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IS 5186 (1994): Design of chute and side channel spillways- Criteria [WRD 9: Dams and Spillways]

IS 5186 : 1994

~~ llFfCf1

(1)~l?fr ;rrm 3li~ '1T~ >r1l1T~ \j~cmcr ~

f~\if~ Cfir +rID~T - +rT'1~g

( 'l~~T ~<{~'~1JT )

Indian Standard

DESIGN OF CHUTE AND SIDE CHANNELSPILLWAYS - CRITERIA

( First Revision)

UDC 627'83

@ BIS 1994

BUREAU OF INDIAN STANDARDSMANAK BHAVAN. 9 BAHADUR SHAH ZAFAR MARO

NBW DELHI 110002

April 1994 Price Groop 5

AMiNDMENT NO.1 OCTOBER 2008TO

IS 5186 : 1994 DESIGN OF CHUTE AND SIDECHANNEL SPILLWAYS - CRITERIA

( First Revision)

(Page 1, clause 2) - Substitute 'IS 11155 1994 Code of practice forconstruction of spillways and similar overflow structures (first revtstoni' for'IS 11155 1984 Code of practice for construction of spillways and similaroverflow structure'

(Page 9, clause 8.2.6) - Substitute 'IS 11155 1994' for 'IS 111551984'

(WRD9)

ReprographyUmt, BIS, New Deihl, India

Spillways Including Energy Dissipators Sectional Committee, RVD 10

FOREWORD

This Indian Standard ( First Revision) was adopted by the Bureau of Indian Standards, afterthe draft finalized by the Spillways Including Energy Dissipators Sectional Committee hadbeen approved by the RIver Valley Division Council.

Spillway i~ an integral part of all river valley project, and is essentially required to pass down tothe fiver 01 to sorne other natural drainage, surplus or flood water which cannot be safelyretained upstream of the storage dam. Provision of a hydraultcally efficient and structurallystrong spillway I~ very Important for the safety of the dam and the life and property along thefiver down below.

Generally the spillway can be provided directly over the dam in case of concrete or masonrydam. But for darns composed of earth or rock, or for dam, over which it is impossible orundcvrrable, for special reasons, to pass water, some form of spIllway adjacent to the dam is to beprovided. These may be either closed conduit or open channel spillways. In open channel spillwayswater I' conveyed from the reservoir to the rrver below the dam or to other natural drainagethrough an excavated and lined open channel with fairly steep slope and placed either alonga dam abutment or through a 'addle 111 the Tim of the reservoir. These consist of a low crestand a paved channel on a steep slope on the natural or excavated earth or rock formation.Generally the control structure is placed normal or nearly normal to the centre line of the channeldownstream. Such a spillway IS termed chute spillway. In narr ow canyons. or otherwise, wherethe site for the control structure is lrmrtcd in Width, the crest IS placed almost parallel to thechannel and the spillway IS then called Side channel spillway. A typical arrangement for chuteand side channel spillway is shown in Fig. 1.

Chute and Side channel spillways can be constructed on all types of foundat ron materials rangingfrom solid rock to soft clays. However. If the foundatton materral is incapable of passing thewater without excessive erosion, It should alway, be protected by concrete paving. Due topossible usc of large amounts of spillway excavation in the dam embankment, these spillwaysgenerally result in overall economy in c.irthfill d.uns, Theve structures are specially suited insrtuut io ns where sound rocky foundatrons required for the conventional type of spillways( vert rca] drop type) are not available. Therefore, due to simplicity of their design and construe­non, adaptabih ty to alrnovt any fo undatron condition, these spillways are used with earthfilldarns more often than any other type.

This standard was first published In 1969. This standard has been revised to update its contentsbased on the experience gained WIth the use of this standard. The principal modifications arein respect of design requirements of outlet channel, floor lining, drainage system and anchors.

Par the purpose of deciding whether a particular requirement of this standard is complied with,the final value, observed or calculated, expressing the result of a test or analysis, should berounded off in accordance with IS 2: 1960 'Rulcs for roundmg off numerical values (revised)'.The number of srgruflcant places retained in the rounded off value should be the same as that ofthe specified value in this standard.

IS 5186: 1994

Indian Standard

DESIGN OF CHUTE AND SIDE CHANNELSPILLWAYS - CRITERIA

( First Revision)

2 REFERENCES

The followmg Indian Standards are necessaryadjun e ts tu this standar d:

1 SCOPE

Tills standard covers the criteria for hydraulicand structural designs anti othcr general rcquu-e,merits of chute and side channel spulways.

