cantilever rw aci

7/25/2019 Cantilever Rw ACI

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IN THE NAME OF ALLAH, THE MOST BENEFICENT,

THE MOST MERCIFUL



CANTILEVERCANTILEVER

RETAINING WALLSRETAINING WALLS



RETAINING WALLSRETAINING WALLS

DEFINATIONDEFINATION It is a structure that holds back soil or other looseIt is a structure that holds back soil or other loosematerial and prevents it from assuming natural angle ofmaterial and prevents it from assuming natural angle of

repose at a location where an abrupt change in groundrepose at a location where an abrupt change in groundelevation occurs. Oelevation occurs. O !tructure which provides stabilit" to loose or!tructure which provides stabilit" to loose orcompacted soil. Ocompacted soil. O

!tructures designed to sustain the lateral pressure of!tructures designed to sustain the lateral pressure ofearth or other material #grain$ ore$ li%uid& and retain it inearth or other material #grain$ ore$ li%uid& and retain it ina steep face slope which otherwise would rupture ora steep face slope which otherwise would rupture orslide down.slide down.



'!E!'!E!etaining walls are used to maintain the width of theetaining walls are used to maintain the width of the

right of wa" in an e(cavation$ cut or embankment inright of wa" in an e(cavation$ cut or embankment inrailwa" or highwa" construction.railwa" or highwa" construction.In buildings$ retain soils for basement wall.In buildings$ retain soils for basement wall. To retain li%uid or other loose material in tanks )silos.To retain li%uid or other loose material in tanks )silos.

etaining walls are most e(tensivel" used in railwa"setaining walls are most e(tensivel" used in railwa"sand highwa"s construction.and highwa"s construction.



TYPES OF RETAINING WALLSTYPES OF RETAINING WALLS*ravit" walls*ravi

t" walls . 'suall" made of stone masonr"$ brick. 'suall" made of stone masonr"$ brickor block masonr" or of plain concrete. It dependsor block masonr" or of plain concrete. It dependsentirel" on its weight for stabilit". It is used for walls upentirel" on its weight for stabilit". It is used for walls upto +,-+ ft high. *abion is also a form of gravit" wall.to +,-+ ft high. *abion is also a form of gravit" wall.



/antilever retaining wall/antilever retainin

g wall . It is most commonl" used. It is most commonl" usedt"pe of wall. All components of this wall i.e. stem$ toet"pe of wall. All components of this wall i.e. stem$ toeand heel act as a cantilever and hence the nameand heel act as a cantilever and hence the name

cantilever retaining wallcantilever retaining wall . used in height range of +,. used in height range of +,to 0, ft.to 0, ft.



Counter fort retaining wallCounter fort retaini ng wall In this t"pe of wall$ the stem and the base slab areIn this t"pe of wall$ the stem and the base slab aretied together b" counter fort$ which are transverse wallstied together b" counter fort$ which are transverse wallsspaced at an interval and act as tension tie to supportspaced at an interval and act as tension tie to supportthe stem wall. Economical for height over 0, 1 0 ft.the stem wall. Economical for height over 0, 1 0 ft.



2'TT E!! ETAININ* 3A442'TT E!! ETAININ* 3A44 A buttress wall is similar to a counter fort wall e(cept A buttress wall is similar to a counter fort wall e(ceptthat the transverse supports are located on the side ofthat the transverse supports are located on the side of

the stem opposite to that of retained material and actthe stem opposite to that of retained material and actas compression strut. !ee figure.as compression strut. !ee figure.2uttress as compression element are more efficient2uttress as compression element are more efficientthan tension counter fort and economical in the samethan tension counter fort and economical in the sameheight range.height range.

A counter fort is more widel" used because counter A counter fort is more widel" used because counterfort is hidden beneath the retained material where asfort is hidden beneath the retained material where asbuttress occupies a useable space in front of the wall.buttress occupies a useable space in front of the wall.

