a=exp( 3n/4_p/2)tan'9

K'7 = passive earth pressure

bearing capacity (1u) equation l0efficient ls gtven as

'

Whcrc c

=

depend using rhe above factor.s, Terzaghis urtimate

oohesioru q = 7Dr and D thc rvidth ol. {boring.

9' How wirl you account for soir cornprcssitriiity iu 1'c.r,:rghi,s r-rcaring capacity equation. No thebretical solution is available for local and pr','n"t,irg slrear failures. Local shear fhilure is conrrnon in cornoressibre *ir an Ioose sands or soft days. In such

"o.aiii""l,,J';r"b;;;"g, rtLnott, r,rr-noi-n ;ir',"j;Ifi';#'"iii*'r"rg,i iiHrrr" bearing capaciry- equarion consider, a incompressible soit. For l3aasrri'.1 . compressible soils Terzaehi nroposed ernpiricai ad;ustm"ni.To rr," ,t rt pur"i"t"r."" and e. The adjusted shei strength p"r.ilild;;1G"0* *j", u, "ur "ngh case, the shear

;;l;i:;i;

$'",Ht:m::::'il*lJ:t

*iiiJ.

correspondirrg to local shear railure are indided as Nc,, No and

\

I0. How to identis a soil is ,ndgl l:9u! or undbr general shear failure in sands ? sandv soils with (c=0) and > 36 i,Ji"r't.' r 5;;;;}il;ffi;rig"r'"iiiTr,t* r."irr* i. likely to occur' sandv soirs *it,, . 9 - r""".""l'ii'i,r,", and.rocar shehr condition rnay be consider.ed. For intermedio," *rr., ol' i"rri,rg""r"p""i,, factors are obtained by Interpolation between rocar and. gcn-erar rr"rr *irr"".r,iriions. sirniiarry if rhe rerative density, D, of a soil is qrearer rh; zoz, g":,,.;.irtr#'i:.il',]r".*ro,rions. relative density, o. ora ioir is'r'eater Similarly if the ^ rhan zo;rt, . ,o,,r.",ruy s.,i.r.i'rh";i be lbr D. Iess than 20yo a local jrear consideied and friturc niay: ;"";;;;;;*d, or intermediate suitable interpolatio, ,nuv values of D.

ztiiJ"li. li

ni',ruo"

il'

tlow thc cllect oflvntcr.

(cr.mirurtion of bearing capaciry ? that the water tabre is rfi:i'*""H?:X,::n'^.roain*riol,.'r','"ui.i" ";;ii;;;.;nrptron ." ,,,ii. a"p*ding on the position of fflr:?J,"J, Terzaghi's egtration which are afiected iable position' are : (i) the tv *,. *utl, werght component C.57BN, and (ii) -'- ' -i::-il,'J" the Terzaghi suggested water tabre correctious io be innoduced in ,rerzagrri.s general equation with modification equation. Thus the for

iir rhe

Terzaghi's bearine canacity "lf. j.^:::::1,,:,:ri, equari.o is b*",t

yDrNo

(le

\'./ ;il

,rr"hr;;";";;;;;;,

water

tr;L"i;'

Cl; l30i - [ouxd iox Er]girlccril)g

\

#l"":r[:,ru,};,i:,yJ:i,Hi",,",:,,f

'

,l J, p, water rabte welt beto* rhe

;j:T,:]:ii, l(Iv = I atrd Ru{ =\. "(r-;q:

.dr'f:$

water table at the ground Detween ground surface , propoftion to depth ofsurc . rue reruns Rw and R.w are inrr.oJu"ced basea .,, unit weight ora .oir ",:o2' i. r,.ri.oriiJ

h$*'**ti-**fii :'ru+'*rutn

.*oare rlrc I2f What

o,l]#";:,H.f:,li*rf, -'6'r!'

motlifications ,^ hn 6/..^..-_ ,

-

rhat rhe avera,e

.

t-il{i],f,-nt:il;'*"1*,'ffi

:f capacity. '|.,rrs the forowing modified #*::3""J,""",#,::*n*",:i .- "-v wys""urs ^-"rvr 3[:11l.ff:[f;,8,i,,.J^,."lx1iit1,.?H /.

oearrng

t erzayhigave

t'|

'|

'l1:"i#ym,t,ii:fJ:**f Mere ,sc,

{fr

equations ror

":,?##[""?,.#1ffi

sq and sr are shape factor corrections

9c,^dq and dr are the depth rc,rq and ir are tre roaa lncrinaiio,

A""i.."r."",i"r.

io.iillli,"oi"rs

;T'ffiit"-,,i.=I:!:?: j,#:rjf

i:U:.ifi (t + dMB), for W.T Rw = 0.5

For square

rootins;:;':' r::

';jl?f

< dqo <

o'

o"liii:',ill,oi*li,l-*::.::,

.

