Delhi-I 10001

Secretary, Maharashtra PWD (Retd.), 72, Pranit J. Palkar Marg,Opp. Podar Hospital, Worli, Mumbai-400025

Emeritus Scientist, Structural Engg. Res. Centre, 399, Pocket E,Mayur Vihar Phase ii, Delhi-I 10091

Managing Director, Tandon Consultants (P) Ltd., 17, Link Road,Jangpura, Extn,, New Delhi

DG (Works), CPWD (Retd.), A-391B, DDA Flats, Munirka,New Delhi-i 10062

(N.K. Jam),M.P. Public Works Department, ‘I)’ Wing, Isi Floor,Satpura Bhavan, Bhopai-462004

(H.P. Jamdar), R&B Department, Block No. 14, 2nd Floor,New Sachivalaya, Gandhinagar-3820l0

(L.K.K. Roy), Public Works (Roads) Deptt., Writers’ Building,Block ‘G’, 4th Floor, Calcutta-700001

(KG. Srivastava), UP. Public Works Department, Lucknow-226001

Punjab P.W.D., B&R Branch, Patiala-14700l

(CC. Bhattacharya), Ministry of Road Transport & Highways,Transport Bhavan, New Delhi-I 10001

KR. Circle, Bangalore-560001

(V. Elango), Highways Research Station, PB. No. 2371, 76,Sardar Patel Road, Chennai-600025

(BK. Basu, VSM, SC), Chief Engineer, Dy. Director General(Bridges), Directorate Director General Border Roads, SeemsSadak Bhavan, Naraina, Delhi Canit., New Delhi-l 10010

(ii)

IRC : 78-200038. The Director & Head

~Civil Engg.)

39. The Executive DirectorRDSO

40. The Addl. DirectorCPWD

41. PresidentIndian Roads Congress

42. DG(RD)

43. Secretary,Indian Roads Congress

44. M.K. Agarwal

45. Dr.V.K.Raina

46. Shitala Sharan

47. S.P, Khedkar

48. The Technical Director

Bureau of Indian Standards, Manak Bhavan, 9,Bahadurshah Zafar Marg, New Delhi-i 10002

(AK. Haiit). Executive Director (Bridges & Structure) Research,Design & Standards Organisation, Lucknow-22600I

(Krishan Kumar), AddI. Director General, CPWD, CentralDesign Orgn., Nirman Bhavan, New Delhi-I 10011

Ex-Officio Members

M.V. PatilSecretary (Roads), Maharashtra P.W.D.Mantralaya, Mumbai-400032

Praflilla Kumar, DO. (RD)& Addl. Seey., Ministry of RoadTransport & Highways, Transport Bhawan, New Delhi-I 10001

0. Sharan, Chief Engineer, Ministry ofRoad Transport& Highways, Transport Bhawan, New Delhi-Il 0001

CorrespondingMembers

Engineer-in-Chief (Retd.), H.No. 40, Sector 16,Panchkula-I 34113

B-I3, Sector-I4, Noida-20I301

Chief Consultant, Consulting Engg. Services (I) Ltd.,57, Nehru Place, New Delhi-I 10019

Hindustan Constn. Co. Ltd., Hincon House, Lal Bahadur ShastriMarg, Vikhroli (W), Mumbai-’400083

(U. Guha Viswas), Simplex Concrete Piles (I) Pvt. Ltd.,Vaikunt, 2nd Floor, 82, Nehru Place, New Delhi-I 10019

(iii)

IRC: 78-2000

S.A. ReddiC.E. (NH), Bhubaneswar(S.K.B. Narayan)S.G. Joglekar

Prof. K.G. RangaRajuD.K, KanhereDr. S.R. KulkarniProf. Gopal RanjanA. SampathkumarRep.of MOST (AK. Banerjee)Rep. of RDSO (K,C. Verma)Rep. of CentralWater & Power

Res. Station(Dr. B.V. Nayak)Ex.-officio Members

DG(RD) & AddL. Secy.,MOST(Prafulla Kuinar)

Secretary,IR.C(S.C. Sharma)

FOUNDATIONS AND SUBSTRUCTURE

BACKGROUND

The “StandardSpecificationsand Code of PracticeforRoadBridges” Section : VII~Foundationsand Substructurewasfirst published in July 1980 as Part I - GeneralFeaturesofDesign. Later first revision was publishedin December 1983incorporatingPartH and amendments1, 2 and 3 to Part I asaUnified Code.The secondrevisionof this codewasundertakenby the Foundationand SubstructureCommittee(B-4) and theinitial draftwasfinalisedbytheCommitteeundertheConvenorshipof Shri R.H. Sarma.Subsequently,the draft was reconsideredanddiscussedin variousmeetingsby thereconstitutedFoundation,Substructureand ProtectiveWorks Committee(B-4) (personnelgiven below)andthedraft was finalisedduring its meetingheldon 1st Februaiy, 1999:

C’onvenor

Co-ConvenorMeniber-Secretaty

MembersP.L. BongirwarA. ChakrabartiC.V. KandVijay KumarA. MukherjeeDr. G.P. SahaShitala SharanG. SharanN. Venkataraman

The President,IRC(KB. Rajoria)

1

IRC : 78-2000

Corresponding Members

MaheshTandon V.R. Jayadas

The draft asfinalisedby (B-4) Committee wasdiscussedbythe Bridges Specifications& Standards(BSS)Committeein itsmeeting heldon 7.12.99and it was decided tomodify the draft bythe Convenorof (B-4) Committeein light of comments offeredduring the meeting. The modified draft was againdiscussedbyBSS Committee in its meeting heldon 19.8.2000 and wasapproved subject to certainmodifications and authoriseditsConvenor to approve the document afterincorporating themodifications, The final draft as approved by Convenor,BSSCommitteewassubsequentlyapprovedby theExecutive Committeein its meeting held on30.8.2000.It was later approved by theCouncil in its 160th meeting held atCalcuttaon 4.11.2000forpublishing the revisedIRC Bridge CodeSectionVII : IRC:78.

700. SCOPE

This code deals with the design and constructionoffoundationsand substructurefor road bridges.The provisionsofthis codeare meant toserve as a guide to both the designandconstructionengineers, but merecompliancewith the provisionsstipulated herein will not relievethem in any way of theirresponsibility for the stability andsoundnessof the structuredesignedarid erected.

701. TERMINOLOGY

The following definitions shall be applicable for thepurposeof this code.

701.1. Abutment

The end supportsof the deck (superstructure)of a bridge,whichalso retains earth,fill ofapproachesbehindfully or partly.

2

JRC: 78-2000

701.1.1. Box type abutment and return waIl : Whenthe returnwalls on two sidesare integratedwith abutmentanda backwall parallelto abutmentis providedat the endof returnswith or without additional internal wall along or across length,this structureis calledbox type abutmentandreturnwaIl, orendblock,

701.1.2. Non-load bearingabutment: Abutment,whichsupportsthe end spanof less than 5 m.

701.1.3. Non-spill through abutment : An abutmentstructurewherethe soil is not allowed to spill through.

701.1.4. Spill through abutment: An abutmentwheresoil is allowed to spill through gaps along the length ofabutment,suchas,column structurewherecolumnsareplacedbelow deck beamsand gap in betweenis free to spill earth.(Spilling of earth should not be permittedabove a level of500 mm below the bottom of bearings).

701.2. Afflux

Therise in the flood level of the river immediatelyon theupstreamof a bridgeas a resultof obstructionto natural flowcausedby the constructionof the bridge and its approaches.

701.3. Balancer

A bridge/culvertlike structureprovidedon embankmenttoallow flow of water from one side of the embankmenttootherside,for purposeof avoiding headingup of water on oneside or for avoiding blocking the entry to the other side.

701.4. Bearing Capacity

The supportingpowerof a soil/rock expressedas bearingstressis referredto as its bearingcapacity.

3

JRC: 78-2000

701.4.1. Allowable bearing pressure: It is themaximum

grosspressureintensity at which neither the soil fails in shear,(after accountingfor appropriatefactor of safety) nor thereisexcessivesettlementbeyondpermissiblelimits, which is expectedto be detrimentalto the structure.

70 1.4.2. Net safe bearing capacity : It is the netultimate bearingcapacitydivided by a factorof safety as perClause706.3.1.1.1.

701.4.3. Net ultimate bearing capacity : It is theminimum netpressureintensitycausingshearfailure of the soil.

701.4.4. Safebearing capacity:Themaximumpressure,which the soil cancarrysafelywithout risk of shearfailure andit is equal to the net safe bearing capacity plus originaloverburdenpressure.

701.4.5. Ultimate bearingcapacity: It is theminimumgrosspressureintensity at the baseof the foundationat whichthe soil fails in shear.

701.5. Bearing Stress

701.5.1. Gross pressure intensity : It is the totalpressureat thebaseof thefoundationon soil dueto thepossiblecombinationsof load and the weight of the earthfill.

70 1.5.2. Net pressureintensity : It is the differenceinintensitiesof the gross pressureand the original overburdenpressure.

701.6. Cofferdam

A structuretemporarybuilt for the purposeof excludingwater or soil sufficiently to permit construction or proceedwithout excessivepumping and to support the surroundingground.

4

IRC: 78-2000

701.7. Foundation

The partof a bridgein direct contact with and transmittingload to thefounding strata.

701.8. Pier

Intermediatesupportsof the deck (superstructure)of abridge.

70 1.8.1. Abutmentpier: Generallyusedin archbridges.Abutment pieris designed for a conditionthat evenif one sidearch span collapses itwould be safe.These areprovided afterthreeor five spans.

701.9. Piles

701.9.1. Bearing/friction piles : A pile driven or cast-in-situ for transmitting the weightof a structure to the foundingstrata by the resistancedevelopedat thepile base and by frictionalongits surface.If it supports the load mainly by the resistancedevelopedat its base, itis referredto asan end-bearingpile, andif mainly by friction along its surface,as a frictionpile.

70 1.9.2. Bored cast-in-placepile : A pile formed withor without a casing by boring a hole in theground andsubsequently filling it with plain orreinforced concrete.

701.9.3. Driven cast-in-placepile : A pile formed inthe ground by drivinga permanent or temporary casing,andfilling it with plain or reinforced concrete.

701.9.4. Driven pile: A pile driven in to the ground bythe blowsof a hammerby a vibrator.

701.9.5. Precast pile : A reinforced or prestressedconcrete pile cast before driving,or installing in bore andgrouted.

5

mc: 78-2000

701.9.6. Raker or batter pile : A pile installed at aninclination to the vertical.

701.9.7. Sheetpile : One or a row of piles driven orformed in the groundadjacentto one anotherin a continuouswall, eachgenerallyprovided with a connectingjoint or inter-lock, designedto resist mainly lateral forces and to reduceseepage;it may be vertical or at an inclination.

701.9.8. TensIonpile: A pile subjectedto tension/upliftis called tensionpile.

701.9.9. Testpile : A pile to which a loadis appliedtodetermineand/orconfirm theloadcharacteristics(ultimateload!working load) of the pile and the surroundingground.

701.9.10. Working pile : One of the piles forming thefoundationof the structure.

701.10. RetainingWall

A wall designedto resist the pressureof earth fillingbehind.

701.10.1. Return wall : A wall adjacentto abutmentgenerallyparallel to road or flared up to increasewidth andraisedupto the top of road.

701.10.2. Toe wail : A wall built at the end of the slopeof earthenembankmentto prevent slipping of earth and/orpitching on embankment.

701.10.3. Wing wail : A wall adjacentto abutmentwithits topupto roadtop level nearabutmentand slopingdown uptogroundlevel or a little aboveat the otherend. This is generallyat 45°to the alignment of road or parallel to the river andfollows profile of eatthenbanks.

6

IRC: 78-2000

701.11. Substructure

The bridge structure,suchas,pier andabutmentabove thefoundation andsupporting the superstructure. It shall includereturns and wing wallsbut exclude bearings.

701.12. Well Foundation

A type of foundationwhere a part of the structure ishollow, which is generally built in parts and sunk throughground or water to the prescribeddepth by removing earththrough dredgehole.

701.12.1. Tilt of a well: The inclinationoftheaxisofthewell from the vertical expressed as the tangentof the anglebetween theaxis of the well and the vertical.

701.12.2. ShIft of a well : The horizontaldisplacementofthe centreof the well at its basein its final positionfrom itsdesigned position.

702. NOTATIONS

For the purposeof this code,the following notations havebeenadopted:

A1 Dispersedconcentric areaA2 LoadedareaB Width between outer facesof pile group in planparallelto the

directionof movementC The allowable bearing pressure withnearuniform distribution

on the founding stratac CohesionCo The permissible directcompressivestress inconcreteat the

bearing areaof the baseD Diameterof pileDb Discharge in cubicmetre/sec(cumecs)permetre widthd Externaldiameterof circular well in metre

7

IRC: 78-2000dd

1~:F

cf

F,,F

epFeqF

er

F.F,F

Fwp

GGb

hKKpKS

1

L

Weightedmeandiameterin mm of bed materialMean depth of scour in metrebelow flood levelLongitudinal force due to brakingCentrifugal forceDeformationeffectsHorizontal forceEarthpressureSeismicforceErectioneffectsFrictional force at bearingsImpactdue to floating bodiesSecondaryeffectsTemperatureeffects [SeeNote (i)]Water currentWavepressure[SeeNote (ii)]Dead loadBuoyancySnow loadMinimum thicknessof steining in metreCo-efficient of active earthpressureCo-efficient ofpassiveearthpressureSilt factorLength betweenouterfacesof pile group in plan parallel to thedirectionof movement

1,,, Movementof deck overbearings,other than due to appliedforce

I Depth of well in metrebelow top of well capN Standardpenetrationtest value

Total active pressureTotal passivepressure

Q Live loadRg Dead load reaction

Live load reactionI”,. Shearrating of elastomericbearingW Wind load~z Horizontal seismic coefficientfi Changethe ratio of long side to the short sideof the footingp Co-efficient of friction0 Angle of internal friction

g

IRC : 78-2000ö SettlementofpileSg Settlementof pile group

Notes: (i) Temperatureeffects (Fe) in this context is not the frictionalforce dueto themovementof bearingbut that which is causedby rib shortening,etc.

(ii) The wave forces shall be determinedby siutable analysisconsideringdrawing andinertia lbrces,etc.,on single structuralmembersbasedon rationalmethodsor modelstudies.In caseof group of piles, piers, etc., proximity effects shallalso beconsidered.

703. DISCHARGE AND DEPTH OF SCOUR FORFOUNDATION DESIGN

703.1. DesIgnDischarge of Foundation

703.1.1. To provide foranadequatemarginofsafety, thescour for foundationshall be designedfor a largerdischargeover the design dischargedeterminedas per IRC:5 as givenbelow:

Catchmentareain k& Increasedischarge

over designin per cent

0- 3000 303000-10000 30 -2010000-40000Above40000

20 -1010

Notes: (i) For intermediatevaluesof catchmentarea, linear interpolationmay be adopted.

(ii) The minimum vertical clearance above the NFL alreadydeterminedas per IRC:5 neednot be increaseddue to largerdischargecalculatedabove.

9

IRC: 78-2000

703.2. Mean Depth of Scour

Themeanscourdepthbelowhighestflood level (HFL) fornatural channelsflowing over scourablebed canbe calculatedtheoreticallyfrom the following equation

where = The design dischargefor foundationper metre with ateffectivelinear waterway.

KS1 Silt factor for a representativesampleof bed materialobtainedupto the level of anticipateddeepestscour.

703.2.1. Thevalueof Db maybedeterminedby dividingthe designdischargefor foundationby lower of theoreticalandactual effective linearwaterwayasgiven in IRC:5.

703.2.2. ‘K5~’is given by the expression1.76(dj~,d~being the weightedmeandiameterin millimetre.

