IRC:SP:82-2008

GUIDELINES FOR DESIGN OF CAUSEWAYS AND SUBMERSIBLE BRIDGES

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IRC:SP:82-2008FirstPublished:November, 2008

Reprinted

: June, 2009

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(All Rights Reserved. No part of this publication shall be reproduced. translated or tranmitted in any form or by any means without the permission of Indian Congress)

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Printed atIndia Offset Press, A-1, Mayapuri, New Delhi-l l0064 (500 copies)

IRC:SP:82-2008

CONTENTS

PagePersonnel oftheBridges Specifications & Standards Committee (i) 1

J

1.2.3.

Introduction Scope General Features Hydrology and Hydraulics Waterway and Afflux Scour and Foundations Design Approaches, Protection Work and Appurtenances References

4 15 60

4. 5. 6. 7. 8. 9.

72

96 130 146

. ...

IRC:SP:82-2008

PERSONNEL OF THE BRIDGES SPECIFICATIONS AND STANDARDS COMMITTEE(As on 29.3.2008)

Sharan, G. (Convenor) 2. Lal, Chaman (Member Secretary) 3. Sinha, vx.

1.

Director General (Road Development), Ministry of Shipping, Road Transport & Highways, New Delhi Chief Engineer (B) (S&R), Ministry of Shipping, Road Transport & Highways, New Delhi Secretary General, Indian Roads Congress

MEMBERS4. Agrawal, K.N. 5. Alimchandani, C.R. 6. Banerjee, A.K. 7. Banerjee, T.B. DG(W) (Retd.), CPWD, C-33, Chandra Nagar, Ghaziabad Chairman & Managing Director, STUPConsultants Ltd., Mumbai Member (Tech.) (Retd.), NHAI B-21 0, Second Floor, Chitranjan Park, New Delhi Chief Engineer (Retd.), Ministry of Shipping, Road Transport and Highways, B-830, Avenue, Indira Puram, Ghaziabad Director (Tech.) B. Engineers & Builders Ltd., Bhubaneswar Joint Director General, Institute for Steel Dev. and Growth, (INSDAG) Ispat Niketan Kolkata Advisor, L&T, B/11 02, Patliputra Co-op. Housing Society Ltd. FourBunglow Signal, Mumbai Managing Director, Consulting Engg. Services (I) Pvt. Ltd., 57, Nehru Place, New Delhi Chief Engineer (Retd.), MOST Consultant, SpanConsultants(P) Ltd. nc, Gurudwara Road, Madangir, New Delhi ChiefEngineer, Ministry of Shipping, Road Transport and Highways, New Delhi Executive Director (B&S) & Structures Directt., Room No. 213, Annexe II, Research Design & Standards Orgn., Manak Nagar, Lucknow Director and Vice-President, STUP Consultants Ltd. P-11, Darga Road, Park Circus, Kolkata ChiefEngineer, of Shipping, Road New Delhi Director (Engg. Core), STUP Consultants Ltd., Plot No. 22A, Sector 19C, Palm Beach Road, Vashi, Navi Mumbai CE (Retd.), MP, PWD, Consultant, -2/136, MahavirNagar, Bhopal Chief Engineer (Retd.) (NH), BlockNo. A-8, BuildingNo. 12, HajiAli Govt. Officers Qtrs. Mahalaxmi, Mumbai DG(RD) & Addl. Secy. (Retd.), MOST, H-54, Residency Greens, Green Woods City, Sector 46, Gurgaon (Haryana) DG(RD) & AS (Retd.), MORT&H, D-86, Sector 56, NaIDA E-in-Ch'ief (Retd.), UPPWD; E-002, Krishna Apra Residency, Sector NOIDA (UP) Scientist-G, Central Road Research Instt. Delhi Mathura Road, New Delhi

(i)

8. Basa, Ashok 9. Bandyopadhyay, Dr. T.K. 10. Bongirwar, P.L. 11. Chakraborty, S.S. 12. Chakrabarti, S.P. 13. Dhodapkar, A.N. 14. Gupta, R.K.

15. Ghoshal,A. 16 Indoria, R P 17. Joglekar, S.G. 18. Kand, Dr.

c.v.

19. Kanhere, D.K. 20. Koshi, Ninan 21. Kumar, Prafulla 22. Kumar, Vijay 23. Kumar, Dr. Ram

IRC:SP:82-2008

24. Manjure, P.Y. Director, Freyssinet Prestressed, Concrete Co. Ltd., Mumbai 25. Mukherjee, M.K. Chief Engineer, (Retd.) Ministry of Shiping, Road Transport & Highways, 401182, Chitaranjan Park, New Delhi 26. Narain, A.D. DG (RD) & Add\. Secretary (Retd.), MOST, B-I86, Sector 26, NOIDA 27. Ninan, R.S. ChiefEngineer (Retd.), Ministry of Shipping, Road Transport & Highways, New Delhi 28. Puri, S.K. ChiefGeneral Manager, National Highways AuthorityofIndia, Plot No. G-5 & 6, Sector 10, Dwarka, New Delhi -29. Rajagopalan, Dr. N. ChiefTechnical Advisor, L&T-RAMBOLL ConsultingEngineers Ltd., 339-340,Anna Salai, Nandanam, Chennai 30. Sharma, R.S. Past SecretaryGeneral, IRC, C-478 Second Floor, Vikas Puri, New Delhi 31. Sinha,N.K. DG(RD) & SS (Retd.) MORT&H, G-I365, Ground Floor, Chitaranjan Park, New Delhi 32. Sinha, S. Addl. Chief Transportation Officer, ClDCO Ltd. ClDCO Bhavan, 3rd Floor, CBD Belapur, Navi Mumbai 33. Tandon, Prof. Mahesh Managing Director Tandon Consultants (P) Ltd., New Delhi 34. Tamhankar, Dr. M.o. Emeritus Scientist BH-l/44, Kendriya Vihar Kharghar, Sector- 1, NaviMumbai 35. Velayutham, Y. DG(RD) & SS (Retd.) MOSRT&H, Flat No.4, Nalanda Appartment, D Block,Vikaspuri, New Delhi 36. Vijay, P.B. DG(W) (Retd.), CPWD, A-39/B, DDA Flats, Munirka, New Delhi 37. Director & Head Bureau of Indian Standards, ManakBhavan, New Delhi (Civil Engg.) Directorate General Border Roads, Seema Sadak Bhawan, 38. Add\. Director General Naraina, New Delhi

Ex-officio Members

1. President, IRC 2. Director General (Road Development) 3. Secretary General

(H.L. Mina), Secretary to the Govt. of Rajasthan PWD, Jaipur (0. Sharan), Ministry of Shipping, Road Transport and Highways, New Dellii (Y.K. Sinha), Indian Roads Congress, New DelhiCorresponding Members

1. Bhasin, P.C. 2. Reddi, S.A. 3. Raina, Dr. V.K. 4. Rao, Dr. T.N. Subba

ADG (B), MOST (Retd.) 324, Mandakini Enclave, New Delhi 72,ZeniaAbad, Little GibbsRoad, Malabar Hill, Mumbai Flat No. 26, Building No. 1110 Road No. 3223, Mahooz Manama-332, Bahrain (Middle East) Chairman, ConstrumaConsultancy (P) Ltd., Mumbai

(ii)

IRC:SP:82-2008

GUIDELINES FOR DESIGN OF CAUSEWAYS AND SUBMERSIBLE BRIDGES1. INTRODUCTION

1.1. TheGuidelines for Design ofCauseways and Submersible Bridges hadbeen under theconsideration ofthe earlier General Design Features Committee since theyear 2004. Later on this Committee wasmerged with the General Design Features (Bridges and Grade Separated Structures Committee (B-1) at the timeofreconstitution in January, 2006. TheGeneral Design Features Committee in itsmeeting held on May, 2004 had constituted asub-group consisting ofShri P.L. Bongirwar, Dr. C.Y. Kand, S/Shri D.K. Rastogi, M.Y.B. Rao and Late Shri N.K. Patel. Thereafter, thedraftas prepared bytheSub-group andShri S.K. Kaiastha wasconsidered by thereconstituted General Design Features (Bridges and Grade Separated Structures Committee, B-1) in a number of meetings andfinalized it in itsmeeting held on 12th October, 2006 subject to incorporation ofcertain comments byits Convenor, Shri Prafulla Kumar.Thepersonnel ofB-1 Committee isgiven below: Kumar, Prafulla Indoria, R.P. Rustagi, S.K.

Convenor Co-Convenor Member-Secretary

MembersAlimchandani, C.R. Arora, H.C. Agarwal, K.N. Bagish, Dr. B.P. Basa,Ashok Bhowmick, Alok Bongirwar, P.L. Chandak, P.R. Jangde, K S Kand, Dr. C.Y. Kumar, Ashok Kumar, Vijay Kumar, Kamlesh Kurian, Jose Naryan, Deepak Reddi, S.A. Ramakrishnan, R. Rastogi, D.K. Reddy, Dr. 1.S.Roy, Be

Rep. ofRDSO,Lucknow (S.C. Gupta) Rep. ofMSRDC, Mumbai (S.M. Sabnis)

Corresponding MembersTandon, Prof. M.C. Taunk,G.S. Mukherjee, M.K.

Ex-officioMembersPresident; IRC (Mina, H.L.) DG(RD), MOSRT&H (Sharan, G.)

Secretary General, IRC (Sinha, Y.K.)

IRC:SP:82-2008 Thereafter, thedraft guidelines for Design of Causeways and Submersible Bridges were considered bytheBridges Specifications and Standards Committee (BSS) initsmeeting held on J'" November, 2007. The Committee formed a Sub-group comprising Shri Chaman Lal, CE(B) S&R, MOSRT&H, Shri M.Y.B.Rao, Dr. C.Y. Kand and Shri Sharad Varshney, Addl. Director (Technical), IRC fortechnical enhancement ofthe document. The Sub-group metthrice on9.1.2008, 1.2.2008 and 23.5.2008 and putupthedraft document again to Bridges Specifications &Standards Committee.1.2. 1.3... The valuable suggestions offered bythe members of General Design Features

(Bridgesand Grade Separated Structures) Committee (B-1) and Bridges Specifications &.Standards Committee are duly incorporated.

1.4. The draftdocument was approved bythe Bridges Specifications and Standards Committee in itsmeeting heldon29.3 .2008, and theExecutive Committee in itsmeeting heldon 11.4.2008 andauthorized Secretary General, IRC toplace thesame before Council. The document was approved bytheIRC Council inits 1851h meeting held on 11.4.2008, atAizwal (Mizoram) for printing subject to incorporation of some comments offered bytheCouncil members.

2

IRC:SP:82-2008 2. SCOPE This document contains guidelines for planning and design ofsubmersible structures like fords, dips, causeways andsubmersible bridges onvarious categories ofroads viz. State Highways, Major District Roads, Other District Roads and Village Roads inthecountry.