:il,ii;1,,1ft 5ii:,,,::,;il;",;f$:lqi

iDr+

B).

trii:i,ffi:fJffii;jil *t i *;$itr,?J..' '

,:flrr,,:pffi".,rrr"r*",;;,

-

o:4 B

t

a ",,* .,,,,,o,, ;;;.,, ".

*n**sl#$utt6***,sid:fru*,*ffi 9or

=

q6- r,P,

Clj lJOj

-

Ibund.!lion JinSineerilg

.

-\r

I I

r wi':'' y.':

the unit rveight of.rhc sor rurd i)1 is ihe deprh of fbr,rndaticn rf Ir is the factor of safety with respect ro shear failure, ihen F ., qur/ q or qr = qnr,'li Here qo is called the net safe bea.ing pressure (qrr) sucrr that q,u qns/F. This leads to another definition called gross safe bearing trissu,e

.

:

r

tqj,'tfruris

where q = yD6 r.e., qs = qnf +q i.e., q, in terms ofTerzaghis bearing capacity factors is got by substituting for

3.lil:fr.

*t,

pressure

is

based

on shear failure and

skempton's propoied a bearing capacity' thbory

The net bearing capaoity

(q"j

.ipr.!.i"r'i, gffi;

io.

'"


qng

not account for permissible

soil? .riu."ut"o ""'t'"' day under qu = 0 condition.

whelc cu = undrained cohesion Nr = 5 (l+0,2 Dfts) with a maximirm limiting value o:f 7.5 for strip footiways. *" = 6 (t+0.2 DflB) with a maxirnurn ilfti;.,,;;;;;;lo?or.qrur. and circular footings ) with a maximum ri,"iii;; i",,nip footings. I:= l,liTfp.i"", r\c - J(l-ru.z uvIJ) (l+0.2 B/c) for rectangt,lar tbotings with DflB < 2.5 N. = 7.5 (l+0.2DflB) for rcctanguln, tooti,ig, *,itt

,;i;;;;i.i

-O;f;r;;' skempton's No value is based on the-ory, lah-orarory t"rt. .J nelA observations. that N" increases with the increass li.rhJ;;;;;

16. Exp_lain

11

;r;6.'

may be seen

Mejerhofs Bearing capacitv lheorv.

In Meyerhof s analvsis-tl-re

,."ri.ilr.e of the soil above the brr" of *," fooilin ;19urir"g is also taken into accountl rhe raitu.e inech;;r;;;; ":l;il;, -'* ," that of Terzasheri with i. difference that the oentral wedge angle is greatet than

0.

Mcrycr'ol'prcscntcr, a si^rprc bc.rirrg r:apaci.y cqLration Ibr. s'arow rbundation as Symbols s, d and i stand-for enrpirical ccr.rection factors called the shape factor, depth

hi, u.

Th. bear.ing capacity factors Ni and

Noare sarne as rhat

\

is given by

*

(Nq - I ) + ran fl.4o). MeyerhoPs bearing capacity lacrors ,,.," h,ar,,nr,. .,,*^!:.-._

Ny

of prandtl and

aepir,

orr*tine,

,lJiln"

.ii"|Jiio,i ill'll'oi:il,oil:I]rilfilion

are the factors conh'it,rting

f.r

-. s or

(,

as in rerzaghi's ) but arso

rhe bcaring capacity of footirrgs in cohesionress

Considering c = 0 for cohesion less soils rve have

Cll

130-!

-

litundatlon Ergjueering

f ll ,l

.-"..

{1'

above cquiiiion the ihclcrs rhal ...q! ,rvve.rr irlvo an inftuence rnrluerce con bearing capacity -.'--"r ofcohesion ul v(rrreulot

flff:ff;T: /;\ e

relative dcnsiiy or rhe a,r.r._ u,'t'' oi'shearingresistance' ^u.^r--

*'a*

,lll

)]]t

!,y.)