703.2.2.1. Thevalueof for variousgradesofsandybedaregiven below for readyreferenceand adoption:

Type of bed material d,,, K1

Coarsesilt 0.04 0.35Silt/fine sand 0,081 to 0.158 0.5 to 0.6Medium sand 0.233 to 0.505 0.8 to 1.25Coarsesand 0.725 1.5Fine bajri andsand 0.988 1.75Heavy sand 1.29 to 2.00 2.0 to 2.42

703.2.2.2. No rational formula or data for determiningscourdepthfor bed material consistingof gravelsand boulders(normally having weighteddiametermore than 2.00 mm) andclayey bed is available.In absenceof anydataon scourfor such

10

IRC: 78-2000

material, themeanscourdepthmay be calculated following theguidelines givenin Appendix-i.

703.2.3. If there is .~nypredominantconcentrationofflow in any part of waterway due to bendof the streaminimmediate upstreamordownstreamorfor anyother reason,like,wide variation of type of bed material across the widthofchannel,then meanscourdepth may be calculateddi’~ridingthewaterway into compartments as per the concentrationof flow.

703.2.4. In caseof bridgemainly adoptedas balancer,the mean scour depth‘d~’may be taken as (HighestFloodLevel-Lowest Bed Level) divided by1.27.

703.2.5. Scour depth may bedetermined by actualobservationswhereverpossible.This is particularly requiredforclayey and boundary strata.Soundings,wherever possible, shallbe takenin the vicinity ofthe siteoftheproposedbridge andforany structuresnearby. Such soundings are best duringorimmediatelyafter a flood before thescourholes have had timeto be siltedup. The mean scour depth may be fixed basedonsuch observations and theoreticalcalculation.

703.3. MaxImum Depth of Scour for Design ofFoundation

703.3.1. The maximum depthofscour below theHighestFloodLevel (HFL) for the designofpiersandabutmentshavingindividual foundations withoutany floor protection maybeconsideredasfollows.

703.3.1.1. Flood without seismic combination:

(i) For piers - 2.0 d

(ii) For abutments - (a) 1.27 d,m with approachretained orlowestbedlevel whicheveris deeper.

(b) 2.00d,a, with scourall around.

11

IRC: 78-2000

703.3.1.2. Flood with seismic combination Forconsidering load combination of flood and seismic loads(togetherwith otherappropriatecombinationsgiven elsewhere)the maximumdepthof scourgiven in Clause703.3.1.1may bereducedby multiplying factorof 0.9.

703.3.1.3. For low waterlevel (without flood conditions)combinedwith seismic combination maximum level of scourbelowhigh flood level canbeassumedas0.8 timesscourgivenin Clause703.3.1.

Note: In respectof viaducts~ROBshaving no possibility of scour,passiveresistanceof soil may be consideredbelow a depth of “excavation+Zm”,

703.3.2. For thedesignoffloor protectionworks for raftor open foundations,the following values of maximum scourdepthmay be adopted:

(i) In a straight reach 1.27 d~m

(ii) In a bend 1.50 d~or on the basisofconcentrationof flow.

The length of apron in upstreammaybe0.7 times of thesamein downstream.

703.4. Special studies should be undertaken fordetermining the maximum scour depth for the design offoundationsin all situationswhereabnormalconditions,suchas,the following are encountered

(i) a bridgebeing locatedin a bendof the river involving a curvi-linear flow, orexcessiveshoal formation,or

(ii) a bridge being locatedat a site wherethe deepchannel in theriver hugsto one side,or

(iii) a bridgehavingvery thickpiersinducing heavylocal scours,or

12

IRC : 78-2000

(iv) where the obliquityof flow in the river is considerable, or

(v) where a bridge is required to beconstructedacrossa canal,oracross a riverdownstreamof storageworks,with thepossibilityof the relativelyclear water inducinggreaterscours, or

(vi) a bridge in the vicinity of a dam, weir, barrage or otherirrigation structureswhere concentrationof flow, aggradationldegradationof bed,etc. arelikely to affect the behaviourof thestructures.

(vii) an additional two-Lanebridge whenlocatednearto theexistingbridge, on majorrivers.

Note: Thesestudies shall be conducted for theincreaseddischargecalculatedvide Clause703.1.1.

703.5. If ariver is of a flashy natureandbeddoesnotlenditself readily to the scouring effectof floods, the theoreticalformula for d~and maximum depthof scour asrecommendedshall not apply. in such cases,the maximum depth shall beassessed fromactual observations.

704. SUB-SURFACEEXPLORATION

704.1. Objectives

The objectivesof the sub-surfaceexploration are

(i) During PreliminaryInvestigationStage

As a part of site selectionprocessto study existinggeologicalmapsandother information, previouslypreparedandavailablesite investigationreports,known data of nearbystructures,ifany,surfaceexaminationaboutriver bed andbanks, etc.,whichwill help in narrowing down of sites under considerationforfurther studies for project preparationstage.

(ii) Detailed InvestigationStage

To determinethe characteristicsof the existinggeo-materials,like, soil, rock, bedmaterial in watercourses,etc. in the zone

13

ERC : 78-2000

of influenceof the proposedbridge sites in sucha way as toestablishthedesignparameterswhich influencethechoiceanddesigndetails of the variousstructuralelements,especiallythefoundationtype.

(iii) During ConstructionStage

To confirm the characteristicsof geo-materialsestablishedinstage (ii) basedon which the design choicesare madeand tore-confirm the sameor modify to suit the conditionsmet atspecific foundation locations.

704.2. Zone of Influence

Zoneof influencementionedin 704.1(u)is definedasthefull length of thebridgeincludingportionofwing/returnwall andpartofapproachescovering,(but not restrictedto), the full floodzone for water courses, and upto depth below proposedfoundationlevelswhereinfluenceof stressesdue to foundationis likely to affect the behaviourof the structure, includingsettlement,subsidenceunder ground flow of water, etc. Thewidth of the land strip on either side of the proposedstructureshould include zones in which the hydraulic characteristicsofriver water are likely to be changedaffecting flow patterns,scour, etc.

704.3. Methods of Exploration

A large variety of investigativemethodsare available. A

most suitable and appropriatecombination of these shall bechosen.Guidelinesfor choiceof typesofinvestigations,propertiesof geo-materialsthat needbe established,the in-situ testing,sampling,laboratorytestingaregiven in Appendix-2. This maybe furthersupplementedby specialisedtechniquesdependingonthe need.

14

IRC: 78-2000

705. DEPTH OF FOUNDATION

705.1. General

The foundationshall be designedto withstandthe worstcombinationof loadsand forcesevaluatedin accordancewiththeprovisionsof Clause706. The foundationshall be takentosuchdepththat they aresafeagainstscouror protectedfrom it.Apart from this, the depth should also be sufficient fromconsideration of bearing capacity, settlement, liquefactionpotential,stability and suitability of strataat the founding leveland sufficientdepthbelow it. In caseofbridgeswherethemeanscourdepth ‘d,m’ is calculatedwith Clause703.2, the depth offoundationshall not be less thanthoseof existing structuresinthevicinity.

705.2. Open Foundations

705.2.1. In soil : The embedmentof foundationsin soilshall be based on correct assessmentof anticipated scourconsideringthe valuesgiven under Clause703.

Foundationmaybetakendownto acomparativelyshallowdepthbelow the bed surfaceprovided good bearingstratum isavailable,and the foundationis protectedagainstscour.

The minimum depth of open foundationsshall be uptostratum having safe bearing capacitybut not less than 2.0 mbelow the scour level or the protectedbed level.

705.2.2. In rocks : For open foundations resting onrock, the depthof rock, which in the opinionof the geologicalexpertis weatheredorfissured,shallbeexcludedin decidingthedepth of embedmentinto the rock existing below. Wherefoundations are to rest on erodible rocks, caution shall beexercisedto establishthe foundationlevel at sufficientdepth,so

15

IRC : 78-2000

asto ensurethat theydo not getundermined,keepingin view thecontinued erosion of the bed. After allowing for conditionsstipulatedabove the minimum embedmentof the foundationsinto therock belowshallbeasfollows, which in caseof slopingrock profile can be provided by properly benching thefoundations.

(a) For hard rocks, with an ultimate crushing strengthof 1.0 MPa or abovearrived at after consideringthe overall characteristicsof the rock, such as,fissures,beddingplanes,etc. : 0.6 m

(b) All othercases : 1.5 m

705.3. WeD Foundations

705.3.1. in soil : Well foundationsshallbe takendownto a depth which will provide a minimum grip of 1/3rd themaximumdepth of scourbelow thedesignscourlevel specifiedin Clause703.3.

705.3.2. In rocks As far aspossible,the wells shallbetakenby all themethodsof sinkingincluding pneumaticsinking(where considerednecessary),dewatering,etc. to foundationlevel and shall be evenly seatedall aroundthe periphery onsound rock (i.e., devoid of fissures,cavities, weatheredzone,likely extentof erosion,etc.)by providing adequateembedment.The extent of seatingand embedmentin each caseshall bedecidedby the Engineer-in-chargekeepingin view the factorsmentionedaboveto ensureoverall and long-term safetyof thestructure.It is advisableto makea sump(shearkey) of 300 mmin hard rock. or 600 mm in soft rock inside the well bychiselling/blasting.Diameterof sump may be 1.5 to 2 m lessthan innerdredge-holesubjectto a minimum sizeof 1.5 m. Sixdowel barsof25 mm dia deformedbarsmaybe anchored1.5 min rock andprojected 1.5 m above.Thesemay be anchoredin

16

IRC: 78-2000

minimum 65 mm dia boreholesand grouted with 1:1 ~/&cementmortar. The seatingof well shall be such that 75 per centperimeteris seated onrock.

705.4. Pile Foundations

705.4.1. In soil, the minimum depth of foundationsbelow thepointof fixity should be the minimumlengthrequiredfor developing fullfixity as calculated by any rational formula.

705.4.2. In rocks, the pile should betakendown to rockstratadevoid of any likely extensionof erosion andproperlysocketedasrequiredby the design.

706. LOADS, FORCES, STABILITY AND STRESSES

706,1. Loads, Forcesand their Combinations

706.1.1. The loads and forces maybe evaluatedasperIRC:6 and theircombinationsfor the purposeof this code willbe asfollows:

Combination(i): G + (Q or Gs) + F + F±Fb+Gh+Ff+F

Combination(ii): (I) + W + F

or

(1) + F + F

or

(O+F. +F~‘ “p

Combination (iii): G+F +G +F +F +F + W or Fb ‘p ~ f

706.1.2. The permissible increase in stressesin thevariousmemberswill be 331/3per centfor the combinationofwind (~9and50 percentfor the combination withseismic(F~)or impact (Firn) The permissibleincrease in allowable base

17

IRC: 78-2000

pressureshouldbe 25 per cent for all combinationsexcept(i).However,whentemperatureeffects~), secondaryeffects(Ft),deformation effects (Fd) are also to be consideredfor anymembersin combinationwith (1) thenpermissibleincreaseinstressesin variousmembersand allowablebearingpressurewillbe 15 per cent.

706.2. Horizontal Forcesat BearingLevel

706.2.1. Simply supported spans

706.2.1.1. For simply supportedspanwith fixed and freebearings(otherthanelastomerictype)on stiff supports,horizontalforces at the bearinglevel in the longitudinal directionshall beas given below

Fixed Bearing Free Bearing

Non-SeismicCombinationsGreaterof the two valuesgiven below:

(i) F~~~U(Rg+Rq)

(ii) Fh/2+I~(Rg+Rq) /A(Rg+Rq)

Seismic Combinations

Fh

whereFh Applied horizontalforce.

R = Reactionat the free enddue to deadloadR Reactionat the free end due to live load

p Co-efficient of friction at the movablebearingwhich shallbe assumedto have the allowablevalues:

(i) For steel roller bearings : 0.03(ii) For concreteroller bearings : 0.05(iii) For sliding bearings

(a) Steel on cast iron or steel on steel : 0.4(b) Greycast iron on grey cast iron

(Mechanites) : 0.3

18

IRC: 78-2000

(c) Concreteoverconcrete : 0.5(d) Teflon on stainlesssteel : 0.03 and

0.05(whichever

is governing)

706.2.1.2. In caseof simply supportedsmall spans upto10metresand whereno bearings are provided, horizontal forceinthe longitudinal direction at the bearinglevel shall be

For jiR~whichever is greater

706.2.1.3.For a simply supported spansitting on identicalelastomeric bearings at eachend and resting on unyieldingsupports.

Force at eachend = —~- + V i,,

= Shearrating of the elastomericbearings1, = Movementof deck above bearing, other than due to

appliedforces

706.2.2. Simply supportedand continuous span onflexible supports

706.2.2.1.The distribution of applied longitudinalhorizontal force (e.g., braking, seismic, wind, etc.) dependssolely on shear ratingof the supportsand may be estimatedinproportionto theratioof individual shearrating of a support tothesum of the shear ratingsof all the supports. Shearratingofa support is the horizontal forcerequiredto movethetop of thesupport through aunit distancetaking into account horizontaldeformationofthe bridge, flexingof the supportand rotationofthe foundation.

19

1RC: 78-2000

706.3. Base Pressure

706.3.1. The allowable bearing pressure and thesettlementcharacteristicsunder differentloadsandstressesmay

be determinedon the basis of sub-soil explorationand testing.Though the help of relevant Indian StandardCodeof Practicemay be taken,the allowablebearingpressuremaybe calculatedas grosssothat thegrosspressureat the basewithout deductingthe soil displacedcan be computed.

706.3.1.1. Factor of safety

706.3.1.1.1. The factor of safety to calculate allowablebearingpressureon ultimate bearingcapacitymay be takenas2.5 for soil.

706.3.1.1.2.The allowablebearingpressureon rock maybe decidedupon not only on thestrengthofparentrock but alsoon overall characteristicsparticularly deficiencies,like, joints,beddingplanes,faults, weatheredzones,etc. In absenceof suchdetails or analysisof overall characteristics,the value of factorof safety basedon unconfined compressivestrength of theparentrock maybetakenas6 to 8 unlessotherwiseindicatedonthe basisof local experience.The allowable bearingpressure,thus, obtainedis to be furtherrestrictedto not over 3 MPaforload combination(1) given in Clause706.1.1.

The disintegrated/weatheredor very soft rock may betreatedas soil.

706.3.2. Allowable settlement/differential settlement

706.3.2.1. The calculateddifferential settlementbetweenthefoundationsof simply supportedspansshallnot exceedI in400 of the distancebetween the two foundations from theconsiderationof tolerableriding quality unless provision hasbeenmadefor rectificationof this settlement.

20

1RC : 78-2000

706.3.2.2. In case of structuressensitive to differentialsettlement,the tolerable limit has to be fixed for eachcaseseparately.

706.3.3. Permissibletensionat thebaseof foundation

706.3.3.1. No tension shall be permitted under anycombinationof loadson soils.

706.3.3.2. In case of rock if tension is found to bedevelopedat the baseof foundation, the baseareashouldbereducedto a sizewhereno tensionwill occurandbasepressureis recalculated.The maximum pressureon such reducedareashould not exceedallowable bearing pressure.Such reducedareashall not be less than 67 percentof the total areafor loadcombinationincluding seismic, or impactof barge,and 80 percentfor other loadcombinations.

706.3.4. Factor of safety for stability

Factorsof safetyagainstoverturningandsliding aregivenbelow. Thesearemainly relevantfor openfoundations

Without With seismicseismic case case

(i) Against overturning 2 1.5(ii) Against sliding 1.5 1.25(iii) Against deep-seatedfailure 1.25 1.15

Frictionalco-efficientsbetweenconcreteandsoil/rock willbeTan0, o beingangleof friction. Foundingsoil in foundationof bridge being generally properly consolidated, followingvaluesmay be adopted:

Friction co-efficient betweensoil andconcrete = 0.5Friction co-efficient betweenrock andconcrete = 0.8 for good

rockandO.7for‘fissured rock

21

IRC: 78-2000

706.3.5. Pile foundations : The allowable load, theallowable settlement/differentialsettlementand the proceduresto determinethe samefor pile foundationsare given in Clause709.

707. OPEN FOUNDATIONS

707.1. General

707.1.1. Provisionof the Clauseunder707 shall applyfor design of isolated footings and, where applicable, tocombinedfootings,strip footings and rafts.