3

IRC:SP:82-2008

3. GENERAL FEATURES3.1. Definitions

Thefollowing definitions shall beapplicable for thepurpose ofthese Guidelines.3.1.1. Bridge

Bridge is a structure having atotal length ofabove 6mbetween theinner faces of the dirt walls for carrying traffic or other moving loads over a depression or obstruction such as channel, road or railway. These are classified as minorandmajor bridges as per classification given below: (a) Minor Bridge A minor bridge is a bridge having a total length of upto 60 m. A minor bridge upto a total length ono missometimes classified as a small bridge. A major bridge is a bridge having a total length of above 60m.f

(b) Major Bridge

3.1.2. High level bridge

A highlevel bridge is a bridge which carries theroadway above the highest flood level of thechannel.3.1.3. Submersible bridge

A submersible bridge is a bridge designed to be overtopped during floods.3.1.4. Causeway

Acauseway isa paved submersible structure with orwithout openings (vents) which-allows flood to passthrough and/or over it.

3.1.5. Ford

A ford is an unpaved shallow portion in a river or stream bed which can be used as a crossing during dry flow.

3.1.6. Culvert

A culvert is a cross-drainage structure having atotal length of6 morless between theinner faces of the dirt walls or extreme ventway boundaries measured atright angles there to.

3.1. 7. Channel

A channel means a natural or artificial watercourse.3.1.8. Afflux

It is the risein theflood level of thechannel immediately onthe upstream of a bridge as a result of obstruction to natural flow caused bythe construction ofthebridge andits approaches.

4

IRC:SP:82-2008

3.1.9. Highest Flood Level(HFL) Highest flood level isthe level ofthe highest flood ever recorded orthe calculated level for the design discharge, whichever ishigher. 3.1.10. Ordinary Floodlevel (OFL) Ordinary flood level isthe level offlood expected tooccur every year. It canbedetermined byaveraging the highest flood levels ofseven consecutive years. 3.1.11. Low Water (LWL)

Low water level is the level ofthe water surface attained generally inthe dryseason. It can also be determined byaveraging thelow water levels recorded inseven consecutive years. 3.1.12. Design Flood Level (DFL)

It isthe highest flood level for which the structure must bedesigned. It corresponds tolevel ofhighest flood of 50 years 100 years returnperiod (whichever is chosen for design) or the highest known flood level ifthe same happens to behigher.3.1.13. Defined Cross-section

It istheundisturbed natural cross-section ofriver which does not exhibit signs oferosion or silting ofbed.3.1.14. Protected Bed Level (PBL)

It is thelevel atwhich thebedsurface is protected against erosion due to flow of water.3.2. Types of SubmersibleStructures

3.2.1. FOI

Fords areunpaved structures andare suitable only for roads having very low volume of traffic. These are thesimplest form ofcrossings where the stream is wide and shallow, velocity of flowing water islow and bed surface isrelatively firm. In case the bedsurface isnot firm enough and notcapable ofcarrying the vehicular traffic, thebedcanbestrengthened and made more even with buried stones justbelow thebedsurface. If thestones arelikely to becarried away inflow, this is prevented byconstruction of barriers made of suitable size of boulders or wooden piles. Boulders ( neither too large which may result in scouring ofbednor small likely tobe carried away byflow) are placed across the river bedat downstream side oftheford to filter the flow ofwater and retain small size particles ofbedmaterial like sand, gravels etc. resulting ina more even surface for vehicular traffic. Fig. 3.1 shows atypical cross-section of suchtype of ford.5

lRC:SP:82-2008

GUIDE POSTS BOULDERS

1I

ROADWAY

-I

GUIDE POSTS

PLUNGE

... :.

---------

fLOW

BED

(A) FORD WITH DOWNSTREAM BOULDERS

1x1m ROCK FILLED GAStON

(B) FORD WITH DOWNSTREAM GABION

GUIDE POSTS

GUIDE POSTS FLOW..

.

'

...

..

100mm

LOGS

2m LONG AT 600mm c/c

(C) FORD WITH TIMBER POSTS

Fig. 3.1. Typical Details of Fords

6

IRC:SP:82-2008

3.2.2. Causeways

There are mainly three types of causeways:(a) Flush causeway

Inthis typeofcauseway which isalso called paved dipor roaddam, thetop level of road is keptsame asthat ofbedlevel ofthechannel. It is suitable where the crossing remains dryfor most of partofyear i.e. thestream is notperennial. Flush causeways arenot suitable for crossing the streams with steep bedslopes causing high velocity even in lowfloods. Thecauseway covers the full width ofthe channel Fig. 3.2.

CUT OFF WALL BURIED

APRON

CARRIAGEWAY

Fig. 3.2. Typical Features of Paved dip/Flush Causeway (b) Vented causeway

A causeway provided withvents to permit normal flow of the stream to passunder thecauseway is known as vented causeway. Vented causeways areclassified as low vented causeways and highvented causeways.(i) Low vented causeway

Low vented causeways areprovided to cross quasi-perennial streams having sandy beds in areas annual rainfall less than1000 andwhere thecarriageway of a7

IRC:SP:82-2008 flush causeway would beliable to getslushy due to post monsoon flow in the stream. The height isgenerally less than 1.20 mabove the bed ofthe watercourse. Inexceptional cases, the height maybe 1.50 mabove the bedlevel. Small sizeof vents in the form ofhumepipes, short span slabs/R.C.C. Box cells areprovided inthewidth of stream. Thesilllevel ofvents iskept about 150 mm- 300 mmbelow theaverage bed level of thestream.(ii) Highvented causeway

Highvented causeway is provided when a roadcrosses a stream having one or more ofthefollowing characteristics: (i) Sizeable catchment areawith annual rainfall more than 1000 mm

(ii) Depth of postmonsoon flow is more than 900mm (iii) Flow is perennial butnotlarge(iv) Banks arelownecessitating construction ofhigh embankment inthe stream bed from considerations of the free boardin non-submersible portion as well as geometric standards of approach roads The heightof the causeway above the bed is generally kept between 1.5 m to 3.0 m and larger size of vents comprising of hume pipes or simply supported/continuous R.C.C. slab superstructure overa seriesof shortmasonry piers or series of arches or boxeswith individual spans less than 3 m are provided.

3.2.3. Submersible bridgeSubmersible bridge isnormally sub-classified ashigh submersible bridge orlowsubmersible bridge depending upondecklevel withreference to OFL. The deck level of high submersible bridge is fixed with reference to OFL and vertical clearance, and as suchthe structure serves as high level bridge during OFL but gets submerged under higherfloods withpermissible number andduration ofinterruptions. Thistypeofbridge is suitable for streams having large variationbetween HFL and OFL. The decklevel oflow submersible bridge is fixed above the OFL so as to ensurethat the interruptions caused to traffic remain within permissible limits.

3.3.

Selection of Type of Submersible Bridge/Causeway

3.3.1. GeneralThetype ofstructure (i.e. high level or submersible) across a watercourse (channel) has to bejudiciously selected on the basisof reconnaissance inspection report andavailable data. The choice mainly depends onthe classification of theproject road, requirements oftheuser authority, hydrology of the watercourse andavailability of funds for the

8

IRC:SP:82-20083.3.2. Considerations in the selection of type of submersible structures

Selection oftype of submersible structures (i.e. ford or causeway or submersible bridge) inter-alia depends on: Requirements of user authority and availability offunds (b) Category, importance of road and traffic intensity (c) Population to be served (d) Nature ofstream i.e. flashy/perennial/seasonal etc. and velocity ofwater during floods (e) Duration, magnitude offloods and interruption to traffic (f) Spread anddepthof waterduring floods and postmonsoon period (g) Extent of catchment area3.3.3. Criteria for avoiding/selection of submersible structures

Intheabsence of any directives/guidelines bytheuser authority, thefollowing criteria may befollowed for selection ofsuitable type ofsubmersible structures including causeways ondifferent categories of roads. (I) These should be avoided onNational Highways (2) These may notbe considered foradoption inthefollowing situations: (i) Roads ofeconomic importance, roads linking important towns orindustrial areas or areas withpopulation more than 10,000 where alternative all weather route with reasonable length ofdetour is notavailable(ii) On roads which are likely to be upgraded or included, from future traffic

considerations, intheNational Highway network(iii) If the length of a highlevel bridge at such crossings would be lessthan 3am

except where construction ofhigh level structure is noteconomically viable (iv) mean velocity ofstIeam during floods is more than 6 mJsec (v) If the cost of submersible bridge with its approaches is estimatedto be more than approximately 70% of the cost of high level bridgewith its approaches, nearabout the same site(vi) Iffirm banks are available and approaches are incutting orheight ofembankment for submersible portion ofapproaches is more than 2 m(vii) Where there arefaults in theriver bed (viii) If after completion ofthesubmersible structures, thenumber of interruptions in

a year caused totraffic andduration ofthe interruptions arelikely to exceed the suggested values given in Table 3.1 below.

9

lRC:SP:82-2008Table 3.1: Permissible Number and Duration of Interruptions

S.No.

Category of Roads

Maximum No. of permissible interruptions in a year

Duration of interruption in hours at a time

1.

State Highways, M.D.Rs., roads linking important towns, industrial estates. O.D.Rs,Village Roads

6

2-6 h duration, less than 2 h not to be considered and more than 6 h not acceptable 6-12 h duration, less than 6 h notto be considered and more than 12 h not acceptable

2.

6

3.3.4. Fords

Fords (i.e. unpaved causeway), though the cheapest typeof crossing, should be avoided as far aspossible andits adoption should be limited to sites where stream is wide, shallow with depthof water not more than 200 mm, velocity of flow is low (lessthan2 m/sec), bed is firm, volume oftraffic islow and thewater isnotlikely tobecome muddy due tothetraffic, endangering theaquatic lifeinthewatercourse ortheenvironment.3.3.5. Causeways

Causeways forcrossing a wide watercourse withlowbanks andhaving nottoo large but perennial flow should be proposed with caution. These should be proposed on rural and less important linkroads, notlikely to generate much traffic innearfuture dueto situations likedead end, low habitation and difficult terrain conditions. causeways may beproposed onstreams of flashy nature with high frequency ofshort duration oratsites where construction ofsubmersible bridge isnoteconomically viable.3.3.6. Submersible bridges

These can be provided in all situations other than those mentioned in paras 3.3.4 and 3.3.5 above where provision of submersible structures is technically feasible and economically viable.3.4. Geometric Standards

3.4.1. General

(a) A road conforming to sound geometric standards resultsin economical operation of vehicles andensures safety. Geometric standards for approach roads to a submersible bridge or causeway depends ontheclassification ofroad (i.e. State Highway (SH) or Major District Road (MDR) orRural Road (RR) which include Other District Road (ODR) and Village Road (VR), location (i.e. inurban ornon-urban area), terrain (i.e. plainorrolling ormountainous or steep), length of crossing and requirements ofthe userauthority (i.e. local, State Govt. etc.).