S.2 Site conditions generally influence thelocation, type, and components of a spillway.1 he steepness of the ten ain traversed by thecontrol and discharge channel, the class andamount of excavation and the possibrlrty forits use as embankment material, the chancesof scour of tile boundi ,g surfaces a nd the needfor hrung, the pel meabrlit y ant! bc.mng capacityof the Iounda tion, and the stabihty of theexcavated slopes should necessarily be consi­dered I n the selection of layout.

6 HYDRAULIC DESIGN

6.1 Chute or side channel spillways in generalconsist of the following components:

a) An approach channel,b) Control structure,c) Side channel trough,d) Discharge channel,e) Energy dissipntor and/or terminal stru­

cture, andf) Outlet chan nel.

6.2 Approach Channel

6.2.1 Where the spillway is located through anabutment, saddle or ridge, an approach channelIS required to draw water from the reservoirand convey rt to the control structure.

6.2.2 Approach velocities should be hrmted andchannel curvatures and transitions should bemade gra-Iual, 111 order to minimize head lossthrough the channel and to obtrun uniformityof flow over the spillway CI est. Head loss III

the approach channel has the effect of reduc­ing the spillway discharge. High velocity mayalso necessitate lining of the channel depend­ing upon the rock. Even distribution of flowshould be ensured over the spillway crest asfar as possible.

6.2.3 The approach velocity and depth belowcrest level have important influence on thedischarge over an overflow crest. Prefer ablythc depth below the crest may be about half ofthc head over the crest for gooJ co-efficient ofdischarge.

Title

lJ772 : 1986

11527 : 1985

IS No.

4410( Part 9 ) : 1982

Glossary of terms relating tor iver valley projcct s : Pal t 9Spillways and syphons (firstrevIsion)

Code of practice for con stru­ction of spillways and srmrlaroverflow structure

Cntcrra for structural designuf energy dtsstpat or s ftJrspillways

Guidelines for devign ofdr aruage arrangements ofenergy dissipators and train­ing walls of spillways

3 TERMINOLOGY

11155: 1984

For the purpose of this standard the definitionsgiven 111 IS 4410 ( Part-9.) : 1982 shall apply.

4 GEOLOGICAL INVESTIGATIONS

Geology of the site w rlI he taken into considera­tion for designing the details of the structure.

5 SPILLWAY LAYOUT

5.1 The outflow charactcnstics of a spillwaydepend o n the particular device selected tocontrol the dischar gc. After having selected aspillway con trol with certain dimensions andcrest level, the maxrmurn spillway dischargeand the maXIl11Um reservoir wat er level may bedetermined by flood routing for adopted design­ed flood. Other comp iuents of the spillwaymay the.i be proportioned to conform to therequired capacity, topography and foundationconditions of the site.

18 5186 , 1994

6.3 Control Structure

6.3.1 The control structure In chute sprllwaysIS generally pi aced normal or nearly normal tothe dXIS or the discharge channel 111 the headreach and In Sl,' e channel spillways the controlsu ucture 15 placed along the side or approxi­mately parallel to the upper por uon of thespi llway lJI~lhdrge channel Control structureIS to limit or prevent outflows below fixedreservoir leve lv an.l to regulate releases whenthe reservoir r ises above that level

6.3.1 Control st ructure III plan may be sti arghtsermcircular, or U shaped The crest may begated or ungat cd The overflow sect ro n maybe agee sh.rpcd, OJ broad crested

6.3.3 The CIevt p ofile should be leslgncd tosuit the "lll huons of g ite opei auo I Atpartial gate openings free fl.iw p otlles ar L likelyto develop neg urve pr cssures In low crestswhu.h Me usually WIth these types Dr spillwaysthe negauv« p essui cs may be ,Ivolded WIthoutany ,tpprell,lble cx tr a cost by adopnng a letflow plofile fOI J. small galt opening fOI thepart or the crcvt downvu earn of the gate SillThe co-efficient of divc har ge III tlu s case ISreduced and can best be WOl ked out on ahydr aulic model

6.4 Side Channel Trough

6.4.1 In Side channe l sprllway the controlstructure IS gene: ally place'! along the stJ e ofor approximately parallel to the upper portronof the spillway discharge channel Plow overthe crest falls into a trough, turns appr oxt­mately at a rrght angle and then continue, Intothe main discharge chan nel The flow into thetrough may enter only on one SIde 111 the caseof a steep hrllside location, or on both SIdesand over the end of the trough if rt IS locatedon a knoll or gently sloping abutment

6.4.2 Reduction 10 discharge over the crestdue to submergence, If It occurs, should betaken into consrderation The vubmci gcncemay be due to some flow conditions alongthe reach of the trough under consi leration ora control section or a construction In thechannel downstream of the trough