707.1.2. Open foundationsmay be providedwhere thefoundationscan be laid in a stratum which is inerodible orwhere the extent of scourof the bed is reliably known. Thefoundationsare to be reliably protectedby meansof suitablydesignedaprons,cut-off walls or/andlaunching apronsas maybe necessary.

707.2. Design

707.2.1. The thicknessof the footings shall not be lessthan 300 mm.

707.2.2. Bending moments

707.2.2.1. For solid wall type substructurewith one-wayreinforcedfooting, the bendingmomentscan be determinedasone-wayslab for the unit width subjectedto worstcombinationof loads and forces.

707.2.2.2.For two-wayfootings,bendingmomentat anysectionof the footing shall be determinedby passinga verticalplane through the footing and computing the moment of theforces acting over the entire areaof footings one side of the

22

IRC : 78-2000

verticalplane.The critical sectionofbendingshall be at thefaceof the solid column.

707.2.2.3.In caseofcircular footingsorpolygonalfootings,the bending moments in the footing may be determinedinaccordancewith any rational method. Methods given byTimoshenkoand Rowe for Plate Analysis are acceptable.

707.2.2.4. For combinedfootings supportingtwo or morecolumns, the critical sectionsfor bendingmomentsalong theaxis of the columnsshall be at the faceof the columns/walls.Further, for determination of critical sections for bendingmoments betweenthe columns/walls,any rational method ofanalysisbe adopted.

707.2.3. The shear strength of the footing may becheckedat the critical sectionwhich is the vertical sectionat adistance‘d’ from the faceof the wall for one wayactionwhere‘d’ is the effectivedepthof the sectionat the faceof the wall.

707.2.3.1. For two-way action for slab or footing, thecritical section should be perpendicularto plan of slab and solocated that its perimeteris minimum, but neednot approachcloser than half the effective depth to the perimeter ofconcentratedload or reactionarea.

707.2.4. To ensureproperloadtransfer,a limiting valueof ratio of depth to length/width of footing equal to 1:3 isspecified.Basedon this, for slopedfootingsthe depth effectiveat thecritical sectionshall be theminimum depthat the endplus1/3rd ofthe distancebetweentheextremeedgeofthe footing tothe critical sectionfor designof the footing for all purposes.

707.2.5. The critical sectionfor checkingdevelopmentlength of reinforcementbars should be taken to be the same

23

IRC 78-2000

section asgiven in Clause 707.2.3 and alsoall other verticalplaneswhere abrupt changes in sectionoccur.

707.2.6. Tensilereinforcement

707.2.6.1. The tensilereinforcementshall provideamomentof resistanceat least equal to the bending momenton the sectioncalculatedin accordance with Clause707.2.2.

707.2.6.2. The tensile reinforcement shall be distributedacross the corresponding resisting section as below

(a) In one-way reinforcedfooting, the reinforcement shall be sameas calculated for critical unit width as mentioned in para707.2.2.1.

(b) In two-way reinforced square footing, the reinforcementextending in each directionshall be distributed uniformlyacrossthe full sectionof the footing.

(c) In two-wayreinforcedrectangularfooting, the reinforcement inthe long direction shall be distributed uniformlyacrossthe fullwidth of thefooting. For reinforcementin the shortdirection, acentral band equal to the short side of the footing shall bemarked along the length of the footing and portion of thereinforcement determinedin accordancewith the equationgiven belowshall beuniformly distributed across the centralband

Reinforcementin centralbandwidth = 2

Total reinforcementin shortdirection (~+ 1)

wherefi = the ratio of the long sideto the short sideof thefooting

The remainderof thereinforcement shall beuniformly distributed

in the outerportions of the footing.(d) In the case ofa circular shapedfooting, the reinforcementshall

be provided on the basis of the critical values of radial andcircumferential bendingmomentsin the form of radial andcircumferential steel.Alternatively,equivalentorthogonalgridcan be provided.

24

IRC: 78-2000

707.2.7. The areaof tensionreinforcementshouldnot beless than 0.15 per cent of the cross-sectionalareawhen usingS4l5 grade barsand 0.25 per centof the cross-sectionalareawhenusing S240gradebars.

707.2.8. All facesof the footing shall beprovided witha minimum steel of 250 mm2/metre in eachdirection for allgradesof reinforcement.Spacingofthesebarsshallnot bemorethan 300 mm. This steelmay be consideredto be acting astensile reinforcementon that face,if requiredfrom the designconsiderations.

707.2.9. In case of plain concrete, brick or stonemasonryfootings, the load from the pier or column shall betakenasdispersedthroughthe footing at an anglenot exceeding450~

707.3, Open Foundations at Sloped Bed Profile

707.3.1. Open foundations may rest on sloped bedprofile provided the stability of the slope is ensured.Thefootings shallbe locatedon a horizontal base.

707.3.2. For the foundationsadjacentto eachother, thepressurecoming from the foundationslaid on the higher levelshouldbe duly consideredon the foundationsat the lower leveldue to the dispersionof thepressurefrom the foundationat thehigher level. The distance betweenthe two foundations atdifferent levelsmaybe decidedin sucha way to minimise thiseffect taking into accountthe natureof soil.

707.4. Construction

707.4.1. The protectiveworks shallbecompletedbeforethe floods so that the foundationdoesnot get undermined.

25

IRC: 78-2000

707.4.2. Excavationon openfoundationsshall be doneafter taking necessarysafety precautionsfor which guidancemay be takenfrom IS:3764.

707.4.3. Where blasting is required to be done forexcavationin rock, andis likely to endangeradjoiningfoundationsor other structures,necessaryprecautions,such as, controlledblasting, providing suitable mat cover to prevent flying ofdebris, etc. shall be takento preventany damage.

707.4.4. Condition for laying of foundations

707.4.4.1.Normally, the openfoundationsshould be laiddry and every available method of dewateringby pumpingordepressionof waterby well point, etc. may be resortedto. Alevelling courseof 100 mm thicknessin M 10 (1:3:6) shall beprovidedbelow foundation.

707.4.4.2. If it is determined before-hand that thefoundationscannotbe laid dry or thesituation is found that thepercolation is too heavy for keeping the foundation dry, thefoundation concretemay be laid under wateronly by tremiepipe. In caseof flowing waterorartesiansprings,theflow shallbe stoppedor reducedas far as possibleat the time of placingof concrete.No pumping of water shallbe permittedfrom thetime of placing of concreteupto 24 hoursafterplacement.

707.4.5. All spaces excavatedand not occupied byabutments,pier or otherpermanentworks shall be refilled withearthupto the surfaceof thesurroundingground,with sufficientallowance for settlement. All backfill shall be thoroughlycompactedand in general,its top surfaceshallbeneatly graded.

707.4.6. In case of excavation in rock, the trenchesaroundthefooting shall’be filled up with concreteofM 15 gradeupto the top of the rock.

26

IRC: 78-2000

707.4.6.1. If the depthof fill requiredis more than1.5 min soft rock or 0.6 rn in hard mck abovethe,foundationlevel,thencoticretemay befilled upto this level by M 15 concrete andportionabove may befilled by concreteor by bouldersgroutedwith cement.

707.4.6.2.For design of foundation on rock in riverbridges, the designloadsandforcesshallbe consideredupto thebottom of footing. The loadof filling need not beconsideredinstability calculations.

708. WELL FOUNDATIONS

708.1. General

708.1.1. Whileselectingthe shape,sizeand the type ofwells for a bridge,the sizeof pier to be accommodated,needforeffectingstreamline flow,thepossibilityof theuseof pneumaticsinking, the anticipateddepth of foundation, and the natureofstrata to be penetratedshould be kept in view. Further, for thetype of well selected,the dredge holeshouldbe largeenough topermit easy dredging, the minimum dimension beingnot lessthan2 in. In case thereis deep standing water, properly designedtloating caissons maybe usedas per Clause708.12.

708.1.2. If the externaldiameterof singlecircular wellexceeds12 m then Engineer-in-chargemaytakerecourseto anyof the following

(a) Stressesin steiniug shall be evaluated using 3-DimensionalFinite Element Method (3D FEM) or any other suitableanalyticalmethod

(b) Stiffening by compartmentsmay be done for the singlecircularwell, Designof such stiffenedwells shall cafl for supplementaldesign and construction specifications.

(c) Twin D-shaped wellmay be adopted.

27

IRC: 78-2000

708.1.3. The conditions arising out of sand blow, ifanticipated, should be duly considered whencircular well isanalysedusing 3D FEM/suitable analytical methodor stiffenedcircular wells are used.

708.2. Well Steining

708.2.1. Thicknessofthesteining shouldbe suchso thatit is possibleto sink the well withoutexcessivekentledgeandwithout gettingdamagedduring sinking or during rectifying theexcessive tilts andshifts. The steining should also beable toresistdifferential earthpressuredevelopedduring sandblow orother conditions, like, sudden drop.

Stressesat various levelsof the steining should be withinpermissible limits under all conditions for loads that may betransferred to thewell.

708.2.2. Useof cellularsteining with two ormore shellsor use of composite material in well steining shall not bepermitted for wells upto12 m diameter.

708.2.3. Steiningthickness

708.2.3.1. The minimum thicknessof the well steiningshall not be less than 500 mm and satisfy the followingrelationship

h= Kd..Jj

whereh minimum thicknessof steining in m

d = external diameterof circular well ordumbbell shapedwell or in caseof twin D wells smallerdimensionin planin metres

I = depth of wells in metre belowtop of well cap orLWL whichever is more(for floating caisson‘I’ may betaken as depthof well in metres below bed level)

28

IRC: 78-2000K = a constant

Value of K shall be asfollows

(i) Well in cement concreteK = 0.03(ii) Well in brick masonry K = 0.05(iii) Twin D wells K = 0.039

708.2.3.2. The minimumsteiningthicknessmaybevariedfrom abovein following conditions

Strata Vtariation fromhe minimum

Recommevariation

ndedupto

(a) Very soft clay strata Reduced 10%

(b) Hard clay strata Increased 10%

(c) Boulder strataor wellresting onrock involvingblasting Increased 10%

708.2.3.3. However, following aspects may also beconsidereddependingon the strata

(a) Very soft clay strata- Main criteria for reductionin steiningthicknessis to preventthe well penetratingby its own weight.When the thickness is so reduced, thesteining shall beadequately reinforced to get sufficientstrength.

(b) Hard clay strata - Dependingon the previousexperience,theincreasein steiningthicknessmay be merethan 10 per cent,

(c) Boulder strata or well restingon rockinvolving blasting, highergradeof concrete,higher reinforcement,use of steel platesinthe lower portions, etc.,may be adopted.

708.2.3.4. The reeommended valuesgiven in Clause708.2.3.2canbe further varied basedon local experienceand inaccordance with decisionof Engineer-in-charge.

29

IRC 78-2000

708.2.3.5. If specialisedmethodsof sinking, suchas,jackdown method, areadoptedthen the steining thicknessmay beadjustedaccordingto designand constructionrequirements.

708.2.3.6.Any variation from dimensionsasproposedinClause708.2.3.1shouldbedecidedbeforeframingthe proposal.

708.2.3.7. Whenthedepthof well belowwell capis equalto or more than 30 metres,the thicknessof the steiningof thewell calculatedas per Clause 708.2.3 may be reducedabovescourlevel in a slopeof I horizontalto 3 vertical suchthat thereduced thickness of the steining should not be less thanrequiredasperClause708.2.3 for the depthof well upto scourlevel with the reduceddiameter.

The reduction in thickness shall be done in,, the outersurfaceof the well. The diameterof innerdredgehole shall bekept uniform.

The minimum steeland the concretegrade in the slopeportion shall he sameas for the steining below scourlevel,

Minimum developmentlengthof afl thevertical steel barsshall beprovidedbeyondthe minImum sectionasshown in tb.,Appendix-?,(F~, !).

The stressin the reducedsectionof steiningshall also hechecked.

708.3. DesignConsiderations

708.3.1. In caseof plain concretewells, the concretemix for the steining shall not normally be leanerthanM 15. Incaseof marine’or othersimilar conditionsof adverseexposure,the concretein the steining shall not be less than leanerthanM 20 with cementnot less than 310 kg/rn3 of concreteandthewater cementratio not more than 0.45.

30

IRC 78-2000

708.3.2. The external diameterof the brick masonlywells shall not exceed6 m. Brick masonrywells for depthgreaterthan20 m shall not be permitted.

708.3.3. For brick masonrywells, brick not less thanGrade-Ahavingstrengthnot lessthan 70 kg/cm2conforming toIS: 1077 shall be usedin cementmortarnot leaner than 1:3.

708.3.4. Forplainconcretewells, verticalreinforcements(whethermild steelor deformedbars)in the steiningshall notbe less than 0.12 per centof grosssectionalareaof the actualthicknessprovided. This shall be equally distributed on bothfacesof thesteining.Theverticalreinforcementsshallbetied upwith hoopsteelnot lessthan0.04 percentofthevolumeperunitlength of the steining, asshownin theAppendix-3, (Fig. 2).

708.3.5. In casewherethewell steiningis designedasareinforcedconcreteelement,it shallbe consideredasa columnsectionsubjectedto combinedaxial loadandbending.However,the amount of vertical reinforcementprovided in the steiningshall not be less than 0.2 per cent. (for either mild steel ordeformedbars)ofthe actualgrosssectionalareaof the steining.On the inner face,a minimum of 0.06 per cent(of grossarea)steel shall be provided. The transversereinforcementin thesteining shallbeprovidedin accordancewith the provisionsfora column but in no caseshall be less than0.04 per centof thevolume per unit length of the steining.

The horizontal annularsectionof well steining shall alsobe checkedfor ovalisation momentsby any rational methodtaking accountof side earthpressuresevaluatedasper Clause708.4.

708.3.6. Theverticalbondrodsin brickmasonrysteiningshallnot be lessthan0.1 percentofthecross-sectionalareaand

31

IRC: 78-2000

shall be encasedinto cement concrete of M 15 mix of size150 mm x 150 mm. These rods shall be equally distributedalong the circumferencein the middle of the steining and shallbe tied up with hoop steel not less than 0.04 per cent of thevolume per unit length of the steining.The hoop steel shall beprovided in a concrete band at spacing of 4 times of thethicknessof the steining or 3 metres, whichever is less. ThehorizontalRCC bandsshall not be lessthan 300 mm wide and150 mm high, reinforcedwith barsof diameternot lessthan 10mm placedat the cornersand tied with 6 mm diameterstirrupsat 300 mm centres,as shown in the Appendix-3,(Fig. 3).

708.3.7. The stressesin well steiningshallbe checkedatsuchcritical sectionswheretensileandcompressivestressesarelikely to he maximumandalsowherethereis changein the areaof reinforcementor in the concretemix.

708.4. Stability of Well Foundations

708.4.1. The stability and design of well foundationsshall be done under the mostcritical combinationof loadsandthrees as per Clause 706. The pressureon foundationsshallsatisfy the provisionsof Clause706.

708.4.2. Side earth resistance

708.4.2.1. The sideearthresistancemay be calculatedasper guidelines given in Appendix-3. The use of provisionsIRC:45 may be usedfor pier well foundationsin cohesionlesssoil.

708.4.2.2. The side earth resistanceshall be ignored incaseof well foundationsresting on rock. If rock stratais suchthat the allowablebearingpressureis lessthan 1 MPa, thentheside earthresistancemay be takeninto account.

32

IRC: 78-2000

708.4.3. Earthpressureon abutments

708.4.31. If theabutmentsare designedto retain earthandnot spilling in front, the foundationsof suchabutmentsshall bedesigned to withstand theearthpressure and horizontalforcesfor the condition of scour depthin front of 1.27 dcm withapproachretainedand 2 dsm with scour all around. In case ofscourall around, live load maynot be considered.

708.4.3.2. However, where earth spilling from theapproachesis reliably protectedin front, relief due to thespilling earth in front may be consideredfrom bottom of wellcap downwards.

708.4.4. Constructionstage

708.4.4.1. Stability of the well shall also be checkedforthe construction stage whenthereis no superstructure and thewell is subjected to design scour,full pressure dueto watercurrent andlor full design earth pressureas in the case ofabutmentwells.