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IRC:SP:82-2008 (b) The geometric standards in general should conform to relevant IRC Publications (i.e. IRC:5, IRC:38, IRC:52, IRC:73, IRC:86, IRC:SP:20, IRC:SP:23 and IRC:SP:48). (c) Thereis no specific separate guideline in theIRC codes regarding geometric design standards for submersible structures including immediate approaches except in IRC:5, which stipulates thatvented causeways/submersible bridges shall provide for at least two lanes of traffic (7.5 m wide carriageway) unless one lane of traffic (4.25 mwide carriageway) isspecially permitted inthe design. However, theprovision forsingle lane width is likely toberevised and has been increased inthese guidelines. Refer Table 3.2. 3.4.2. Width of cross drainage structures Cross-drainage structures aredifficult to widen ata later date. As such, road width should be selected carefullyat the planning stage itself. In case a road is likely to be upgraded in the foreseeable future, it is desirable to adopt higher roadway width. Minimum carriageway widthof submersible structures, measured at rightangles to the longitudinal center line ofthestructure, between theinner faces ofdiscontinuous kerbs/safety kerbs wherever provided or between the guideposts/stones (without kerbs), should be as given in Table 3.2.Table 3.2: Minimum Width of Carriageway for Submersible Structures

I

Category of road

Minimum Width of Carriageway*(m) Plain & Rolling Terrain Mountainous and Steep Terrain

Single lane Two lanes

6.8

5.5 7.5

7.5

Note:

*

Minimum width of carriageway should be suitably increased as per IRe:?3 in case of structures located on curves.

In case footpaths are provided, the width offootpaths should notbe lessthan 1.5 111 each. Thewidth of discontinuous safety kerbs, if provided should notbeless than600mm. Overall width between the outer faces of discontinuous kerbs/safety kerbs wherever provided or guideposts/stones/railings (without kerbs) of the structures with lengthupto 30 m should preferably be a little more to match withthe roadway width of immediate approaches Table 3.3. 3.4.3. Geometries of approach roads(i) Alignment ofthe road generally governs the site ofa submersible structure if thelength

of crossing isless than 60m. However, ifthe length ofthecrossing is more than60m,11

IRC:SP:82-2008 the suitability of the site for thesubmersible structure andthe geometric design of immediate approaches both should be considered together. In case the length of crossing ismore than 300 m, the most suitable site for the bridge should bethegoverning criteria.(ii) The approaches oneither side ofastraight submersible bridge should have a minimum straight length ono m and should be suitably increased, where necessary, to provide for theminimum sight distance for a vehicular speed of 35 km/h.(iii) Horizontal curves in immediate approach roads fora length of about 100 m on either

side of a submersible structure orcauseways should beavoided. Ifhorizontal curves have to beprovided intheapproaches, thesame should belocated beyond thestraight portion on either side and theminimum radius of curvature, thesuper-elevation and transition length should beprovided inaccordance with relevant stipulations contained in IRC:38. Radii ofhorizontal curves in case of immediate approach roads however should, not be lessthan 60m in case of plain androlling terrain and 30m in case of hilly terrain from road user safety consideration.3.4.4. Design speed

From consideration of safety ofroad users, lower design speed thanthatrecommended in IRC:73 shouldbe adopted for the immediate approaches to a submersible bridgeor causeway. Theinformatory boards installed on approaches should indicate permissible speed of35 km/h in case of plainand rolling terrain and20 km/h incase of mountainous and steep terrain irrespective of anyhigher speed adopted in the design of theroad.3.4.5. Roadway width

Width ofroadway should be as shown in Table 3.3.Table 3.3: Width of Roadway (m) S.No. I. Road Classification Plain & Rolllnz Terrain Steep Terrain State Highwaysi)&

**

single lane ii) two lanes i) single lane ii) two lanes

12.0* 12.0

6.25## 8.8

2.

Major District Roads

9.0 9.0

6.25## 8.8

3.

Rural Roads

i) single lane ii) two lanes

7.5*** 9.0

6.0## 7.5

12

lRC:SP:82-2008Notes: 1

* For single lane State Highways, width of roadway might be reduced to 9 m if the possibility of

I.

widening, the carriageway to two lanes is considered remote. 2. ** The roadway widths in mountainous and steep terrain, given above are exclusive of parapets (usual width 0.6 m) and side drains (usual width 0.6 m). 3. *** Roadway width for rural roads in plain and rollers terrain also may be reduced to 6.0 m in case where traffic intensity is less than 100 motor vehicles per day and traffic is not likely to increase due to situations like dead end, low habitation and difficult terrain conditions. 4 ## On roads subject to heavy snow fall. where regular snow clearance is done over long periods to keep the road open to traffic, the roadway width may be increased by 1.5 m. 5 The roadway widths for Rural Roads are on the basis of a single lane carriageway of 3.75 m. 6 In hard rock stretches, or unstable locations where excessive cutting might lead to slope failure, width of roadway may be reduced by 0.8 m on two-lane roads and 0.4 m in other cases. 7. On horizontal curves, the roadway width should be increased corresponding to the extra widening of carriageway for curvature.

3.4.6. Camber/crossfall The camber/crossfall on straight sections of immediate approaches andon submersible structures shouldbe unidirectional towards the downstream and as recommended in Table 3.4 depending on typeof surface of pavementTable 3.4: Pavement Camber/Crossfall Surface Type For all categories of roads Unidirectional Cross fall (%)I

I

l.

High Type bituminous surfacing or cement concrete Thin bituminous surfacing for approaches Brick/stone set pavement

2.0 2.5 3.0

2. 3.

Note: Shoulders of approach roads likely to be submerged during floods should be paved to same cross fall towards downstream as for pavement.

3.4. 7. Superelevation

Superelevation to beprovided onhorizontal curves iscalculated from thefollowing formula subject to the maximum values indicated in Table 3.5. Superelevation in m per m = (Design speed in km/h)' 1(225 x radius of curvein 111)Table 3.5: Maximum Permissible Superelevation

1.2.

Plain/rolling terrain and snow bound hill roads Hill roads not affected bysnow

7% 10%I"

13

iac. SP: 82-20083.4.8. Gradients

As ageneral rule, values ofruling gradients specified inIRe:?3 should beadopted. However, incase of immediate approaches tosubmersible structures, carrying substantial slow traffic, flatter gradients than ruling values should bepreferred. Nevertheless, gradients inimmediate approaches unless, otherwise permitted by user authority, should not exceed 5.0% (l in 20) irrespective of nature ofterrain.

I

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lRC:SP:82-2008

4. HYDROLOGY AND HYDRAULICS4.1. Hydrology

4.1.1. General

Forthedesign of anefficient andeconomical hydraulic structure, knowledge ofhydrology and the characteristics of theStream/River are of paramount importance. Abriefabout hydrology isgiven in Appendix 4.1. Inmost cases hydrological record ofthestream particularly data regarding floods may notbeavailable. Arational estimation of design flood discharge for thespecified return period leads to economical design of bridge foundations for submersible bridges. Thefailures of hydraulic structures arevery expensive as in mostcases, the indirect costs aremany times larger than thedirect costofbridge replacement. Some hydraulic structures especially bridges have failed inthepastmainly due to inadequate assessment ofHFLIDesign flood discharge andrarely due to structural failures. Due attention to the determination of hydrology of the structure needs to be paid as anirrational approach canlead to loss and destruction of the structure due to floods higher than thedesign floods.4.1.2. Determination of design discharge

Thedesign discharge for which thewaterway ofmost of thebridge including submersible bridges isto be designed should bebased ontheflood discharge corresponding to highest observed flood level, irrespective of the return period of that flood orthe flood years' return period whichever is higher, except in thecaseof important bridges whenreturn period may be takenas 100 years. The design discharge canbe determined bythefollowing methods: (1) (2) (3) (4) Empirical Methods SlopeArea Method Rational Method UnitHydrograph Method

4.1.2.1. Empirical methods

I

Based on studies conducted, some empirical formulae for specific regions have been evolved. Theempirical formulae for flood discharge suggested areintheform:(4.1 )

Where,

QA C n

= = = =

Max. flood discharge in m3/s Catchment Area in sq. km AnEmpirical Constant, depending uponnature andlocation of catchment A Constant

15

IRC:SP:82-2008

The mostcommonly adopted empirical formulae and recommended for use are:(i)

Dicken's formula based on dataof rivers in Central India, (ii) Ryve'sformulabased on Rivers in South India and(iii) Inglis formula based onWest Indian rivers inthe old Bombay Province. Details of these emperical formulae aregiven in Appendix 4.2.

Theempirical formule should, however, beused withduecaution as given below: (i) These weredeveloped forparticular region andfor small catchments and, therefore, have obvious limitations. The value ofC' at the bestis validonlyfor the region for whichit hasbeendetermined, as eachbasin has its owncharacteristics affecting run off

(ii) These involve only oneknown variable factor viz. areaof thecatchment andtherefore a large number of remaining factors that affect the run-off such as shape, slope, permeability of catchments etc. are to be accounted for in selectingan appropriate valueofthe coefficient 'C'.(iii) A correct value of' C' canonly bederived fora given region from anextensive analytical studyofthe measured flood discharge vis-a-vis characteristics ofthe basin. The value of'C' willtherefore be valid onlyfortheregion for whichit has beendetermined, as each basin has its own characteristics affecting run-off. Anew designer should use these formulae onlyunder the guidance of an experienced designer or expert.'

..

4.1.2.2. Slope area methodIn this method the maximum water level reached in a historic flood is estimated on the evidence of local witnesses, which may include identification of flood marks on structures or trees closeto the bridge site.The discharge is then calculated by: Q= AV Where, Q = dischargein m and A = wetted area in m2 V velocity oft1owin ill/see whichcan becalculated by the Mannmg's formula:(4.3)

(4.2)

Where, R = hydraulic mean depth. S = the energy slope which may be taken as equal to bed slope and n = rugosity coefficient. The details of the method are given in Appendix 4.3. This method has also considerable roomfor errordueto:(i)

..

The variability of bed profile slope etc. duringfloods from those measured during survey.

\

16\

(ii) The computation of stream velocity is dependent upon a subjective selection of an Empirical Coefficient of rugosity for different conditions of bed out of the various values recommended by Manning. 4.1.2.3. Rational method The rational method forflood discharge takes into account the intensity, distribution and duration of rainfall as well as the characteristics of the catchment area, such as shape, slope, permeability and initial wetness ofthecatchment. Therational formula is asfollows:(4.4)

Where,

QA Io

=

Maximum flood discharge in m' /s = Catchment area in hectare Max. intensity ofrainfall incrn/h Function depending upon characteristics ofthe catchment in producing peakrun off and given by0.056 fPt c +1

(4.5)

Where, 'f" is the areacorrection factor, 'tc 'is thetime of concentration in hours and' P' is permeability coefficientofthe catchment depending on the soil cover conditions and slope of catchment Thedetails about Rational Method aregiven in Appendix 4.4. The formulae may generally be adopted for catchment areas upto 500 sq. km and upto 2000 sq. km in exceptional cases. 4.1.2.4. Unit hydrograph method

stormrun-offat a given pointin the river, resulting from an isolatedrainfall of unit duration (normally taken as 6 h to 12h) occurring uniformly overthe catchment and producing unit run-off. The unit run-offadopted is 1 em depthover the catchment area.(ii) A Committee of Engineers appointed by Govt. ofIndia recommended a rational methodology based onuse ofdesign storms andunithydrographs forestimating design floods for different zones/sub-zones oflndia. Alist of thesezonesand sub-zones is givenin 'Annexure A' of Appendix 4.5. The report as preparedjointly by CWC, RDSO (Railways), MoSRT&H and IMD have been published by ewc, Govt. of India. These reports give methodology througha set of charts and graphsfor quick estimation of designflood of 25, 50 or 100 years of return periods for ungauged catchments.17

lRC:SP:82-2008(iii) Unithydrographs areprepared either by computation from direct run-offhydrograph for gauged streams or aresynthetically prepared from catchment characteristics for ungauged catchments and then used for finding design flood of desired return period. The detailed procedure for constructing Synthetic unit hydrograph andhowto obtain designHood from storm of corresponding returnperiod is illustrated in an example given in Appendix 4.5.