6.4.3 The crest structure should be designedas In 6,3,3

6.4.4 Cross-SectIon of Trough

The cross-sectIOnal shape of the Side channeltrough IS ll1flucncLd by the overllow crest onone SIde and by bank conditIOns on the oppo.site Side A trapeZOidal cross-section Withminimum WIdth to depth ratio 15 rccommended(or the SIde channel trough However, themmlmum WIdth should be commensurate WIth

2

both pi actrcal and sti uc tura1 aspects If thewidth to depth ratio IS large, the depth of flow111 the channel Will be shallow, resulung inpoor diffuvion of mc re.rsing flow WIth thechan nel flow Moreover, with greater bedWidth the cxcnvauo.i wrll i nc re ase

6.4.4 I Bccau-,e of lUI bule Ices and VIbrationsmhe, C It 'n SI 'L ch mn el 110w the trough shouldbe set w -ll Into the orrgrnal formation forsafety The sule slope' sho\l\d be tnmmed tothe st ccpe-t anulc at wl-u.h the mater ral wrllsafely q I rd and hned wu h corn.r etc anchoredch cctly to the rock

6,4.5 Slope

F0r the sul-crtt rcal -tage In the t i ough t he mcorn­/ 19 fl iw wrl l not dcvc.I ip high II .msverve vclocitresbcc.iuvo 01 t h, low drop bcfor e It meets thechan u.l fl iw thus dfLttlng a good diffusionWith the wucr hulk In the Hough Suu.e bothth , iucom mg vc lo c i tn s and the channel velo­tlt,.; Will b ,e'lllv.ly slow, a farr ly completemtci nuughng of the 11 iws will take place,thereby pr uuclng ,Illlmpdldtively smooth flowIn the side ch.m .c l Where the channel flowI' vupercr r rc t l t hc ch In lei ve locrtres will behigh a lei the mt c: nux ing of the high-energyti ans vcr s fI W With t hc c haunc l su , irn WIll berough and turbulent 1 he n an,verse flowswill tend to S veep t hc c hanuel flow to the farSide of the ch.mnel, producmg VIOlent waveactro n With at t e nd mt vibr atrons Thereforefor good hydraulic pel forman cc the Side channeitrough should have mrld slope 01 a steep slopeWith 01 cont rol scr tion at the downstream endof Side channel trough '0 that the flow IS sub­Critical in the trough The slope depends onsite co nd I t Ions aud should be so chosen as toreducc the exc avauon to .1 rmrumum

6,4.6 Control Section

The control section IS a sccuon downstream ofSide channel trough where the depth of flowchange, nom subcritica I to supercrrtrcalControl section may be provided by constrrct,1l1g the channel SIdes or elevating the channelbottom The best location of a control sectionIS usually at point where bed slope has to besteepened to keep the channel on the groundSpecial coridruons may require another Iocatron,For example, the sectron may be placed Im­mediately downstream of the dlschal ge trough.

6.4.7 Water SlIrface Profile

The water ,urfdce profile on the Side channeltrough may be determillcd uSll1g the followll1gequat 10 n which IS based on the law of Lonserva­tlOn of Itnear momentum, assummg that the onlyforces producmg motIOn In the channel result

from the fall In the water surface In the drrectronof the aXI~ and that the entire energy of flow overthe crest I' dissipated through Its mterminghngwith ih, channel flow and I... therefore of noassistance .n moving the water along thechannel Ax ral velocity's produced only afterthe mcormng wat er par trcles JOII1 the ch an ne lstream

6.=yg, [ (VI ~ V,) J[ev,- V,) 1-V'(Q,_ Q,)]g (Q, +Q.) Q,

wher c

6. y = drop in water surface m a small reachbetween Section I and Secuon 2 m rn,

Q, - dl ... charge at Sccuon I. In m'h,g = ac celcru m due to gravity In m/s',

V, - vclocrty at Scctron I, In in]«,

V2 - velocny at Scctron 2. In tnfs, andQ, - disc.harge at Section 2 In m"ls

Q, and Q, may be c il cul tted for a particularreach knowi rg the d rs charge per unit length ofthe cre-r