"rii" #"iiLf'"

depth ofrhe foorin!. unir weighr of the

iil

romffi*;lt**$*$fi+#ffi$n:ffi IS, What factors influencc th

;;t;ffi

.,,,,,Y1111f ,n".iu'i#,,ii,.r,tnn*r."

!l

f r_)

(t

I

,-,,ffi

l,:i:?':',iff l"'J:'fl.::1,::,::1i,*saruratedcray? ry or pure

cohesive soil with

u."

rpu

,n], i"""ieh, or.oil

.

depth offoundation

l*ffi $f,*:iii+kft"*fi,,",ffi r#;#*ffi ;

;gE61ffi$'.u#i*i}u#*s,}}tliffi

i+;[

For square and circular footings

$ti,}#"[:ffiH H::[$trfjffi::::

CE

,."-,*

.nd irnecessa' ror di,ahncy

l30j - |oundation llnginecr.ing

(

E ron

20. What is the concept of useful wiCth

?

Meyerhof introduced the concept of usetirr rviirir.ro compute the bearing capacity when the resultant load on the footing acts eccenrricafly ,r,iri, ,.spJci io the center of the footin8. In 'i""*rllgir,".,rsions order to account for ttre eccintricitv ,ir.

;i rili;;

are modified in such a 'tt,. ,.iur"a ,t-i;;;"r;;, of the fo;iinr;. Considering a r€ctangular. footing, there can be-eccentricity of loading on both directions. sav ex and ev in t-he width *ilrgiiiai.".ti"", way that the load becomes concentii. to

he: se

io rit

the reduced dimensions of the

B'=B-2ex

f""tirg

"*

"rrrrrt":"iretrillif.lr.'rr"ii e;*?i:r"il;j;;.;,"., ",

L' = L-2 ey This least modified width B. is used in the bearing capacity equation and in the of shape factor. me toroL,c.ri.ai ir;;;;;::,rpured

f$l'lf:, 11.

using the effective area

rr Yl,,:, rc I hc corrr lxrncl

;TJ??,rTT:T"nt

ts ol. tot:rl scl i Irrrrcrr I ol. soil .l S may be visualised as rhc surn r:f.rhree componenrs,

viz.,

where Si = imrnediate or distortion settlement

:

consolidation settlement = secondary oompression settlement. The immediate comDonent is that portion of the settlement which occurs immediatelv with. Ioad application. This is computed assurning soil as an iit".i"i. combinedly called as the time dipendant "r"rir" ,rr" settremenr due to primary comprosslon due to cxDursron or*uie.. s, is i-t.,e';;;;;",;";;rpression due to reconciliation ofsoil panicles. Sc & br are compuled based un consoridation resurts. Sc

Ss

*ttr;;;;.

-

22, What is permissible settlement ? settlernent may be crassified as.uniform,

-!"'i,

'ilfftffi:

t

t or non- uniform. Tirt and non-uniform settrement rnrro.," ."ttie."ni i. ,nu"h more simple than the estimation of differential senrement. on1ou. oii".. T5yo of totalsenrement mav be taken as differentiar cause differential settrement. Estimation or

i*;;;;;;.,

ffirililIilililI

settrement. r", J""rv iyp. ril"irr" L,,a'r"; settlement,is fixed caned as pennissibtc ,"Ltt",,ii,it. "i ii,_ structure should not exceed these limits. Inttian stanaari coJe'prov;aes permissibre values of settlement for different types ofsrructures.

.iri'rra'iiif"r;";iilil##,;if:

23, What ls allowable soil iressure The rate of settlement

Ioad ln the initiar

?

is dirccrly proportional -^iiu to. the applied increase in i, r"oL"i at higher roads the rate of

stage trre"?-f"1:d^1i?, rate of settremen,

settlement is extreming large. ground or have experienced

1

i;r;;ri". is saia to have broken into the / -lil.'.ria"n, a bearing *pi.i,i irif,r". tht distinction between settlement and failure uv i."rii"g"i,ri";; is, in ;.,il mhny instances, quite ;["d.t At this

stage ah;

Thus every foundation has to satisry two irrdependenr conditions. The first condition is that there should be adequate facor of.safetv of foundarion. Second. the settlement of the structure shourd not "g;r;;-;;;';rji;re u" g,Jri".r",,gr,'i" or*rg" ,rr" structure. out ofthese whichever gives a lower

:ffi

;:::lt|!:t

';ii"

CE 1305

"r

-

i",i'r,".*iii'i.