(iv) The unithydrograph method can givefairly preciseresults for drainage areas upto 5000 sq. km. Variation in assumptions madefor largerareas (>5000 sq. km) in the method areusually too great to be ignored.

4.1.2.5. Fixingdesign dischargeFlood discharge can be estimated by three or more different methods and the values obtained should becompared. The highest ofthese values should beadopted asthedesign discharge providedit does not exceed the next highest discharge by morethan 50%. If it does,restrict it to that limit.

4.1.3. Discharge through a submersible bridgeThe total discharge in the stream after the constructionof a submersiblebridge can be found by the method suggested by Johnson Victor as given below: Total discharge Q =

+ Qb + Qc(H + h )3/2 - hH3/2

(4.6) (4.6.1)

2 and Q = A x ---- Ca 3

Q b

=

Ab X

c,

(4.6.2) (4.6.3)

=Where,

x Cc

= Discharge between afflux upstream water levelanddownstream

waterlevelandA is its areaofflow

Qb = Discharge between downstream water levelanddecklevelAll

= Areaof flowbetween downstream waterlevelanddecklevel

Qc = Discharge through vents andAc is the areaof ventsC C, & Cc are coefficients of dischargeH

= Afflux

\8

IRC:SP:82-2008

haCa C,

= =

Head dueto velocity of approach.

0.625 for equation (4.6.1)

= Cc=O.9 for equations (4.6.2) and (4.6.3)

(Refer Fig. 4.1 for various parameters of flow.)(

.

4.1.4. In cases where the cross-section of the stream has wide spill zones of shallow depth, the discharge through causeway or low level submersible bridge can also be found by adding the calculated discharge of the threepartsviz. (a)Discharge through vents of areaAI, ( b) Flow over the causeway/submersible bridge proper through area A2 and (c) Flow over shallow triangular compartments of area A3 on eitherside of the main stream at the crossing. (See Fig 4.2).

AFFLUXED HFL HFL-\

lH=AFFLUX

Aa Ab

t

RTL Ac SOFFIT LEVEL

CROSS-SECTION

uS

AFFLUXED HFL

--,I

H HFL

D!STOP OF SLAB BOnOM OF SLAB

-cAVERAGE BED LEVEL

LONGITUDINAL SECTION

Fig. 4.1. Total Discharge at a Submersible Bridge19

IRC:SP:82-2008

TOP LEVEL OF PROTECTED BED

AREA Al

I

AREA AVAILABLE A1

FLOW AT

CAUSEWAY A=A1+A2+A3

AREA OF VENTS. PROTECTED AREA Of fLOW OVER EITHER SIDE. SLOPING APPROACHES

A2 = AREA OF FLOW OVER THE HORIZONTAl. PORTION OF THE

Fig. 4.2 Typical Vented Causeway

4.2.

Forces due to Water 4.2.1. HydroStatic Force

Force of stationary water on a solid surface is called thehydrostatic force. It force due to the afflux head and the force of buoyancy. A body submerged in water experiences an upward force dueto water pressure and this force is called' Buoyancy'. It mustbe considered for stability of structure ifthere is possibility where while considering combination of forces, stability ofthestructure is to beaffected. It is recommended thatwhile checking forminimum pressure on foundation, the maximum uplift pressure at high water level should beconsidered. Further, while checkingfor maximum pressure theminimum uplift pressure atthelowwater level should betaken into account. In case of submersible bridges, full buoyancy effect onthesuperstructure alsoneeds to be ed. 4.2.2. Hydrodynamic force of water current 4.2.2.1. Water current forces onfoundation above scourleveland on substructure Water currentcauses hydrodynamic force onthe submerged partof a body. These forces on a member canbe calculated bythe following formula as given in Clause2l3 ofIRC:6. P = 52KV 2 Where, P=

(4.7)

Intensity of pressure dueto water current in kg/m'

20

IRC:SP:82-2008 V K=

Thevelocity ofthecurrent atthepoint where thepressure intensity is being calculated in meter persecond and A constant having the following values for different shapes ofmembers as given inTable 4.1. Table 4.1: Shapes of Bridges Piers & Value ofK

VALUES OF K

SHAPES OF

iN PLAN

Ii .50

WITH SQUARE ENDS (AND FOR SUPERSTRUCTURE)

0.66

I

0.50

CIRCULAR OR SEMICIRCULAR ENDS

TRIANGULAR (THE ANGLE INCLUDED BETWEEN THE BEING DEGREES OR LESS)

0.50 TO 0.70

TRIANGULAR (THE ANGLE INCLUDED THE FACES BEING MORE THAN 30 OIGREES BUT 'LESS THAN 60 DEGREES)

0.70 TO 0.90

TRIANGULAR (THE ANGLE INCLUDED BETWEEN THE FACES BEING 60 TO 90 DEGREES OR LESS

0.45

EQUILATERAL ARCS OF CIRCLES

u.50

INTERSECTING AT 90 DEGREES

The maximum velocity at the top surface of flow shall be assumed to be times the maximum mean velocity ofthe current. Square ofvelocity at a height X from thepoint of deepest scour = U2 = 2 V 2 X H Where V isthemaximum mean velocity. Thevalue of V' intheequation (4.8) is assumed to vary linearly from zero at thepointof deepest scour tothesquare ofthe maximum velocity atthefree surface of water (Fig. 4.3).(4.8)

21

IRC: SP: 82-2008

FREE SURFACEOF WATER

t I

POINT OF DEEPEST SCOURI

Ii

\

4.2.2.2. Water current forces on superstructure

(i) The importance ofwatercurrent forces onthe superstructure is significant dueto the extent of obstruction offered bythebridgesuperstructure and its location. Sincethe submerged areaofsuperstructure exposed towater current forces is sufficiently large and the velocity of currentat its levelis alsohigh, the stresses on foundations dueto watercurrent forces actingon the submerged superstructure are quitepronounced. (ii) Flowingwater produces twotypes of forces on a submerged or partially submerged superstructure viz. the drag force and the lift force. Theseare characterized by two factors i.e. thedrag force co-efficient (Cd) andcoefficient oflift (CL) . Bothdragforce and lift force depend largely onthe shapeof the bodyand several otherfactors and these canbe bestdetermined byconducting hydraulic model studies, as explained in Appendix 4.6.

(iii) The results of modelstudies conducted so far do not conclusivelyrecommendany andco-efficient oflift (CJ. However, generalized values of co-efficient of drag presently the following method is adoptedfor calculation of drag force and uplift pressure onsuperstructures, in cases where it is not feasible oreconomically viable to conduct hydraulic model studies:

.

(a) Theexpression P = 52KV2 as givenin para4.2.2.1 be adopted with value ofK as 1.5for drag force. (b) Theexpression p = wh maybe adopted for calculating upliftpressure, Where 'w' is the unitweightof water and 'h' is the upliftheadunderthe deck and can be estimatedas h = thickness of slab + wearing coat andaffluxafter deducting the head loss due to increase in velocity through vents. The head loss is givenby the expression (V} - V2)l2g, Where Vv is the velocity through vents and V is velocity of approach.

II

22

IRC:SP:82-2008

Appendix 4.1A BRIEF ON HYDROLOGY

I ,

Hydrology deals with depletion and replacement of our water resources. The basic knowledge ofthis science ismust for Civil Engineer, particularly the one who isengaged indesign planning and construction ofhydraulic structures such as Bridges.I.

The Hydrologic Cycle: Most oftheearth's water sources such asrivers, lakes, oceans and underground sources, etc. gettheir supply from the rains, while therain water in itself istheevaporation from these sources. Water islost totheatmosphere asvapour from the earth, which is thenprecipitated back intheform ofrain, snow, hail, dew, sleet orfrost, etc. This evaporation and precipitation continues forever and thereby, a balance ismaintained between thetwo. This process isknown asHydrologic Cycle. It canbe represented graphically, as shown in Fig. 4.4./ / Precipitation Le. /(Rain, Snow, Hail, Sleet etc.)

r

/

/

/

/

Transpiration from Ve etations

Evaporation

-

.

25 .I

s

I

75"

25

-eOC

69..

X

..t '

!...

v: I\\

.)

r-.\J'I

I

....

I \ 897'I IL

\

(

\\ \ \ \ \ \

su

2T

b

75

-, -,

/!ffl.I

)I

1_!

)1

i

+-21

1. SUB ZONE BOUNDARY

2. RIVERSTOWNSl ... .

ARABIANSEA... ....

5. BRIDGE

x 129IN THE HAVE BEEN ROUNDED UP UP AFTER CONVERSION FROM FEET TO

7,.

..

NCONTOURS

1

IRC:SP:82-2008 Plate 4 for conversion of 50year24-h point rainfall to 50year 16-h pointrainfall since TD = 16 h 50 year 16 h point rainfall thus worked out to be 32.00 x 0.905 = 28.96 ern. Areal reduction factor of 0.915 corresponding to a catchment area of136.36 sq.km forTD = 16h was interpolated from Fig. 4.9 for conversion of point to areal rainfall. 50 year 16h arealrainfall = 28.96x 0.915 = 26.50 em. 1____

o z UJ oUJ

o4-HC UR

zI

2

Z

6

10

14

18

22

26

AREA 1x102 Sq. Km

Fig. 4.9 Step 7: Time Distribution ofAreal Raifnall 50-year 16-h areal rainfall = 26.50 em wasdistributed withthe distribution coefficients (Col. 16 of Table 4.6)to get 1h rainfall increments as follows: Thehourly rainfall increments in col.(4) ofthe above table were obtained by subtracting the successive rainfall values from 1h onwards. Step 8: Estimation of Effective Rainfall Units Designlossrate of 0.45 cm/hhas beenadopted for this sub-zone Tabie 4.7thecomputation of 1h effective rainfall units inCol. (4)bysubtracting thedesign loss ratein Col. (3)from l-h rainfall increments in Col. (2). The Column(2) in Table 4.8 is taken col. (4) of Table 4.7

43

RATIOS OF 24-HR. POINT RAINFALL TO SHORT DURATION RAINFALL.

-e00I

0.100 0.95 0.90 0.85 0.80 0.75 0.70 0.65

(mes.)

