Is 14262 Revetment of River Embankment

8/9/2019 Is 14262 Revetment of River Embankment

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I ndian St andardPLANNINGANDDESIGNOF

GUIDELINES

UDC 627,417 026 )

Q BIS 1995

REVETMENT

BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

April 1995 Price Group 4

( Reaffirmed 2001 )


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River Training and Control Works Sectional Committee, RVD 22

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by theRiver Training and Control Works Sectional Committee had been approved by the River ValleyDivision Council.

It is a common practice to use revetment for protecting the river bank, flood embankments, guidebunds, spurs, etc, from the fury of floods. The protection work of this type is known by differentnames such as stone pitchmg, rip-rap, revetment, etc. However, the most common technical term isrevetment. The size and mass of stone to be used for revetment is required to withstand flow velocity,tractive force, etc, taking into consideration specific gravity of material in revetment, porosity, bankslope, angle of repose of bank and protecting material, etc. A filter is also required below the protec-tion layer to prevent possible soil loss. This standard covers the planning and design of revetment forbank protection works. The construction and maintenance aspects of revetments are being covered ina separate Indian Standard.


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IS 14262 : 1995

Indian Standard

PLANNINGANDDESIGNOFREVETMENT

GUIDELINES

1 SCOPE

This siandard lays down the guidelines forplanning and design of revetment used forembankments and bank protection works incase of alluvial rivers and canals.

2 REFERENCE

The Indian Standard ‘IS 8237 : 1985 Code ofpractice for protection of slope for reservoirembankments ($rsl revision ’ is a necessaryadjunct to this standard.

3 GENERAL DESIGN FEATURES

3.1 Dry Revetment

Stone used in revetment for river bank protec-tion is subjected to hydrodynamic drag and liftforces. These destabilizing forces are expressedin terms of velocity, tractive force, etc. Thestabilizing forces acting against these are com-ponent of submerged weight of stone and down-ward component of the force caused by contactof the stones.

Weight of the stone on horizontal bed may beexpressed as:

s,W = 0.023 23 (X, _ 1 1Q V6where

w=St? -V===

weight of stone in kg,specific gravity of stone, andmean velocity of water in m/s overthe vertical under reference.

The weight of stone worked out is the minimumrequired. Use of higher weight stones will bebased on the material available at site, ease ofconstruction, factor of safety, etc.

3.2 Effect of Specific Gravity

In practice, density of stone could varyfrom 2 000 to 3 300 kg/ma. The actual densityof stone should be determined for calculatingthe weight of stone given in 3.1.

3.3 Effect of Bank Slope and Angle of Repose

The weight of stone estimated for horizontalbed would not be sufficient for same velocity onthe sloping bank because only component ofself-weight normal to the slope acts as a stabi-lizing force. Therefore, for sloping banks, the

weight has to be increased. The limiting valuefor the slope is the angle of repose of materialof sub-base. Correction factor K for computingweight of stone on sloping face may be obtainedfrom the following equation:

K=Jl ( sin’ B/sin% #Jwhere

ti = angle of bank slope with horizontal,and

4 = an;i;;\“f repose of material of protection_.Thus the weight of stone would be

Weight of stone may also be calculated usingthe nomograph given in Fig. 1 ( see page 3 ).For river training works, sub-base is to begraded to a stable slope depending upon theangle of repose and cohesion of bsnk material

under saturated condition, and the height ofthe bank. For high bank a berm may benecessary. For important works stability ofbank with designed slope and berm should bechecked by slip circle method or by soildynamic testing procedures. Mere large sizestones/crates would not be adequate for pro-tection if the same is not laid on a stable base.For normal bank protection a slope of 2H : 1 Vor flatter is recommended.

3.4 Size of Stone

Size of the stone D, may be determined fromthe following relationship:

where

W = weight of stone in kg, andSS = specific gravity of stones.

Minimum dimension of the stones should not beless than Ds as obtained above. From theworked out weight and known specific gravity,the volume of stone should be calculated.Generally, the size of stone should be such thatits length, width and thickness should be moreor less the same, that is stone should be approxi-mately cubical. Round stones or very flatstones having small thickness should beavoided.

1


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IS 14262 1995

3 5 Thickness of Protectioo Layer

Minimum thickness of protection layer isrequired to withstand the negative head createdby velocity. This may be determined by thefollowing relationship:

TZV$

2g(Ss-- 1)

where

T = thickness of protection layer in m,V velocity in m/s,g = rtcdeleration due to gravity in m/s’,

& = specific gravity of stones.

For safety purposes, two layers of stonesaccording to the size obtained in 3.4 aboveshould be provided.