2 ID*E A2'T5ENT2 ID*E A2'T5ENT A wall t"pe bridge abutment acts similar to a retaining A wall t"pe bridge abutment acts similar to a retainingwall e(cept that the bridge deck provides an additionalwall e(cept that the bridge deck provides an additionalrestraint at the top of the stem. This abutment isrestraint at the top of the stem. This abutment is



designed as a beam fi(ed at bottom and simpl" supported ordesigned as a beam fi(ed at bottom and simpl" supported orpartiall" restrained at the top.partiall" restrained at the top.



Earth pressureEarth pressureIn their ph"sical behaviour$ soil and other granularIn their ph"sical behaviour$ soil and other granularmasses occup" position between li%uid and solids.masses occup" position between li%uid and solids.

If a pit is dug in cla" soil$ its sides can usuall" be madeIf a pit is dug in cla" soil$ its sides can usuall" be madevertical over a considerable depth without support butvertical over a considerable depth without support butif this pit is flooded$ the sides will give awa" andif this pit is flooded$ the sides will give awa" andsaturated cla" will be nearl" converted into a li%uid.saturated cla" will be nearl" converted into a li%uid.If a vertical wall retains soil$ the earth pressureIf a vertical wall retains soil$ the earth pressureincreases proportionall" to the depth and itsincreases proportionall" to the depth and itsmagnitude ismagnitude is

p6/a.p6/a. 77 .h.h wherewhere 77 is unit wt of soil and /a is coefficient ofis unit wt of soil and /a is coefficient ofearth pressure and depend on t"pe of soil and methodearth pressure and depend on t"pe of soil and methodof depositing and compacting.of depositing and compacting.



If the retained soil surface subtends an angleIf the retained soil surface subtends an angle 88 with thewith thehori9ontal$ then according to ankine theor"$ /a is given b"hori9ontal$ then according to ankine theor"$ /a is given b"

For fre%uent case of hori9ontal surface$For fre%uent case of hori9ontal surface$ 88 6, and6, and

/a6#+-sin/a6#+-sin :: &)#+;sin&)#+;sin :: &&Fill materials behind retaining walls are rarel" uniform and dr".Fill materials behind retaining walls are rarel" uniform and dr".<roper drainage of the fill is ver" important to reduce pressure<roper drainage of the fill is ver" important to reduce pressurebut even in well drained soils the pressure will temporaril"but even in well drained soils the pressure will temporaril"increase during heav" storm and sudden thaw.increase during heav" storm and sudden thaw.



MANY WALLS THAT HAVE EEN !ESIGNE!MANY WALLS THAT HAVE EEN !ESIGNE!WITHO"T REGAR! TO THESE FACTORS HAVEWITHO"T REGAR! TO THESE FACTORS HAVEFAILE!# !ISPLACE! OR CRAC$E!%FAILE!# !ISPLACE! OR CRAC$E!%

Sele&t &on'er(ati(e (alue ofSele&t &on'er(ati(e (alue of )) # '*aller t+an# '*aller t+ana&tual te't (alue% Ta,le ,elow gi(e' (alue ofa&tual te't (alue% Ta,le ,elow gi(e' (alue of -- ## )) an. &oe/&ient of fri&tion#an. &oe/&ient of fri&tion# 00 ,etween &on&rete,etween &on&retean. 'oil'%an. 'oil'%



NoNo Soil t12eSoil t12e "nit wt"nit wtl,'3&uftl,'3&uft

)) 00

44 San. or gra(el w3oSan. or gra(el w3o

5ne' +ig+l1 2er*ea,le5ne' +ig+l1 2er*ea,le

44674467

486486

997:6997:6 6%;76%;7

6%<6%<88 San. an. gra(el wit+San. an. gra(el wit+

'ilt *i=ture# low'ilt *i=ture# low2er*ea,ilit12er*ea,ilit1

48674867496496

8;79;8;79; 6%:76%:76%;6%;

99 Silt1 'an.# 'an. an.Silt1 'an.# 'an. an.gra(el wit+ +ig+ &la1gra(el wit+ +ig+ &la1&ont&ont

44674467486486

8979689796 6%976%976%:6%:

:: Me.iu* or 'ti> &la1Me.iu* or 'ti> &la1 46674667486486

8;79;8;79; 6%876%876%:6%:

;; Soft &la1# 'iltSoft &la1# 'ilt ?67446?67446 8678;8678; 6%876%87

6%96%9



Earth pressure for common conditions of loadingEarth pressure for common conditions of loading In computing earth pressure on walls$ three common conditionsIn computing earth pressure on walls$ three common conditionsoften encountered are shown belowoften encountered are shown below %%

=ori9ontal surface of fill at the top of the wall=ori9ontal surface of fill at the to p of the wall



!loping and hori9ontal surface with surcharge$s.!loping and hori9ontal surface with surcharge$s.



T+e in&rea'e in 2re''ure &au'e. ,1 unifor* T+e in&rea'e in 2re''ure &au'e. ,1 unifor*'ur&+arge# ' i' &o*2ute. ,1 &on(erting it' loa.'ur&+arge# ' i' &o*2ute. ,1 &on(erting it' loa.into an e@ui(alent# i*aginar1 +eig+t of eart+#into an e@ui(alent# i*aginar1 +eig+t of eart+#

+'# a,o(e t+e to2 of t+e wall 'u&+ t+at+'# a,o(e t+e to2 of t+e wall 'u&+ t+at +' B'3+' B'3 --<ressure on wall due to surcharge6/a.<ressure on wall due to surcharge6/a. 77 .hs.=.hs.=

T+i' 2re''ure i' a''u*e. to ,e a&ting atT+i' 2re''ure i' a''u*e. to ,e a&ting at*i. +t%*i. +t%



Fa&tor' a>e&ting 2re''ure on retaining wallFa&tor' a>e&t ing 2re''ure on retaining wallT"pe of backfill used.T"pe of backfill used.!easonal condition of backfill material!easonal condition of backfill materialDrainage of backfill materialDrainage of backfill materialT"pe of material underneath the footingT"pe of material underneath the footing<ossibilit" of backfilling overload e.g. truck or<ossibilit" of backfilling overload e.g. truck or

e%uipment near the walle%uipment near the wallDegree of care e(ercised in backfillingDegree of care e(ercised in backfilling<ossibilit" of vibration in the vicinit" of wall<ossibilit" of vibration in the vicinit" of wall4evel of water table4evel of water tableDegree of rotational restraint between variousDegree of rotational restraint between variouscomponent of retaining structurecomponent of retaining structure



The most important single factor is that 3ATE mustThe most important single factor is that 3ATE mustbe prevented from accumulating in the backfillbe prevented from accumulating in the backfillmaterial.material. 3alls are rarel" designed to retain3alls are rarel" designed to retain

saturated material$ which means that ade%uatesaturated material$ which means that ade%uatedrainage must be provided.drainage must be provided.3hen vehicle ma" travel near and e(ert their load or3hen vehicle ma" travel near and e(ert their load orwhen buildings are constructed near the top of thewhen buildings are constructed near the top of thewall$ lateral pressure is increased.wall$ lateral pressure is increased.For e(act evaluation of such loads$ refer to an" bookFor e(act evaluation of such loads$ refer to an" bookon soil mechanics ) AA!=TO specification.on soil mechanics ) AA!=TO specification.



E(ternal stabilit"E(ternal stabil it" A retaining wall ma" fail in two different wa"s> A retaining wall ma" fail in two different wa"s>

? Its individual parts ma" not be strong enough to resistIts individual parts ma" not be strong enough to resistacting forcesacting forces

? 3all as a whole ma" be bodil" displaced b" the earth3all as a whole ma" be bodil" displaced b" the earthpressure without breaking up internall".pressure without breaking up internall".