708.4.4.2. During the constructionof wells when it hasnot reachedthe founding level or has not been plugged, thewells are likely to be subjectedto full pressuredue to watercurrent upto full scour. This may resultin tilting, sliding andshifting. As a part of the safetyduring construction, thisshouldbe considered andsafety of well must be ensured by suitablemethods, where required.

708.5. Tilts and Shifts

708.5.1. As far aspossible,thewells shall be sunk plumbwithout any tilts andshifts. However, a tiltof 1 in 80 and a shiftof 150mm dueto translation(both additive)in a direction whichwill cause most severeeffect shall be consideredin thedesignofwell foundations.

33

JRC: 78-2000

708.5.2. If the actual tiltsand shifts exceed the abovelimits, then the remedialmeasureshave to beresortedto bringthe well within thatlimit. If it is not possible thenits effect onbearing pressure,steining stressand otherstructural elementsshall be examined, and controlledif necessary and feasible byresorting to changein spanlength. The Engineer-in-charge maylike to specify the maximum tilts andshifts upto which the wellmay be accepted subject to thebearingpressureand steiningstress being withinlimits, by changing the span lengthif needed,and beyond which thewell will be rejectedirrespectiveof theresult of any modification.

708.6. Cutting Edge

708.6.1. The mild steel cutting edge shall be strongenoughandnot lessthan 40kgIm~tofacilitate sinkingof the wellthrough thetypes of strata expectedto be encounteredwithoutsuffering anydamage.It shall be properlyanchored to thewellcurb. For sinkingthroughrock cutting edgeshould besuitablydesigned.

708.6.2. When there aretwo or morecompartmentsin awell, the lowerend of the cutting edgeof the middle stemsofsuch wells shall be kept about300 mm above thatof the outersternsto preventrocking, as shownin theAppendix-3, (Fig. 2).

708.7.’ Well Curb

708.7.1. The wellcurb should be such that it will offerthe minimumresistancewhile the well is being sunkbut shouldbe strongenoughto be able to transmit superimposed loadsfromthe steiningto the bottom plug.

708.7:2. The shapeand the outline dimension of thecurb as given in Appendfr-3, (Fig. 2) may be takenfor

34

IRC : 78-2000

guidance. The internal angle of the curb ‘cx’ as shown inAppendix-3,(Fig. 2) should bekeptat about30°to37°andmaybe increasedor decreasedbasedon past experienceand geo-technicaldata.

708.7.3. The well curbshall invariably be in reinforcedconcrete of mix not leaner than M 25 with minimumreinforcementof 72 kg/cu.m. excluding bond rods. The steelshall be suitably arrangedto preventspreadingand splitting ofthe curb during sinking and in service.

708.7.4. In caseblastingis anticipated,the inner facesofthewell curbshallbeprotectedwith steelplatesofthicknessnotlessthan 10 mm upto thetop ofthe well curb. If it is desiredtoincreasethe steellining abovethe well curb thenthe thicknesscanbe reducedto 6 mm for that increasedheight. In any case,,this extraheight of the steelshould not be more than 3 metresunlessthereis a specific requirement.The curb in sucha caseshould be provided with additional hoop reinforcementof 10mm dia mild steelor deformedbarsat 150 mm centreswhichshall also extendupto a height of 3 m into the well steiningabovethecurb. Additional reinforcementabovethis heightuptotwo times the thicknessof steiningshould beprovidedto avoidcracking arising out of suddenchangein the effective sectiondue to curtailmentof plate.

708.8. Bottom Plug

708.8.1. The bottomplug shallbe provided in all wellsand the top shall be kept not lower than300 mm in the centreabovethetop ofthe curb,asshownin theAppendix-3,(Fig. 2).A suitable sump shall be below the level of the cutting edge.Beforeconcretingthe bottom plug, it shall be ensuredthat itsinside faceshavebeencleanedthoroughly.

35

IRC 78-2000

708.8.2. The concretemix used in bottom plug shallhavea minimum cementcontentof 330 kg/rn3 and a slump ofabout150 mm to permit easyflow of concretethroughtremietofill up all cavities. Concrete shall be laid in one continuousoperationtill dredgehole is filled to requiredheight. For underwater concreting,the concreteshall be placedgently by tremieboxesunderstill watercondition andthecementcontentsofmixbe increasedby 10 per cent.

708.8.3. In casegroutedconcrete,e.g.,concreteis used,thegroutmix shallnot be leanerthan 1:2 andit shallbeensuredby suitablemeans,suchas,controllingthe rateof pumpingthatthe grout fills up all inter-sticesupto the top of the plug.

708.8.4. If anydewateringis requiredit shall be carriedout after 7 dayshaveelapsedafter bottom plugging.

708.9. FIlling the Well

708.9.1. The filling ofthe well, if considerednecessary,abovethe bottom plug shall be done with sandor excavatedmaterial free from organicmatter.

708.10. Plug over Filling

708.10.1, A 300mm thick plug of M 15 cementconcreteshall be provided over the filling.

708.11. WeliCap

708.11.1. Thebottomofwell capshallpreferablybe laidas low as possibletaking into accountthe L.W.L.

708.11.2. As many longitudinal barsaspossiblecomingfrom the well steining shallbe anchoredinto the well cap.

708.11.3. The designof the well cap shall be basedonanyacceptedrationalmethod,consideringtheworstcombinationof loadsand forcesasper Clause706.

36

IRC: 78-2000

708.12. Floating Caissons

708.12.1. Floating caissonsmay be of steel, reinforcedconcreteor any suitablematerial.They shouldhaveat least 1.5metres free board above the water level and increased, ifconsiderednecessary,in casethere is a possibility of caissonssinking suddenly owing to reasons,such as, scour likely toresult from lowering of caissons,effect of waves, sinking invery soft strata,etc.

708.12.2. Well caissonsshould be checkedfor stabilityagainstoverturningand capsizingwhile beingtowed,andduringsinking, dueto the actionofwater current,wavepressure,wind,etc.

708.12.3. The floating caissonshall not be consideredaspart of foundationunlesspropersheartransferat the interfaceisensured.

708.13. Sinking of Wells

708.13.1. The well shall as far aspossiblebe sunk trueand vertical. Sinking should not be startedtill the steininghasbeencuredfor atleast48 hours. A completerecord of sinkingoperations including tilt and shifts, kentledge, dewatering,blasting, etc. done during sinkingshall be maintained.

For safe sinking of wells, necessaryguidance may betaken from the precautionsas given in Appendix-4.

708.14. Pneumatic Sinking of Wells

708.14.1. Where sub-surfacedata indicate the need forpneumaticsinking, it will benecessaryto decidethemethodandlocation of pneumaticequipmentand its supportingadapter.

708.14.2. In caseswhereconcretesteiningis provided,it

37

IRC : 78-2000

shall be renderedair tight by restrictingthe tensionin concretewhich will not exceed3/8th of themodulusof rupture.For thecircular wells, the tension in steining may be evaluated byassumingit to be a thick walled cylinder.

708.14.3. The steining shall be checked at differentsectionsfor anypossibleruptureagainstthe uplift force and, ifnecessary,shall be adequatelystrengthened.

708.14.4. The design requirements of the pneumaticequipment,safety of personneland the structureshall complywith the provisions of IS:4l38 “Safety Code for Working inCompressedAir”. It is desirablethat the height of the workingchamber in a pneumaticcaissonsshould not be less than 3metresto providesufficientheadroom whenthe cuttingedgeisembeddeda short distancebelow the excavatedlevel and inparticular to allow for blowing down. The limiting depth forpneumaticsinking shouldbesuchthatthe depthofwaterbelownormalwaterlevel to theproposedfoundationlevel upto whichpneumaticsinking should not exceed30 m.

708.15. Sinking of Wells by Resorting to Blasting

Blastingmaybe employedwith prior approvalof competentauthorityto helpsinkingof well for breakingobstacles,suchas,boulders or for levelling the rock layer for squareseatingofwells. Blastingmaybe resortedto only whenothermethodsarefound ineffective.

709. PILE FOUNDATION709.1. General

709.1.1. Piles transmit the load of a structure tocompetentsubsurfacestrataby the resistancedevelopedfrombearingat thetoe or skin friction along thesurfaceorboth. The

38

IRC: 78-2000

piles maybe requiredto carry uplift and lateral loadsbesidesdirect vertical load.

709.1.2. The constructionof pile foundationrequiresacarefulchoiceofpiling systemdependinguponsubsoilconditionsand load characteristicsof structures.The permissiblelimits oftotal and differential settlement,unsupportedlength of pileunder scourand any otherspecial requirementsof project arealso equally important criteria for adoption.

709.1.3. DesIgn and construction : For design andconstruction of piles guidancemay be taken from IS:291Isubject to limitations/stipulations given in this code.Appendix-Sgivesthedesignformulaeandtheir applicability.

709.1.4. For piles in streams,rivers, creek~,etc., thefollowing criteriamaybe followed:

(1) Scourconditions areproperly established.

(ii) Permanentsteelliner shouldbe provided at leastuptomaximumscour level. In caseof marine clay or soft soil or soil havingaggressivematerial, permanentsteel liner of sufficient strengthshall be usedfor the fill depth of such strata.The minimumthicknessof liner should be 5 mm.

709.1.5. SpacIng of piles and tolerances

709.1.5.1. Spacingof piles : The spacingof piles shouldbe consideredin relation to the nature of the ground, theirbehaviourin groupsand theoverall costof the foundation.Thespacingshould be chosenwith regardto the resultingheaveorcompactionand should be wide enoughto enablethe desirednumberof pilesto beinstalledto the correctpenetrationwithoutdamageto any adjacentconstructionor to the pilesthemselves.

The costof a capcarrying the load from the structure to

39

IRC : 78-2000

thepile heads,orthesizeandeffectivelengthof a groundbeam,may influencethe spacing,type and sizeofpiles.

The spacingof piles will bedeterminedby:(a) the method of installation,e.g., driven or bored;

(b) the bearingcapacityof the group.

Working rules which are generally, though not always,suitable,areasfollows:

Forfriction piles,the spacingcentreshouldbenot less than theperimeterof the pile or, for circular piles, threetimes the diameter.The spacing of piles deriving their resistance mainly from endbearingmay be reducedbut the distancebetweenthe surfacesof theshaftsof adjacentpiles shouldbe not lessthanthe leastwidth of thepiles.

709.1.5.2.Permissibletolerancesforpilesshall beasunder

(i) For vertical piles 75 mm at piling platform level and tilt notexceeding1 in 150;

(ii) For taker piles tolerance of I in 25.

709.1.6. Themaximumraketo bepermittedin piles shallnot exceedthe following

(i) 1 in 6 for all boredpiles;(ii) 1 in 6 for driven cast-in-situpiles; and

(iii) 1 in 4 for precastdriven piles.

709.1.7. The minimum diameterof piles shall be asfollows:

Bridges on Land River Bridges

Driven cast-in-situpiles 0.5 m 1.2 mPrecastpiles 0.35 m 1.0 mBoredpiles 1.0 m 1.2 m

40

IRC: 78-2000

709.1.8. The settlement, differentialsettlement, lateraldeflectionat caplevel may belimited for any structure as per therequirement.

709.1.9. For both precast andcast-in-situ piles, thevalues regarding gradeof concrete,water cementratio, slumpshall be asfollows:

Tremie ConcreteCast-in-situ

Driven Cast-in-situ

PrecastConcrete

Gradeof concrete M 35 M 35 M 35Mm. cementcontents 400 Kg/rn 3 400 Kg/rn3 400 Kg/rn3Max, W.C. ratio 0.4 0.4 0.4Slump (mm) 150-200 100-130 50

709.2. Requirement and Steps for Design andInstallation

709.2.1. The initial designof an individual pile, groupof piles and final adoption should pass through two typesofmajor investigationand tests asfollows:

(i) Comprehensiveanddetailedsub-surfaceinvestigationfor pilesto determinethe design parameterof end bearing capacity,friction capacity and lateral capacityof soil surrounding thepile.

(ii) Initial load test on trial piles for confirmation/modificationofdesignand layout and routine load test on working piles foracceptanceof the same.

709.2.2. The stepsfor designand confirmationby testsare given below

(i) Subsoilexplor3tion to establish design soil parameters.

(ii) Requiredcapacityof pile groupbasedon tentativenumberanddiameterof piles in a group.

41

IRC: 78-2000

(iii) Capacity of pile based on static formula consideringgroundcharacteristics.Theallowabletotal/differentialsettlementshouldbe duly considered.This step alongwith step (ii) may beiterative.

(iv) Structuraldesignof piles.

(v) Initial load test for axial capacity, lateral load capacity anduplift load capacityon trial piles to verify/confirm or modifythe designconsiderationof piles doneby steps(ii), (iii) and(iv). The load tests may be conducted for the ultimatecapacities.Initial load testshall becyclic load test.If the initialload test gives a capacity greater than 25 per cent of thecapacitycalculatedby static formula, anothertwo load testsshall be carried out to confirm the earlier valueand minimumof the threeshall be consideredas initial load test value. Thenumberof initial testsshall be determinedby the Engineer-in-chargetaking into considerationthe borelog and soil profile.

For load testing of piles, reference is made to IS:29l I(Part-IV).

(vi) Routine load testsmay be conductedagain to reconfirm ormodify theallowableload.Testsshouldbeproperlydesignedtocoverparticular groupfor single pile testand doublepile test.The lateral load test may be conductedon two adjacentpiles.

709.2.3. For abutment,it is importantto consideroverallstability of thestructureandabutment.The piles shouldalsobedesignedto sustainsurchargeeffect of embankment.

709.2.4. RoutIne tests : Routine load testsshould bedone on one pile for alternate foundation for bridges. Thenumber may be suitably increased/reducedtaking intoconsiderationthe borelogand soil profile.

709.3. Capacityof Pile

709.3.1. For calculatingdesignedcapacity of pile/pilegroupmethods/recommendationof IS:291 1 shouldbe followed.

42

mc : 78-2000

Appendix-5givesformulaefor estimating pilecapacitybasedonsoil/rock interaction withpile.

709.3.2. Factorof safety:The minimumfactorofsafetyon ultimate axial capacity computed on the basisof staticformulashall be2.5 for piles in soil. For piles in rock, factorofsafety shall be5 on the bearingcomponent and10 on socketside resistancecomponent.

709.3.3. Capacity of piles/groupaction : The axialcapacityof a groupofpiles should bedeterminedby a factortobe applied to thecapacityof individual piles multiplied by thenumberof piles of the group.

(i) Factor maybe takenas I in caseof purely end bearingpileshaving minimumspacingof 2.5 timesthe diameterof pile andfor frictional pileshavingspacingofminimum3 timesdiameterof pile.

(ii) For pile groupsin clays, the group capacityshall beminimumof the following:

(a) Sumofthe capacitiesof theindividual piles in the group.

(b) The capacity of the group basedon block failureconcept, where theultimate loadcarrying capacityof theblock enclosingthe piles is estimated.

709.3.4. Settlementof pile group

709.3.4.1. The capacityof a pile group is also governedby settlementcriterion. Settlementof a pile group may becomputedon the basisof following recommendationsorby anyother rational method.

709.3.4.2.Settlement of pile group in sands : Thesettlementof a pile groupis affected by the shape and sizeofgroup,length, spacingandmethodofinstallationof piles. Thereis no rational method availableto predict the settlementof group

43

IRC: 78-2000

ofpiles in sands.It is recommendedto useempiricalrelationshipproposedby Vesic for obtainingthe settlementofpile group.Inthis method,the settlementof the groupis predictedbasedonsettlement of a single pile obtained from load test. Thefollowing table indicatesthe relationship

Width of Group/Pile din SettlementRatio .5g/5

5 2.525 550 7.560 8

where og = settlementof pile group

S settlementof single pile

709.3.4.3. Settlement of pile group in clays : Thesettlementofpile groupin homogeneousclaysshall beevaluatedusingTerzaghiandPeckApproach which assumesthat the loadcarriedby the pile group is transferredto the soil through anequivalentfooting locatedat onethird ofthepile lengthupwardsfrom the pile toe. The load under the equivalentfooting isassumedto spreadinto soil at a slopeof 2 slopeof2 (vertical):1 (horizontal).

