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IS 12720 (2004): Criteria for structural design of spillwaytraining walls and divide walls [WRD 9: Dams and Spillways]

.

IS 12720:2004

Indian Standard

CRITERIA FOR STRUCTURAL DESIGN OFSPILLWAY TRAINING WALLS AND

DIVIDE WALLS

( Second Revision)

ICS 93.16

@ BIS 2004

BUREAU OF IN DIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARC

NEW DELHI 110002

October 2004 Price Group 4

Spillways Including Energy Dissipators Sectional Committee, WRD 10

FOREWORD

This Indian Standard (Second Revision) was adopted by the Bureau of Indian Standards, after the draft finalizedby the Spillways Including Energy Dissipators Sectional Committee had been approved by the Water ResourcesDivision Council.

The provision of downstream training wall is made to guide the flow from the spillway into the down streamchannel and to retain the draft earth envelope in some cases. Upstream training walls are sometimes providedto retain earth dam faces where wrap around is not provided or partially provided and to guide the flow towardsthe spillway. The structural design of the training walls and divide walls therefore assumes importance.

Divide wal Is are provided to separate bays having different type of energy dissipation arrangement or to separatebays having the same type of energy dissipation arrangement but with different parameters/levels, etc, keptfrom geological/other consideration or to allow for unsymmetrical operation of spillway gates in order tominimize cross/return flows, eddies, etc. Also divide walls are provided to separate out the power house, siltexcluders, etc, located adjacent to the spillway. Sometimes low or submerged divide walls are also provided toeffect economy.

Walls of approach channels, spillway glacis and energy dissipators maybe masonry/concrete gravity, reinforcedconcrete cantilever or relatively thin concrete anchored wall/lining placed against steep rock surfaces anchoredto the rock by steel dowel bars grouted into drill holes in the rock. Where the strata above foundation at theends/sides of the spillway consists of earth or poor rock, the walls should be masonry/concrete gravity walls.Where suitable rock is available from the general ground level, the side walls may be in the form of a thinconcrete lining. Sometimes combination of gravity section and concrete lined walls are used. In some specialcases where the channels or stilling basins are narrow, it may be economical to design the walls and the channelor basin floor as an integral reinforced concrete U-frame.

This standard was first published in 1989. First revision was undertaken in 1993 to incorporate the latest practicesbeing followed in the field. The important changes effected in this revision were as follows:

a)

b)

c)

d)

Modifications in design loading conditions, computation of forces and stability criteria,

Reference to IS 11772:1986 ‘Guidelines for design of drainage arrangements of energy dissipators andtraining walls of spillways’ was given for drainage arrangement of training and divide walls.

Reference to 1S 456:2000 ‘Code of practice for plain and reinforced concrete (third revision)’ wasgiven for design of stem and base slab of divide walls, and

The computation of stresses and design of anchorages based on one of the method were covered in aspecial publication SP 55: 1993 ‘Design aid for anc~orages for spillway piers, training walls and dividewalls’.

This revi@n is being taken up on the basis of comments received from the users and to incorporate the latestpractices being followed in the field. Modifications have been made with regard to design loading conditionsand the forces to be considered in the design of training walls.

The composition of the Committee responsible for the formulation of this standard is given in Annex A.

For the purpose of deciding whether a particular requirement of this standard is complied with the final valueobserved or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with1S 2: 1960 ‘Rules for rounding off numerical values (revised)’. The number of significant places retained inthe rounded off value should be the same as that of the specified value in this standard.

.,.

IS 12720:2004

Indian Standard

CRITERIA FOR STRUCTURAL DESIGN OFSPILLWAY TRAINING WALLS AND

DIVIDE WALLS

( Second Revision)

1 SCOPE

This standard lays down the criteria for structuraldesign of upstream and downstream training walls anddivide walls.