00---

ji

2

3 4 5

6

7

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

.I

0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05

I I 00 II

oz oW

>

ou

oo

[2

iii

I

II

I

i

I

I

I

I

I

I

I

I

I

I

I

I

I

I

0.360 0.505 0.570 0.620 0.665 0.700 0.730 0.760 0.780 0.805 0.825 0.850 0.860 0.875 0.890 0.905 0920 0.930 0.945 0.960 0.970 0.980 0.990 1.000

4

5

6

71 8

910 11 12 13 14 15 16 17 18 19 20 21 22 23 24

DURATION

(HOURS)

Plate 4

IRC:SP:82-2008

Table 4.6:Time in Hour Distribution

Distribution Coefficients ofAreal, Rainfall, Mahi and Sabarmati Basin, Subzones (a)h

Coefficient for Design Storm Duration of

I

2 (2)

3 (3)

4 (4)

5 (5)

6 (6)

7 (7)

8 (8)

9 (9)

10 ( 10)

II(I 1)

12 (12)

13

14 ( 14)

15 (15)

16 (16)

17 ( 17)

18 (18)

19 (19)

20 (20)

21 (21 ) (22)

23 (23)

24 (24) 1.00

25 (25) 24 23 22 21 20 19 18 17 16

(1 )24 23 22 21 20 19 18 17 16 15 14 13 12 11 \0 9 8 7 6 5 4 3 2 1

(13)

\.00 \.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.87 0.94 0.75 0.95 0.88 0.68 0.96 0.93 0.82 0.61 0.97 0.93 0.87 0.76 0.54 0.98 0.96 0.87 0.80 0.68 0.50 0.98 0.96 0.92 0.84 0.74 0.66 0.43 0.42 0.98 0.96 0.93 0.86 0.82 0.63 0.99 0.99 0.95 0.90 0.84 0.77 0.71 0.58 0.39 0.99 0.97 0.96 0.92 0.86 0.82 0.75 0.67 0.57 0.37 0.99 0.98 0.96 0.93 0.88 0.84 0.79 0.73 0.65 0.52 0.98 0.96 0.94 0.94 0.87 0.83 0.78 0.72 0.66 0.58 0.47 032 0.98 0.97 0.94 0.92 0.89 0.86 0.82 0.76 0.70 0.64 0.56 0.45 0.30 0.98 0.97 0.95 0.92 0.9\ 0.87 0.83 0.79 0.75 0.68 0.62 0.55 0-43. 0.29 0.99 0.98 0.96 0.94 0.91 0.88 0.86 0.82 0.77 0.73 0.66 0.60 0.53 0.41 0.28 0.99 0.98 0.97 0.94 0.93 0.89 0.86 0.83 0.80 0.76 0.70 0.64 0.58 0.52 0.40 0.24 0.99 0.97 0.96 0.94 0.93 0.90 0.87 0.85 0.82 0.76 0.73 0.68 0.62 0.57 0.51 0.39 0.22 0.98 0.97 0.96 0.94 0.91 0.88 0.85 0.82 0.78 0.76 0.72 0.66 0.63 0.56 0.50 0.41 0.33 0.22 0.99 0.98 0.97 0.95 0.93 0.89 0.86 0.84 0.80 0.76 0.74 0.70 0.65 0.61 0.55 0.48 0.40 0.32 0.21 0.98 0.97 0.96 0.95 0.93 0.90 0.88 0.84 0.82 0.78 0.75 0.72 0.68 0.63 0.59 0.53 0.47 0.39 0.31 0.18 0.99 0.98 0.96 0.95 0.93 0.90 0.88 0.85 0.83 0.80 0.77 0.74 0.71 0.67 0.62 0.58 0.52 0.46 0.38 0.30 0.16 0.99 0.98 0.97 0.95 0.94 0.92 0.89 0.86 0.84 0.80 0.78 0.76 073 0.69 0.65 0.61 0.57 0.51 0.43 0.36 0.28 0.14

0.99 0.98 0.97 0.95 0.94 0.93 0.90

0.84 0.82 0.78 0.77 0.74 0.7\ 0.67 0.63 0.59 0.55 0.50 0.42 0.35 0.27 0.13

15 14

12 1110

9 8 7 6 5 4 3 2

1

Note: Hourly rainfall distribution coefficients are given in the vertical columns for various design storm durauons from 2 io

45

IRC:SP:82-2008Table 4.7Durations (h) Distribution Co-efficients (Col. 16 of Table 2) Storm rainfall= Rainfall x Distribution coefficient (em)

l-h rainfall increment (em)

(1)

(2) 0.28 0.41 0.53 0.60 0.66 0.73 0.77 0.82 0.86 0.88 0.91 0.94 0.96 0.98 0.99 1.00

(3) = (2) x 26.50 7.42 10.86 14.04 15.90 17.49 19.34 20.40 21.73 22.79 23.32 24.11 24.91 25.44 25.97 26.23 26.50

(4) 7.42 3.44 3.18 1.86 1.59 1.85 1.06 1.33 1.06 0.53 0.79 0.80 0.53 0.53 0.26 0.27

1. 2. 3. 4. 5.6.

7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

Table 4.8Durations (hrs)

l-hour rainfall (em)

Design loss rate (em/h)

l-hour effective rainfall (em)

(1)

(2) 7.42 3.44 3.18 1.86 1.59 1.85 1.06 1.33 1.06 0.53 0.79 0.80 0.53 0.53 0.26 0.27

(3) 0.45" "

(4) 6.97 2.99 2:99 1.41 1.14 1.40 0.61 0.88 0.61 0.08 0.34 0.35 0.08 0.08

1. 2.:

3. 4. 5. 6. 7. 8. 9.

""

"

"" " "

10.11. 12. 13. 14. IS. 16.

"" " " " "

-

-

47

IRC:SP:82-2008 Step-9: Estimation of BaseFlow Thedesign base flow for thissub-zone is recommended to be computed bythe following formulae: qb = 0.1091 AO. 126 qb = 0.109/(136.36)126 = 0.059 cumecs/sq.km Total BaseFlow = 136.36 x 0.059 = 8.04 cumecs Step 10: Estimation of 50-Year Flood (Peak Only) Fortheestimation ofthe peak discharge the effective rainfall units were re-arranged against the unitgraphordinates such thatthe maximum effective rainfall wasplaced against the maximum U.G. ordinate, (obtained from the UGdiagram plotted afterStep4), the next lower value ofrainfall effective againstthe nextlower value of U.G. ordinate andsoonas shown inCols. (2) and (3) and summation oftheproduct ofU.G. ordinate and rainfall gives the totaldirect run-off asin Table4.9below:Table 4.9Time(1)l.

D.G Ordinate (cumecs) (2) 9.00 25.00 58.00 71.50 61.00 44.50 32.70 24.50 18.00 12.70 9.50 5.70 3.50 2.00

l-h Effective Rainfall (cm) (3) 0.34 1.14 2.73 6.97 2.99 1.41 1.40 0.88 0.61 0.61 0.35 0.08 0.08 0.08

Direct Runoff (cumecs) (4) 3.06 29.07 158.34 498.35 182.39 62.74. 45.78 21.56 10.98 7.75 3.32 0.46 0.28 0.16 1024.24 Base Flow 8.04 50-Year Flood Peak 1032.28cumecs

2. 3. 4. 5.

6.7. 8. 9.

10.11. 12. 13. 14.

48

IRC:SP:82-2008 UnitHydrograph Method cannotbe applied safely to large catchments more than5000 sq.km. and therefore for large Bridge projects one should go in for detailed analysis supported byProject specific Hydro-meteorological investigations. The total drainage area has to be divided into anumber of subbasins. Separate hydrographs may be derived for each subbasin from analysis ofdifferent storms byusing routine method. Calibration of flood hydrographs and flood routine parameters isessential. Forlarge catchments, flood frequency analysis ispreferred method.

49

IRC:SP:82-2008

Appendix 4.6A NOTE ON MODEL STUDIES FOR DETERMINING DRAG AND LIFT FORCES

Bothdrag force and liftforce depend largely onshape of a body andseveral other factors and as suchanalytical calculations forthese forces cannot be done accurately, therefore recourse to hydraulic models studies isgenerally taken to determine magnitude ofdrag and liftcoefficient inthecase ofimportant structures. 2. Model studies began to beused for thestudy ofwater flow phenomenon inthelater of nineteenth century and today model-studies are accepted asuseful for Engineering practice. Model studies cost aninsignificant fraction ofthe expenditure ofa project, butthese suggest vital improvement in design asthese studies enable the designers to visualize the whole problem, eliminating doubts and indecisions due to close conformity between the model andthe prototype. Therefore recourse to model studies is generally taken to determine the magnitudes of coefficient of lift(CL) andcoefficient of drag(Cd) for evaluation of these forces on superstructures ofimportant submersible bridges.Model Studies carried out for Bridges in theformer CentralProvince

3.

3.1. Several submersible bridges situated informer Central Province (CP) were damaged during floods of 1938-39 andthe deckslabs were carried away bodily, Govt. ofCP got model studies done at Central Water and Power Research Station, Khadakvasla,(CWPRS), Pune. Annual reports of 1938-39, 1939-40 and 1941-42 of CWPRS, inter-alia deal with the coefficient ofdrag onsubmerged bodies particularly with reference tobridge superstructure. Theresults arrived at bytheResearch Station are summarized below.(a)

Drag Force: -

The dragon a bodykept in steady now is expressed as

Fd = C A'/2 P V2 dWhere, Cd A PV

(4.8)

= = = =

co-efficient ofdrag characteristic projected areaofthe body Mass density offluid Undisturbed free stream velocity

The value of Cd is dependent on shape of body, roughness of the surfaceand Reynolds number (R) whichis expressed as or p where V=Velocity, D=Representive e . dimension ofbody, = Dynamic viscosity offluid, u=Kinematic viscosity offluid, p=Mass density offluid. Thedrag force mentioned above takes into account 'Skin-Friction-Drag' and'Form-Drag'.

50

IRC:SP:82-2008 (i) Skin-Friction-Drag: Itdepends upon viscosity ofthefluid and it forms only a small part of the total dragforce (10to15 %) Form-Drag: It isindependent ofviscosity and depends largely onshape ofthe body immersed in fluid andtherefore form drag can be found accurately in geometrically similar models with similar Froud's number Theratio oflnertia force (F1) and Gravity force (F g) is Froud's number i.e.