6.4.8 Design Procedure

The fol lowmg steps are recommended for thedesign of a 'Ide channel trough

a) Dcsrgn the ,Ide channel crest controlled01 uncontrolled, .l~ required The lengthof the ("l est should be deterrruncd by thetota 1 dr-charge to be passed and the sur,chat ge allowed,

b) Choose a surtabl e cross secuon, b iuornprofile and locauon and the datum ofthe control sect: 1I1,

c) Calculate the crrucal depth of flow at thecout i o l,

d) If the contro I section I' not at the down.srre.irn end of -trough, calculate thehydraulrc propcr tres of the down ... n eamend of the trough uSing Bernoulli's t heor­rem and by trial and error method,

c) Detcrm irie the water surface profile Inthe trough usmg the equation given In6.4.7,

f) Fit the channel profile to the crest datumby rclatmg the water surface profile tothe' eservou level such that the ... ubrner­ge lce of thc overflow IS comlstent withthe condition a,sumed for eV.lluatlllg thedlsch,uge over the cre~t. and

g) VarIOus ,'esIgn> ,hould be made by,I~sumlng dIfferent hottom wldth~. dlffc.rent channel ~Iopes and varylllg control

IS 5186: 1994

secttons The most economical designthus achieved by comparing severalalternatives should be adopted.

6.5 Dlscharge Channel

6.5.1 flow rclea...ed through the control struc­lure I~ conveved to the ternunal structure orstream bed b~low dam III an open channelexcavated aIo ig the ground surface, Thepr ofilc of the channel rn.iy be val rably flat orsteep, the eros...·, L'IO 1 I11dy be var rably rectan­gular or trapezoidal It may be Wide or narrow,long or short

6.52 Di-charge channel duru.nsror, ... arc gover­ned primarily by hydr.ruh c requrremcnts, butthe velectron of the p' ofilc, cross sec t.onalshape. etL," mfluen c d by the geological andtopographn.al charn c i er rvuc-, of the srte Inplan the ch.mnc] m,ly be ,tI.ught or curved,wuh s ides par allcl , con vet gent, divergent orcombm.itton of these Where the dischar gechann. I IS cu.ved , sui table <upcr clevatronrn.iy be adopted DI ... ch.n ge channel should.i lways be cut through or hned WIth matenalwhu h IS resistance to the scour ing action ofthe acceler.rtrng velocu re-, and which 1~ st ru­ctural ly adequate to wuh-tand the forc es frombackfill, uplift. water load .... etc

6.S.3 Profile

6.5.3.1 Fhe profile of d ,... ch.u ge chan ne! shouldusually be selected to confoi m to topographicand geological srtc cond rt rons and should beprovided WIth uniform -Io pe JIl reaches jornedby vel ureal curves Shat p convex or cone1vecurves should be avo ided to prevent un sans­factory flow 111 the channel

6.5.3.2 ConVLX curve should be sufficientty flatto rn.untam posiuve pre...sures an.' should,therefore, be flatter than the free flowt raj..ctory at the specific l-nergy at which theflow enters the curve The curvature shouldappr oximat e the curve given hy the equation

x'- y = x tan 8 + 4 k (d ~ h )LO~. 8

where

x, y = co-ordinate axes.

o= slope angle of the floor up... trearn ofthe curve,

k = factor of s.ifetv to en-ure pO>Jtlvepre,sure on the flJIH ,lilt! ,hould beequ.ll to Ol gl L.ltel th,ln I 5,

ci= depth of flow <it the beginning oftran'11Ion, .111d

h = velocity head It the begll1l11ng oftran>Jtlon

IS 5186 : 1994

6.5.3.3 Concave curve should have a sufficicnt lylong radius of curvature to mrr muze thedynarmc force on the floor due to cernrrfugal

force and should not be less than 2 x Wd~,p~

where W I~ Ul11t weight of water, g I~ accelerationdue to gravity, d I~ depth of flow, V I' velocityand p IS perrrussible lntensrty of d) narnicpressure In no case the radius should be lesvthan 10 d except at the toe of the ~I evt where Itmay be 5 d.

6.5.4 Slope

6.5.4.1 DIscharge generally passes through thecr rtrcal stage In the sprll way control <tructurcor at the control section downstrcam of Sidechannel trough, and enter, the discharge chan­nel as superci urc.i l or ,hooting flow To avorda hydrauhc Jump below the control, the 110wshould necessarily remain at the supercrrtrcalstage throughout the length of the channelThe flow In the channel Oldy be un If01 111,

accelerated or decelerated depcn.hng on theslopes and dimensron-, of the channel Wheredifferent slopes Me encountered durrng thelength of thc channel, It I' de su able that thesteeper slopes are adopted at the tail of thechannel so that h kely scour due to high ve lo­cmes IS as far dW\Y a' p rssible from th : c mt: 01structure.