2 REFERENCES

The following standards contain provisions, whichthrough reference in this text, constitute provisions ofthis standard. At the time of publication, the editionsindicated were valid. All standards are subject torevision, and parties to agreements based on thisstandard are encouraged to investigate the possibilityof applying the most recent editions of the standardsindicated below:

IS No. Title

456:2000 Code of practice for plain and rein-forced concrete (~hird revision)

1893 (Part 1) : Criteria for earthquake resistant2000 design of structures: Part 1

General provisions and buildings(jl@ revision)

6512:1984 Criteria for design of solid gravitydams @-sr revision)

7365:1985 Criteria for hydraulic design ofbucket type energy dissipators(first revision)

11722:1986 Guidelines for design of drainagearrangements of energy dissipatorsand training wails of spillways

3 TRAINING AND DIVIDE WALLS

3.1 Training Walls

3.1.1 Gravity Walls

Gravity walls for spillway approach channel andenergy dissipators generally retain backfill or damembankment fill against their back side. For approachwalls not retaining a dam embankment, perviousbackfill with drainage may be economical anddesirable to reduce loading under empty or drawdownconditions, but the drainage system should not create

a short seepage path to the downstream side of thecontrol section. The top width of the training wallshould be kept 1.5 m, minimum with the arrangementof steps and railings to serve as walkway duringinspection. For the downstream walls of spillwayglacis and energy dissipators, free draining backfillwith drainage arrangements should be provided toreduce seepage pressures.

3.1.2 Anchored Walls

For concrete anchored walls the rock is excavated to astable slope, normally 0.5 (H) to 1 (V) or otherwisedepending upon the geology of the site and thenconcrete of required thickness (minimum 300 mm) islaid against to this slope. The concrete should beanchored adequately into the rock by dowel barsgrouted in holes drilled into the rock. A carefulinvestigation of the rock should be made beforedesigning the anchorage system. The anchorage andthe concrete should be able to withstand the probablehydrostatic head in the rock or residual hydrostatichead if adequate drain hoIes are provided therein (seeFig. 1).

3.1.3 Combination of Gravity and Anchored Walls

In cases where partly overburden and partly rock facesare met with, the section of the wall should be aconcrete anchored wall in the lower rock face portionand gravity wall above in the overburden portion. Thistype of combination wodld be economical in suchcases (see Fig. 2).

3.1.4 Cantilever/Counterjort Walls

Cantilever/counterfort walls may also be provided astraining walls depending upon the height of the wall.

3.2 Divide Walls

The divide walls are normally provided in line with thecrest piers so as to have minimum disturbance in theflow. As far as possible, the walls should beconstructed in reinforced cement concrete so thatsection is thin and offers minimum obstruction to theflow. The divide wall need not be taken too high butmay be kept slightly above the maximum tail water

1

IS 12720:2004

WATERDRAIN ~

y

TEMPERATUREREINFORCEMENT STABLE SLOPE

—.... --’.- - a

+100mmDRAIN PIPE

----’->= ----j

y +75mm DRAIN HOLE ‘

.

z’CONSTRUCTIONJOINT

FIG. 1 TYPICAL ANCHORED WALL

level in the energy dissipator when clear separation ofthe flows is required. Sometimes submerged walls arealso provided which provide a clear separation offlows at lower discharges and would be submerged athigher discharges. However, the extent ofsubmergence of the wall should be decided by carryingout the model studies. The length of the divide wallshould normally be kept up to the downstream end ofthe energy dissipator or as may be required based onmodel studies.

Divide walls can also help in provision of coffer damto facilitate dewatering and repairs of spillwayaprordbucket, etC.

a)b)

c)d)e)

f)g)

h)

Dead load;Reservoir and tail water pressure and

hydrodynamic load due to flow, whereverapplicable;Wave pressure, if significant;Uplift pressure;Earthquake force;Earth pressure;Hydrostatic pressure on embankment/back-fill/rock face due to ground water or seepage,etc; andLive load or surcharge due to earthmovingmachinery and other equipment.

3.3 The drainage arrangements for training and divide4.2 Design Loading Conditions

walls should be kept according to IS 11722. 4.2.1 In all cases loading selected for design of walls

4 DESIGN OF TRAINING WALLSfor spillway approach channel and energy dissipatorsshould include the most severe load combinations

4.1 Forres anticipated. Typical loadhg conditions to be used forthe upstream and the downstream’ masonry or concrete

The following forces should be considered in the training walls have been described in 4.2.2 and 4.2.3.design of training walls: The design loading conditions for the anchored walls

2

IS 12720

EARTH EMBANKMENT=

2004

+100mm WEEP HOLESSTAGGERED

GRADED FILTER

.----- . .

