Disclosure to Promote the Right To Information Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public. इंटरनेट मानक “!ान $ एक न’ भारत का +नम-ण” Satyanarayan Gangaram Pitroda “Invent a New India Using Knowledge” “प0रा1 को छोड न’ 5 तरफ” Jawaharlal Nehru “Step Out From the Old to the New” “जान1 का अ+धकार, जी1 का अ+धकार” Mazdoor Kisan Shakti Sangathan “The Right to Information, The Right to Live” “!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता ह ै” Bhartṛhari—Nītiśatakam “Knowledge is such a treasure which cannot be stolen” IS 12169 (1987): Criteria for design of small embankment dams [WRD 9: Dams and Spillways]
Transcript
Disclosure to Promote the Right To Information
Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.
इंटरनेट मानक
“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda
“Invent a New India Using Knowledge”
“प0रा1 को छोड न' 5 तरफ”Jawaharlal Nehru
“Step Out From the Old to the New”
“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan
“The Right to Information, The Right to Live”
“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam
“Knowledge is such a treasure which cannot be stolen”
“Invent a New India Using Knowledge”
है”ह”ह
IS 12169 (1987): Criteria for design of small embankmentdams [WRD 9: Dams and Spillways]
IS : 121. ·1887«R••ttlrmecl 1"7)
Indian StandardCRITERIA FOR
DESIGN OF SMALL EMBANKMENT DAMS
( FUll Reprint FEBRUARY 1999)
UDC 627.81 : 624.136 : 624.31
C Copyright 1988
BUREAU OF INDIAN STANDARDSMANAK BRAVAN, 9 BAHADUR SHAH ZAFAR MARO
NEW DBLHI 110002
Gr5 Feb",d'" 1988
IS • 12169 • 1'.7
Indian Standard
CRITERIA FORDESIGN OF SMALL EMBANKMENT DAMS
Dams ( Overflow and Non-Overflow) Sectional Committee. BDC 53
HiDduitaD CoDitructloa Company Ltd, Bombay
Public Work. Department, GoverDment of TamilNadu, Madr..
R'lr'J,."ill,Irrigation Departmeal, GoverDment of Gujarat,
GandhiDa.ar
DIB.CTOB ( Eat RDO-I )D•• VTY DJBBOTOR
( E Ie RDD-I ) (Al",n,,',)DJBBOTOR, IN8'1·ITOTB ur HYDaAO
Lice & HYDROLOGYSU...I.TDDIMG E.GI....
( D.B.G•• ) ( M,,,,..,, )So. M. V. S. IY••GAB
Kefale State Electricity Board, TrivandrumDbakra Be.. Management Board, NaDlal
TownlhipSRRI J. S. KaURA•• ( ~l"'"," )
S.81 H. S. BSAT In perlOD.I capaeity (No. 599, 10thCross,]a),,-MI", B.,.,Glor, )
SRBI M. V. BRAR.. Tata ConiultiDI EDliaeen, BaDla10r.S8BI R. SlYAB••ltAR ( AI,,,,,.,.)
SBRI B. K. CRADSA Coalulting EDlineering Services ( India) PrivateLtd, New Delhi
Pao.. HARI KRISB.A ( AI'"IUII, )Pao.. M. C. CS.A.TURVEDJ Indian In,titute or TechnololY, New DelhiCBIBI' EMOIN1i:BR (RANIIT SAGAR Irrilation Department. Government of Punjab,
DAM) Chandi.erhDIRBCTOR (R.A.lfIIT SAGAB
DAM ) ( Alt6rnc', )SBRI C. ETTY DAICoWlN In penonal capacity ( P. O. Mu".da, TriotJ"drUfll )DJ.acToR Central Water It Power Research Station, PUDe
SRal S. L. MOKA8HI (All""''')DJB.OTOR OP DB810.N8 Irri.atioD "Waterways Departmeae, Govern-
ment of Welt BeDlal, Calcutta .CeDtral Water CommialioD, New Delhi
CA.ir",.,.SOl V. B. PATBL
M""6,,,8.81 R. BAL••AMA.1tSaBI R..K. BBA81.