."r".."a to as the alrowabie

Fouirdntion Engincering

i

z,

1,:'

)

!'

.

r.,:r,:.t,,:jj.

r.'i

-------.----.-------.-..--

{3;,i1;,1;;T',::ii,::::::l'r",1ij:,on,piiti;d,

,,.,"'

i .l

a.'.,i1,;:X'::,,:J,';;fi, ;"i'lli;jiil:,,,-;:::1..::l iu.,,, u*ar; or dirrbrent geomerricar tlltjlici{i. 'l i:': .rr:il is ;r.;r s'Urnerrrca jlXfr *l;Jl"lr,."irr-i]ti'..oi pxrarrrit,xs [lii,liii,""r,,J',1;:*,JJ,r,f ii,i;;i;il,?il,i'i',l,,lfff ffi:T] ,,."

la:,,irc.i. dlasric

t:iffi oi ths soil,

.no ,,ujiision,s ,.urio. ,r"1,., arr: ;ffi:iT -,,,,;'ji'l:

i:':I.r,T,;lli":iliiitriljl;:ffi,:Iil:Xl'ff,"J ili,,lji:l;l-.,r,io.," -'; .;x;J[x,'i, lxi ,r* ;lnl,l.,*l*]:;lni:i,i:ii";;:'mpliti[*:,f*ilJ,i ri"ri .t,iiio;1";if:[,t"I;:;:.#]fi:llilj;;l?:lil**ffi]ilT l::.!,":iii1,::, Si - clij (l-lt2)/E Ii Whcrc q is tho rrct I()r/rldirliori _ igitliry i , pt ^,..... or;sutc r:,ci Il is;

rur*l

,r;

r

;i;;;;;;.""'

I

r

rrrr

,

I r

,ri,,

,

r,i

ihc inllr;i:rco lictor dopondirrg o, shapc

3l;lluff

settrement :LL*l';: ;J::1i11":'^fi'on: llie data available firur settle,ent is calcu#;;;r""'r"ed a cons.rlidation

data. The

\\/here Ev = Vertical strain = e/l +e0 in void ratio -Change Initial void ratio Height of compressible layer

Loeftrcient of cornpressibllit_v

SffiH,ruinr'ii" "", pl'.* Applied effective pressure Change in uppfi"a,in 26. How secondary consolida

"ff""riuc

r

u

;r

i,y

pressure.

#,*ir*ffi lt***r*u'["d]i,*t***nlu**ffi where Ae is the decrease in

;,mru;s

s

ffi Tiilj['h**'::l;#,H[ri*,J;::r.,?.1],j:r.,",,,,"

t

f 6

i,:,'#il*":T,...,H::x;:::1ilHiii,r:,i;[:.,-,r,u,

ilff:lP"1ig;;" "u'oit "u'iai,i,l,,.'""' iir? v*r"ii", jf j

(tv) ,l

"i "i",,l,ii[, Over stressing of

:,i

],X"J,

:i;";l,l;.,ii,,,,

^i

"n,a

r road

in

g.

site Jue to heiivy sir.rcrures and interference distriiui,o,iro"'t"'" of Unequal expans;6,r.,irr^.^;, ,..- . pressure

lrl

3,, ffi,,f:,T ttt#,Tliii"!:,:rJ;_itl?llii;,* or tr'n*ing,.r,inrrg;ffi:Jffff:i:s

voiun,e crrsnge due

pr sti

of str co.

to

freezins and

rvi

/ CE ll05 _ t:,ru,tdatiori F,lrBinc..)ririg

sqd

t

:ia!i!xE

,r 2'1,

List the cruses ofsi.til

s.fl

irrs{r r:cttrrca.

.;;;; ;i;;;;:'j1""""t

,ll, llll

Ij;i;",,;'.::l'r":;;iii,";,ffffi,1:,,'j11,,0i,,,,,. Elastic

orrire rbii.wing racrors:

cdmpression

ofsoil (ul) Lowering of,g,:-ulg tvaler Cue ro pumping or ratuml causes. Shrinkage due to seasonal 1,Y) chnn,,.,'" (v) cround mbverncr,r,Jr" i;,;;;;:;.;..1irri-rnar,L, (vi.) Shrinkaged erosrolvih"f;;;i_;;,;;..,,,,- cL,,.rses. 29.Lisr flre mcthoCs of confroliirrg $ctthlr cnt_ provisiorr"ri,rlJL,iri",,ra.,;",,r

(i)

(iD

ltrrvittirrg rJccp bi

I

ro"ui"g ro deeper and ress compressibre l[fiP:-;r.:;it:,nj,rion soir. pocl
"";il;'

"""" brackets

,.,0.,;1.",1,,?.1J.'"king

irt column to reveal the

:,cilitj:,iJl,li?,"oli#;.,,",,," ilrli,gnTJf,,,J"1;ff (vii) Use appropriate type ofpile suited foithe situation.