GRADE

iMASONARY CONCRETEGRAVITY W LL .

ANCHORED WALL -:

ANCHORS

CONSTRUCTIONJOINT

NOTE — Drainage gallery to be suitably located, if planned.

FIG. 2 TYPICAL SECTION OF GRAVITY AND ANCHORED WALL

have been described in 4.2.1.1. Hydraulic modelstudies are generally necessary for estimating the totalwater pressure due to static and hydrodynamic loads(pressure fluctuations artd/or centrifugal action, etc)and their associated frequencies on the training wallsand divide walls.

4.2.1.1 The anchored walls should be designed for thesudden drawdown condition considering (a)hydrostatic pressure on rock face due to groundwateror seepage etc, (b) water up to minimum tail waterlevel on river side, unless the rock behind the wall isdrained by an adequate system of drain holesextending deeper than anchorage system in which caseit may be designed considering partial drainage effectand anchorage provided for balance pressure (seeFig. 1). The foundation level, that is, bottom of theanchored walls should be provided up to the level

obtained from the criteria given in IS 7365 or based onmodel studies.

4.2.2 Upstream Training Wall

4.2.2.1 Normal loading condition

a) Water in the reservoir up to the full reservoirlevel, including wave forces, if significant;

b) The backfill submerged up to the same level;and

c) Full uplift pressure.

4.2.2.2 Severe loading condition

Loading as in 4.2.2.1 above buteffect/wave forces.

with earthquake

4.2.2.3 Sudden drawdown condition

a) Earthfill/embankment submerged up to the fullreservoir level.

3

IS 12720:2004

b) Minimum drawdown level on the reservoirside, and

c) Corresponding full uplift pressure.

4.2.2.4 Spillwcryfunctioning loading condition

a) Water in the reservoir up to maximum waterlevel,

b) The backfill submerged up to the same level,and

c) Corresponding full uplift pressure.

4.2.3 Downstream Training Wall

4.2.3.1 Normal loading condition

a) Minimum TWL/No water on the river side,b) Earth pressure and hydrostatic pressure on em-

bankmentibackfilllrock face due to grot.rndwater or seepage (drains effective), and

c) Full uplift varying uniformly from correspond-ing water head in the backfill side to zero onthe river side.

4.2.3.2 Severe loading condition

Loading as in 4.2.3.1 but with earthquake effect.

4.2.3.3 Sudden drawdown condition (whereverapplicable)

a) Earth pressure and hydrostatic pressure on em-bankment/backfill/rock face due to groundwater or seepage (drains clogged),

b) Water up to minimum tail water level on riverside (drains clogged), and

c) Full uplift varying uniformly from correspond-ing water head in the backfill side to minimumon the river side.

4.2.3.4 Spillway functioning loading condition

a) Earth pressure and hydrostatic pressure on em-bankment/backfill/rock face due to groundwater or seepage (drains effective),

b) The hydrostatic and hydrodynamic loads due

to the flow in the energy dissipator. In case offlip buckets, the hydrostatic load should alsoinclude centrifugal force in addition to depthof water ‘dl’, and

c) Full uplift varying uniformly from correspond-ing water head in the backfdl side to the depth(all) on the river side.

Unless drainage galleries are provided.

NOTES1 Due to intense turbulence of flow in the energy dissipator, theensuing turbulence and surges may produce hydrodynamicforces which may be far in excess of the normal hydraulicloading. These hydrodynamic forces exerted on training wallwould have considerably wide band of frequency, It should beensured that the natural frequency of training wall is not in theneighbourhood of the predominant frequency of the forceexerted to avoid resonance (see 5.3.2).2 Passive pressures or earth pressure at rest, as applicable fromthe backfill may be considered in thk condkion which may,however, be limited to the hydrostatic and hydro-dynamic Iodds.