(C.,.,j"",d ." /HIg' 2 )
(f) e.t1ri,,,, 1988BUREAU or INDIAN STANDARDS
TIaII publlcatlaD II protected uacler tb. ,.... e."n,,,, ~,' (XIV or 1957 ) aDdnprocl~ ia wbol. 01' iD part by ua, me.. eac.pt with written permiaioD of thepubl'" ..... be d..... to be aD iIIIriap.eat 01 copyrilbt uDder tbe said Act.
III 12169 • 1987
( C.",in",d f,om /NI" I )
SRBI P. M. SOMI ( Al'ma.', )SUI R. AK IQBAL 8111GB
M,mHrs b/W6unlin,O..FICBR-ON-S PEe I A L D U T Y, Irrigation Department, Government of ADdhr.
( DAK8 ) ( COO ) (AI,,,,,.,,)Sa.1 M. U. PUROBIT IrrigatioD Department, Government of Gujarat,
Gandbinag.r
SSBJ O. N. T••p.& (AI,,,,,.,, )SUBI G. RAJI£N, Director General, SIS (&-01"10 M'rtlbn )
Director ( Civ Enll )
Irrigation Department, Government of UuarPradelh, Lucknow
SRal BISHAX LAL JATA•• ( A.l'"",," )S••I M. S. RAilA RAO K.rnataka Power Corporation Ltd, BangaloreS••J M. S. RBDDY Central Water Commission, New DelhiRlCpa8sBNTATIVII 1••titutioD of Engineers ( India ), CalcuttaSECRETARY CeDtral Board of Irrigation & Power, New Delhi
DIRJtc'roB ( CIVIL) ( Alt","", )S".JtRINTlIiNDJNO Elf Q I N B • B Irrlladon Department, Government of Mahara-
( MD ), CDO shtra, BombaySaBI K. N. VSNKATAB••AN Major. Medium &t Minor Irrigation Department,
GoYerDmeDt of Madhya Pradttsb, Bhopal
SIn,'.",I SBBI K. K. SHABKA
JoiDt Director ( Ciy Enll ), BIS
Earth and Rockfill Dams Subcommittee, BDC 53 : 2
Co"",,,.,S.al M. U. PUROHIT Irri.atiOD DepartmeDt, GovernmeDt of Gujarat,
OaDdhiaalarMIfIINr,
SUP.RllfTDDI_O EJfQI~J aDO(AI.,,,.,. to Shri M. U. Purohit).BBI N. K. A.o.... Shallra Bea M......m••t Board, NaDiaI
TowDihip8Bal K. K. S. BBAJlD....1 (MImudI )
PROI' M. C. CHATUav.DI ladiaalnltitute of Techaol.,. Ne. DelblS••IIl. P. C80..... Natio.a1 Project. CoaatructioD Corporatioa L'd,
New DelbiS... K. N. TA.IIl. (~".,,..,,)
8••1 It. R. DAT". fa penoaal capacity ( .".. M"'II No.2, 14.S.B.,S••,,,".-, C"'N, ...",)~ lallC.rOa ( It • RDD-I ) CeDlral Water ColDmillloa, New D.lbi
D•• u~y DI •• o~o.( B a RDD-I ) ( ~1InMI, )
(c...-.,." 20)
2
AMENDMENT NO.1 OCTOBER 2008TO
IS 12169 : 1987 CRITERIA FOR DESIGN OFSMALL EMBANKMENT DAMS
(Page 12, footnote ",arud *) - Substitute the following for the existingfootnote:
'Freeboard laIuircments in emblDkment cIamI- Guidelines (fir" MluloII). •
(Page 18,clause 7.2.1) - Insertthe following sentenceat the ead:
&After assessment of geo-technical panmeters of flyash and based on technoeconomic considerations, tlyash conforming to IS 3812 : 1981 may be used intherandom zones ondownstream of inclinedfilter in a zoned dam.'
(WRD9)
Ropropaphy Unit,DIS,New Delhi.India
III 1218 • 1987
Indian Standard
CRITERIA FORDESIGN OF SMALL EMBANKMENT DAMS
o. FOREWORD
0.1 This Indian Standard was adopted by the Bureau of Indian Standardson 24 August 1987. after the draft finalized by the Dams ( Overflow andNon-overflow) Sectional Committee had been approved by the CivilEngineering Division Council.
0.2 A fairly large number of small embankment dalM are being built allover the country. These are generally designed locally and central designfacilities are not made use of. In designing, a small embankment dammany of the provisions specified in IS: 8826-1978· are required to bemodified or relaxed. It was, therefore, felt that a separate standard shouldbe prepared for guiding the design of small embankment dams.