6.5.4.2 The he.u! losses which occur In thechannel are friction, turbuleuce , Impact andtransi tro n la, .cs, SIl1CC In most channels change,are made gradually, 01 dinarrly ,III losses exceptthose due to fi n.uo n should be neglected Thevelocrucs a long t he channel should. thci cfore,be worked out by applying Bcmo ullr's theoremIn sec t rons:

6.2 + d l + hi = dB + h, ~ hr

where

6.2 = drop of head from Se cuous I to 2in m;

d). d. = depth of flow at Sections I and 2In m;

hI' h. z= velocity head at Sections and 2 111

m/s; andh: = total loss of head 111 the reach 6.L

In m;= sL6., where S IS average friction slope

= i (SI + S. ) 6.Lwhere

SI' s. = fric no n slopes at sections I and 2.Frrctron slope s may be expressed by Mannmgsformula:

4

v = ~,'J8 Sl/.n

or

s = (,~: )"

where

V = velocuy of flow 111 m]s;

n = coefficient of roughness; andr = hydi auhc mean depth In m.

6.5.4.3 The coefficient of roughness, n, Willdepend on the nature of the channel surface.Thc fi ic t ron 10;,s should be maxirmzed forW01 king out the depth of 110w for f. ee board,and rrummizcd for WOI king out net energy atthe vt rll i ig basm for the design of the basin.For conci cte Irnmg the value of n mdY be takena;,0018 fot free board to acco unt for airentram ment and swelling, and 0008 for thedesign of st rlling basin.

6.5.5 Convergence and Divergence

From ec o normc c onsrderntrons the channelsec tio 1 m.iy be 11111 owe, or Wider than ertherthe crest 01 the terrmrial structure thus requir­mg co nvcrgrng or drvci grng tran-auous to fitthc various cornpo rents together. Side wallconvergence In disch.rrge channel should bemade gradual to 'avoid cro .s, waves ride ups'on the walls and uneven drstrrbution of flowaci oss the channel Srrrnlarly the rate ofdrvergenc; of the "Ide w,tll, should be gradualto ensure the flow to spread unIformly over theentire Width of the channel and to avoid unde­virublc flow conditions .rt the terminal structureand scpar auo n offlow at the SIde walls

The <ide tr ansrtrou for convergence or diver­gence should be provided at an angle grven bythe fo llowmg cq nation.

Itan 0( ='JF

where

0( = angle of convergence or divergence;dnd

VF = Froude number given by '=­

v'gd

whereV = average of the velocuies at the begm­

ning and end of transttron;

g = acceleration due to gravity; and

d = average of the depths of flow at thebegrnnmg and end of transruon;

6.5.6 Curves

The centre line of the spillway should be keptstraight as far a" possible. However. on pl.ice­where It has to be curved owmg to un.ivordableCircumstances particular attention should bepaid to the degree of superelevauon to be pro­vided at the outside of the bend The 'UpCI­elevation should be determined by hydraulicmodel studies. Sloped SIde" of sprllway ch.m­nel should be avoided on the outside of sharpbends because they cause a higher supereleva­tron of water surface than that bv verticalwalls

6.5.7 Free Board

6.5.7.1 The tree boar d provided for d ischargechannel where flow J~ supercrrncal should benot lcs-, tban that given by the followingformula

Free board ( In m ) = 061 + 0037 8vd" 3

where

v = maximum velocity of !low III m/>. andd = depth of flow In m

6.5.7.2 Where Side wall-, of ~tI11II1g basm arcnot desired to be overtopped by waves. WI JCS.splash or spray. the free b v ird f ir the sidewalls III th e basin. In the absence of Illy modeltests, should be grvcn by the fo llowrug formula

Free board ( In m ) = 0 I (VI + d. )

whereVI = mcormng velocity to the basin In ill/",

andd, = conjugate tad water depth In m

6.6 Terminal Structure or Energy Dissrpator

6.6.1 In order to avoid excesvive scour on thedownstream of discharge channel, the excessiveenergy of water should be dissipated before thedischarge IS returned to the downstream rrverchannel

6.7 Outlet Channel

6.7.1 Outlet channel conveys spillway flow fromthe terminal structure to the rrver channel belowthe dam It should be of sufficient size to passthe anticipated flow WIthout forming a controlwhich WIll affect the tarlwater levels for energydissrpators

6.7.2 The dimension of channel a-id i equn c­ment of protective measui e-. by lining or riprap should depend upon the nature of ch mnelbed and the velocny .ichu,vcd after the energydisstpator 1 he scourmg of channel affectsthe tall water levels.

