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Disclosure to Promote the Right To Information

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IS 4880-2 (1976): Code of practice for design of tunnels

conveying water, Part 2: Geometric design [WRD 14: Water

Conductor Systems]

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IS I 4880 ( Part II ) - 1976

I ndian St andardCODE OF PRACTICE FOR

DESIGN OF TUNNEJ .3 CONVEYING WATERPART II GEOMETRIC DESIGN

( Fi rst .Rev i si onThird Reprint SEPTEMBER 1991

UDC 624.191.1=624.196:627.842

@ Cofiyright 1976BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHAljUR SHAH ZAFAR MARQ

NEW DELHI 110002Gr 3 September 1976

( Reaffirmed 2000 )

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IS I 4880 ( Part II ) - 1976

I ndi an St andardCODE OF PRACTICE FOR

DESIGN OF TUNNELS CONVEYINGPAHT II GEOMETRIC DESIGN( Firs t Revision

,

WATER

Water Conductor Systems Sectional Committee, BDC 58ChairmanSHRI P. M. MANE

Ramalayam, Pcddar Road,Bornbay 400026Members

SRRI 8. P. BHATRepresenting

Public Works and Electricity Department, Govern_ment of Karnataka, BangaloreSHRI K. R. NARAYANARAO ( Alternate )CHIEBENQINEER( CIVIL ) Kerala State Electricity Board, TrivandrumSHRI K. RAMABEADRANNAIR ( Alternate )CIIIEF ENGINEER CIVIL )SUPERINTENDINGENGINEER Andhra Pradesh State Electricity Board, Hyderabad( DESIQN AND PLANNING ( A!tcmata )CHIEF ENQINEER ( IRRITATION Public Works Department, Government of Tam3Nadu, MadrasSIJPERINTENDIN~ENQINEER( DESIONS) ( Aftem& 3 1

CHIEF ENGINEER PROJEOTARD Tamil Nadu Electricity Board, MadrasCONSTRUCTIONSUPRUINTEND~N~ENGINEER( TECRNICAL/CIVIL ( Alternate )SHRI 0. P. DATTA Beas Designs Organization, Nangal TownshipDIRECTOR HCD ) Central Water Commission, New DelhiDEPUTY DIRECTOR PA-I ) ( Altern& )DIRECTOR, PRI Irrigation Department, Government of Punjab,ChandigarhSHRI H. L. SH~RMA ( Alternate )SHRI R. G. GANDHI Hindustan Construction Co Ltd, BombaySHRI R. K. JOSHI ( Alternate )

( Continued oripage 2 )

@ c&right 1976BUREAU OF INDIAN STANDARDSThisOBublication is protected under the Indian Gfyright Act ( XIV of 1957 ) anduction in whole or in part by any means except with written~u$isher shall be deemed to be an infringement. of copyright un 8 rmission of theer the said Act.

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SSr4880(PartII)-1976( Confinucd fr om page 1 )

Mem hersDR S. P. GARO

RefwestntingI rrigation Department, Government of Uttar Pradesh.

SHBI M. S. TAIN-LucknowGeologicalSurGes ot India. Calcutta

SHRI N.-K. MANDWAL (Al ternate ) -J OINT DIRECTOR STANDARDS ( SM ) Ministry of Railways, New DelhiDEPUTY DIRECTORSTANDARDS ( B & S )-I ( Alternate )SHRI B. S. KAPR~ Irrigation Department, Government of Maharashtra,BombaySHRI S. M. BE~ALF.RAO Alternate )SHRI D. N. KOCRRAR National ProjectsConstruction Corporation Ltd, NewDelhiSHRI G. PARTHASARTHY ( Alternate )SHRI Y. G. PATEL Pate1 Engineering Co Ltd, BombaySHRI C. K . CROK S~~I Afternate )

SHRI S. N. PHIJ KANSHRI S. C. SEN ( &tsY?latF Assam State Electricity Board, ShillongSHRI A. R. RAICEUR R. T. Shah & Co Ltd. BombavSHRI S. R. 3. SASTRYSHRI G. N. TANDONSARI B. T. U

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IS I 4880 Part II) - 1976I ndian Standard