0.3 For the purpose of deciding whether a particular requirement of thisstandard is comr1ied with, the final value, observed or calculated. expressing the result 0 a test or analysis, shall be rounded off in accordance withIS : 2·1960·. The number of significant places retained in the rounded offvalue should be the same as that of the specified value in this standard.
1. SCOPB
1.1 This atandard la)'l down guidelinel for design of 'small embankmentdams.
2. TERMINOLOGY
2.0 For thep~ of this ..taDcIard. the (ollowing definitions in additionto those given in IS : 8826-1978* ahall apply.
2.1 Bm-·.....t Dam - A dam composed of any type of IOU including rock.
2.2 B.......... BlDh....t Dam - AD embankment dam compoled or linBle type of material.
eOuld.li.. lor dee••01I MIt""" rock.1I clam..tllu•• for rOUDdiDI • DU aI,•• ( ,,.,. ).
3
2.3 Lar•• Dam - A dam exceeding 15 m in height above deepest riverbed level and a dam between 10 and 15 m height provided volume ofearthwork exceeds 0·75 million ml and storage exceeds 1 million rnl orthe maximum flood discharge exceedI 2 000 cumecs.
2.'.1 Modifi'd HomDII",DfU E",6""lcm,,,' Dam - An embankment dam inwhich Imall quantities of pervious material. selected to control the actionof seepage, are carefully placed in an otherwise homogeneous dam ($I,Fig. 1 ).
2.4 RockfUI Da. - An embankment consisting of various sizes of rockt? provide Itability and an impervious core of membrane to provide watertightness.
2.5 Sman D.... - A dam not satisfying the criteria of a large dam( sI,2.3 ).
2.6 Zea'" Bmb••m.at Dam - An embankment dam composed ofzon~. of difF~rent types of soil ( '" Fig. 2A and 2B ).
S. COMPONENTS OP EM8AKMBNT DAM
3.1 An embankment dam generally consists of the following components( Fig.2A and 2B ).
a) Cut-offjb) Core;c) Caling;d) Internal drainage .yltem and foundations;e) Slope protection; andr) Surface drainage.
3.2 The following componenta are provided in lpecial cues:
a) ImpervioUi blanket; andb) R.eliefwell.
~. lVNarJON8 AND DBIION RBQ,UIRBMBNTI
f.' The (unctions and deaigD requirement. of the components are dambed in f.1 to fA.
4.1 Cae..•
••1.1 The cut-off is required for the following Coaction.:a) To reduce lou of stored water through foundationl and abut
mentaj andb) To prevent subsurface erOlion by piping.
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f.~.2 The type of cut-off should be decided on the basis of detailedgeological investigation. It is desirable to provide a positive cut-off.Where this is not possible, partial cut-off with or without upstream impervious blanket may be provided. In any case, adequate drainage arrangements may be provided on the downstream which may, inter-alia, includerelief well. Cut-off may be in the form of trench, sheet piling, cementbound curation, diaphragm of bentonite, concrete or other imperviousmaterials,
f.l.3 Recommendations for location and size of cut-off are givenin 4.1.3.1 to 4.1.3.6. A drainage cut-off is the most common form ofcut-off.
f.I.S.l The alignment of the cut-off should be fixed in such a waythat itl central line should be within the base of the impervious core.
4.1.3.2 In case of positive' cut-off, it should be keyed at least to adepth of 0-4 m into continuous impervious sub-stratum or inerodible rockformation.
4.1.3.3 The partial cut-off is specially suited for horizontaUy stratified foundations with relatively more pervious layer near top. The depthof the partial cut-off in deep pervious alluvium \\ jlJ be governed by:
a) Permeability of substrata; andb) Relative economics of depth of excavation governed usually by
cost of dewatering versus length of upstream impervious blanket.
4.1.3." The bottom width of the cut-off trench may be fixed takingfollowing factors into consideration:
a) Provide sufficient working space for compaction equipments;b) Provide sufficient working space to carry-out curtain grouting;
andc) Provide safety against piping.