(ii)

pD2Y2----------==

y2gD(4.9)

P gD3 Thesquare rootofthisratio, is

Where D is representative characteristic dimension ofthebody Thenon-dimensional ratio is called Froud'sNumber (F,or F) aud it is the ratio

ofdynamic force to weight. It has greater significance while carrying outmodel studies for free surface or open channel flow. Thenature offree surface flow (i.e. rapidor tranquil) depends upon whether Froud's number is greater or less thanunity.(b) Lift-Force - Liftforce isthefluid force component onimmersed body acting vertically at

rightangle to the approach velocity. Theliftforce largely depends uponthe shape ofthe body andcomprises hydrostatic force and hydrodynamic force. Thehydrostatic force is generally referred as Buoyancy andacts vertically upwards. This force is independent of theshape ofthebody. When a body is immerged ina flowing fluid thebody experiences in addition to hydrostatic force, a force dueto 'Kinematic energy' of flow and is termed as HydrodynamicUplift force. This force depends onvelocity of flow, Reynold's Number andshape ofbody. This liftforce onabody can beexpressed inform offollowing equation:

y22(4.10)

Where,

C1p

= =

coefficient ofUplift, A=plan or chord area Mass density offluid, Y=Stream Velocity

Theratio oflntertia Force (FI) andViscous Force (F is Reynold's Number i.e.--------- ==

(4.11)

Where, ---- = u, thekinematic viscosity ofthefluid.p51

IRC:SP:82-2008

VDThis non-dimensional ratio is called Reynold's Number (Re or N) and it is the ratio of r dynamic force to viscous force. Acritical value ofReynold's Number makes distinction between Laminar and Turbulent flow. Studies have shown that both drag and liftforce are highly sensitive to Reynold's Number, particularly in lower range of Reynold's Number. Its value beyond 1.0 Xl 06 gives steadyvalue of C. Notes: (1) If 'Frictional orViscous force' governs themotjon,thenReynold's Number will be applicable. (2) If 'Gravity' is the onlyforce producing the motion then 'Froud's Number' will be applicable. 3.2 The above results give value ofcoefficient ofdrag onvarious shapes ofsolid slabs having aspect ratio (width/depth) in range of 12to 15 and, therefore, arenot applicable for box section havingaspect ratio usually in range of 5 to 5.33. Further, the CWPRS station, Pune in 1940 did notestimate theliftforce onsuch shapes and values for thesame even for rectangular shapes arenotavailable. In the absence of information on coefficient of drag and lift forces for box-type superstructures for submersible bridges, model studies were got done to study the effect of water current forces onthefollowing for submersible bridges. (i) Submersible Bridge on 'Chambal River' onNH-3 near Dholpur.(Rajasthan)(ii) Submersible Bridge on'Bhima River atSangam Village onTembhumi-Akluj Road Distt. Solapur (Maharashtra)

4.

During these model studies itwasdecided to observe value ofcoefficient ofdrag (Cd) coefficient oflift onbox-girder superstructure for various depths ofsubmergence and various velocities ofwater current. 4.1. Submersible Bridge at Chambal River - on (NH-3) Near Dholpur (Rajasthan) (a)In absence ofvalue of'k' for box-type deck submersible bridge intheIRC codes, Rajasthan P.W.D. andMinistry of Shipping Road Transport & Highways (MoSRT&H) tookdecision that model studies be gotdone at Indian Institute of Technology, Mumbai, for the box section adopted for superstructure forthereconstruction ofdamaged submersible bridge at Chambal (NH-3), sothatvalues ofcoefficient ofdrag (Cd) andcoefficient oflift (CI) are evaluated andaccordingly precautions are taken indesign and construction for drag andlift forces. At present, IRC Codes does notprovide any value for Cd andC1forAerofoil box Section.

Theshape anddimensions oftheAerofoil boxsuperstructure adopted at Chambal bridge aregiven below in Fig. 4.10.52

IRC: SP:82-2008

____",_"" .. ._.. _ ,. __ _ __. " _.. _.. .

a

a

oIIIIII II

----RCC ANCHOR

II!I

..,,__ II II

II IIII II II

STAINLESS STEEL ANCHOR

" "II

"II II

I

II II

II II III-

il

Fig. 4.10. Cross-Section at Support ofChambal Bridge (42.70 m Span)

(b)

The brieftechnical details for theChambal submersible bridge are asfollows: (i) Maximum design discharge = 5097.6 cumec(ii) Maximum design velocity offlow = 4.57 m/sec(iii) Maximum depth offlow = 27.13 m

(iv) Deck level is at 8.23 mbelow the maximum design flood level (v) Length ofindividual span = 43.28 m Experiments were carried outfor two conditions offlow: Corresponding to maximum designed flood level passing over thebridge deck. (b) Upstream water just grazing atbridge decklevel. The main obj ective ofthis study was todetermine thecoefficient of drag, (Cd) and the coefficient oflift(C I) (c) For similitude between prototype and model, thescales selected were 1:25 and 1:75 geometric. Theformer for detailed measurement of coefficient oflift (CI) with the help of piezometric taps, and coefficient of drag (Cd) was measured with help of strain gauge on 1:75 scale model. (d) Results ofmodel studies onSubmersible Bridge at Chambal onNH-3 are shown in Table 4.10.53

IRC:SP:82-2008

Table 4.10 Model - Test-ResultsS.No. Froud's No. Flow condition Results in 1:75 modelCd Cd C\

Resultsin 1:25 modelCd Cd C1

Total

Pressure

Total Pressure Flow Normal

1.

0.265

Design conditions at (15 ft/sec) 4.573 mls velocity Upstream waterjust grazing the top of deck at (12 ft/sec) 3.66 mls velocity

1.79

1.32

0.63

1.60

1.22

2.10

2.

0.27

1.55

1.36

0.54

1.70

1.53

0.60

Flow at 28 oblique3. 0.265

Design conditions at (15 ft/sec) 4.575 mls velocity Upstream waterjust grazing the top of deck at (12 ft/sec) 3.66 mls

1.75

-

-

1.60

1.26

2.04

4.

0.27

1.46

-

1.26

1.11

0.04

(e) As canbeseen form result in above tablethatvariation in value ofcoefficient of drag (i.e. Cd) obtained during model studies atlITMumbai was very small, maximum value of Cd obtained is 1.79 andminimum 1.55 for normal flow. Also there isno substantial difference in value of Cd underobliqueflow. However, it is seenthat value of C, (Coefficient of drag) are more than 1.5 i.e, the values recommended by (IRC:6),and therefore, thrust-blocks were provided to prevent sliding of the superstructure. (ref. Drawing Annexure-A-1 & A-2).) (f) It wasinformed by lIT, Mumbai thatthecoefficient oflift (C1 observed during model

experiments includes buoyancy i.e. hydrostatic effects also. Thevariation incoefficient oflift (C1) values obtained fordifferent conditions of submergence were large from 0.04 to 2.10 as given in Table 4.10 above. The value of C1 obtained inmodel studies gave mdlcation that streamlined shape of superstructure are also likely to be unstable against lift forces and need extra anchorages to prevent lifting of the superstructure.

4.2.

Submersible Bridge at Bhima River-Maharashtra

In absence of more information for value of 'k' in IRC code for Aerofoil box type superstructure it wasdecided byMaharashtra Govt. to getmodel studies done at CWPRS, Pune. The Aerofoil deck adopted for submersible bridge at Bhima river is given inFig. 4.11. (a)

Thebrieftechnical details ofBhimaBridge aregiven below: Length ofthebridge 350 m Design discharge 2436.2 cumecs

54.

IRC:SP:82-2008Design flood velocity Design maximum high flood level Design deck level225 .._---------------_._---------_ .

5.26 m/sec 463.95 m 458.83 m225

500

..

.: .

TH.

__.... ,.

500..

0'

200150

I

150150200

2575

Fig. 4.11. Cross-Section of Submersible Bridge on BhimaRiverThe model studies were carried outtoevaluate coefficient ofdrag andliftforces for different depths of submergence andvelocities onAerofoil shaped box girder. (b) Thepiezometric observations were done onmodels with approach velocities ranging from 6.0 m/sec forsubmergence ofthedeck slab by 5.13 m,andotherwithwater level grazing deck slab's top and having approach velocity 4.0 m/sec. The coefficient of drag (Cd) variedfrom OJ7 to 2.10 forthe above range ofvelocities. Thesevariations in Cd values areplotted asa function of Reynold's Number for differentsubmergences and areshown in Fig. 4.12.

o0

-u

10W

Z

0

w

oII I6

I6

I 6 6 lax 10

o

2x10

6

4xl0

6x10

8xl0

REYNOLD'S NUMBER

Fig. 4.1255

IRC:SP:82-2008 (c) The coefficient oflift (CI) for Phase I studies for the velocities as given in para(b) above varied from 0.04 to 0.41. These C1values were worked outbyexcluding the hydrostatic force which is to be accounted for separately. The variation of C, vis R, is shown in Fig. 4.13.. .. REYNOLD'S NUMBER

0 0 -0-10 -0-20 -0-30 -0-40 -0-50u,

6 6 6 2X10 4X10 6X10

8X10

6

6. 10X10

-0-60 -0-70 -0-80 -0-90 -1-00 -1-10 -1-20

0

z

w w 0

Fig. 4.13 (d) From the above values of Cd andC1asworked out aftermodel studies onBhimaBridge, thefollowing inferences can bedrawn:(a) Coefficient of Drag

(i) Values of mcreases.(ii) The co

shows atendency to decrease as value ofR, (Reynold's Number) ag d) varies withdepth of submergence

(iii) Forvery low R, thevalue ofCd isabnormally high. (b) Coefficient of Lift (C I)

Values of Ct vary with Re (Reynold's Number). For low R, and maximum submergence, thecoefficient of liftC, isthehighest attaining value of(-) 0.86. 4.3 State ofMaharashatra also got carried outmodel studies from CWPRS Pune for conventional rectangular shape ofboxsuperstructure (Fig4.14). On above rectangular box section CWPRS, Pune carried out model studies for different conditions ofsubmergence and velocity. The results indicate thatcoefficient of drag varied56

(a)

IRC:SP:82-2008

..

290

300

;n

4746 4.4

40

39

38

.24 25

26

40'0'

5

6

7 8

NI

910 11

23 22 2120

!

I

12 13 1415 16

17

.

Fig. 4.14. Models of BoxType Submersible Bridge from about 0.5 to 2.8 under various depths of submergence andapproach velocity. It was seen thatvalue of C, varied substantially for the submergence of5.13 m and 2.5 m, the variation in valuesof submergence for 2.5 mto 1.25 m was negligible. The graphs showing variation of Vs R, are given below in Graph 4.2.WLi

S

Iuo

o0

,

, Zu.

0

U

0

o

2REYNOLD'S NUMBER Re=

6' X10

Graph 4.2 (b) 4.4. The coefficient oflift wasvarying from (-)0.2to (-)0.9. andareshownin Fig 4.15.

Briefdiscussion onresults of studies carried outinthefollowing cases: (i) CWPRS, Punemodel studies (1938 to 1942), for bridges in Central Province

(ii) lIT Mumbai model studies on submersible Chambal bridge on NH-3 - Dholpur (Rajasthan)(iii) CWPRS, Pune model studies on submersible bridge at Bhima

(Maharashtra)

57

IRC:SP:82-2008

6 REYNOLD NUMBER Re ==YD X10

0

2

4

6

10

I

I

I

IWL

-02-03 -040..

Sy

I

0

-05 -06

u,

0

z -07wu,

x

-08w 0

-09-10

S-2.5m

Fig. 4.15

4.4.1. The Tests carried out by Central Water and Power Research Station (period 1938 to 1942) pertain to thesolid slab deck where thewidth to depth ratio is very high (inrange of 12 to 15) and velocities simulated were inlow range of 1.83 m/sec to2.44mJsec inprototype i.e. 0.56 m/sec to 0.74 m/sec in model. Comparison of theseresults with recent model studies done for Box Aerofoil Superstructures for Chambal andBhima river bridge will not be correct. Moreover, observations carried outbythe Central Water andPower Research Station in 1940 were only qualitative innature forestimating theliftforce. 4.4.2. Recent studies carried out by 1.1.1. Mumbai for Chambal river bridge and by Central Water Research Station forBhimariver bridge havebeenexamined in depth. It willbe noticedt a n ge an Bhima river bridge are apparently similar butthere are some difference's also. The overall widthof decks of both thebridges aremore or less the same asalso thewidth of straight portion of soffit, butthe depth ofthebox being different, therefore, the angle subtended byinclined soffit withdeck top for Chambal bridge is 37.875 andthe same for Bhimariver bridge is only 22.25. Due 'to this, there is a difference intheaspect ratio (width to depth). In the former casethis ratio is 3.85, while inthe latterit is 5.678 andthis inequality could give rise to different streamlines. Asa result, thevalues of Cd and C1are bound to be different inthesetwo case studies also. 4.4.3. Inferences from Model Studies at lIT, Mumbai for Chambal Bridge on NH-3. (i) The IndianInstitute ofTechnology (liT) Mumbai carried outmodel studies byadopting geometric scale of 1:25,with model Reynold's Numberof about 1xl O' which is58

IRC:SP:82-2008 considered close tohydraulically unsteady zone. Therefore, it was necessary toadopt more appropriate scale.(ii) In lITMumbai model studies, the variation in values oftotal drag was very small.