To design against first possibilit"$ it is re%uired toTo design against first possibilit"$ it is re%uired todetermine necessar" dimensions$ thickness anddetermine necessar" dimensions$ thickness andreinforcement details to resist moment and shearreinforcement details to resist moment and shearTo safeguard the wall against bodil" displacement$ itTo safeguard the wall against bodil" displacement$ it

would re%uire special considerations.would re%uire special considerations.The force that tends to slide is the hori9ontalThe force that tends to slide is the hori9ontalcomponent$ <h of the earth pressure$ <. The resistingcomponent$ <h of the earth pressure$ <. The resistingfrictional force isfrictional force is 00 %R(%R( where v63;<vwhere v63;<v



d ff f



To provide sufficient safet"To provide sufficient safet" @@ #3;<v& +. <h#3;<v& +. <h

If the re%uired sliding resistance can not beIf the re%uired sliding resistance can not be

developed$ a 2A!E BEC must be provided to increasedeveloped$ a 2A!E BEC must be provided to increasehori9ontal resistance.hori9ontal resistance.It is necessar" to ensure that the pressure under theIt is necessar" to ensure that the pressure under thefooting does not e(ceed the permissible bearingfooting does not e(ceed the permissible bearingpressure.pressure.

%ma( 6 v)4#+; e)4& and%ma( 6 v)4#+; e)4& and

%min 6 v)4#+- e)4&%min 6 v)4#+- e)4&

l h ld l h ddl h d f h bl h ld li i hi iddl hi d f h b I



esultant should lie within middle third of the base. Itesultant should lie within middle third of the base. Itwill reduce the magnitude of ma(imum bearingwill reduce the magnitude of ma(imum bearingpressure and prevent large non uniformit" of pressure.pressure and prevent large non uniformit" of pressure.

A third mode of failure is the possibilit" of overturning A third mode of failure is the possibilit" of overturningof wall about point 2 due to hori9ontal pressure$ <h.of wall about point 2 due to hori9ontal pressure$ <h.If the resultant strikes within middle third$ ade%uateIf the resultant strikes within middle third$ ade%uatesafet" against overturning e(ists and no special checksafet" against overturning e(ists and no special check

is needed.is needed.If resultant lies outside the middle third$ a factor ofIf resultant lies outside the middle third$ a factor ofsafet" of at least +. , should be maintained againstsafet" of at least +. , should be maintained againstoverturning. Note that stabili9ing moment is providedoverturning. Note that stabili9ing moment is providedb" weight$ 3.g ; <v.4b" weight$ 3.g ; <v.4

f & l



a'i' of 'tru&tural .e'igna'i' of 'tru&tural .e' ignThe design of a cantilever retaining wall is based onThe design of a cantilever retaining wall is based onthe anal"sis of t"pical +ft slice i.e. + ft hori9ontal.the anal"sis of t"pical +ft slice i.e. + ft hori9ontal.

The investigation of a retaining wall for e(ternalThe investigation of a retaining wall for e(ternalstabilit" is based on calculation of actual earthstabilit" is based on calculation of actual earthpressure and on computed !E GI/E dead and livepressure and on computed !E GI/E dead and liveload> all with load factor of +.load> all with load factor of +.The structural design of a retaining wall is based onThe structural design of a retaining wall is based onfactored loads. 4oad factor of +.H is used for dead loadfactored loads. 4oad factor of +.H is used for dead loadand +. for live load$ lateral earth pressure andand +. for live load$ lateral earth pressure andsurcharge.surcharge.

P li i ! ! i! " !# il i i llP li i

! ! i! " !# il i i ll



Preliminary r! !rti!n" !# cantilever retaining wallPrelimin ary r! !rti!n" !# cantilever retaining wallThe design of a retaining wall begins with a trialThe design of a retaining wall begins with a trial

section and appro(imate dimension. The assumedsection and appro(imate dimension. The assumedsection is then checked for e(ternal stabilit" andsection is then checked for e(ternal stabilit" andstructural ade%uac". The following thumb rules ma" bestructural ade%uac". The following thumb rules ma" beused to determine appro(imate si9es of different parts ofused to determine appro(imate si9es of different parts ofa cantilever retaining wall.a cantilever retaining wall.