CODE OF PRACTICE FORDESIGN OF TUNNELS CONVEYING WATER

PART II GEOMETRIC DESIGN( Fi rst Rev i si on

0. FOREWORD0.1 This I ndian Standard (Part II ) (FirstRevision) was adopted by theIndian Standards Institution on 24 J uly 1976, after the draft finalizedby the Water Conductor Systems Sectional Committee had been approvedby the Civil Engineering Division Council.0.2 This I ndian Standard was first published in 1968. Its revision was takenup with a-view to keeping abreast with ~the echnological developments thathave taken place in the field of tunnel design and construction. This revi-sion incorporates modified Fig. 1 which more clearly illustrates A-lineand B-line. A new geometric shape, egglipse, has also been added to thelist of sections recommended for adoption for tunnels. The details fordrawing the egglipse curve have been included as Appendix A.0.3 Tunnels are generally used for conducting water through high groundor mountains, in rugged terrain where the cost of a surface line is exces-sive and elsewhere as convenience and economy dictate.0.4 This standard has been published in parts. Other parts of thestandard are as follows:

( Part I )-1975 General -design( Part I I I )-1976 Hydraulic design (@t reuision(Part IV)-1971(Part V)-1972 Structural design of concrete lining in rockStructural design of concrete lining in soft strataand soils( Part VI )-1971 Tunnel supports(Part VI I)-1975 Structural design of steel lining0.4.1 This part (-Part I I ) lays down only general guidance in regard tothe shape of various sections generally used for tunnels. However, fc:particular project the judgement of the designer is required for making afinal choice of a section considering the prevailing site conditions; sinceno general -recommendations can be made to fit in each and everyindiyidual case.

3

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is: m (Part IX) - 19760.5 This code of practice represents a standard of good practlee mdtherefore, takes the form of recommendations.

1. SCOPE1.1 This standard (Part II ) lays down general requirements and criteriafor geometric design of tunnels conveying water under pressure orunder free-flow conditions. This standard does not, however, coverthe geometric design of other tunnel structures.2. TERMINOLOGY2.0 For the purpose of this standard, the following definitions shall apply.2.1 Minfmom Excavaltion Line (~A-Lime)--It is the line withinwhich no unexcavated material of any kind and no supports other thanpermanent structural steel supports shall be permitted to remain ( seeFig. 1 ).

SUPPORfSSECTION XX

IA HORSE SHOE SECTION WITHAND Wll tiOuT SUPPORT 18 CIRCULAR SECTtON WITH AN0WITHOUT SUPPORTFxc. 1 TYPICAL SECTION OF CONCRETE-LINED TUNNELSSHOWING A- AND B-LINES

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IS t 4880 ( Part II ) - 19762s Pay Line ( B-Line ) - It is an assumed line (beyond A-line ) tpWbiFchayment of excavation is made whether the actual excavation fallsinalde or outside it ( see Fig. 1 ). Sometimes B-line may merge with A-line.lt is a common practice to adopt B-line for payment for concrete lining.3. SHAPES3.1 The following shapes are-generally used for tunnel cross sections:

4b)44e>f>

Circular section (see Fig. 2 ),D Section (UC Fig. 3),Horse-shoe section ( see Fig. 4 ),Modified horse-shoe section ( see Fig. 5),Egg shaped section (see Fig. So), andEgglipse section ( see Fig. 7).

NOTE - For tunnels excavated to horse-shoe section and concreted to circular section,see Fig. 1.

4.4.1

FIG. 2 CSRCULARSECTIONGEOMETRIC DESIGN Cross section of a tunnel depends on the following factors:a) Geological,b) Hydraulic,c) Structural, andd) Functional.NOTE ---It is not uncommon that the sections get modified during the course ofconstructlon.