Maximum Cd total is 1.79 and minimum C,total is 1.55 for normal flow. Also, there is no substantial difference in valueof Cd total' under oblique flow. However, the values of Cd obtained are more than 1.5, thevalue as recommended by the Indian Roads Congress forsuperstructure.(iii) Variations incoefficient oflift (C,) obtained under different conditions arevery large giving its values from 0.04 to 2.10. As a matter offact, these values giveriseto an apprehension thatsuch streamlined shaped bodies arelikely to beunstable against flowing water and, therefore, should beused with caution and need extra anchorages to prevent lifting up of the sub-structure, are to be provided (as done in case of Chambal bridge atDholpur).

4.4.4. Inferences from Model Studies at CWPRS Pune for Bhima River Bridge Maharashtra The graph of Cd vs. obtained in model tests carried outat CWPRS, Pune, gives higher values ofCd for rectangular shape box than stream line box under maximum submergence. Asfor condition for water level atdeck level, coefficient ofdrag for rectangular box section is less than the line section. It isdifficult to explain why C, islower forrectangular shaped box compared toAerofoil shaped box.

59

IRC:SP:82-2008

5. WATERWAY AND AFFLUX

5.1. Waterway 5.1.1. General

Thearea through which the water flows under a bridge superstructure isknown asthe waterway of the bridge. The linear measurement of the waterway along the bridge is known as linear waterway. The linear waterway isequal to thesum ofthelength of allthe clear spans. The natural waterway is theunobstructed area offlow ofthe river/stream at thebridge site. The waterway adopted should be adequate to passthe design flood of specific Return Period. Theopening hasto be capable of passing thedesign-flood without overtopping thedeck in case ofhigh level bridges, and thedesign :floods estimated upto a level at which thedeckis fixed in case of submersible bridges, without endangering these structures.5.1.2. Fixingdecklevel of submersible bridges

(i)

Specific number ofovertopping thedeck ispermitted during annual floods in case of submersible structures, which areprimarily low cost and economical solutions compared to high level structures. It is, therefore, necessary to first decidethe permissible duration andfrequency of such overtoppings. Generally, ithas beenobserved that high flood occurs threeto four times during monsoon, butwater level rises sofast andfalls again sorapidly thatthepeaklevel of these floods lasts only for a short time. Iflevel offloods is plotted on vertical axis and dates offloods onhorizontal axis, thenonecaneasily decideaboutthe deck level as seen from Graph 5.1 which is a typical example ofyearly floods in a river during monsoon. Based an the flood dataduring monsoon season, the deck level of submersible bridge is so fixed that the facility will satisfy the criteriaof frequency and time period of interruptions to traffic as specified byuser Authority and as indicated in

(ii)

(iii)

25

30

10

15 20 25

30

5

10 15 20

25

5

10 "5 20

25 30

5

10

15 20

__

OCTOBER

Graph 5.160

IRC:SP:82-2008 Table 3.1 ofthese guidelines. The concerned Department hasto collect flood data for a representative monsoon season and decide theOFL above which deck level ofsubmersible bridge is sofixed thatit satisfies thecriteria of frequency and time period ofinterruptions oftraffic. 5.1.3. Constriction of waterway (i) Any constriction of waterway either laterally or vertically reduces the natural waterway ofstream which results inchange innormal flow pattern from thatexisting before the constriction and inafflux onupstream. Higher theconstriction ofnatural waterway, higher will betheafflux and the velocity of flow through the vents. It is therefore, desirable to keep theconstriction ofwaterway to theminimum inorder toreduce expenditure onproviding raised face walls and protection ofbed. However constriction to varying degrees becomes unavoidable, depending onthe type of structure thatmay be selected foradoption based onvarious othertechnical and economic considerations. The constriction of waterway that canbe permitted in any particular case depends onseveral site specific conditions the more important ones being the nature of soil in the river bed and the adopted RoadTop Level (RTL) inrelation tothedesign HFL. (a) If the bed material is easily erodible, it wouldbe desirable to avoid high constriction tokeep thevelocity offlowthrough thevents within manageable limits. (b) Similarly, higher constriction can be provided for low level submersible structures like causeways but, ifthedepth offlow below RTL inrelation tothe depthbelow the design HFL is high as would generally be the case when higher submersible bridges are provided, theconstriction must bekept low so asto keep the hydrostatic forces onthestructure within manageable limits.(ii)

Several States inthecountry, which have been constructing submersible structures for a long time, have their own practices with regard tothepermissible constriction, basedontheirexperience andsiteconditions prevaIlIng In the respectIve States. These practices may vary from State to State andit isrecommended thattheStates maycontinue to follow theirsuccessful practices inthisregard. Alternatively, the following recommendations may befollowed: (a) For lowlevel submersible structures likecauseways, provide a ventareaof about 40percent butnotless than 30percentoftheunobstructed area of the stream measured between the proposed roadtop level andthestream bed. In scanty rainfall areas where annual rainfall is less than 600 mm, thevent area canbereduced upto 20percent to30percentofunobstructed area. However, the available areaof flow under design HFL condition should always be at least 70per centof the unobstructed areaof flow between the design HFL and thestream bedi.e. theobstruction under design HFL condition should not be more than30 per cent.61

1

IRC:SP:82-2008 (b) Forsubmersible bridges, which would generally beprovided with relatively higher road top level, theavailable area offlow under thestructure should not be less than 70 per cent of the unobstructed area ofthe stream measured between the stream bedprofile andthe proposed roadtoplevel.(iii)

RTL should notbeabnormally high over vent opening asthiscauses heading upof water onu/swhich intummay result inhigh velocity (itcaneven beinthe range of hypercritical) tofailure and outflanking. Hence RTL should bekeptaslow as possible. The increase invelocity under thebridge should bekeptbelow theallowable safe velocity forthe bedmaterial. Typical values of safevelocities for different bed material are as below:Type of Material Loose clayandfine sand Coarse sand Fine gravel, sandy orshift clay Coarse Gravel/Weathered rock! Boulders upto 200 mmsize Larger boulders (200 800mmsize) or rocky strata SafeVelocity (m/sec) upto 0.5 upto 1.0 upto1.5

(iv)

upto2.5 2.5 to 6.0

(v)

In casethe velocity exceeds the above specified values for scourable beds, then bedprotection consisting of flooring with proper cut-offwall should be provided on bothupstream anddownstream side onthebridge as discussed indetail in para 6.4 of Chapter 6. A typical arrangement of floor protection works is given inFig. 5.1.

(vi)

Inthepost protection works, thevelocity offlow under structure should notexceed 2 rn/sec. Thedepth of drop wall should besuch thatit does notget undermined. If a flooring is not provided, then maximum depth of scour should be calculated carefully anddepth offoundations beprovided accordmgly.

5.2. Afflux 5.2.1. General

(i)

Affluxcan be defined as a rise/heading up of water surface above normal water level on the upstream side of a bridge. It is caused when the effective 'linear waterway' through thebridge isless than thenatural width ofthestream immediately upstream of obstruction. Afflux canalso becaused incase of a bridge where there is reduction inoverall width ofthe waterway over thenatural width of stream, due to the obstruction of piers and projecting abutments as indicated in Fig. 5.2. Afflux governs thedynamic action of water current. The greater theafflux greater willbe thefall of water level from upstream to downstream and therefore greater62

(ii)

- - - - - - - - - - - - - - -_ _

_I .....

.. "-'.....

,0".:"

.. ,.

7500"

. ..COLLAPSIBLE RAILING

.... :.-

-.

lJ/S

I

DisI

!

....TH. STON PAVING IN 1:4

C.C. , :3:6

I

CONCRETE BLOCKS (M-20 GRADE)

APPRON;

...

,

. -

..J ....-J'300. ..

..

",

o:

..

8'500mm TH. BOULDERS

TH. BOULDERS,

(ALL DIMENSIONS ARE IN mm)

Fig. 5.1. Typical Section through Bridge Floor

00I

00

IRC:SP:82-2008

\

IFlUXi

:

I\ d__

_

....

_

__1

)

__

Fig. 5.2.Afflux caused by obstruction of Piers & Abutments

will bethe velocity offlow onthe downstream side leading to greater scour, thereby requiring deeper foundations.(iii)

Anestimation ofafflux isnecessary (i) for fixing thebottom face-line ofthebridge deck afterallowing foradequate free board, (ii) forfixing levels ofthe approach road (iii) for determining the increased velocity as required for designing the foundation andbedprotection works.

5.2.2. Estimation of aft1ux for non-scourable bedsmay be computed approximately by use of empirical formulae given below:

(a) Molesworth formula (b) Rebbock's formula (c) formula However. Molesworth Formula the afflux atbridge constrictions: isgiven below is usually adopted to estimate

0015

1

(5.1)

Where,hA a=

V -= =

aftluxinm velocity ofapproach inm/sec natural waterway areaof the - constricted areain sq.m.64

in sq.m.

IRC: SP:82-2008 5.2.3. Estimation of afflux by broad crested weirand orifice formulaeThe afflux(h), the discharge (Q)the unobstructed stream width (W)andthe linear waterway (L) areall interrelated. Greater the reduction in linear waterway, the greater is the afflux. Sincedownstream depth (Dd) is not affected bythe bridgeobstruction as the same is governed by the hydraulic characteristics ofthe channel downstream, it can be safely assumed thattheupstream (uls) depth which prevailed before thebridge construction is same as the downstream depth (Dd) that prevails eveL- .ter the bridge construction. Hence(Dd) is the depth thatprevailed at bridgesitebefore the construction of the bridge. Toestimate afflux wemustknowthe discharge (Q)in the channel, the value ofD d' value of Wand L, then afflux canbe calculated by applying weirandorificeformula as given below.

(a)

Broad Crested Weir Formula"Theweirformula asgiven below applies only when standing waves areformed i.e. solong as the afflux is not less than D Q Where,Cw=

1.706 C L D + II 2gW

U2J 3/2

(5.2)

DII

=

coefficient to account forlosses infriction upstream waterdepthand Dd = Downstream water depth

2g

= head dueto velocity of approach

The parameters areindicated in Fig. 5.3.

;--PIER

z- - X ..

-

rH

-

89.0-4.83

= RL 84.17RL83.2

Deepest BedLevel (DBL) =

Assume scourlevelas D.B.L. i.e.RL83.2beingon conservation side.