The settlementfor equivalentfooting shallbeevaluatedinaccordancewith IS:8009 (Part II).

709.3.4.4,Settlementof pile group in rock : Settlementof piles founded in rock may be computedas per IS:8009 (PartII) considering the value of in-situ modulusof rock mass.

709.3.5. Resistanceto lateral loads

709.3.5.1. The ultimate lateral resistanceof a group ofvertical pilesmaybe takenasthe passivepressureactingon the

44

IRC : 78-2000

enclosed area of the piles. Such passive pressuremay becalculatedover an equivalentwall of depth equal to 6D andwidth equal to L + 2B.

where D — Diameterof pile

L Length betweenouter facesof pile group in planperpendicularto direction of movement

B = Width betweenouter facesof pile group in planparallel to the direction of movement

Theminimum factorofsafetyonultimatelateralresistanceshall be 2.5.

709.3.5.2. The safe lateral resistancemust not exceedthesum of lateralresistanceof the individual piles. Thesafe lateralresistanceof individual pile shall be correspondingto a 5 mmdeflectionat groundlevel in accordancewith IS:29ii with full‘E’ value and for appropriatepile-head condition in LoadCombination, I of Clause 706.1.1. For river bridges withscourablebed, the 5 mm deflection may be taken as thedeflectionat scourlevel.

709.3.6. Uplift load carrying capacity

709.3.6.1. Piles may be requiredto resistuplift forcesofpermanentor temporary nature when used in foundationssubjectedto large overturningmoments or as anchoragesinstructures, like, underpassessubjected to hydrostatic upliftpressure.

709.3.6.2. The ultimate uplift capacitymay be calculatedwith the expressionof shaftresistance/skinfriction only, of thestatic formulae for compressionloadsand applying a reductionfactor of 0.50 on the same.However, in the caseof rock, thelengthofsocketneednot berestrictedto 0.5x dia ofsocket.The

45

IRC : 78-2000

weightof pile shall alsoact againstuplift. Pull out tests may beconducted for verificationof uplift capacity.

709.3.6.3. The uplift capacityof pile groupis lesserof thetwo following values:

- the sum of the uplift resistanceof the individual piles in thegroup, and

- the sum of the shear resistance mobilisedon the surfaceperimeterof the groupplusthe effectiveweightof the soil andthe piles enclosedin this surfaceperimeter.

709.3.6.4. Pilesshouldbe checked for structural adequacyagainstuplift forces together withotherco-existentforces, ifany.

709.3.6.5. The minimum factorof safetyon ultimateupliftload calculatedon the aforesaidbasis shall be2.5.

709.3.7. PIles subjectedto downwarddrag A pilemay be subjected toadditional load on accountof downwarddrag resulting from consolidationof a soft compressible clay,layer dueto its own weight, remoulding or surfaceload. Suchadditionalload comingon pile may be assessed on thefollowingbasis:

(i) In the caseofpile derivingits capacitymainly fromfriction, thevalueof downwarddrag forcemaybe takenas 0.2 to 0.3timesundrainedshear strength multipliedby the surfaceareaof pileshaft embeddedin compressiblesoil.

(ii) In caseof pile deriving its capacitymainly from endbearing,the value of downwarddrag force may be consideredas 0.5times undrained shear strength multipliedby thesurfaceareaofpile shaft embeddedin compressiblesoil.

(iii) For a group of piles, the drag forces shall also be calculatedconsideringthe surfaceareaof the block(i.e., perimeterof thegroup timesdepth)embeddedin compressiblesoil. In the event

46

IRC: 78-2000of this valuebeinghigher thanthe numberof pile in thegrouptimes the individual downwarddrag forces,the same shall beconsideredin the design.

709.4. Structural Design of Piles

709.4.1. A pile as a structural member shall havesufficientstrengthto transmitthe loadfrom structureto soil. Thepile shall alsobe designedto withstandtemporarystresses,ifany, to which it may be subjectedto, such as, handling anddriving stresses.The permissible stressesshould be as perIRC:21.

709.4.2. The piles may be designed taking intoconsiderationall the load effects and their structural capacityexaminedas a column. Theself load of pile or lateral loaddueto earthquake,watercurrentforce,etc.on theportionof free pileupto scour level and upto potential liquefaction level, ifapplicable,should be duly accountedfor.

709.4.3. For the horizontal load at the cap level, themoment in the pile stem can be determinedby any rationaltheory. In the absenceof any rational theory, the methodgivenin IS:291 1 (Part I/Sec 2) may be adopted.If the pile group is~provided with rigid cap, thenthe piles shouldbe consideredashaving fixed head for this purpose.Horizontal force may bedistributedequally in all piles in a groupwith a rigid pile cap.

709.4.4. Minimum reinforcement : Thereinforcementsin pile shouldbe provided for the full length of pile, asper thedesignrequirements.However,theminimumareaof longitudinalreinforcementshall be 0.4 per cent of the areaof cross~sectionin all concretepiles. Lateral reinforcementshall beprovided inthe form of links or spirals with minimum 8 mm diametersteel,spacingnot less than 150 mm. Cover to main reinforcementsshall not be lessthan 75 mm.

47

IRC: 78-2000

709.4.5. The reinforcementshould comply with theprovisionof !RC:21 for resisting stresses due to lifting,stackingand transport, any uplift or bending transmitted from thesuperstructureand bending due to any secondary effects. Thearea of longitudinal reinforcement shall not be less than thefollowing percentagesof the cross-sectional areaof the piles:

(a) For piles with alength less than 30 times the leastwidth — 1.25per cent;

(b) Forpiles with a length 30 to 40 times the leastwidth — 1,5 percent; and

(c) For piles with a length greaterthan40 timesthe leastwidth —

2 per cent.

709.5. Designof Pile Cap

709.5.1. The pile caps shallbe ofreinforcedconcreteofsize fixed taking into considerationthe allowable tolerances asin Clause709.1.5.2.A minimum offset of 150 mm shall beprovidedbeyondthe outerfacesof the outer-mostpiles in thegroup. If the pile capis in contact with earth at the bottom, alevelling courseof minimum80 mmthick plaincementconcreteshall be provided.

709.5.2. The topof thepile shall project50 mm into thepile cap and reinforcementsof pile shall befully anchoredinpile cap.

709.5.3. In marineconditions or in areas exposed to theaction of harmful chemicals, etc., useof dense compactedconcrete shallbe made. In addition, the pile cap shall beprotected with asuitable anti-corrosivepaint. High alluminacement, i.e.,quick setting cement shall not beusedin marineconstructions.

48

IRC : 78-2000

709.5.4. Theminimumthicknessofpile capshouldbeatleast0.6 m or 1.5 times thediameterofpile whicheveris more.

709.5.5. Castingof pile cap shouldbe at level higherthan water level unlessfunctionally it is requiredto be belowwaterlevel at which time sufficientprecautionsshouldbe takento dewater.The forms to allow concretingin dry condition.

709.6. ImportantConsideration,Inspection!

Precautions for Different Types of Piles

709,6.1. Driven cast-In-situ piles

709.6.1.1. Exceptotherwisestatedin this code,guidanceis to be obtainedfrom IS:29l1(PartI/Section I).

709.6.1.2. While concreting the uncasedpiles, voids inconcretemaybe avoidedandsufficientheadof concreteis to bemaintainedto preventinflow of soil or water into the concrete.It is also necessaryto take precautionduring concretingtominimise the softeningof the soil by excesswater. Uncasedcast-in-situpilesshallnot be allowedwheremudflow conditionsexist.

709.6.1.3. Thepile shoeswhich maybeeitherofcastironconicaltypeor of mild steelflat type shouldhavedoublereamsfor properseatingofthe removablecasingtube insidethe spacebetweenthe reams.

709.6.1.4. Beforecommencementof pouring of concrete,it should be ensuredthat there is no ingressof water in thecasingtube from the bottOm. Further adequatecontrol duringwithdrawal of the casing tube is essentialso as to maintainsufficientheadof concreteinsidethecasingtubeat all stagesofwithdrawal.

49

IRC: 78-2000

709.6.1.5. Concrete in piles shall be cast upto a minimumheight of 600 mm above the designed top levelof pile, whichshall bestrippedoff to obtain sound concrete eitherbefOre finalset or after 3 days.

709.6.2. Bored cast-in-situ piles

709.6.2.1. The drilling mud, such as,bentonitesuspensionshall be maintained at alevel sufficiently above thesurroundingground waterlevel to ensure thestability of the strata whichisbeing penetratedthroughoutthe boring process until the pile hasbeenconcreted.

709.6.2.2. The boresmust bewashedby freshbentonitesolution flushing to ensureclean bottom at two stagesprior toconcreting andafter putting reinforcement,.

709.6.2.3. In caseof bored cast-in-situ piles tremiesof200 mm diametershall be used for concreting. The tremieshould have uniform and smooth cross-section inside, and shallbe withdrawn slowly ensuring adequate heightof concreteoutside the tremie pipe at all stages of withdrawal. Otherrecommendations for tremie concretingare:

(i) The sidesof the boreholehaveto be stablethroughout;

(ii) The tremieshall be watertight throughoutits length and havea hopper attachedat its headby a watertightconnection;

(iii) The tremie pipe shouldbe loweredto the bottom ofborehole,allowing ground wateror drilling mud to rise inside it beforepouring concrete;

(iv) The tremie pipe should always bekept full of concreteandshould penetratewell into the concretein the boreholewithadequate marginof safetyagainstaccidentalwithdrawal if thepipe is surgedto dischargethe concrete.

50

IRC: 78-2000

709.6.3. Driven precast concrete piles

709.6.3.1. Exceptotherwisestatedin this code,guidanceis to be obtainedfrom IS:29ll(Part I/Section3).

709.6.3.2. This type of piles for bridgesmay be adoptedwhen length of pile as per designrequirementis known withreasonabledegreeof accuracy.Extra length of pile may he castto avoid lengtheningofpilesas far as possible.Whenunavoidable,the splicing for lengtheningof steelmay beusedonly after themethodof splicing is testedandapprovedearlier.

The longitudinal reinforcementshall bejoined by weldingor by mechanicalcouplers.The concreteat top of original pileshall becut downto sufficient lengthto avoidspallingby heatofwelding. Location of mechanical couplers in neighbouringreinforcementshallbesuchasto permit concretingbetweenthebars.

709.6.3.3. During installation of piles, the final set orpenetrationof piles per blow of hammer should be checkedtaking an averageof last 100 blows.

710. SUBSTRUCTURE

7 10.1. General

710.1.1. In caseof plain concretesubstructure,surfacereinforcementat the rateof 2.5 kg/rn2 shallbe providedin eachdirection, i.e., bothhorizontallyandvertically. Spacingof suchbars shallnot exceed200mm. In caseof substructurein highlycorrosiveatmosphere,the surfficereinforcementcanbe dispensedwith if specificallyallowedbut thedimensionofthesubstructureshouldbe soproportionedto keepthe stressesonly upto 90 percentof the allowablestress.

51

IRC: 78-2000

710.1.2. For the designof substructurebelow the levelof the top of bed block, the live load impact shall be modifiedby the factorsgiven below

(i) For calculatingthe pressureat the bottomsurfaceof the pier/abutmentcap 0.5

(ii) For calculatingpressureon the top 3 M of Decreasingsubstructurebelow piei/abutmentcap uniformly

0.5 to zero

(iii) For calculatingthe pressureon the portion of zerothe substructuremore than3 M below thepier/abutmentcap.

710.1.3. Structuresdesignedto retain earthflil shall beproportionedto withstand pressurecalculated in accordancewith any rational theory. No structure shall, however, bedesignedto withstand to horizontal pressure less than thatexertedby afluid weighing480 kg/rn3,in additionto the live loadsurchargeif any.

710.1.4. The backfill behind the wing and return wallsshall conformto the specificationsin Appendix-6with provisionfor proper drainage.

710.2. Piers

710.2.1. Piers in streamand channelshould be locatedto meetnavigationalclearancerequirementsandgive aminimuminterferenceto flood flow. In general, piers shouldbe placedparallel with thedirectionof streamcurrentat flood stage.Piersin other locations, like, viaducts or land spans should beaccordingto the requirementof the obstaclesto crossover.

710.2.2. Wherenecessary,piersshall beprovidedat bothends with suitably shaped cut waters as given in IRC:6.However,cut and easewaterwhereprovidedshall extendupto

52

IRC: 78-2000

affluxed H.F.L. or higher, if necessary, fromconsiderationoflocal conditions, like, waves, etc.

710.2.3. Pier may bein PSC, RCC, PCC or masonry.Only solid section should be adoptedfor masonry piers. Thedesignof masonry piers shouldbe based onpermissiblestressesas providedin IRC:40.

710.2.4. The thicknessof the wallsof hollow concretepiers should notbe less than 300 mm.

710.2.5. The multi-column piersofbridges across riverscarrying floating debris, treesor timber should bebracedthroughout the height of the piers by diaphragm wall ofminimum 200 mm thickness.Unbraced multiple column piersmay be allowed dependingupon the performanceof similarstructures in similar conditions of river. However, type andspacingof such bracing, when adopted, shall be predetermined.

710.2.6. Piers shall be designed towithstandthe loadand forcestransferredfrom the superstructureand the load andforces on thepier itself apart from the effectof its self-weight.In general,pier may besolid, hollow or framed structures.

710.2.7. In caseofpiers consistingtwo ormorecolumns,the horizontalforcesat the bearing can be distributedon all thecolumnsin proportionto their relativerigidities, if the thicknessof the pier capis at leastone and a half times the thicknessofthe column.

710.2.8. If the piers consistof either multiple pilesortrestlecolumns spaced closer thanthreetimes the widthofpiles!columns across the directionof flow, the group shall be treatedas a solid pierof the same overall widthand the value of Ktaken as1.25 for working out pressure dueto water current

53

IRC 78-2000

according to relevant Clause 213.7 of JRC:6. If such piles/columnsarebracedthen thegroupshouldbe considereda solidpier irrespectiveof the spacingof the columns.

7 10.2.9. Hollow piers shall be provided with suitablylocatedweep-holesof 75 to 100 mm diameterfor enabling freeflow of waterto equalisethewater levelson inside andoutside;consideringrate of rise/fall of floodltide water. The pier wallsshould be checked for expecteddifferential water-head~wavepressureand silt pressure.

7 10.2.10. Thelateralreinforcementof thewalls ofhollowcircular RCC pier shall not be less than 0.3 per cent of thesectionalareaof thewalls of thepier. This lateral reinforcementshall be distributed60 per cent on outer faceand40 per cent oninner face.

710.3. Wall Piers

710.3.1. Whenthe length of solid pier is morethan fourtimes its thickness,it shall also be checkedas a wall,

710.3.2. The reinforced wall should have minimumvertical reinforcementequal to 0.3 per centof sectionalarea.

710.3.3. For eccentric axial load, the wall should bedesignedfor axial load with moment. The momentsand thehorizontal forces should be distributed taking into account thedispersalby any rational method,

710.3.4. The verticalreinforcementneednot be enclosedby closedstirrups, wherevertical reinforcementis not requiredfor compression.However,horizontalreinforcementshould notbe less than 0.25 per centof the gross areaand open links (orS-loops) with hook placed around the vertical bar should beplacedat the rateof 4 links in one squaremetre.

54

IRC :78-2000

710.3.5. Whenwalls are fixed with superstructure,thedesignmomentand axial load should beworkedout by elasticanalysisof the whole structure.

710.4. Abutments

710.4.1. The abutmentswill carry superstructurefromone side. It should be designed/dimensionedto retainearthfromthe approachembankment.

7 10.4.2. Theabutmentsshould bedesignedto withstandearthpressurein normalcondition in addition to loadand forcestransferredfrom superstructure.In addition, any load acting onthe abutmentitself, including self-weight, is to be considered,

7 10.4.3. In case of spill through type abutment, theactivepressurecalculatedon the width of the column shall beincreasedby 50 percentwheretwo columnshavebeenprovidedand by 100 per cent wheremore than two columnshavebeenprovided.