=eight of wall.=e ight of wall. The overall height of the wall is e%ualThe overall height of the wall is e%ualto the difference in elevation re%uired plus J-H ft$ whichto the difference in elevation re%uired plus J-H ft$ whichis the estimated frost penetration depth in cold areas.is the estimated frost penetration depth in cold areas.This depth will also ensure firm natural soil level.This depth will also ensure firm natural soil level.

Thickness of stemThickness of stem . The thickness of stem is. The thickness of stem iscalculated from ma(imum 2ENDIN* 5O5ENT andcalculated from ma(imum 2ENDIN* 5O5ENT and!=EA criteria which occurs at the base. The stem!=EA criteria which occurs at the base. The stemthickness ma" be estimated as +)+, -+)+H # -+,K& of thethickness ma" be estimated as +)+, -+)+H # -+,K& of the

h i h $ Th hi k h " b dh i ht$ Th thi k t th t " b d t



height$ =. The thickness at the top ma" be assumed toheight$ =. The thickness at the top ma" be assumed tobe L -+, . It is advisable to provide a batter #taper& ofbe L -+, . It is advisable to provide a batter #taper& ofM )ft height to compensate for forward deflection. ForM )ft height to compensate for forward deflection. For

short height up to +, ft$ a constant thickness ma" beshort height up to +, ft$ a constant thickness ma" beadopted.adopted.

4ength of base4e ngth of base . An initial estimate of length of base. An initial estimate of length of baseis H, - K of the wall height. The front face of the wallis H, - K of the wall height. The front face of the wall

should line up with the desired position of the soilshould line up with the desired position of the soilpressure resultant. 4ength of toe is +) J -+)H of basepressure resultant. 4ength of toe is +) J -+)H of baselength.length.Thickness of baseThickness of base . It is governed b" !=EA criteria.. It is governed b" !=EA criteria.5a" be estimated as +)+0 -+)+, # -+, K& of height$ =.5a" be estimated as +)+0 -+)+, # -+, K& of height$ =.

The base ma" be of uniform thickness or tapered toThe base ma" be of uniform thickness or tapered tothe end of toe and heel where 2.5. is 9ero.the end of toe and heel where 2.5. is 9ero.



! i il'!

i il'



!rainage an. ot+er .etail'!ra inage an. ot+er .etail'Two ma or causes of failure or damage to retainingTwo ma or causes of failure or damage to retainingwall are>wall are>

overstressing of soil under the walloverstressing of soil under the wall? Insufficient drainage of the backfill materialInsufficient drainage of the backfill material

Allowable soil pressure should be selected with great Allowable soil pressure should be selected with greatcare. Investigate up to a depth e%ual to ht of wall.care. Investigate up to a depth e%ual to ht of wall.Foundation to be laid below frost depth i.e.J -H ftFoundation to be laid below frost depth i.e.J -H ftbelow ground level.below ground level.3eep holes are provided b" -L dia pipe and3eep holes are provided b" -L dia pipe and

placed -+, hori9ontall" and J -H verticall".placed -+, hori9ontall" and J -H verticall".<rovide a minimum of +cu ft of crushed stone behind<rovide a minimum of +cu ft of crushed stone behindweep hole.weep hole.Overflow from weep holes to be carried off safel".Overflow from weep holes to be carried off safel".

Alt ti l" b d h i9 t l d i i lAlt ti l" b d h i9 t l d i i g l



Alternativel" embed a hori9ontal drain in gravel or Alternativel" embed a hori9ontal drain in gravel orcrush stone at the rear of the wall at one or more level.crush stone at the rear of the wall at one or more level.Efficient drainage is provided b" a la"er of crushedEfficient drainage is provided b" a la"er of crushed

stone at the rear of the retaining wall.stone at the rear of the retaining wall.If possible$ top surface of the fill should be paved orIf possible$ top surface of the fill should be paved orcovered with a la"er of low permeabilit" material andcovered with a la"er of low permeabilit" material andgiven a proper slope for good drainage.given a proper slope for good drainage.