4.3 Computation of Forces

4.3.1 Dead Load

The dead load to be considered comprises of theweight of the masonry and/or concrete plus the weightof the backfill. For the preliminary design, the unitweight of concrete and masonry may be taken as23.50 kN/m3 and 22.5 kN/m3 respectively. The weightof backfill should be according to type of the backfillresting over the wall slopes and the conditions of thebackfill such as moist, saturated or submergeddepending upon water level/phreatic line on backfillside. The unit weight of water should be taken as9.81 kN/m3 (see IS 6512).

4.3.2 Reservoir and Tail Water Pressure and Hydro-dynamic Load Due to Flow Wherever Applicable

4.3.2.1 Reservoir and tailwater load

For the upstream training wall linear distribution of thestatic water pressure acting normal to the face of wallshould be considered. Wave forces should also beconsidered for the upper part of the wall. For thedownstream training wall, the larger of the hydrostaticand the hydrodynamic loads, including centrifugalforce where applicable, should be considered.

4.3.2.2 Water pressure in still water

The intensity of pressure in still or slowly movingwater varies directly with the depth. This pressure isexpressed as:

p = yWh

The total horizontal force on a unit length of a verticalwall will be:

F = 112yWh2, and

The moment will be:

M = 1/6ywh3

where

yW = unit weight of water in kN/m3, and

h = depth of water in m.

4.3.2.3 Water pressure in a steeply inclined stream onthe spillway glacis

In a stream flowing down a steeply inclined slope, thepressure pattern is modified from the static condition.The water, which is supported on a spillway slope, hasa negligible shearing value. Therefore, the floorsupports only the normal component of the weight ofthe water and this produces the pressures on the floorand on the sidewalls. The overturning force at the floorand on the base of the side wall for a unit lengthmeasured along the glacis is expressed as:

F = 1/2ywh2cos et

4

and the overturning moment as:

where

Y. =h =

a=

However,

M = 1/6ywh3cos ct

unit weight of water,

depth of water normal to the floor, and

floor angle with horizontal in degree.

for calculating reinforcement steel invertical direction, the bending moment qer unithorizontal length should be taken as M/cos ct andshear force per unit horizontal length as F/cos U.

4.3.2.4 Water pressure in a deflected stream

If a flowing stream is deflected by a curving vane, suchas a vertical curve in a flip bucket at the bottom of aspillway, the water pressure is increased by centrifugalforce. This increase in pressure maybe evaluated by:

where

Pc =

Y. =d, =

Va =

r=

~=

increase in pressure,

unit weight of water,

depth of flow entering bucket,

actual velocity of flow entering bucket,

radius of bucket, and

acceleration due to gravity.

The maximum and minimum centrifugal pressure in abucket occur at the lowest and highest points of thebucket respectively. The approximate bucket pressureand the maximum side wall pressures are obtained byadding the computed centrifugal pressure to thehydrostatic pressure at the section under

consideration. The total horizontal force on the unitlength of the wall due to centrifugal pressure will be:

Fc = l/2P, dl

and moment

M. = l/6pc d?

4.3.2.5 Hydrodynamic forces

The hydrodynamic forces to be considered are givenin 5.3.2.

4.3.3 Upliji Pressure

The upIift pressure should be assumed to act over 100percent of the base area. The uplift should be assumedto vary uniformly along the base width of the wall. Itmay be safe to assume that uplift pressures are notaffected by an earthquake.

4.3.4 Earthquake Forces

The earthquake forces should be considered inaccordance with IS 1893.

5

IS 12720:2004

4.3.5 Earth Pressure

The earth pressure should be considered in accordancewith IS 1893.

4.4 Stability Criteria for Upstream andDownstream Training Walls

4.4.1 The maximum foundation pressure should notexceed the safe bearing capacity of the foundation.

4.4.2 The compressive strength of concrete/masonryshould be in accordance with IS 6512.

4.4.3 No tensile stress should be permitted in thenormal loading condition. Nominal tensile stressesmay, however, be permitted in other loadingconditions and their permissible values should notexceed the values given in Table 1.

Table 1 Values of Permissible Tensile Stress inConcrete and Masonry

s]No.

(1)

Oii)

iii)iv)

Loading Condition Permissible Tensile Stress

f \For Masonry For Concrete

(2) (3) (4)Normal loading condkion Nil NilSevere loading condition 0.01fc 0.02fcSudden drawdown condition 0.01fc 0.02fcSpillway functioning condition 0.01 fc 0.02fc

where fc is the cube compressive strength of concrete/mortar formasonry.