A minimum width of 4·0 m is recommended. A bottom width or 10to 30 percent of hydraulic head may be provided to satisfy requirement ofpiping. This may be suitably increased to satisfy other requirements ofmechanical equi pments and curtain grouting. The side slopes dependupon sub-strata. Side slopes of at least 1:1 or flatter may be provided incase of overburden, while i: 1 and i: I may be provided in soft rock andhard rock respectively. The back fill material for cut-off trench shall havesame properties as those specified for impervious core in 4.2.1.
4.1.3.5 The cut-off in the flanks on either side should normallyextend up to the top of impervious core.
8
IS I 1218' • 1117
4.1.3.6 At the abutment contacts of the cut-off trench, care shouldbe taken to avoid seepage by outflanking.
4.1.4 Necessity of grouting below the bed of cut-off trench will arise ifthe cut-off trench is terminated in rock formation and the rock is weathered or having cracks, joints and crevices. Necessity of grouting may bedecided based on percolation tests. Rock having a lugeon value of morethan 10 should be grouted so as to bring post-grouting lugeon value ofabout 5. The depth of grouting does not normally exceed half the headof water at the level from which grouting is done. The necessity of grouting below the bed in case of partial cut-off trench will be governed by thecost and effectiveness of the grout curtain vis-a-vis the value of water lossthrough seepage below and beyond the partial cut-off trench If groutingis done, provisions of IS : 4999-1968* may be followed. Alluvial stratahaving permeability in excess of 10-1 emls shall be treated thoroughly bygrouping with a suitable material. Strata of permeability between10'" emls and 10-8 emls may be treated to reduce the permeabilityto the extent possible. The grouping or strata having permeability lessthan 10-1 emil will be difficult, expensive and time consuming.4.2 Core .
f.2.1 The core provides impermeable barrier within the body of thedam. Impervious soils are generally suitable for the core. IS: 1498-1970tmay be referred to for suitability of soils for the core. Appendix A Rivesrecommendations based on IS : 1498·1970t. However, soils having highcompressibility and liquid limit and having organic content may be avoided, if possible, as they are prone to swelling and formation of cracks.
f.2.2 The core may be located either centrally or inclined upstream.The locations will depend mainly on the availability of materials, topography of site, foundation conditions, diversion considerations, etc. Themain advantage of a central core is that it provides higher pressure at thecontact between the core and the foundation reducing the possibility orleakage and piping. On the other hand, inclined core reduces the porepressure in the downstream part of the dam and thereby increases itssafety. It also permits the construction or downstream casing ahead of thecore. The section with an inclined core allows the use of relatively largevolume of random material on the downstream side.
4.2.3 The following practical considerations govern the thickness of thecore:
a) Availability of suitable impervious material;b) Resistance to piping;
• Recommend.tioDI (or lroutlul or previous loill.tClu.iftcatioD and identificatioD of soil. Cor general engineering purposes (first
"';S;otI ).
9
II • 12181 • 1117
c) Permiilible seepqe through dam;d) Availability of other materials for casing, filter, etc; ande) Minimum width that will permit proper construction.The minimum top width of the core should be 3 m, Its thickness at
any sectlen Ihall not be lesser than gO percent (preferably Dot lesserthan 50 percent ) of maximum head of water acting at that section.
4.2.t The top level of the core should be fixed at 0-5 m above MWL.4.3 ea.la.
f.3.1 Tbe function of caling is to impart stability and protect the core.The relatively pervioul materials, which are not subject to cracking ondirect exposure to the atmosphere, are suitable for casing. IS : 1498-19iO·may be referred to for auitability of loils for casing. Appendix A givesrecommendationa baaed on IS : 1498·1970*.f." late..... DnIa.,. By.te_
4.4.1 Internal drainage sy.tem comprises an inclined or vertical filter,a horizontal filter, a rock toe, a toe drain, etc. For the design of thecomponents of the internal drainage system IS: 9429-1980t may bereferred to. AI far as possible locally available sands, gravels, etc, shouldbe used.
4.4.2 The design of filter consisb of applying the conventional filtercriteria which take into account only the grain size distribution and theshape of the grainse However, in addition to the grain size, the stabilityof the base soil adjacent to a given filter depends on its resistance to dragforces.