s

IS 5186 : 1994

67.'?! The tailwater level in the outlet channelmay be affected by the scour of channel bed asabove, and by retrogression in the river beddue to relatively cleat water from the reservo irIn case the outlet channel I" only a pilorchannel 11l crrodi ble mat crra l, the errodedmaterral may form Istands or bar" In thc channeldownsu cam and raive the tarlwatci level sThese hkely changes III the tailwater levelshould be taken care of In design of energydiss rpators

6.7.4 Where two or mo re types of energy drss i­pators have been used for the set vice orauxihary spillwav, adequate CMe should betaken to assess through model studre-, andtaking Into considcratron the eflect c f t hceroded materral and It, depovit ron furt herdownvtream 111 th, ovcr a ll pl mnrng dnd June­tiorung of l-nergy di ssipator s and otherappurtenant structures such a, t.ul rave channelsof the power houvcs so thelt the eroded matcrralor its deposition does not Interfere With energydtssrp.itor-, or the appui tenant structures

7 HYDRAULIC MODEL TESTS

7.1 Where necessary the de"gn should bechecked by conducuug tevt s on geo n tr icallysumlar or disto: ted mode Is

7.2 With proper care III hydrauhc studies whei ethe shape of the crest and ot hcr fc atui ," aresuch that precedent IS avarlablc , hydraulicmodel tests may not be necessary However,for unusual condition, and whc: eVll ther c '" abend In channel, appropriate model test> shouldbe made

8 STRUClURAL REQUIREMENTS

8.1 Side Walls

Where rct ammg wall> for SIde" of cntran cechannel, discharge channel and stilhng basmare used, they should be de-igned to wnhvtan dall possible combmauons of various loadmgs,for example, backfill, earth or ruck pressure.water pressure, hv e 10id surcharge, upliftpressures and force, due to horizontal orvertical seismrc accclcrauon

8.2 Floor Lining

Where velocity of 1low and type of bed rockwarrant protcctro n of bed rock agamvt erosion,the bed rock vhould be 11l1~d with ~()I11C pro te­clive material wruch generally t .kc-, the fo t mof concrete 11l1111g The luung may be I cqUl' cd111 entrance channel, discharge trough 01 channeland strllmg ba-rn.

IS 5186 : 1994

8.2.1 Thickness of LiningDUring spillway flows the floor lmmg I~ sub­jeered to hydrostatic forces due to the weightof the water In the channel, to boundary cragforces due to frictional resistance along thesurface to dynamic forces due to flow Impinge­ment, to uplift forces due to i educt ron ofpressure along the boundary surface, or to upliftpressure caused by Lakage through JOints orclack, When there IS no spill, the III1Ing ISsubject to the action of exp.insron and contrac­tion due to temperature var ratrons, alternatefreezing and thawing. weatheung and chemicaldctenoratron, to the eff cts of settlement andbuckling, 01 to uplift pressures due to underseepage or high ground water condition SInceIt IS not possible to evaluate the v-mous forceswhich might occur and also not to make thehrung heavy e iough to resist them the thick­ness of the luung " est ablished on a more orless ernpmcal basis, and under drains anchors,cut off>, etc, are provided to st abrhze theIlI1l11g

8.2.1.1 The thickness of IlI1l11g of approachchannel Will depend upon the velocrnes, depthof flow and poor rOl.kj'OlI cond mons Thethickness (If the order of 15 ern to 30 ernhave been found satisfactory for normalcircumstances8.2.1.2 In the discharge channel, where thevelocrty of water I~ usually very high, thedesign of the floor slab should depend on thefoundation (for example unyielding rock,r elatrvelv yielding rock or earth), vclocuyand intensity of flow, uplift head and othersirmlar factors mcludmg the location of spill­way with respect to dam Probable hydro­stanc uplift forces under adverse condrt ionmay be considered parttally rchevcd by thedrainage <yst em The fOII.L, should be estimatedconservatively for partu.ular foundation anddramage system To piuvide a relativelywater tight functional hrung which may wuh­stand reasonable weathering and abrasion andwill hold up against normal experienced forces,a rnuumum thickness of 20 ern IS recommendedfor small spillways, where the 11l11ng IS placeddirectly on rock When the III1Ing IS placedon foundations other than rock and subjectedto forces other than normal experiencedforces, a detailed design should be carriedout and slab thickness arrived at accordingly8.2.1.3 Sttlltng basm floor llnmgStdllng basrn floor lining should be as given111 IS 11527 1985 ( under revlrlon )8.2.1.4 The reinforcement III slabs should beprovided as follows

a) For slabs on rock, a mrrumum shrinkage/temperature reinforcement equal to 0 15

percent of the cross sectional area maybe provided on the top face both waysfar thicknevs up to 450 mm For thick­ness greater than 450 mrn, only 450 mmmay be considered In case of high strengthdeformed steel bars, t his percen tage maybe reduced to 0 12 percent

b) For <labs on yielding foundations likeca rth/poor rock, depending upon theactual site COndl[IOI1>, the Iemfor cementshould be designed suitably