710.4.4. All abutmentsand abutmentcolumnsshall bedesignedfor a live load surchargeequivalentto 1.2 in height ofearthfill. The effective width of the columns need not beincreasedas in Clause710.4.3 for surchargeeffect when spillthrough abutmentis adopted.

710.4.5. Abutment should also be designedfor watercurrent forcesduring ‘scour all round’ condition.

710.4.6. The abutment may be plain or reinforcedconcreteor ofmasonry.Theabutmentmay beeither solid type,buttressedtype, counterfort typeor spill throughtype. For spillthrough abutment,column type or wall type analysismay becarried out as for piers. Counterfort type abutment may betreatedas T or L type as the casemay be andthe slab may bedesignedas continuousover counterforts.

55

IRC : 78-2000

710.4.7. Fully earth retaining abutments should bedesignedconsideringsaturated unit weightof earth duringH.F.L. or L.W.L. condition. In caseof footings, the submergedunit weightofsoil whereconsideredshall not beless than 1000kg/m3.

7 10.4.8. The weightof earthfilling materialon heelmaybe considered. In caseof toe, the weight may beconsideredifthe bedis protected.

710.4.9. In caseof spill through type abutment,it shouldbe ensured that the slopein front of the abutmentis wellprotected by meansof suitably designed stone pitchingandlaunchingaprons.

710.4.10. In caseof abutments having counterfort,theminimum thicknessofthe front wall shouldnot belessthan 200mm and the thicknessof the counterfortshould not belessthan250 mm.

710.5. Abutment Pier

710.5.1. Abutment piers may haveto be provided atlocations where there may bea need of increasingwaterwaysubsequently.The designof such abutment piers shall be suchthat it shouldhe possible to convert them to the similar shape aspiers in the activechannel.,

710.5.2. For multiple spanarch bridges,abutmentpiersshall be provided after every fifth spanor closer.

710.6. Dirt Walls, Wing Walls and Return Walls

710.6.1. Wing walls shall be of sufficient length toretain the roadway to the required extent and tofurnishprotection againsterosion.

56

IRC : 78-2000

710.6.2. A dirt wall shall be provided to prevent theearthfrom approachesspilling on the bearings.A screenwall ofsufficientdepth(extendedforat least500mm depthinto thefill)to preventslippingof thebackfill in casethe abutmentis of thespill throughtype, shall be provided.

710.6.3. The wing walls may be of solid type. Thereturnwalls may be of solid or counterforttype. The materialusedmay be plain or reinforcedconcreteor masonry.

710.6.4. Dirt walllballast wall and screenwall shall beprovidedwith minimum thicknessof 300 mm.

710.6.5. Thewing wallsshould bedesignedprimarily towithstandthe earthpressurein addition to self-weight.

710.6.6. The top of the wing/return walls shall becarried abovethe top of embankmentby at least100 mm topreventany soil from beingblown orwashedaway by rain overits top. A drainagearrangementfor returnwall/wing wall maybe provided similar to that for the abutment specified inAppendfr-6.

710.6.7. The cantilever returns where adoptedshouldnot be more than 4 metreslong.

710.6.8. In caseof open foundations,wing and returnwalls shouldbe providedwith separatefoundationswith a jointat theirjunction with the abutment.

710.6.9. Wing walls maybe laid at anysuitableangletotheabutment.In caseofriver bridges,thesearenormally splayedin planat 45 degrees.Thereturnwalls maybeprovidedat rightangles to the abutment.Return waIls shall be designedtowithstanda live-load surchargeequivalentto 1.2 m height ofearthfill.

57

IRC: 78-2000

710.6.10. The box type return wall at right angles at bothendsof theabutmentsconnected bywall type diaphragm may beadoptedwhere found suitable. However, in such cases,noreduction in the earthpressurefor the designof the abutmentshould be considered. The topof diaphragm should slopeinwards to the centre of carriageway for facilitating properrolling of the embankmentbehindthe abutment.

710.6.11. Solid typeof wing/return wallson independentfoundationscan be suitably steppedup towards theapproachesdependingupon the pattern of scour, local ground conditionsand its profile, safe bearingcapacity,etc.

710.6.12. In case of wing walls or return walls, thefoundationshall be takenadequatelyinto the firm soil.

710.7. Retaining Walls

710.7.!. The minimum thicknessof reinforced concreteretaining ~vallshallbe 200 mm.

710.7.2. The retaining walls shall be designed towithstand earth pressureincluding any live load surchargeandotherloadsactingon it including self-weightin accordance withthe generalprinciples specified for abutments.Stone masonryand plain concrete wallsshall be of solid type. Reinforcedconcrete walls may beof solid, counterfort, buttressedorcellular type.

7 10.7.3. The verticalstemsof cantilever walls shall bedesigned as cantilevers fixed at the base.Th~vertical or facewalls of counterfort typeand buttressed type shallbe designedas continuousslabssupportedby counterforts or buttresses. Theface walls shall be securely anchoredto the supportingcounterfortsor buttressesby meansofadequate reinforcements.

58

IRC: 78-2000

710.7.4. Counterfortsshall be designedas T-beamsorL-beams.Buttressesshallbe designedasrectangularbeams.Inconnectionwith themain tensionreinforcementof counterforts,thereshallbe a systemof horizontaland verticalbarsor stirrupsto anchorthe facewalls and baseslab to the counterfort.Thesestirrupsshallbe anchoredasnearto theoutsidefacesof the facewalls and asnearto the bottom of the baseslab aspracticable.

710.8. Pier and Abutment Caps

7 10.8.1. The width of the abutmentand pier caps shallbe sufficient to accommodate

(I) the bearingsleaving an offset of 150 mm beyondthem.

(ii) the ballast wall.

(iii) the space for jacks to lift the superstructurefor repair/replacementof bearings,etc.

(iv) the equipmentfor prestressingoperationswherenecessary.

(v) the drainagearrangementfor the water on the cap.

7 10.8.2. The thicknessof cap over the hollow pier orcolumn typeof abutmentshouldnotbe lessthan250mm but incaseof solid plain or reinforcedconcretepier and abutment,thethicknesscan be reducedto 200 mm.

710.8.3. Pier/Abutmentcapsshouldbesuitablydesignedandreinforcedto takecareofconcentratedpoint loadsdispersingin pier/abutment.Caps canti]everingout from the supportsorresting on two or morecolumnsshall be designedto cater forthe lifting of superstructureon jacks for repair/replacementofbearings.The locations of jacks shall be predeterminedandpermanentlymarkedon the caps.

710.8.4. In casebearingsare placedcentrally over thecolumnsand the width of bearings/pedestalsis locatedwithin

59

IRC : 78-2000

half the depth ofcap from any external face ofthe columns,theload from bearingswill be consideredto have been directlytransferred to columns and the cap beam neednot be designedfor flexure.

710.8.5. The thicknessof the capovermasonrypiers orabutmentshallnot be less than500 mm. Theminimumwidth atthe top of suchpiers and abutmentsof slab and girderbridgesjust below the capsshall be asgiven below:

Span in metres 3m 6m Urn 24m

Top width of pier carryingsimply supportedspansin in 0.50 1.0 1.2 1.6

Top width of abutmentandof pierscarrying continuousspansin m 0.40 0.75 1.0 1.3

710.8.6. Except the portion under bearings, the topsurfaceof caps should have suitable slope in order to allowdrainageof water.

710.9. Cantilever Pier and Abutment Cap

7 10.9.1. Whenthe distancebetweenthe load/centrelineof bearingfrom the faceof the support is equalto or less thanthe depth of the cap (measuredat the support~the capshall bedesignedasa corbel.

710.9.2. Theequivalentsquareareamaybe workedoutfor circularpier to determinetheforceof supportfor calculatingbendingmoments.

7 10.9.3. In caseof wall pier and thepiercapcantileveringout all aroundthe measurementof distancefor purposeof thedesignasbracketandthedirectionofprovisionofreinforcementshould be parallel to the line joining the centre of load/bearingwith the nearestsupportingspaceof pier.

60

IR.C: 78-2000

710.9.4. Where a part of the bearinglies directly overthe pier, calculationof such reinforcement shoul4 be restrictedonly for the portion which is outside the faceof the pier.Moreover, in such cases theareaof closed horizontalstirrupsmay be limited to 25 per cent of the area of primaryreinforcement.

710.10. Pedestalsbelow Bearing

710.10.1. The pedestalsshould be soproportionedthat aclear offset of 150 mm beyond the edgesof bearings isavailable.

710.10.2. For pedestals whoseheight is less thanitswidth the requirementof the longitudinal reinforcement asspecifiedfor short column need notbe insistedupon.

710.10.3. The allowable bearing pressurewith nearuniform distribution on the loaded areaof a footing or baseunder a bearing or column shall be givenby the followingequation:

C =

where C0 = the permissibledirect compressive stress in concreteat the bearingareaof the base

A1 = dispersed concentric area whichis geometricallysimilar to the loaded areaA2 andalso the largest areathat can be contained in the planeof A1 (maximumwidth of dispersion beyondthe loaded area faceshall be limited to twice theheight)

A, = loaded areaand the projection of the bases orfooting beyondthe face of the bearing orcolumnsupportedon it shall not belessthan 150 mm in anydirection.

61

IRC: 78-2000

710.10.4. The two layersof mesh reinforcement- one at20 mm from top and theotherat 100 mm from top of pedestalor pier cap each consistingof 8 mm bars at100 mm in bothdirections, shall be provided directly under the bearings.

62

IRC: 78-2000

Appendfr—1GUIDELINES FOR CALCULATING SILT FACTOR FORBED MATERIAL CONSISTING OF GRAVELS ANDBOULDERS

(Ref. Clause 703.2.2.2)

In absenceof any formula ‘K5~’may bedeterminedas perClause703.2.2 and may be adopted basedon site informationand behaviourhistoryof any existing structure. The clayey bedhavingweighteddiameter normallyless than 0.04 offers moreresistance to scour than sand though mean depthof scour as perthe formula givenin Clause 703.2 indicates more scour. Inabsenceof any accepted rational formulaor anydataof scour atthe site of the proposedbridge; the following theoreticalcalculation maybe adopted:

(i) In caseof soil having4~<l5°and c (cohesionof soil) >0.2 kg/cm

2, K!/ calculatedas follows:

K1 = F(l+ ~ where c is inkg/cm

1

where F = 1.50 for 4 > 100 and <15°

= 1.75 for 4,> 50 and <100

= 2.00 for 4, <5°

(ii) Soils having 4,~l5°will be treated as sandy soil evenif c is

more than 0.20kg/cm2 and silt factorwill be as perprovisionsof Clause703.2.2.

63

IRC: 78-2000

Appendi~c-2

GUIDELINES FOR SUB-SURFACEEXPLORATION

(Ref. Clause 704.3)

1. GENERAL

The objectiveofsub-surfaceexplorationis to determinethesuitability of the soilor rock, for thefoundationof bridges.Thesub-surfaceexplorationfor bridgesis carriedout in two stages,namely, preliminary and detailed. Itmay require additional!conformatory exploration during constructionstage.

Guidancemay betakenfrom the following:

(i) IS:1892 — Codeof Practicefor Site Investigationfor Foundationsmay be utilised for guidance regarding investigation andcollectionof data.

(ii) Test on soils shallbe conducted inaccordancewith relevantparts of IS:2720 — Methods of Test for Soils. The tests onundisturbed samples be conducted as far as possible atsimulated field conditions to get realisticvalues.

(iii) IS: 1498 — Classificationand Identificationof Soils for generalengineering purposes.

Forpreliminaryanddetailedsub-surface investigation,onlyrotary drills shall be used. The casing shall also be,invariablyprovided with diameters notless than 150 mm upto thelevel ofrock, if any. However, use of percussionor wash boringequipmentshall bepermittedonly to penetratethroughboulderyor gravelly strata for progressingthe boring but not forcollection of samples, while conducting detailed bbrings, theresistanceto the speedof drilling, i.e., rateof penetration,coreloss,etc. shall be carefullyrecordedandpresentedin “Borelog

64

IRC : 78-2000

chartanddata sheet” to evaluate the differenttypes ofstrata anddistinguish specially sand from sandstone,clay from shale, etc.

For preliminaryand detailedsub-surface investigation,onlydoubletubediamond drillingmethod shall be used.In soft andweak rocks suchtufTs, soft shalestriple tube diamond drillingshall be used.

2. PRELIMiNARY INVESTIGATION

2.1. Preliminaryinvestigation shall includethe study ofexisting geological information, previous sitereports,geologicalmaps,etc., and surface geologicalexamination.These will helpto narrowdown thenumberof sitesunder consideration andalsoto locate the mostdesirable location for detailed sub-surfaceinvestigation.

3. DETAILED INVESTIGATION

3.1. Based on data obtained after preliminaryinvestigations, the bridge site, the typeof structurewith spanarrangement and the locationand type of foundations, theprogrammeof detailedinvestigations, etc. shall be tentativelydecided.Thereafter thescopeof detailedinvestigationincludingthe extentof exploration,numberof bore holes, type of tests,numberof tests,etc. shall be decidedin closeliaison with thedesignengineer and the explorationteam, so that adequate dataconsiderednecessary for detaileddesign and execution areobtained.

3.2. The exploration shallcover the entire lengthof thebridge andalsoat either end a distanceof zoneof influence, i.e.,about twice the depth below bed of the last main foundation toassess the effectof the approachembankmenton the endfoundations. Generally,the sub-surfaceinvestigationsshould

65

IRC: 78-2000

extendto a depth below the anticipated foundationlevel equal toabout one and ahalftimes the widthofthe foundation. However,wheresuchinvestigationsend in any unsuitableor questionablefoundation material, the exploration shall be extended toasufficient depth into firm and stablesoils or to rock.

3.2.1. Additional drill holes : Where the data madeavailableby detailed exploration indicateappreciablevariationspecially in case of foundationsresting on rock, it will benecessary to resortto additional drill holes to establishacompleteprofile of theunderlyingstrata.Location and depth ofadditionaldrill holes will have to be divideddependingupon theextent of variation in local geologyand in consultationwithdesignengineer.

3.3. The scope of the detailed sub-surfaceexplorationshall be fixed as mentioned in para3.1 and3.2. However, as ageneral guide it shall be comprehensive enough to enable thedesigner to estimateor determine thefollowing:

(i) engineeringpropertiesof the soillrock;

(ii) location and extentof weak layersand cavities,if any, belowhard foundingstrata;

(iii) the sub-surfacegeological condition,such as, type of rock,structureof rock, i.e., folds, faults, fissures,shears, fractures,joints, dykes andsubsidencedue to mining or presenceofcavities;

(iv) ground waterlevel;

(v) artesian conditions,if any;

(vi) quality of water in contactwith the foundation;

(vii) depth and extentof scour;

(viii) suitable foundation level;

66

IRC: 78-2000

(ix) safe bearingcapacityof foundationstratum;

(x) probablesettlementand probable differentialsettlementof thefoundations;

(xi) likely sinking or driving effort; and

(xii) likely constructiondifficulties.

4. CONSTRUCTION STAGE EXPLORATION

Such explorations may become necessary toverif~’theactually met strata vis-a-vis detailed investigation stage or whena changein the sub-soilstrata/rockprofile is encountered duringconstruction.In suchsituations,it may be essential to resorttofurther explorations to establish the correct data,for furtherdecisions.

5. METHOD OF TAKING SOIL SAMPLES

The size of the bores shall be predeterminedso thatundisturbed samples as requiredfor thevarioustypesof tests areobtained.The methodof taking samples shall be as given inIS:l892 and IS:2132. The tests on soil samples shall beconductedas perrelevantpart of IS:2720.

6. DETAILS OF EXPLORATION FOR FOUNDATIONSRESTING ON SOIL (ERODIBLE STRATA)

6.1. The type andextent ofexploration shall be divided into the followinggroupskeepingin view thedifferentrequirementsof foundation designand the likely methodof data collection:

(i) Foundationsrequiring shallow depthof exploration;

(ii) Foundationsrequiring large depth of exploration; and

(iii) Fills behind abutmentsand protectiveworks.