In view of this, when the soil containing 20 percent or more clay iaused .s a base soil and hal Don-dispersive properties, the filter criteriamay not be enforced Itrictly and the clean land available locally may beused irrelpective of the gradation. This relaxation should be applied todam. up to 10 m height only. For dams of height more than 10 m, thecriteria for filtea protecting cohesive soil may be relaxed by the designerdepending upon his judgement and experience,
".".3 Inclined or vertical filter together with the base filter. if required,il desirable to be provided especially to protect silty core material. However, the inclined or vertical filter may be deleted in zoned sections havingperviOUI downltream abell and clayey cores but a transition filter betweenthe core and the downltream shell would be necessary in case of damswhere rockfill is used .. Ihell material. In case of dam reaches, where thebead of water il 3 m or JCII, it may not be necessary to provide blanket orchimney filte,.. Adequate toe protection shall, however, be provided.
·C1UlificatloD aDd identification of 1011. for general ~nllneeriDI purpOiN (fir,',lr/isiDII ).
+c'.ode or practice lor draiDa.e IYlt8m Corearth and rockSl1 dam••
10
4.4.~ Wherever there is silty material to be filled in the cut-off and thedownstream face of the cut-off is sufficiently open to receive soil particlesmigrating under high seepage Rradienu, it is adviaable to provide a protectivc filter layer along the downstream face of the cut-oft' trench also.
4.5 Slope ProteetloD
4.5.1 Upstr'flm Slop, - The upstream slope protection is ensured byproviding riprap. For design of the riprap, IS : 8237-1985* may be referred. A minimum of 300 mm thick riprap over 150 mm thick filter layermay be provided.
4.5.2 Dowllsl""", Slop, - The downstream slope protection is ensuredby providing riprap or turfing. It is usual practice to protect the downstream slope from raincuta by providing suitable turfing on the entireslope. For details of downstrcam slope protection, IS : 8237·1985* may bereferred.
4.6 Sarface Oral_aBe - For surface drainage of the downstream alopcof the dam, reference may be made to IS : 8237-1985*.
4.7 Impervlo•• Blaaket
. 4.7.1 The horizontal upstream impervious blanket is provided toincrease the path of seepage when full cut-off is not practicable on pervious foundations. The impervious blanket may be provided either with orwithout partial cut-off. Impervious blanket shall be connected to core ofthe dam as shown in Fig. 2B.
f.7.2 The material used for impervious blanket should have far lesspermeability than the foundation soil. To avoid formation of cracks, thematerial should not be highly plastic. Reference may be made toIS : 1498-1970t for suitability of soils for blanket. Appendix A lives recommendations based on IS : 1498.197Of. A 300 mm thick layer of randommaterial over the blanket is recommended to prevent cracking due toexposure to atmosphere.
4.7.3 The impervious blanket may be designed in accordance withIS : 8414·1977~. As a general guideline, impervious blanket with a minimum thickness of 1·0 m and a minimum length of 5 timcs the maximumwater bead measured from upstream toe of the core may be provided.
f.8 ReHel WeD. - If relief wells are provided, I they should meet therequirements of IS : 5050-1968§.
·Cocle or practice for protection of .lope Cor relervolr embaDkmlDti (fi'" "WI;'" ).tcl...iftcatioD aDd identificatioD of .oill Cor leDera. eDliDeerlDI purpose (fi',',.si.II i,~GuideliDeiCor de.ilD or uDder-.eepage control meaaure for eartb.rockfill dam••ICode of practice Cor de.iID, cOD.truction and maiDtelWlce orrelW weill.
11
II. i2169 .1981
S. BASIC DESIGN REQ,UIREMENTS
5.1 The basic requirements for design of embankment dam are to ensure:
a) safety against overtopping,b) stability, andc) safety against internal erosion.
5.1.1 Ovnto/J/Jing - Sufficient spillway capacity should be provided toprevent overtopping of embankment during and after construction. Thefreeboard should be suffici~nt to prevent overtopping by waves and shouldtake into account the settlement of the embankment and foundation. Freeboard for wave run up on slope shall be provided in accordance with theprovisions contained in IS = 10635-1983*.
5.1.2 Stability Analysis
5.1.2.1 The slopes of the embankment shall be stable under all loading conditions. They should also be flat enough so as not to imposeexcessive stresses on foundation.