8.2.2 Waterstops and Jotnts

The hrung should be laid In panels .lppIOXI­mately 10 m x 10 m so a> to make the entrancechannel lining ,t reasonably water tight upstreamapron to reduce uphft on the control su ucturesWherc I equired, the JOInts In the IJl11ng shouldbe provided With waterstops In all the joi ntsThe requu cmcnt of waterstops In the IJl11ng ofdischarge channel Will depend upon the degreeof water t rgh tnc.vs required agarnst the cxter iorwater hc-uls Where a laver of gravel has beenprovrded under the hnmg the prOVISIOn ofwater stop- m ty not be necessary, other wisewatcrstops should be provided 111 the longitudi­nal JOInts , and In rransv e: se joints at theconcave curves Bee.ruse of high velocity flowpassrrig dU"~ the JOint With lin offset( see 8.2.2.2) the povs ibrl rt y of water scepmgwater the transverse jomts IS very little 1 hedown stops should not be pi ovided In ti ansvci seJ01l1ts unlcvs complete water tightness againstexrei ior water hc ads i-, required because thesetransverve jo m ts should otherwise serve as a reliefagainst built up of high uphft pressure under thehrung III case of any povsible chockrng of underdrams Where the foundations are permeable,waters top, should be provided 111 the j ornts ofstilling basm floor Irn mg '0 as to avord circu­latrng flow und ci the 1II1Ing due to differentialhead on the JOInts 111 the zone of hydraulicjump

8.2.2.1 The water stops should also be provided111 the JOints of Side walls where seepage offlow behmd the wall> IS u idesrrable

8.2.2.2 The transverse jornts should be providedWith 13 mm offset, as shown In Fig 2 so as toaVOId high velocity flow strrkmg against theedge of the lower floor cause water to seepthrough the JOint under a very 11Igh pressureand dtslodge or uplift the lmrng To furtherensure ag unst this, the lifting of upstream edgeof lower slab due to drffcrentral settlements orheaving should be checked by providing cut-off( see 8.2.3 l, especially when the lming IS found­ed on a layer of gravel or earth

'<''' lIfilUNC... : ..."co....

.~.

FIG. 1 TYPICAL SlOE CHANNEL AND CHUTIl SPILLWAY ARRAl'GEMENT

IS 5186 : 1994

" ......

jIo -,

lSrnm lEA.N CONCRETE""'/

t OF IISOmm SEWER PIPEDRAIN WITH OPEN JOINTS

1200

j to> 100 mm SEWE~PIPE DRAIN WITH

I -, OPEN JOINTS

---' 300 L "- ANtHOR 6A.R

All drmensrons in millimetre.

FIG. 2 TYPICAL DETAILS OF TRANSVERSE JOINTS

7

IS SI86 : 1994

8.2.2.3 The offset in the downstream slab at thetransverse joint, as shown in Fig. 2, shouldalso be provided in the joints of side walls( Fig. 3 ).

..All dimensions 10 rmllunetrcs.

FIG. 3 DETAILS Of JOINTS IN SIDE WALLS

CONTRACTION JOINT

BURLAP

8.2.3 Cut-offs

Where the lining is placed on earth on a steepgradient OT the lining is placed on a layer ofgravel and not anchored to the foundation, acut-off should be provided on the upstream endof each panel to check the creeping (FIg. 2 ).This cut-off should also check the lower slablifting above the lower edge of the upper slab.These cut-offs should also form barriers againstseepage of water in the gravel layer or amongthe contact of lining and foundations, anddivert the seepage water to the transversedrains.

8.2.3.1 Similar small cut-offs should be providedin the longitudinal jornts as well. where liningis founded on a layer of gravel as shown inFIg. 4A. Typical joint details for lirung onrock arc shown in Fig. 4B.

loA JOINT DETAILS FOR LINING ON GRAVEl

CONTRACTION JOINT

BURLAP

125mm SAND

LEAN CONCRETE

SEWERPIPE DRAIN WITHOPEN JOINTS

48 JOINT DETAILS FOR lI»ING ON ROCKAll dimensions in rmlllmetres.

FlO. 4 DETAILS OF LONGITUDINAL JOINTS

8

8.2.3.2 Cut-offs should also be provided at theupstream end of the spillway to reduce seepageof flow along the hrung, Increase path of per­colatron, Intercept permeable strata and reduceuphft under the spr! Iway and adjacent struc­turcs Cut-offs should aha be provided at thedownstream end r f spillway to check eros ionand underrmnmg of the su uctures The depthand thickness of such cut-offs "auld dependupon the nature of the foundations