67

IRC: 78-2000

6.2. Foundations Requiring Shallow DepthExploration(Open Foundation)

These shall cover caseswhere the depth of exploration isnot deep and it is possibleto take samplesfrom shallow pits orconduct direct tests, like, plate load tests, etc. This will alsocover generally the foundation soil for approach embankments,protective works, etc.

6.2.1.The primaryrequirementsare stabilityandsettlement,for which shearing strength characteristics, load settlementcharacteristics,etc. needdetermination.

6.2.2.Tests shall be conducted onundisturbedrepresentativesamples,which may be obtained from open pits. The useofplate load test (IS:1888-Methodof Load Test on Soils) isconsidereddesirablefor ascertainingthe safebearingpressureand settlementcharacteristics,A few exploratory bore holesorsoundings shall be madeto safeguard againstpresenceof weakstrataunderlyingthe foundation. This shall extendto a depthofabout I ‘/~times theproposed width of foundation.

Note: For better interpretation, itwill be desirableto correlate thelaboratory results with the in-situ tests, like, plate load tests,penetrationtestresults.

6.2.3. The tests to be conducted at various locations forpropertiesofsoil, etc. are differentfor cohesiveand cohesionlesssoils. These are indicated below and shall be carriedoutwherever required according tosoil type:

1. CohesloniessSoils

(a) LaboratoryTests

(i) Classification tests, index tests, densitydetermination,etc.

68

!RC : 78-2000

(ii) Shear strengthsby triaxial/direct shear,etc.

(b) Field Tests

(i) Plate Load Test

(ii) StandardPenetrationTests (as per IS:2131)

Use of Dynamic Cone PenetrationTest as perIS:4968 (Part I or Part 2) may be conductedwhere consideredappropriate).

II. CohesiveSoils

(a) LaboratoryTests

(i) Classification tests, index tests, density

determination,etc.(ii) Shearstrengthsby triaxial/directshear,etc.

(iii) Unconfinedcompressiontest (IS:2720Part X)

(iv) Consolidationtest (IS:2720Part V)

(b) Field Tests

(i) Plate Load Test

(ii) Vane ShearTest(IS:4434)

(iii) StaticCone PenetrationTest(IS:4968 Part III)

Note: Wheredewateringis expected,the samplesmay be testedforpermeability (IS:2720 Part-XVII).

6.3. FoundationsRequiring Large Depth ofExploration

6.3.1. In this group arecoveredcasesof deepwells, pilefoundations,etc. where the useof boring equipment,specialtechniquesof sampling,in-situ testing,etc. becomeessential.Inaddition to the problemsof soil and foundationinteraction animportant consideration can be the soil data required fromconstructionconsider~ttions.Often in the caseof cohesionless

69

IRC: 78-2000

soils, undistrubedsamplescannotbe takenand recoursehas tobe madeto in-situ field tests.

6.3.2. Thesub-surfaceexplorationcanbedivided into threezones:

(i) betweenbed level andupto anticipatedmaximumscour depth(below H.F.L.)

(ii) from the maximumscourdepth to the foundation level, and

(iii) from foundationlevel to about lV2 timesthewidth of foundationbelow it.

6.3.3. Sampling and testing (in-situ and laboratory)requirementwill vary in eachcaseand hencearerequiredto beassessedanddecidedfrom caseto case.The sub-soilwatershallbe tested for chemical propertiesto evaluate the hazard ofdeteriorationto foundations.Wheredewateringis expectedto herequired,permeabilitycharacteristicsshould he determined.

6.3.4. For thedifferent zonescategorisedin para6.3.2., thedata required,method of sampling, testing, etc. are given inTable I. Samplesof soils in all casesshall becollectedat everyI to I V2 metreor at changeof strata.

Table 1. Sub-soil data required for deep foundations

Zones DalaRequired Samplingand Remarks— IncludingTesting limitahons

Bed levds to (i) Soil Sampling (i) Laboratory tests to beanticipated classification For (i) and (ii) conducted according to themaximum (ii) Particles size disturbedsamples relevant parts of IS:2720.scour depth distribution may be collected.

For (iii) and (iv) (ii) Undisturbed samplingundisturbed samples cohesionless soils is ashall he collected, difficult and expensiveIn-Situ Tests process.In general, inCohesionless Soils such cases, n.situ testsDynamic Penetration may be adopted.

70

IRC : 78-2000

Maximumanticipated scourlevel to thetundation level

Tests as per details inpam 704.4.2.3.CohesiveSoils —

(i) Static penetrationTests — cone andskin resistance tobe obtained.

(ii) Field vane sheartest may be done.

LaboratoryTests(i) Classification Tests

including particlesize distribution.

(ii) Shearing strength—Triaxial tests tobe done onundisturbed samples.tJnconfinedcompression teststo be done onundisturbed andremoulded samples.

(i) Soil classification Same as above(ii) Shearing strength

characteristics(iii) Compressibility(iv) Permeability-where

dewatering isexpected.

(v) Moisture content,density, void ratio

(iii) Boring and samplingtends to cause remouldingof sensitive clays.E)isturbance and stresschanges for fissured orlayered clays may also makethe sample not trulyrepresentative of the in-situcondition. In such cases useof in-situ tests may giveresults more representativeof the actual soilcharacteristics.

Note: use of sophisticated equipment, like, the pressure meter may be made, if suitable co-relations forinterpretation ofdata collected are available.

Same as above

Foundation level (i) Soil classification Same as above and Same as aboveto about I times (ii) Shearing strength Consolidation test to beof the width of (iii) Compressibility done on undisturbedfoundation below it samples

71

IRC: 78-2000

6.4. Fill Materials

Representative disturbed samples shallbe collected fromthe borrowpit areas.Laboratory tests shall be conductedfordeterminingthe following:

(i) classificationandparticle size(ii) moisture content

(iii) densityvs. moisture content relationship

(iv) shearing strength

(v) permeability

Note :The shearing strength shall be obtained for the density

correspondingto the proposeddensity for the fill.

7. DETAILS OF EXPLORATION FOR FOUNDATIONSRESTING ON ROCK

7.1. Basic Information Required from Explorations

(1) Geologicalsystem;

(ii) Depth of rock and its variation over the site;

(iii) Whetherisolated boulderor massive rock information;

(iv) Extent and characterof weathered zone;

(v) The structureof rock — including beddingplanes, faults, etc.;

(vi) Propertiesof rock material,like, strength, geological formation,etc.;

(vii) Quality and quantityof returningdrill water; and

(viii) Erodibility of work to the extent possible.

7.2. Exploration Programme

If preliminaryinvestigationshave revealedpresenceofrockwithin levels where the foundationis to rest,it is essentialto takeup detailed investigation to collect necessaryinformationmentionedin the precedingpara.

72

IRC : 78-2000

7.2.1. The extentof explorationshall be adequate enoughto give a completepictureof the rock profile both in depth andacross the channel width for assessing theconstructionaldifficulties in reachingthefoundationlevels.Keeping thisin viewit shall be possible to decide the typeof foundations, theconstruction method to be adoptedfor a particularbridge, theextent of even seating and embodiment into rockof thefoundations. Itis desirableto takeatleast onedrill holeperpierand abutmentand oneon eachside beyond abutments.

7.2.2. The depthof boring in rock dependsprimarily onlocal geology, erodibilityof the rock, theextent of structuralloads to be transferredto foundation, etc.Normally, it shall passthrough the upperweatheredor otherwise weak zone, well intothe soundrock. The minimum depth of drilling shall be asperpara 3.2 above,

7.3. Detailed Investigations for Rockat Surface or atShallow Depths

In caseofrock at shallow depths whichcan be convenientlyreached, test pits or trenches are the most dependableandvaluablemethods,sincetheypermit a direct examinationof thesurface, theweatheredzoneandpresenceof any discontinuities.For guidance,IS:4453- Codeof Practicefor exploration by pits,trenches, draftsandshafts may be referredto. In case structurallydisturbed rocks, in-situ tests may be made in accordance withIS:7292 - Code of Practicefor in-situ determinationof rockpropertiesby flat jack, TS:7317 - Codeof Practice forUni-axialJacking Testfor DeformationModulus and1S:7746-. Code ofPracticefor in-situ Shear Teston Rock.

7.4. Detailed Investigation for Rock at Large Depths

7.4.1. This coverscaseswhere recourseis to be madeto

73

TRC 78-2000

sounding, boring and drilling. An adequate investigationprogrammehasto beplannedto coverthewholeareaforgeneralcharacteristicsand in particular the foundation location, forobtaining definite information regarding rock-depth and itsvariationover the foundationarea.The detailedprogrammeofexplorationwill dependon the type and depth of overburden,the size and importanceof the structure,etc. To decide this,geophysicalmethodsadoptedat the preliminary investigationstagemay be helpful.

7.4.2. Theinvestigationof the overburdensoil layersshallbe doneasper detailsgivenfor the foundationsrestingin soil.However, in case of foundations resting on rock, tests onoverburdenshall be carried out only when necessary,e.g.,foundationlevel lower thanscour le’~’els.

7.4.3. The coresshall be stored properly in accordancewith 15:4078-Codeof Practicefor IndexingandStorageofDrillCores.

7.4.4. Therock coresobtainedshallbesubjectedto teststoget necessarydatafor designasfollow:

(i) Visual identification for

(a) Texture(b) Structure(c) Composition(d) Colour(e) Grain size(f) Petrography

(ii) Laboratorytestsmay be done for

(a) Specific gravity

(b) Porosity(c) Waterabsorption(d) Compressivestrength

74

IRC: 78-2000

Note: Generally,shearstrengthtestswill suffice for designpurposes.Other tests may needto be done in special case.The shearstrengthtestscanbe done as unconfmedcompression,triaxialcompressionor direct sheartest.

7.4.5. Use of in-situ tests for measuringstrength anddeformati6ri characteristicsmay be made. Use of bore holephotographywill be desirableto evaluatethepresenceof faults,fissuresor cavities,etc.

7.5. SpecialCases

7.5.1. Investigation for conglomerate : A drill hole shallbe made same as for rock. The samplescollected shall besubjectedto suitable tests dependingupon the material. Specialcare shall be taken to ascertainthe erodibility of the matrix.

7.5.2. Investigation for laterites : The investigation shallgenerallybe similar to that requiredfor cohesivesoils. In caseof hard laterite, recoursemay haveto be’~madeto coredrillingas for soft rocks.

8. CLASSIFICATION AND CHARACTERISTICSOF ROCKS

8.1. Identification and classification of rock types forengineeringpurposesmay, in general,be limited to broad,basicphysicalconditionin accordancewith acceptedpractice.Strengthof parent rock alone is of limited value becauseoverallcharacteristicsdependconsiderablyon character,spacinganddistributions of discontinuitiesof the rock mass, suchas, thejoints, beddingplanes,faults and weatheredseams.

8.2. ClassIficationof Rocks

Rocks may be classified or identified based on theirphysical condition as indicatedbelow. For foundationdesign,theseare to be classified in threegroupsas in Table 2. As a

75

IRC : 78-2000

guide, the allowable bearingvalues of the rocks of differentconditionsmaybe takenfrom thevaluesgiven in Table2, dulymodified aftertaking into accountthe variouscharacteristicsofrocks.

Table 2

Types of Rock/Condition SuggestedAllowable BearingValues for Average Condition

Hard Rocks 2.0 to 3.0 MPa

Soft Rocks 1.0 to 2.0 MPa

WeatheredRocks,Conglomerates Not morethanand Laterites 1.0 MPa

9. PRESENTATION OF DATA

The presentationof data collected shall be done asillustrated in SheetsNo.1 and 2.

76

90-

85.

80

75

Notes

1. Cross section of River at AA’ looking down ~ream2. Numbers in the circles represent field S.P.T. n values3. The detaileshown are as a sample only

-90

65

80

75

70

05

Go

“5

‘50

45

40

~5

‘0

- 25

- 20

- IS

SUB SOIL PROFILE

R.L. IN METRESLEFT BANI~ SUB SOIL PROFILE RIGHT BANK

ERC:78-2000SHEET NO.2

AITICIPATED MAX.. SCOUR LEVIL

PROPOSED DESIGNEDFOUWDAIION LEVEL

B H .1

RFF~R~P~CE~

70

McI

1.WL 7T.OO

b.b~.4

toe of SORE KOt~

2 ~ 1. 15’ co ‘.: ~. ! : POORL1 ,c~R.AoED .~5i:~D::®///m/”~//~ I /~*(~ MEDIUM PLA~A

/ / ,f,/, 7,7 ,~ / 7/ ,~I1H SOME KANKA~- / ‘‘ ,‘ ~

,A~O~ HIGH PLAcTICIT ~

/7 ,‘,~ ~

/ / // ~. / / -- ,

-~ .7 .c~.

.‘ / ,‘: , ~ ~ , /

/ / ,.. .. , , / , / /, / . . , , ,‘ - - - /, , // ‘(Ill

/ - 7 /~ ,/ .., .. , / 7-

42.70

7’ - /7

/ , / / /,~/,, , / , /,~

, . ,

- /~

,, ,-~. ,/ ,,7, ‘ , ,

., , , , ,/ / , 7. /

- , , /7 7

7, / 7~ /7

_., ., / ‘-I. / , / /

ADED SAND

~GP.

SAND STONE/

Cw.

-k---

IRC : 78-2000

(ii) Abutment wells in both cohesiveand non-cohesivesoils

In the caseof abutment wells, theactivepressureon soil abovethe maximumscourlevel (Triangularverification of pressure)shall beseparatelyevaluatedandconsideredas loadscombinedwith the other loads acting on the abutmentand no factor ofsafety shall be taken for theabove components of activepressure. Effectsof surcharge due tolive load should berestricted only upto the abutmentportion.

(iii) However, the lateralresistanceof soil below the scourlevel atultimate value shall be divided by theappropriatefactor ofsafety, viz., (Pp_Pa) f.o.s.asstatedin the caseof pier wells.

(iv) Pointof rotation

For the purposeof applying theabove formulae, it may beassumedthat the pointofrotation lies at thebottom of the well.

80

IRC : 78-2000

Appendix-3

PROCEDURE FOR STABILITY CALCULATION

(Ref. Clauses708.2 & 708.3)

I. FORMULAE FOR ACTIVE OR PASSIVE PRESSURE IN SOIL

The active and passivepressureco-efficient (ka &respectively)shall be calculatedaccordingto Coulomb’sformulataking into accountthewall friction. Forcohesivesoils, theeffectof ‘c’ maybe addedto thesameasperproceduregivenby Bell.The valueofangleofwall friction maybe takenas2/3rdof 4) theangleof reposeis subjectto a limit of 22Y2 degrees.Both thevertical and horizontal componentsshall be consideredin thestability calculations.

2. SKIN FRICTION

The relief due to skin friction shall be ignored unlessspecifically permittedby the Engineer-in-charge.However, incaseof highly compressivesoils, skin friction, if any,maycauseincreasedbearingpressureon the foundationand shall be dulyconsidered.

3. FACTOR OF SAFETY OVER ULTIMATE PRESSURES

The factor of safety in assessingthe allowable passiveresistanceshall be 2 for load combinationswithout wind orseismic forces and 1.6 for load combinationswith wind orseismic forces.Themannerof applying factor of safetyshallbeas indicatedbelow:

(i) Pier wells foundedin cohesivesoils

The factor of safety asstipulatedfor the type of soil shall beappliedfor the net ultimate soil resistance,viz., (P-P) whereP and P are total passiveand active pressurerespectivelymobilisedbelow the maximum scourlevel.