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IS : 4669 Part II ) - 1976

Fro. 3 D ~SECTION

0~0293dTER = 392670

FIG. 4 HORSE-SHOE ECTI.ON-4.1.1Circular Section -Th e circular section is most suitable from structuralconsiderations. However, it is difficult for excavation, particularly wherecross-sectional area is small. .For tunnels which are likely to have to resist

heavy inward or outward radial pressures, it is desirable to adopt acircular section. In case where the tunnel is subjected to high internalpressure, but does not have good quality of rock and/or adequate rockcover around it, circular section is considered to be the most suitable.6

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IS t 38SO ( Part l-l)- 1976

i

b-8 -ir = 0,987 580 R

whereR = Radius of Hydraulically Equivalent Circle

Area of Section = 3.253 572 ra-Perimeter of Section c 6.426 334 rHydraulic Radius = O-506 287 r

A - O-780 776 rB B 1561 553 re s 31 22 01

FIG. 5 MODIFIED% ORSE&&E SECTION

FIG. 6 EGG SHAPED SECTION7

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IS I 4880 (Part II) - 1976

-D------+FICL 7 TYPICAL EGGLIPSE SECTION

4.1.2 D Sect i on D section would be found suitable in tunnels locatedin massive igneous, hard, compacted, metamorphic and good qualitysedimentary rocks -where the external pressures due to water or unsoundstrata upon the lining is slight and also where the lining is not requiredto be designed against internal pressure. The principal advantages of thissection over horse-shoe section (see 4.1.3) are the added width of theinvert which gives more working floor space in the heading duringdriving and the flatter invert which helps to eliminate the tendency ofwet concrete to slump and draw away from the tunnel sides after it hasbeen screeded.

4.1.3 Horse-shoe and M odi fi ed H orse-Shoe Secti ons These sections area compromise between circular and D sections. These sections arestrong in their resistance to external pressures. Quality of rock andadequate rock cover in terms of the internal pressure to which thetunnel is subjected govern the use of these sections. Modified horse-shoesection offers the advantage of flat base for constructional ease andchange over to circular section with minimum additional expenditure inreaches of inadequate rock cover and poor rock formations.4.1.4 Egg Shaped and Eggl i psc Sect i ons- Where the rock is stratified,soft and very closely laminated ( as laminated sand stones, slates,*micaceous schists, etc ) and ~where the external pressures and tensile forces

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IS : 4880 ( Part II ) - 1976in the crown are likely to be high so as to cause serious rock falls, eggshaped and egglipse sections should be considered. Inthe case of thesesections there is not much velocity reduction with reduction in discharge.Therefore, these sections afford advantage in cases of $ewage tunnelsand tunnels carrying sediments. Egglipse has advantage over egg shapedsection as it has a smoother curvature and is hydraulically more efficient.Details for drawing,egglipse curve are given in Appendix A.

4.1.5 Other Sections - In addition to the sections mentioned in 4.1.3to 4.1.4 there may be other composite geometrical sections which may beadopted particularly for tunnels which are free flowing and often onlypartly lined. If characteristics of a rock formation are fairly well knownit may be possible to evolve a section which is likely to fit the shape inwhich the rock will break naturally. Thus, while a horse-shoe or Dsection is fairly easy to obtain in some formations there are others wherethe tunnel crown tends to break into a form more nearly square, and ifthere is no risk of heavy external pressure upon the lining or if the tunnelis to be unlined there is no reason why the designed cross section shouldnot be made to suit the-characteristics of the rock.4.1.6 The typical geometry of both A- and B-lines for some sectionsare shown in Fig. 1 and the distance between A- and B-lines depends onthe nature and geology of rock and method of tunnelling.

APPENDIX A( Clauses 0.2 and 4.1.4 )

DETAILS FOR DRAWING. EGGLIPSE CURVEA-l. GOVERNING RULEA-l.1 F,, Fa and Fa are the focal points ( see Fig. 8 ) of the egglipse.The radii A P, Fa P and Fa P are designated as rr, 12 and 18 respectively.The governing rule for any point P on the egglipse is

z1,+ 0 + rs = K .* . . . . . . . . . . . . . ( 1)where

X is a constant.9

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IS t 4880 ( Part XI) - 1976EGGLIPSE,

Fro. 8 DETAIL OF EGGLIPSECURVEA-2. BASK: EQVATlONSA-2.1 The basic equations for the egglipse are

x=-4cose . . . . . . . . . . . . . . . ( 2 ) - ( a2 Sin B rtL Co9 0 )1/sy = 0 Sin 6 -

Sin e. . . . . . . . . . . . . . . ( 3 )

wherea is the major axis, andb is the minor axis.

NATE - In equations ( 2 ) a& ( 3 ), use (I for a, for right side curve and use a for a,for left side curve, q and u, are the right major axis and-left major axisrespectively.

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