5.1.2.2 For small dams stability analysis may not be necessary provided a good foundation is available and the designer with his experiencecan decide adequate side slopes. However, where weak foundation conditions viz. fissured clay, expensive soils, shales, over consolidated highlyplastic clays, soft clays dispersive soils, etc, are met within the substratumin the dam-seat, extensive investigations of the foundation soil and borrowarea soil are required to be carried out and the design of the embankmentdam carried out in accordance with IS : 7894-1975t
5.1.2.3 The design of small embankment dam sections may be divided into the following three categories based upon the height of theembankment in its deepest portion.
a) Embankments where the height is below and up to 5 m;b) Embankments where the height is more titan 5·0 m and up to
10 m; andc) Embankments where the height is above 10 m and up to 15 m,
For small dams under category Cal and (b) above the stabilityanalysis may not be necessary. General guidelines of the sections and therecommended slopes are given in Table I for guidance of the designer.The average properties considered for different soils are given in Table 2.However, the designer with his experience and judgement may decide the
·GuideIiDe. for Cree board requirement. ID embankment dams.tCode of practice for stability aDaly.is of .arth dam••
12
.1.1218.1.7
adequate side slopes where special technical or economic considerationsmay have to be taken into account. Stability analysis may be carried outin accordance with IS : i894·1975· based upon the detailed foundationand borrow area investigation and laboratory testing if the soil stratabelow the dam seat consist of weak foundation as given in 5.1.2 2 and/orthe height of embankment is more than 10 m.
6. SPECIAL DESIGN REQ,UIREMENTS
6.0 In addition to basic design requirements given in 5, the followingspecial design requirements, should also be satisfied for embankmentdams.
6.1 Coatrol of CracklDI - Cracking of impervious zone results in thefailure of an embankment dam by erosion, piping, breaching, etc. Dueconsideration to cracking phenomenon shall, therefore, be Riven in thedesign of embankment dam. For classification of cracks and their importance, &.1.1 to 6.1.3 of IS : 8826-1978t may be referred.
6.1.1 ~1'(Jsu"'fo, Control '!f Cratki", - Following measure! are recommended for control of cracking:
a) Use of plastic clay core and rolling the core material at slightlymore than optimum moisture content, In case orl~ss plastic clay,2 to 5 percent bentonite of 200 to 300 liquid lirnit may be mixe dto increase the plasticity.
b) Use of wider core to reduce the possibility of transverse or horizontal cracks extending through it.
c) Careful selection of fill materials to reduce the differential movement. To restrict the rockfill in lightly loaded outer casings andto use well graded materials in the inner casings on either side ofthe core.
d) Wide transition zones of properly graded filters ofadequate widthfor handling drainagr. if cracks develop.
e) Special treatment. such al preloading, presaturation. removalof weak material, etc, to the foundation and abutment. ifwarranted.
f) Delaying placement of core material in the crack region till mOltof the settlement takes place.
R) Arching the dam horizontally between Iteep abutments.h) Flattening the downstream slopes to increase slope stability in the
event of saturation from crack leakage.j) Cutting back the steep abutment slopes.
-Code of practice for I'ability analysis of earth dams.tGuidelincl £01' deailD of larle eanb aDd rocldill dams.
13
III 1218 • 1917
6.2 ltablU*7 at J_.ctl... - Junctions of embankment dam withfoundation abutments, masonry structures, like overflow and non-overflowdams and outlets need special attention with reference to one or all of thefollowing criteria:
a) Good bond between embankment dam and foundation;b) Adequate creep length at the contact plane;c) Protection of embankment dam slope against scouring action;
andd) Easy movement of traffic.
6.2.1 JII1I,';01l wi'h Fo"ndtlli01l - Embankment dam may be founded onsoil overburden or rock. For foundation on soils or non-rocky strata, vege- /tation like bushes, grass roots, trees, etc, should be completely removed.'After removal of these materials, the foundation surface should be moistened to the required extent and adequately rolled before placing embankment material. For rocky foundation, the surface should be cleaned of aHloose fragments including semi-detached and overhanging surface blocksof rocks. Proper bond should be established between the embankment andthe rock surface prepared.
8.2.2 ]"",tio", wil" AlJutmlnlJ - The rocky abutments should be suitablyshaped and preapred in order to get good contact between the imperviouscore of the embankment and the rock over-hangs, if any, should beremoved. Vertical surfaces should be excavated to form slopes, not steeperthan 0·25 H to 1 V. A wider impervious zone and thicker transitionsshould be provided, at the abutment contacts to increase the length ofpath of seepage and to protect against erosioD.