3.6 Stones io Crates

At high velocities, weight of stone determinedfrom relationship given in 3.3 works out veryhigh which makes handling and placing ofstones difficult. Under such circumstances,small stones in crates are generally used. How-ever;the specific gravity of the crate is differentfrom that of the individual stone due topresence of voids. Porosity in crates may beworked out by the formula:

where

DE0 = mean diameter of stones used incrate in cm.

Mass specific gravity S, of crates may then bedetermined from the equation:

S, = ( 1 -- e ) S,

Volume of the crate should be determined

using S,,.Crates should be laid with longer dimensionalong the slope of the bank. The size of themesh of crate should be smaller than thesmallest stone in the crate. The mesh shouldbe double knotted. GI wire of minimumdiameter 4 mm should be used for crates. Crateunits may be tied to each other by 5 mm GTwire as additional precaution.

If crates are provided in layers, each layershould be tied to lower and upper layer at

suitable intervals with 4 mm GI wire.Launching apron should not be tied to crateon slope. A nomograph to determine the sizeand weight of stone or crates for revetment isgiven in Fig. 1.

Typical dry stone revetment is shown in Fig. 2on page 5.

3.7 Filter

A graded filter of 150 to 300 mm thickness con-forming to IS 8237 : 1985 should normally beprovided below the revetment to prevent failureby sucking action of high velocity flow.Syntheticigeotextile filter may be used from thepoint of view of quality control and conveni-ence of laying. The criteria for synthetic filteris given in Annex A. A 150-mm thick sandlayer should be provided over the filter fabricto prevent the mechanical rupture of the fabricby revetment stones.

4 REVETMENTS IN MORTAR

4.1 Sizes of the Stooes

Stones, bricks or concrete blocks may be usedfor revetment in mortar. Size of stone, con-crete block, etc, in this type of pitching, is nota critical aspect of design as every individualpiece is bonded by mortar. Average size of theavailable stone may be used for the purpose.Thickness should, however, be decided usingequation given in 3.5 to achieve stabilityagainst lifting. Typical revetment in mortar isshown in Fig. 3 ( see page 5 ).

4.2 Paoelling

Mortar revetment should not be constructed ina continuous or monolithic form. To avoidcracks, joints at suitable interval are requiredto be provided. Generally, revetment is dividedinpanels ofsize3m x 3mor3m x 5morso( see Fig. 4 on page 5 ). The size of the panelmay be varied depending upon the river reachto be protected and the length of bank s1ope’.Standard granular filter or synthetic fabricfilter should be provided below the joint.

4.3 Drain Holes

Drain holes or weep holes are required to beprovided in each panel for free drainage of pnrewater from the saturated bank soil beneath it,.Depending upon the size of the panel, one ormore drain holes need to be provided. The pipeprovided in the drain hole should be up to thenatural bank. Inverted filter or synthetic filterfabric should be provided at the end in contactwith soil to prevent escape of soil particles.Other end of the drain pipe should be flush withthe revetment face ( see Fig. 3 on page 5 ).

5 TOE PROTECTION

To prevent the s iding and failure of the revet-ment on slope, toe is required to be protected.This may be in the form of simple key, a toewall, a sheet pile or a launching apron. Diffe-rent types of toe protections are also shownin Fig. 2 to 6 ( see pages 5 and 6 ).


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I S 4262: l YYS

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Velocity : 3 m/s

Bank alopc : 2 : 1Angle of repose : 30 egree%SpcciRc gravity : 2.65


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As in the Original Standard, this Page is Intentionally Left Blank


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IS 14262 : 1995

HFC ‘(I ---

FREE BOARD

-.. .:. - . ..;. - *.*s -.

FIG 2 DRY PITCHING WITH APRON

.\: r FREE BOAR0. ’

.b. .

.

--- -k-t -=%bWEEP PIPE WITH FILTER

JOINT OF PANEL WITH FlLTER

INVERTED FILTER

i.RODIHLE STRATA

i I NFRC,I~IRLF SIRAT,

FIG 3 PITCHING IN MORTAR WITH TOEWALL

PANEL JOINT

w *_IFIG 4 FRONT VIEW OF PANEL


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IS 14262 195

5 1 Simple key may be provided at the toe whenrock or unerodible strata is available at theriver bed and the overlying banks are underattack and subjected to erosion. The key is inthe form of stones, bricks or concrete blocksfilled in trench at the toe below the hard riverbed for depth equal to the thickness of pitchingfor proper anchorage ( see Fig. 5 ). Sole pur-pose of this key is to provide lateral support.The stones, bricks or blocks may be laid inmortar if pitching on slope is in mortar.

5.2 When hard strata is available below theriver bed at a reasonable depth, toe wall isrecommended. The thickness of toe walldepends upon the height of the wall and heightof the overlying protection works. This wallmay be constructed in masonry ( see Fig. 3 )and designed as a retaining wall with weepholes, etc.