<rovide e(pansion oint at P, ft interval and<rovide e(pansion oint at P, ft interval andcontraction oint at not more than J, ft.contraction oint at not more than J, ft.



l t i i f A/I / dl

t i i f A/I / d



elevant provisions of A/I /odeelevan t provisions of A/I /ode/antilever retaining walls are designed as fle(ural/antilever retaining walls are designed as fle(uralmembers according to provisions of chapter +, of A/Imembers according to provisions of chapter +, of A/I

/ode. #A/I /ode +H.+.0&./ode. #A/I /ode +H.+.0&.=ori9ontal reinforcement is governed b" A/I=ori9ontal reinforcement is governed b" A/I/ode+H.J./ode+H.J.=ori9ontal reinforcement=ori9ontal reinforcement ..

? 5inimum rft ratio for deformed bars ,f NO and5inimum rft ratio for deformed bars ,f NO andsmaller and f" not less than , ksi 6,.,,0smaller and f" not less than , ksi 6,.,,0? ft ratio 6,.,,0 for other deformed bars.ft ratio 6,.,,0 for other deformed bars.

<lacing of reinforcement<laci ng of reinforcement ..? 3alls more than +, thick e(cept basement wall shall3alls more than +, thick e(cept basement wall shall

have rft placed in two la"ers such that>have rft placed in two la"ers such that>? E(t face will have , - K of total rft re%uired forE(t face will have , - K of total rft re%uired for

each direction and placed not less than 0 nor moreeach direction and placed not less than 0 nor more

+39+39 f (t i ffrom e(terior face



+39+39 from e(terior face.from e(terior face.

? Interior face. Other la"er consisting of balance of steelInterior face. Other la"er consisting of balance of steelin each direction shall be placed not less thanin each direction shall be placed not less than Q norQ nor

more than h)J from interior face.more than h)J from interior face.5a(imum spacing of rft5a(imum s pacing of rft .# A/I +H.J. & Three times the.# A/I +H.J. & Three times thewall thickness or +L which ever is smaller.wall thickness or +L which ever is smaller./oncrete cover /oncrete cover ..

? /ast against and permanentl" e(posed to earth6 J/ast against and permanentl" e(posed to earth6 J? /oncrete e(posed to earth or weather /oncrete e(posed to earth or weather ? NO and larger bars6 0NO and larger bars6 0

? No and smaller bars 6+.No and smaller bars 6+.Termination of bars in tension 9one. A/I /ode +0.+,.Termination of bars in tension 9one. A/I /ode +0.+,.and +0 .+,.0 RJ.and +0 .+,.0 RJ.



GRAVITY RETAININGGRAVITY RETAININGWALLSWALLS

*ravit" walls are normall" constructed from plain*ravit" walls are normall" constructed from plainconcrete$ stone masonr" and rarel" from brick)blockconcrete$ stone masonr" and rarel" from brick)blockmasonr".masonr".

T"pical proportions of a gravit" wall are shown below.T"pical proportions of a gravit" wall are shown below.The wall ma" be vertical)trape9oidal in shape with theThe wall ma" be vertical)trape9oidal in shape with thebase having back and front protrusion in order tobase having back and front protrusion in order todistribute the base pressure to a more uniform shape.distribute the base pressure to a more uniform shape.Fle(ural stresses that develop in the wall are of littleFle(ural stresses that develop in the wall are of littleconse%uence.conse%uence.



The optimum design of an" retaining wall is a matterThe optimum design of an" retaining wall is a matter



The optimum design of an retaining wall is a matterThe optimum design of an retaining wall is a matterof successive appro(imation. easonable dimensionsof successive appro(imation. easonable dimensionsare assumed based on e(perience and conditions ofare assumed based on e(perience and conditions ofstabilit" are checked.stabilit" are checked.On the basis of first trial$ dimensions are read ustedOn the basis of first trial$ dimensions are read ustedand one or two trial result in favourable design.and one or two trial result in favourable design.



ANYANY

D"ESTION D"ESTION

cantilever rw aci

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