79

IRC: 78-2000

INNER DREDGE HOLE

h = Kd IT~

hi = Kdl TT~

WHERE dl OUTER DIA OF WELLAFTER REDUCTION INSTE1NING THICKNESS

IS = DEPTH OF WELLUPTO MSL

Id = 3 (h—hi)

ti &,t2 ARE THEDEVELOPMENT LENGTHSFOR THE STEEL BEYONDTHE MINIMUM SECTION

Fig. 1. Sketchfor Reductionof SteiningThickness

OUTERSURFACE

81

IRC : 78-2000

Appendix-4

PRECAUTIONS TO BE TAKEN DURINGSINKING OF WELLS

(Ref. Clause 708.13)

1. CONSTRUCTiON OF WELL CURB AND STE1NINC

1.1. Cutting edge and the topof the well curb shall beplacedtruly horizontal.

1.2. The methods adopted for placingof the well curbshall dependon the siteconditions,andthe cutting edgeshall heplaced on dry bed.

1.3. Well steining shall he built in lifts and the first liftshall belaid after sinking thecurb atleastpartially for stability.

1.4. The steining shall be built in one straightline frombottom to top andshall alwaysbe at right angle to the planeofthe curb. In no case itshall be built plumbin intermediate stageswhen the wellis tilted.

1.5. In soft strata prone to settlement/creep,theconstructionof the abutmentwells shall be taken upafter theapproach embankment fora sufficientdistancenear the abutmenthas been completed.

2. SINKiNG

2.1. A sinking history record be maintained atsite.

2.2. Efforts shall be made tosink wells true to positionand in plumb.

2.3. Sumps made by dredging below cutting edge shallpreferably notbe more thanhalf the internal diameter.

84

IRC: 78-2000

2.4. Boring chart shall be referred to constantly duringsinking fortaking adequate care while piercing different typesofstrataby keeping the boring chart at the site and plotting thesoilas obtained for the well steiningand comparing it withearlierbore datato take promptdecisions.

2.5. When the wells haveto be sunk closeto each otherand the clear distanceis lessthan thediameterofthewells, theyshall normally be sunkin sucha mannerthat the differenceinthe levelsof the sump and the cutting edgein the two wellsdonot exceedhalf the cleargap betweenthem.

2.6. Whengroupofwells areneareachother, special careis needed that theydo not foul in the courseof sinking and alsodo not causedisturbanceto wells alreadysunk. The minimumclearancebetween the wellsshall be half the externaldiameter.Simultaneousand level dredging shall becarried out in thedredging holesof all the wells in the groupand plugging of allthe wellsbe donetogether.

2.7. During constructionpartially suck wells shallbetaken toa safedepth below the anticipated scour levelsto ensuretheir safety during ensuingfloods.

2.8, Dredged material shall not bedeposited unevenlyaround thewell.

3. USE OF KENTLEDGE

3.1. Where a well is loaded with kentledgeto provideadditional sinking effort, such load shall be placed evenlyon theloading platform, leaving sufficient spacein the middle toremove excavatedmaterial.

3.2. Wheretilts are present or thereis a dangerof welldevelopinga tilt, the positionof the lOad shall be regulatedin

85

IRC: 78-2000

sucha manneras to provide greater sinking effort on thehigherside of the well.

4. SAND BLOWS IN WELLS4.1. Dewatering shall be avoided if sand blows are

expected.Any equipment and men working inside the well shallbe broughtout of the well as soon asthereare any indicationsof a sand-blow.

4.2. Sand blowing in wells can often beminimisedbykeepingthe level ofwater inside the wellhigherthan the watertable and also by adding heavykentledge.

5. SINKING OF WELLS WITH USE OF DIVERS

5.1. Useof divers may be madein well sinking both forsinking purposes,like, removal of obstructions,rock blasting,etc. asalso for inspection.All safety precautions shall betakenas perany acceptable safety code for sinking with diversor anystatutory regulationsin force.

5.2. Only persons trained for thediving operation shallbeemployed.Theyshall work under expertsupervision.The divingarid otherequipments shallbe of an acceptablestandard.It shallbe well maintained forsafe use.

5.3. Arrangement for amplesupply of low pressurecleancool air shall beensuredthrough an armoured flexible hosepipe. Standby compressor plant will have to be providedin caseof breakdown.

5.4. Separate high pressureconnection for use ofpneumatictools shall be made. Electric lights, whereprovided,shall be at50 volts (maximum). The raisingof the diver fromthe bottomofwells shall be controlled sothat thedecompression

86

IRC 78-2000

rate for rivers conforms to the appropriate rate as laid down inthe regulation.

5.5. All men employed for diving purposes shall becertified to be fit for diving by an approved doctor.

6. BLASTING

6.1. Only light charges shall beused under ordinarycircumstancesand should be fired under water well below thecutting edge so thatthere is no chanceof the curb beingdamaged.

6.2. There shall beno equipment inside the wellnorshalltherebe any labour in the closevicinity of the well at the timeof exploding the charges.

6.3. All safety precautions shall be taken as perIS:4081“Safety Code for Blasting and Related Drilling Operations”,tothe extent applicable, whenever blastingis resortedto. Use oflarge charges,0.7 kg. or above,may not be allowed exceptunder expert direction and withpermissionfrom Engineer-in-charge.Suitable patternof charges may be arranged with delaydetonators to reduce thenumberof charges fired ata time. Theburdenofthe charge may be limited to1 metre and the spacingof holesmay normally be kept at0.5 to 0.6 metre,

6.4. If rock blastingis to be donefor seatingofthe well,the damage caused by the flying debris should beminimisedbyprovisionsofrubber mats covered over the blasting holes beforeblasting.

6.5. After blasting, thesteining shallbeexaminedfor anycracksand corrective measures shall betakenimmediately.

87

IRC : 78-2000

7. PNEUMATIC SINKING

7.1. The pneumatic sinking plant and other alliedmachineryshallnot only be of properdesignand make,but alsoshall be workedby competentand well trainedpersonnel.Everypart of the machinery and its fixtures shall be minutelyexamined before installation and use. Appropriate spares,standbys,safetyof personnelasrecommendedin theIS:4 188 forworking in compressedair mustbekept at site. Safetycodeforworking in and other labourlaws and practicesprevalentin thecountry,as specified to provide safe, efficient and expeditioussinking shall be followed.

7.2. Inflammable materials shall not be taken into airlocks and smokingshall-beprohibited.

7.3. Whenevergasesare suspectedto be using out ofdredgehole, thesameshall beanalysedby trainedpersonnelandnecessaryprecautions adopted to avoid hazard to life andequipment.

7.4. Where blasting is resortedto, it shall be carefullycontrolled and all precautions regarding blasting shall beobserved.Workers shall be allowed inside after blasting onlywhen a competent and qualified person has examined thechamberand steining thoroughly.

7.5. The weight of pneumaticplatform and that ofsteining and kentledge,if any, shall be sufficient to resist theuplift from air inside,skin friction beingneglectedin this case.

7.6. If at anysectionthe total weightactingdownwardsisless than the uplift pressureof air inside, additional kentledgeshall be placedon the well.

7.7. if it is not possibleto makethe well heavy enough

88

IRC: 78-2000

during excavation.“Blowing Down” may be used.The menshould be withdrawn and the air pressurereduced.The wellshouldthenbeginto movewith asmall reductionin air pressure.“Blowing Down” shouldonly beusedwherethegroundis suchthat it will not haveup insidethe chamberwhenthepressureisreduced.When the well doesnot move with a reductionin airpressure,kentledgeshould be added.Blowing down should bein short stagesandthe dropshouldnot exceed,0.5 metreof anystage.To control sinkingduringblowing down,useofpacksorpackagingsmay be made.

8. TILTS AND SHIFTS OF WELLS

8.1. Tilts andshifts shall becarefullycheckedandrecordedregularlyduringsinking operations.Forthepurposeofmeasuringthe tilts along and perpendicularto the axis of thebridge, levelmarksat regularintervalsshallbe paintedon the surfaceof thesteining ofthe well.

8,2. Wheneverany tilt is noticed, adequatepreventivemeasures,like, putting eccentric kentledge,pulling, strutting,anchoringor dredgingunevenlyand depositingdredgematerialunequally, putting obstaclesbelow cutting edge, after jettingetc.,shallbeadoptedbeforeany furthersinking.After correction,the dredgedmaterial placedunevenlyshall be spreadevenly.

8.3. A pair of wells closeto eachotherhavea tendencyto comecloserwhile sinking. Timber struts may be introducedin betweenthe steining of thesewells to preventtilting.

8.4. Tilts occurring in a well during sinking in dippingrocky stratacanbesafeguardedby suitablysupportingthe kerb.

89

IRC: 78-20009. SAND ISLAND

9.1. Sandislandwhereprovidedshallbe protectedagainstscourandthetop level shallbesufficiently abovetheprevailingwater level so that it is safeagainstwave action.

9.2. The dimensionof the sandislandshall not be lessthan threetimes the dimensionin planof the well or caisson.

90

IRC : 78-2000

CAPACITY OF PILE BASED ON PILEINTERACTION

(Ref. Clause709.3.1)

Appendix-S

SOIL

where ApD

V

N&qN

VN~

Cp

Q,1 =R,~+

1. AXIAL CAPACITY OF PILES IN SOIL

Axial loadcarryingcapacityofthepile is initially determinedby calculating resistancefrom end bearing at toe/tip or waIlfrictionlskin friction alongpile surfaceorboth.Basedon the soildata,the ultimate loadcarryingcapacity(Q~)is given by:

where, R = Ultimate baseresistance

R1 = Ultimate shaft resistance

1.1. Rn’, i.e., Ultimate baseresistancemay be calculatedfrom the following:

= Ap(½D.yN7+P~Nq) + A~N~C~,

= Crosssectionalareaof baseof pile

= Pile diameterin cm

= Effective unit weight of soil at pile tip in kg/cm3

Bearing capacityfactorsbasedon angle of internalfriction at pile tip

= Bearingcapacity factor usually takenas 9

= Average cohesionat pile tip (from unconsolidated

undrainedtest)

= Effective overburdenpressureat pile tip limited to20 times diameterof pile for piles having lengthequal to more than 20 timesdiameter

91

IRC : 78-2000

2. R~i.e., Ultimate side resistancemay be calculatedfrom the following:

= ~KPd tanö A~+ aC ~

where K = Coefficient of earthpressure

= Effective overburdenpressurein kg/cm2 alongtheembedmentof pile for the ith layerwhere i variesfrom / to n

8 = Angle of wall friction betweenpile and soil indegrees.It maybe takenequalto angleof internalfriction of soil

Asi = Surfaceareaof pile shaft in cm2 in the ith layer,

wherei varies from I to n

As = Surfaceareaof pile shall in cm2

a = Reduction factor

= Average cohesion in kg/cm2 throughout theembeddedlength of pile (from unconsolidatedundrainedtest)

3. While evaluatingeffectiveoverburdenpressure,totaland submergedweight of soil shall be consideredabove andbelow water table respectively.

4. Theinitial valueofK maybe takenas1.5 which canbe further increasedupto 1.8 in particularcasesas specifiedinClause709.2.2 (v).

5. Thefollowing valueof a maybe adopteddependingupon consistencyof soil:

92

IRC : 78-2000

Qu = ~ A,, +/. A,

= Point resistanceat baseto be takenas averageofthe value over a depth equal to 3 times thediameterof pile aboveandone time the diameterof pile below the tip.

A,, = Cross-sectionalareaof baseof pile

f = Average side friction and following co-relationmay be usedas a guide:

Type of soil

Clay

Side Friction, f

q,/25Stiff q/15

Mixture of silts andsand with tracesof clay

q,/50q,/100

LooseDense

= Static point resistance

Consistency N Value Bored pilescast-in-situ

Driven cast-in-situ piles

Soft to very soft clay

Medium

Stiff

Very stiff

<4

4-8

8-15

>15

0.7

0.5

0.4

0.30

1

0.7

0.4

0,3

6. For piles in over consolidatedsoils, the drainedcapacitymay be evaluated.

7. When full static penetrationdatais availablefor theentire depth, then

where q~,

Soft

q~

93

IRC : 78-2000

8. Where soft compressible clay layer is encountered,anycontributiontowardscapacityof pile from suchsoil shallbeignoredand additional load on pile on accountof downwarddragon pile dueto consolidationof soft soil shallbeconsidered.

Note: For factorsof safetyof piles in soil, referClause709.3.2.

°. CAPACITY OF PILES IN ROCK

A pile socketedinto rock derives its capacityfrom endbearingand socketside resistance.The ultimate load carryingcapacitymay be calculatedfrom

QR~+Rq~=K~p.q~,4A6+Aq

where

Qa = Ultimate capacityof pile socketedinto rock

Re = Ultimate endbearing

= Ultimate side socketshearK,,~ = An empirical co-efficient whose value ranges

from 0.1 to 0.4

= Averageuniaxial compressivestrengthof rock attip level

= Crosssectionalareaof baseof pile

= Depth factor= i + 0.4 x Lengthof socketDia. of socket

Lengthof socketmay be limited to 0.5 x dia. ofsocket

A, = Surfaceareaof socket

= Ultimate shearalongthe socketvalueofq, may betakenas 50 kg/cm

2 for normal rock which may bereducedto 20kg/cm2 for weatheredrocks.

Note : 1. For factorsof safetyon Re & R~,refer Clause709.3.2.2. The maximum allowable end bearingpressureshould

belimited to 30 kg/cm2 after applying factorof safety.

94

IRC: 78-2000

Append&x-6

FILLING BEHIND ABUTMENTS, WING ANDRETURN WALLS

(Ref. Clause710.1.4)

1. FILLiNG MATERIALS

The type of materials to be used for filling behindabutments and other earth retaining structures, should beselectedwith care.A generalguide to the selectionof soils isgiven in Table 1.

Table I. General Guide to ~beSelectionof Soils on Basis ofAnticipated Embankment Performance

Soil groupaccordingtolS:l498-l970

Visualdescriptian

Max. drydensityrangekg/rn3

Optimummoisturecontentrangepercent

AnticipatedembankmentperformanceMost probable Possible

GW, GP, GM,SW, HP

. Granular

materials1850-2280 7 - 15 Good to Excellent

SB, SM, GM,GC, SM, SC

- Granularmaterialswith soil

1760-2160 9 - 18 Fair to Excellent

SP - Sand 1760-1850 19 - 25 Fair to Good

ML, MH, DL CL, SM,SB, SC

Sandy Silts& Silts

1760-2080 10 - 20 Fair to Good

2. LAYING AND COMPACTION

2.1. Laying of Filter Media for Drainage

Thefilter materialshallbewell packedto athicknessofnotless than 600 mm with smallersizetowardsthe soil andbigger

95

IRC : 78-2000

size towards thewall and provided over the entire surface behindabutment, wings orreturn walls to the full height.

Filter materials need not be providedin case the abutmentis of spill throughtype.

2.2. Density of Compaction

Densitiesto be aimed atin compaction shall be chosen withdue regard to factors, such as, thesoil type, height ofembankment,drainage conditions,position of the individuallayersand type of plant availablefor compaction.

Each compactedlayer shall be testedin the field fordensity and accepted before the operationsfor next layer arebegun.

3. EXTENT OF BACKFILL

The extentof backfill to beprovidedbehindthe abutmentshould be asillustrated in Fig. 1.

4. PRECAUTIONS TO BE TAKEN DURING CONSTRUCTION

4.1. The sequenceof filling behindabutments, wingwalls

and return walls shall be so controlled that the assumptionsmade in the design are fulfilled and theyshould clearly beindicatedin the relevant drawings.For example, if the earthpressurein front of the abutmentis assumed in the design, thefront filling shall also be done simultaneously alongwith thefilling behindabutment,layerby, and in case the filling behindabutment before placing the superstructureis considerednotdesirable,the filling behind abutmentshould alsobe deferredto

a later date, In caseof tie beams andfriction slabs,special careshall be taken in compactingthe layer underneathand. above

96

IRC: 78-2000

Fig. 1.

them so that no damage is done to them by mechanicalequipment.

4,2, Special precautions should be taken to prevent anywedging action against structures, and the slopes bounding theexcavation for the structure shall be stepped or stnitted toprevent such wedging action.

4.3. Adequate number of weep holes not exceeding onemetre spacing in both directions should be provided to preventany accumulation of water and building up of hydrostaticpressure behind the walls. The weep holes should he providedahove the low water Level.

La— ewfl.crOs ,~u.

APPROACH

Wt6P KOLRSnawip *7

I —in

I I

57