5.3 When firm strata is not available at areasonable depth below the river bed, toe pro-tection in the form of sheet piles is recommend-

ed. The sheet pile may be made up of RCC orsteel or bamboos depending upon the availabi-lity of material. Sheet piles should be driverbelow the anticipated maximum scour plusgrip length ( see Fig. 6 ).

Depth of scour may be worked out from theequation:

D L 0.473 ( Q/f)l/sor DL = 1.33 ( q’/f )],a, 2nd

f = 1.76 42

whereDr = scour depth below HFL in m,

Q = discharge in ma/s,q = discharge per unit width in ms/s;lm,f = silt factor, andd =

mean particle diameter of river bedmaterial in mm.Maximum anticipated scour for launching apronmay be taken as = 1.5 DL.

rJ HFL

FREE BOARU 5s

ERODIBLE STRATA --

,- LlNEROOlBLE STRATA

Tr THICKNESS OF

PROTECTION LAYER

FIG 5 TOE K Y

BED PROFILEBEFORE SCOUR

BED PROFILEAf7ER SCOUR

FIG. 6 TOE PROTECTION WITH PILE ND TOP KEY


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I S 14262 : 1995

5.4 Sheet piles are difficult to drive. Launchingapron is, therefore, preferred and generallyprovided for dry rubble revetments ( seeFig. 2 ).

5.5 Launching apron should be laid at normalwater level or at as low a level as techno-*economically viable. The stones in the apronshould be designed to launch along the slope ofthe scour and provide a strong layer that mayprevent further scooping out of the river bedmaterial. The size and shap: of the aprondepends on the size of the stone, thickness ofthe launched apron, depth of scour and slope.of launched apron. Weight and size of the stonefor launching apron should be determined asin 3.3 and 3.4. Thickness of launching apronshould be determined as in 3.5.

5.6 The slope of launching apron may be taken

as 2 H : 1 V. Adequate quantity of stones for theapron has to be provided to ensure completeprotection of the whole of the scoured faceaccording to levels and slopes. The quantity ofstones so calculated may be provided in awedge shape having width of 1.5 DL seeFig. 2 ) and average thickness T. Thickness of

the laid apron may be kept 0.8 T near the toe ofthe revetment and l-2 Tat the river end.

5.7 Filter as mentioned in 3.7 should be provid-ed below launching apron.

6 ANCHORING

6.1 Proper anchor is required for keeping therevetment in place and serving the desiredfunction.

Upstream edge from where the revetmentstarts, should be secured well to the adjoiningbank. Similarly, downstream edge where thepitching ends also need to be secured well tothe adjoining bank. For this purpose, therevetment should be properly anchored to theground at its two ends by sultably extending itas may be required at site ( see Fig. 7 ).

Anchorage is also required to be provided onthe top for submerged bank ( see Fig. 6 ). Ifthe top of bank is above HFL, the revetmentshould be raised above HFL with adequatefree board. Under such situation, anchorage atthe top is not required ( see Fig. 2 ).

FIG. 7 UPSTRE M ND DOWNSTRE M KEY FOR RBVBTMENT

7


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IS 14262 : 1995

ANNEX A

( Clause 3.7

CRITERIA FOR SELECTION OF FILTER FABRIC

Geotextile filters may be recommended becauseof ease in installation and their proven effective-ness as an integral part of protection works.The following criteria, depending on thegradation of bed material, may be used to selectthe correct filter fabric:

a) For granular material containing 50 per-cent or less fines by weight, the followingratio should be satisfied:

8.5% passing size ofbed material (mm)

-- -.-Eqmvalent opening ) 1.0

size of bed of fabric (mm)

In order to reduce the chances of clogg-ing, no fabric should be specified with anequivalent opening size smaller than

b)

c)

0.149 mm. Thus the equivalent openingsize of fabric should not be smallerthan 0.149 mm and should be equal to orless than 85 percent passing size of thebed material.For bed material containing at least50 percent but not more than 85 percentfines by weight, the equivalent openingsize of filter should not be smallerthan O-149 mm and should not be largerthan O-21 1 mm.

For bed material containg 85 percent ormore of particles finer than O-074 mm, itis suggested that use of non-woven geo-fabric filter having opening size andpermeability compatible to the equivalentvalues given in (a) above may be used.


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Amendments are issued to standards as the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicates thatno changes are needed; if the review indicates that changes are needed, it is taken up for revision.Users of Indian Standards should ascertain that they are in possession of the latest amendments oredition.

This Indian Standard has been developed from Dot No, RVD 22 140)

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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Is 14262 Revetment of River Embankment

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