89

IRC:SP:82-2008Maximum Scour

AtH.F.L. Around Piers Expression 6.62 dsm R.L. Around Abutments Expression 6.8 Expression 6.7 1.27 dsm 2[95.22-82.0= 13 .22] = 26.44 m 68.78 68.78 78.41

AtF.L. (10 Years) 2[92.2-81.2]= 22.0m 70.20 70.20 78.23

At O.F.L. 2 x 4.83 = 9.66 m 79.34 79.34 L.B.L. 83.20

90

IRC:SP:82-2008Appendix 6.2

(Reference Para 6.1.4.1) PROCEDURE TO WORK OUT THE WEIGHTED MEAN DIAMETER OF PARTICLES FOR A STRATUM

The weighted mean diameter ofparticles for a stratum may be worked outaspermethod illustrated inthe Table 6.6.Table 6.6.

Sieve Designation

Sieve Openings (mm)

Weight of soil retained (gm)(w)

y= [Col (5)1 Percentage of Average size percentageof weight retained ofopening (mm) weightof material (p) = col(3)x (Total retained on the next small size sieve] weight ofsample) x ICol(4)jI I

1 5.60

2 5.60

3

4 0

5

6 0 4.80x PI

SayO

4.80*

4.00

4.00

w

P 3.40 3.40x P,

2.80

2.80 1.90 1.90 x P3

1.00-;

1.00

w3

PJ 0.712 0.712xP4

425 micron

0.425

w4

P4V .JVL.

U.jUL. X

P,

180 micron

0.180

Ws

Ps 0.127 0.127xP 6

75 micron

w6

P6 0.0375 0.0375 x P7

< 75 micron in PanWi (Total weight

w7100

P7YI

of sample)* (5.60+4.00)/2 = 4.80 mm and so on

dm - - - (rounded off to two decimal places) 100

91

lRC:SP:82-2008

Appendix 6.3(Reference: para 6.4.3.3)Table 6.7: Thickness of Slope Patching for various Grades of Sand and Slopes of RiversBedSlope

4.73

14.2

18.9

28.4

37.9

(10.5)Sand classification Very coarse Coarse Medium Fine Very Fine Thickness of stone pitching in (em)

4158 71

48

SO

7179

7179 88

86

102 109 124117

86

102 109 117

102.........'.. a

132

37.9

-.._ _-.-_ .. .........

..--_

71

....

.....85

__

. ....

_

.....

-.

102

117

.... .......

_-...

..

..

'0 ConI:) " , or

23.0

" .10

2/1

5/3

"

.

.

,C.2

Fig. 6.2. Showing Pressure Distribution under Floors with different Slopes92

IRC:SP:82-2008Appendix 6.4

(Reference para DESIGN OF BED PROTECTION (Worked out example) Given Data:Design discharge Total effective waterway Depth of flow above floor level at designed flood level Width ofthefoundation Meandesigned velocity (Maximum permissible velocity as perIRC:89 is 2.0m/s) Areaavailable for discharge Discharging capacity = = 250 x 2.70 675 x 2 = 675 m' 1350 cumecs> 1000 cumecs

= ==

1000 cumecs 250m 2.70m 500mm 10.0m

= ==

2.0m/s

Hence OK Width ofthe foundation LengthofflooringasperIRC:89 {Para6.4.2 (ii) refers} Depthof upstream sidecut-offwall (Minimum required as per IRC:89 is 2.0m) Depth of downstream sidecut-offwall (Minimum required as perIRC:89 is 2.50m)(I)

= 10.0 + 3.0 + 5.0

= = = =

10.0m 18.0m 2.50m 3.50m

As per Bligh's Creep Theory Total lengthof water path =2 x 2.50 +18 + 2 x 3.50 = 30.0 m Assume difference of headbetween upstream anddownstream sides as 1.0m as perPara 6.4.3.1 against value ofafflux of500 mm. Hydraulic gradient = 1.0/30.0 i.e. 1 in30 As the gradient of 1in30 is far lessthaneventhe flattestpermissible gradientof 1 in 18 (value of creep coefficient forvery fine sand or silt), asper Table 6.4,thelength offlooring provided is adequate. r As per Lane's Weighted Creep Theory The equivalent length Lw = 1/3 x 18.0+ 2'x'2.50 + 2 x 3.50 Creep ratio C 1= 18/1.0= 18.0

(ii)

=18.0 m

93

IRC:SP:82-2008 Thus the creep ratio ismuch higher than the requirement (Table 6.4 refers). Hence flooring length provided is adequate.(iii)As per Khosla's Theory

Using Expressions 6.31 and 6.32 for exitgradient i.e.H=

x

1

Where

=

1 + (l+a 2 )

------

2

and

H is theheadof water d2 isthedepth ofdownstream cut-offwall Listhelength offloor

= = =

= 18.0/3.50 =1 + (1 2 1----

=2)

1.0m 3.50m 18m 5.14 3.12 1/19.42

=x 1

Exitgradient (G E) =

3.5

=

The exitgradient is within thepermissible values (Table 6.5) Hence the proposed length of the floor as 18 m and depth of cut-off wall as 3.5 mare adequate.Check for adequacy of the thickness of the proposed flooring by Khosla Theory

Assume thefollowing composition oftheflooring asperPara6.4.2 (iv): 150mm thick cement concrete levelhng course (M1 0) + 300mmthickcement concrete (M 15) + 150 mm thick brick masonry incement mortar 1:3. = = 3.50/18.0=0.194 From Khosla'sgraph, Pressure atthebottom ofthe cut-offwall onthe u/s side = 100 = 100 - 26.2 = 73.8 % Pressure atpoint ofbeginning ofthefloor onthe U/S side = 100 =

100 - 38.3 = 61. 7 %

Loss ofpressure from bottom of U/S cut-offwalls to beginning offloor = 12.1 % Correction forthickness offloor = 12.1xO.6 3.5

= 2.07 %

IRC:SP:82-2008 Correction for interference ofdis cut-offwall

Where, d)L' L

==

depth ofu/s cut-offwall and d, = depth of dis cut-offwall distance between thetwocut-offwalls length offloor

=

As cut-offwalls are proposed at the endof flooring therefore L = L' C3.5/l8 x

3.5+2.5

=

=

18

2.79 %

Corrected pressure at underside of floorwhere it begins==

61.7 + 2.07 + 2.79 = 66.56 %

Average densityof floor = [0.450 (concrete) x 2.2 + 0.15 (brick masonry) x 1.9] 0.6=

2.125 t/m'

Densityof floorallowing for 100% buoyancy == 1.125 t/m' Thickness offloorrequired = 0.6656 xl

==

1.125

0.592 m

againstproposed thickness of 0.6 m. HenceOK

..

95

lRC:SP:82-20087. DESIGN 7.1. Site Inspections

7.1.1. General

Site inspections play an important role right from the conception stage to the endof pre construction stage for successful implementation of any project. The purpose of site inspection ranges from identification ofdata needs and collection ofraw data atelemental level to anoverall appraisal oftheproj ectto aidinanalysis, decision making andfinancing. Assuch, each inspection shouldbe carefully planned keeping in view the requirements of the user authority and to aid judgments for most economical and feasible solution. The number ofsite inspections depend upon the type of proposed submersible structure (i.e. flush/vented causeways, bridge) length, site conditions, importance ofthecrossing etc. The siteinspections should be carried outbyexperiencedbridge engineers asthese form thebasis for arriving atthebasic design parameters for theproject, especially incase ofsubmersible structures andimmediate approach roads which are subjected to frequent submergence.7.1.2. Types of site inspections

Based onthe stage oftheproject, site inspections canbe classified as under: I Pre-construction stage inspection(i)

(ii)(iii)

Pre-feasibility stage inspection Feasibility stage inspection Detailed engineering stage inspection

II

Construction/Implementation stage inspection Post construction/Maintenance stage inspectionements of site inspection

III

7.1.3. Broad

7.1.3.1. Pre-feasibility stage inspection

A reconnaissance visitto the areaoftheintended submersible structure siteis generally sufficient to examine the general area and to identify theproject, its requirements, utility, present arrangements of crossing, nature ofthecrossing, traffic intensity, land marks and broad features for the crossing etc. The inspection report at this stage should give broad idea of area, intended project andin general inter-alia cover thefollowing:(i)

(ii)

Requirements oftheuser authority incharge oftheroad anditslimitations, if any, regarding availability offunds for theproj ect; Category ofroad (i.e. SHIMDR/RR/E&I road/industrial road/link road etc.);

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1(iii)

IRC:SP:82-2008 Population ofthe area likely to bebenefitted with theconstruction ofthe proposed facility Existing alignment ofroad indicating deficiencies/constraints, ifany Salient details ofthe existingroad i.e. condition of the road, type of surfacing, carriageway width, number of lanes, formation width, shoulders etc. Type of terrain, type of present traffic (i.e. slow moving/ fastmoving etc.) Present traffic intensity including broad breakup (onrough percentage basis) of traffic i.e. heavy/light commercial vehicles, passenger cars, slow moving vehicles e.g.bullock carts, tongas etc.

(iv) (v)(vi) (vii)

(viii) Nature ofthe water channel (i.e. Perennial, seasonal, steady, flashy, approximate rateof riseof flood leveletc.) (ix)

Approximate velocity of stream andmaterial likely to float down inthe channel during floods i.e. debris! branches of trees andtheir approximate size Condition ofbanks (i.e. their slopes, whether low orhigh, erodible ornon-erodible) Present arrangement for crossing during dry season and floods (i.e. boats, motorized ferry etc), availability of alternative route andlength of detour etc. Approximate depths of water andwater spreads during dryseason andfloods (at HFL OFL and LWL) Characteristics of riverbed(i.e. alluvial, quasi-alluvial, presence of bigboulders affecting thevelocity of stream, scourable or non-scourable etc.) Presence of rocky strata Possible location of submersible structure withrespect to the most suitable site for the high level bridge Period of'cut-offofthearea with duration atatime and number ofsuch interruptions in a year and population affected

(x) (xi)(xii)

(xiii) (xiv) (xv) (xvi)

(xvii) Expected land acquisition problems, if any, for immediate approaches (xviii) Broad details of existing CD works (bridges or causeways) onthe same channel inthevicinity. The details should include; (a) description liketype, distance from the proposed site etc. (b) approximate lengthand depthof submergence and frequency (including duration) of interruptions peryear totraffic (c) number and length of spans/size of vents, clear waterway, adequacy or otherwise of waterway withspecial reference to siltedup spans or signs of under scouror attacks on abutments and approaches in case of bridges etc.

(xix) Broadjustification forthe project and (xx) Any other aspect considered important bythe inspecting officer.97

IRC:SP:82-20087.1.3.2. Feasibility stage inspection

During thefeasibility stage, data in general, should becollected in line with theprovisions of IRC:5, IRC:78 & IRC:SP:54 (Project Preparation Manual) toenable thecontrolling authority to takea decision about thetype, length, foundation etc. of submersible structure. At leastone visitshould be carried outin the beginning ofthis stage, to identify the data required to be collected pertaining to the items mentioned under para 7.1.3.1 above in various stages andto establish coordination with different departments responsible forsupply of dataetc. Incase of a flush causeway