4.4.4 Criteria for Design Against Sliding

The factor of safety against sliding maybe calculatedin accordance with IS 6512 on the basis of partialfactor of safety in respect of friction (Fe) and partialfactor of safety in respect of cohesion (FJ as given

below. The factor of safety against sliding should notbe less than 1.0.

Loading Condition Fm F.

Normal 1.5 3.6Severe 1.2 2.4Sudden drawdown 1.2 2.4Spillway functioning 1.2 2.4

4.4.5 The reinforcement for cantilever/counterfortwalk+ should be designed in. accordance with IS 456.

5 DESIGN OF DIVIDE WALLS

5.1 Forces

The following forces should be considered in thedesign of divide walls:

a)b)

c)d)

Dead load,Water pressure including hydrodynamic pres-sure,Uplift pressure, andEarthquake force.

IS 12720:2004

5.2 Design Loading Conditions

5.2.1 The divide walls should be designed for thefollowing loading conditions.

5.2.1.1 Unsymmetricals pillwayo perationcondition

a) Hydrostatic and hydrodynamic loads due tothe unsymmetrical flow in the energy dis-sipator. In the case of flip buckets the hydros-tatic load should also include centrifugal forcein addition to depth of water, and

b) Corresponding full uplift.

5.2.1.2 Spillway not discharging condition

a) Water up to minimum tail water level on oneside,

b) No water on the other side assuming it to bedewatered,

c) Corresponding full uplift, andd) Earthquake forces.

5.3 Computation of Forces

5.3.1 The dead load, uplift pressure and earthquakeforces should be calculated as given in 4.3.

5.3.2 Estimation of Hydrodynamic Pressures

For estimation of hydrodynamic pressures on accountof turbulence and surges, model studies are desirable.However, till these forces are ascertained from modeltests criteria given below may be followed forestimation for the forces for preliminary design in casea stilling basin arrangement is provided:

a) Assume depth of water on one side of wallequivalent to maximum depth (H) occurringafter the hydraulic jump has taken place;

b) Assume a rectangular water pressure distribu-tion due to water load on the flow side of thewall;

c) Assume Westergaard’s Parabola to further ac-count for the hydrodynamic effects of surgesusing an acceleration factor of 0.15 g (seeFig. 3). In a seismic area, earthquake loads maygovern over surge loads; and

d) Proportion the divide wall such that the naturalperiod of vibration of the wall is less than0.2 s.

NOTE — The natural period of vibration for either agravity or fixed-free cantilever wall maybe found by thefollowing approximate formula:

Ts=Fxg

where

H=

b=

F=

height of the wall, in m;

base width of the gravity wall or thickness of thecantilever wall, in m; and

factor which is a function of geometry.

For gravity walls up to 30 m in height, F = 0.001394s/m may be used. For fixed-free cantilever wa!ls up to30 m in height and with b/H not exceeding 0.50,F = 0.0021 S/m, maybe used.

5.4 Stability Criteria for Divide Wall

The divide wall should be designed to withstand theoverturning moments for the conditions given in 5.2.The maximum foundation pressure should not exceedthe safe bearing capacity of the foundation.

5.5 Design of the Reinforcement for Stem and BaseSlab of Divide Walls

5.5.1 The reinforcement for stem and base slab shouldbe designed according to IS 456. In case the wall isfounded on sound rock, the base slab may bealternatively designed as given in 6.

6 ANCHORAGES

When the training/divide walls are resting on aconcrete block laid over sound rock, stresses will beinduced in the concrete block and the rock below theconcrete due to loading on the wall. The diffusion ofstresses into the base block is of considerableimportance for determination of depth of anchoragesof reinforcing bars.

P. =

Pew =

c. =

where

Y. =H=

T=

ah =

Pw =

Pew =

Ce=

r~ H2

213 C. H2 tx~

8.0143

[)

2

1-0.72 A304.8T

unit weight of water in kN/m3,

depth of water in m,

earthquake foundation vibration periodins.

horizontal acceleration coefficient (to betaken as 0.15 g for design calculation),

total horizontal water pressure with arectangular distribution in kN/m,

additional water pressure in kN/m, and

factor in kN/m3.