6.2.2.1 The bond between rocky or non-rocky abutment should beestabU.hed al in 6.2.1. In additioD, sufficient creep length should ~provided between impervious aection of the dam and the abutment, 10 alto provide safety ag&lDlt ~ping. The creep length mould be not leal than4 times the hydraulic bead. \ .
1.2.3 .1.,"'",11 wit"N'''-DWi/ID. Da", - Junction of Don-overftow masonryconcrete dam with embankment dam is provided by a better not .teeperthan 0-5 H to 1 V to the end race or the non-overSow block cominl incontact with the imperviOUI core. A wider impervioUi zone and thickertransitioDi shall be provided at the abutment CODtaetl to increue thelenBth 01path of leepale and to protect alainlt eroaiOD. Sometimes thaecontact layen are mixed with 2 to 5 perceDtbentonite with liquid Umit of200 to 300 to callie expansion and hence to have ti.ht joiDta. Sometimesthe junction of earth dam with Don-ovdflow dam ia provided with earthretaining wall. perpendicular or akew at. the jUDctioa or DOD-ovcr8ow clam
a) Cot.drained loil Not Iuitable Not luitlble Not luitable for core(OW. p.SW, SP) Suitable for cum, Iooe
b) CoIne IralDed lOiI (H) (V) (H) (V) (H) (V) (H) (V) Section to be decided baaed UpoD(GC. GM, SC, 8M) 2 : 1 2: I 2 : 1 2: I the 'tibilitllaDlly. iaaccord-
lice with S: 7894-1975
c) FiDe ~rained 1011 (H) (V) (H) (V) (H) (V) (H) (V) do(eL. L, CI, MI) 2: I 2 : I 2'5: I 2'251 : I
d) FiD, pined lOiI (H) (V) (H) (V) (H) (V) (H) (V) do(CH,MH) 2: I 2: I 3'75: 1 2'5: I
iii) H_,IODe Not required May be provided Nuaary
a) Top width 3m Sm
b) Top level 0'5 mabove MWL 0'5 Dlabove MWL
iv) Rock toe beilbt Not leeeuary up to 3m, Above Neceury NecessarySmheiahl, IDl htl or rock Ht5. where Hiltbe heilht H/S. where H it tbe beilht ortoe .IYbe provid ofembWm.at emblDkmeD'
v) Bera Notoec_ry Notnle." The berm may be provided uper del:. Tbe miJaimum bermwidth II b.3m, The bermmay be provided alto on tb,_Iream lIope ror (acilitiesduriq maiDt.....
is
18 , 12169 • 1981
TAILE 2 AVlRAGI PROPERTIES 'ORDmERENT TYpg or lOlLS(Cilu5.1,2.3)
i) GO >1840 <15 NA >0'60ii) OM >1830 <15 NA >0'67iii) SM 1830 ±16 15 ±04 500±500 O'58:!: 0'07iv) so 1840 ± 16 IS:!: Off 1100 Z 600 0'6 ±0'07v) ML 1650 :I: 16 19 ±0'1 900 ±NA 0'62 ±0'04
'Claujfication ud ideDti6catioD or loil. for ,eneral eD,meeriDl purpolea (firs' ,,,"ill ).
SOIL Co'I'AftI '01RICO.IIIDIDSLOP.t" --.A.-__--""
MDD OMC CobIll. TID'kl/ml percelt kl/m'
I800 IS I 100 0'60
1650 19 900 0'55
1300 35 1sao 0'35
16
with the overftow dam. Such retaining walls shorten the length of nonoverflow dam (transition length) but they themselves add to the cost.The alignment or the dam and the junction may sometimes have to bemodified to suit smooth transition of road on top ofdam from non-overflowsection to embankment dam section.
6.2.t Ju"ctio" with Outl,tr - Proper bond should be provided betweenthe earthwork and the outlet walls. Staunching rings should be providedalong the outlet conduits in the impervious zone, at intervals, so as toincrease the path of percolation along the contact. Backfilling of thetrench for the outlet conduit should be done with concrete up to the topof rock surface and the portion of the trench above the rock level shouldbe refilled with impervious material compacted with moisture contactabout 2 percent more than optimum. The shape of conduit ceming incontact with earthwork shall be given a aide better of 0·25 H to 1 V toprovide a better contact with the earthwork. Sharp corners at the topshould be avoided. Special care should be taken to ensure tigbt contactsbetween the trench fact and the backfill.