8.2.4 Drainage System

A~ mentioned 111 8.2, the stabihty of'flooi lmmgI' lOCI cased by pr ovrdmg underdrams Thesedrams reduce the uplift on the hrung Thedrainage f(1J 11 .or hrung, energy drssipators andtrarrnng wall> of spillways and the drarnage forbackfill <hould be a ccordrng to the provrsionsgrven III IS 11772 1986

8.2.4.1 Where the foundation IS sufficrent lyImpel vrous to prevent leakage from drauuugaway OJ whet e It I> subject to di aw moisture tothe undersrde of the hrung by capil l.u y action,a conunuou-, gravel blanket should be providedunder the lirung, e-pecrally where the ar ea I~

subject to fJost 'ictron This blanket shouldserve to insulate the f iundattons against frostpenetr.uro-i The thickness of gravel layerwould depend upon the clunite of the ruea andvusccpubihty of the foundauon to frost heavmg,

8.2.4.2 The gravel blanket should be well gradedto safeguard against movement of foundationmaterral WIth the seepage flow

8.2.4.3 The drains under the hrung vhouldconsist of a network of pipe drams which shouldfollow the joints III the hrurig The dramsshould either be perf01 ated or non-perforatedclay or cement sewer pipes laid With open JOints111 gi avel and bedded on a mortar or porousconcrete pad to prevent the foundation materialfrom being leached into the pipe

8.2.4.4 Where the stratifications III foundationrock are almost parallel to channel bed, verticaldram ige holes prercing through the layers ofstratrfic mons, backfilled WIth gravel should beprovided to I eheve uphft on the layers of foun­dation due to seepage or gi ound water. Theseholes should be connected to the pIpe drams.

8.2.4.5 The drains under the discharge channelshould have therr outlets either In the dischargechannel itself through the Side walls, or Into

IS ~186 : 1994

drainage gallery in case of wide and longspillway. The outlets should be connected tothe pipe drains.

8.2.4,6 The drains under the hrung belowmaximum tailwatei level and strlhng basrnshould have thcrr outlets IJIto the chute blocksof the basm The dramage system of st ilhngbasrn floor should, however, be kept separatefrom that of the other floor lmmg

8.2.4.7 Sewer pipe drams WIth open jointsshould also be provided at the toe of the heelof the Side walls to collect seepage water fromthe backfill and relteve the Side walls fromwater pressure These pipes should have theiroutlets In the discharge channel through theSIde walls or mdependen t outlets elsewhere

8.2,5 AnchorsThe floor of the chute should be anchored tothe foundation by anchor bars to mcrcase theeffective weight of the slab against displacementdue to uplift and other forces

8,2.5.1 Por chute spillways on rock foundation,It may be generally sufflcicnt to provrde norm­nal anchors, say 25 rnm mild steel rounds 3 mlong at the rate of 15m centre to centre( staggered) 111 the rock With SUit ib!e drainagearrangement, In the absence of any analys isAnchors below an I around the energy drssrp.r­non arrangement should be desrg red acc ordmgto IS 11527 . 1985

8.2.5.2 The diameter of hole Into which theanchor bars should be placed and groutedshould not be less than one and a half tunesthe maximum transverse dtrnensron of the bar

8.2.5.3 Actual pull out tests should be carriedout at the site to deter mille the depth andspacing of anchors, diameter of holes and typeof anchors to be provided

82.5.4 In soft rocks where bond bewtcen rockand grout IS very poor, or III earth, bulbanchors as shown In Fig 5 should be used

8.2.6 Surface FInishBecause of very high velocity of flow rn chuteor SIde channel spillways, the concrete surfacefinish against which water should flow, IS ofparamount Importance The abrupt or gradualirregularrttes for such formed or unformed sur­faces should be reduced to the rmrumurn andshould conform to the details given InIS 11155 , 1984

IS 5186 : 1994

ENLARGED BOTTOM FORBULB ANCHORAGE

-,-,,,

ANCHOR BAR

AUGERED HOLE BACKFILLWITHCONCRETE

/I

/

/'APPROXIMATE EFFECTIVEADDED WEIGHT OBTAINEDBY ANC.HORAGE

All dimensions in millimetres,

PIG. S DETAILS Of BULB ANCHORS

10

Bareaa .r lulu Stuulard.

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Amendments Issued Since Publication

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