NOTE — If the value of T is not available, C, may be taken as8.2 kN/m3.

6

IS 12720:2004

.

RD’SA

FIG.3 WATER PRESSUREINDIVIDEWALL

7

IS 12720:2004

ANNEX A

( Foreword)

COMMITTEE COMPOSITION

Spillways Including Energy Dissipators Sectional Committee, WRD 10

Organization

Sardar Sarovar Narmada Nigam Ltd, Gandhi NagarBhakra Beas Management Board, Narrgal Township

Bodhi Water Resources Department, Bhopal

Central Design Organization, GandhinagarCentral Water & Power Research Station, Ptme

Centml Water Commission, New Delhi

Consulting Engineering Services (I) Ltd, New Delhi

Gujarat Engineering Research Institute, Vadodara

Hindus(an Construction Company Ltd, Mumbai

Indian Association of Hydrologists, New DelhlIndian Institute of Technology, Roorkee

Irrigation Department, Government of Andhra Pradesh, Hyderabad

Irri@ion & Water Ways D~rectorate, Govemrnent of West Bengal,Distt Darjeeling

Irrigation Department, Government of Orissa, Bhubaneshwar

irrigation Department, Government of Punjab, Chandigarh

Irrigation Department, Government of Uttaranchal, Roorkee

Irrigation Department, Government of Kamataka, KarnatakaIrrigation Department, Government of Maharashtra, Nasfrik

Jaipmkash Industries Ltd, New Delhi

Nathpa Jhakri Power Corporation, Shimla

Na[ional Hydroelectric Power Corporation Ltd, Faridabad

Sarchir Sarowtr Narmada Nigam Ltd, Gandhi Nagar

Wapcos (India) Ltd, New Delhi

BIS Directorate General

Representative(s)

SHRIN. B. DESAt (chairman)

SUPERINTENDINGENGINEER

EXECUTtVEENGINEER(Ahernare)SHRIJ. K. TtWARt

SHRtR. K. CHACHONDIA(Ahemate)SUPERINTENDtNO~GtNEER

SHrttP. B. DEOLALIKAR

SHRIMATIV. V. BHOSEKAR(Alternate)DIRECTOR(CMDD-N & W)

DIRECTOR(SSD & C) (Alternate)SHRIV. K. KAPUR

SHRIP. K. SANGHI(Alternate)SrstttV.S.BRAHMABHAIT

RESEARCHOFFICER(Afternafe)SHRIR. G. VARTAK

SHRIK. R. VISHWANATFt(Alternate)SHRt~tTAM SINOHDIRECTOR(WRTDC)

DR NAYANSHARMA(Alternate)CHIEF ENGINEER

SUPERINTENDINGENGtNEER(DAMS) (Ahernafe)&JPERINTENDtNOENGINEER

EXECUTtVEENGtNEER(Alternate)CHIEF ENGINEER(D& R)

DIRECTOR(HEAD WORKS) (Afremate)CHIEF ENGINEER(RSDD)

DIRECTORSPILLWAY(RSDD) (Alternate)CHIEF ENGINEER& DIRCTOR

SUPERINTENDING~GtNEER (Alternate)DtRECrOrtSUPERINTENDINGENGINEER(MD)

EXECUTtVEENGtNEER(MD-5) (Ahemute)SHRID. G. KADKADE

SHRINARENDRASINGH(Alternate)SHRIR. S. CHAUHAN

SHRIV. K. VERMA (Alternate)Strra S. C. MITTAL

SHRISANTOSHKUMAR(Ahemafe)SHRIG. L. JAVA

SHRIS. J. DESAI(Aftemate)SHRIS. R. NAttAYANAN

SHRI A. P. CHOUDHARY(Alternate)SHRIS. S. SETHI,Dlreetor& Head (WRD)[Representing Director General (Ex-o@icio)]

Member SecretarySHRIMATIROSY DHAWAN

Joint Director (WRD), BIS

8

-—

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This Indian Standard has been developed from Dot: No. WRD 10 (323).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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