7. SELECTION OF DAM SECTION
7.1 No single type or core-section of embankment dam is suited for aU liteconditions. The adoption of the particular type of embankment sectiondepends upon the following factors:
a) Availability of the suitable local material in sufficint quantitywithin reasonable range;
b) Foundation conditions and cut-oft' requirements;c) Types of construction plant, earth moving, compaction and other
equipment;d) DivenioD consideratioDi and construction Icheduleie) Climatic conditions in relation to placement, moisture content
control, lublequent moisture content change, etc; andr) Safety with respect to ltability and seepage.
7.2 7.0'-- - If only one type of lUitabJe material is readily availablenearby, a homOleneoua section iI genenlJy preferred. If the materialavailable 11 impervious or aemi-perviouI, a amall quantity or perviouamaterial II required u cuiDB Cor proteclioD asUDII cr.cki~l. On the otherhand, if it it perviou.. a thin imperviOUI memberane iI required 10 .. toform. wat~rbarrier.
17
IS I 12169 • 1981
7.2.1 A zoned dam ii, however, preferred where different types oflOilaare available from borrow area. I t also facilitates the we of compulsoryexcavation from foundation, approach channel, tail channel, etc. Thezoned embankment dam is generally composed of an impervious corebounded by transitions and/or outer casing of pervious material. In zonedembankment dam, the weaker materials are oflen utilized most econmically in the form of random zones. Maximum utilization of the materialavailable from compulsory excavation should be aimed at. Random zoneaare generally provided below minimum draw down level on upstream sideand on downstream of inclined filter. When upstream casing zone is ofrelatively impervious mateI ial J horizontal filters at suitable intervals, say5 to 6 m, may be provided to limit the drawdown pore pressures for damsof height more than 10 m, ( &, Note below Fig. 2A).
7.2.2 The zoning of embankment dam as planned in the design mayhave to be altered or modified during execution stage in view of thelollowing:
a) The materials estimated are not available according to requirement;
b) Different types of material encountered whicb could not be ascer-tained during investigations;
c) Construction difficulties;d) Construction schedule; ande) New foundation features.
7.3 Top Wiclt. --.,. The width of the dam at the crest should be fixedaccording to the working space required at the top. No dam should havecrest width of leal than 4·5 m,
III 12169 • 1117
APPENDIX A( Claus" 4.2.1, 4.3.1 and 4.7.2 )
SUITABILITY OF SOIL FOR CONSTRUCTION OP DAMS
R,I.,irJ' HomtJlnuoul ~o",d Dam l",JImIitnuSu;lflbility Dylc" r-------v-------~ Bl""k"
Impervious PerviousCore Casing
Very 8uitable GO GC SW,GW GO
Suitable OLtOI OL,OI OM CL,OI
Fairly suitable SP,8M GM,GO SP, GP OR, 8MOR SM, SC, OR SO, GO
Poor ML,MI,MH
Net suitable OL, 01, ORPt.
NOTB - R.Cer to IS : 1498-1970 ·CI...ifie.doD and id~Dtific.tion of lOll. forleDeral eDliDeeriDI purpOlea (firs' r.isi.,. ) ••
SRBI BaIlENDBA KOMAR SHARMA National Hydro-Electric Power CorporatioD Ltd.New Delhi
IrrilatioD Departmeat, GovernmeDt of Bibar,Pataa
Irril_doD Department, GoVel1lmflDt or Mahan.btra, Bombay
( CIIfIIirIuHft.", Pa,' 2 )
M""IJ", R.",."",DIBIlCTOB (DAII) ( It .& )I J I T Irri,adon Department, Governmeat or PUDjab.
SAOAR DAM) Chandilarh8a81 Y. B. MATHUR (All"..,,)
DB M. C. GOBL Water R.esource. Development and TraininlCentre. Univenity of Roorkee, Roorkee
Irrigation Department. Government of UttarPrade.h, Lucknow
SR.I Bllt8AM BALDBV RAJ ( All"."" )SRaI D. G. KADEAD. Jaiprakaah Aaociated Private Ltd, New DelhiSHaI T. K. NATABAJAJf CeDtral Road Research IDlthule (CSIR), New
DelhiIrritratioD Department, Governm~Dt or ADdbr.
Pradesh, Hyderabad
20
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