" "T"".T:ffi,:'#ffi,[13]#:-q:.r,ol j"ffiH;,:,:ffi L #J,H

cqurt settrcr'ent carried out ?

[tlill.i[i;','#,r;i-j l]l ;:,Xinf :;,1*::liilhilXl;

HI*Ifi #fi :+,ifl l,*#.:,,i*;ffi n:itr##,r',ffi orcorcr*torases,"wa;;-m;'trrt

,to'"g. no6.,,

ri,.g-.ffi#:;J'#,ff|;"I',ili,lilii

t

31.Give the permissibte setdemenr thr i"^r^,...r _.roundatioos, tb" isolat.(l E*ry

.

;;;;;.il;]'j"T:""1 be scftie more thnn

se$rement as per the Bureau of rrirlr'r"roilJ."u. "o6".

lf;l

)1 ''fi"''

the

a,d rtrfts on satrd and dav. 'permissible

perrnissible setlements

1"[i *t'a"iil**

,." .";o;;";;:;';;

;:x*ru;:x1tirj"L$i}"ft ,,i,}l:111fl [:,,J#:ffi *Jlil.,*tfr J"#f# rne maximum _

d.ifferen1i6l sslllstnent lnust not exceed 4cm ctavey soils and 2.s"m in . . oirou-n;il'";:,i::i:'_exceed or toundations on sandy soils. "ase

,.""Ij,1?#:;l",ii3tlll#::

cohesive soir

wiil rvoid

in

case

of foundation on

a co[apse ?

ffq*'tp*ltr,*r*,ffit,$t*ffi

fs.What is a plate load tesi

?

.,,"..11',?1",;":1,:T:J::,J;[i:.J]ffil,if,.,,"i]::".,,#:,;ff_l#Ti?,;,*".ii,rr,lll? CE i305

-

I

c,:udtlioll llniri ceiirrg 9

let

at the proposed revel of the lbirr,ciaticn. Lo;iiJ. is apprierl in suitabre increments depending on soit' Loads on the tesi nlate nrav be.apprt"; ;), d;r;),'iffiing or reaction toading. Load is applied till fairure. Sertrernent at i,,.,.",r*,... oi i,riinii. 'n,,"urur.o. A road settremenr _ "icrr curve with load-intensity on x-axis and scilrerncnt:,r y-ax'is is protted. The two libs of the curves are extended to lit thc ultinrare loeri in,!cnsiiv. the

34'How the data frorrr a orat-r*aa test is use* to estiillate the setreme,t of a footing ? Terzaghi and Peck have recomrnend"a tr.,ot ili" *ti"ni",ii ot: o noting on cohesionless soir can the settlement experlenccd r':' i"'ipiut" oi tr," tr"iffi":;],]f#rn

i"r. r""Jiit.";il;;;

"

whcre Sr= settlement ol'a lourrdation oi-wirkh I)1(rn ) irr cnr sI,: scttlcmcnr rcst prirrc or'r.vitrrrr Ilp

oI

t.,,,

il,i',i'i..r,"

,"".r intonsity

In clayey soil the following appioxinrate exprcssion can be used

as on tho rbun
:

35.How bearing capacitv is detcrntined based on come pcnetration test.i Meverhoff has given formurae.for ail"*.bG .;r;'G;r'rJill] on cone penetrarion resr values limiting the settrement to 25 mm. rner" ior-rtue based on Terzaghi and peck,s curves for spread or strip footings on dry sand as

il

**o

These fonnurae are based on the approxirnate rure that the N value resistanr:e. The value of q." obtained, uring

is

quarter

oftle

static come

tfr. oUoul-.quution. sf,orfa bo reduced by 50% it . the sand within the stressed zone is submerled. vr"y*rr"'ii"rtr,". suggests that the values have

to be doubled for raft or pier foundation.

36.What are the conditions which are favorable for combined footing ? A combined footins is often thought to be more .*norni"uL *r,'"n the area covered by isorated rootings teras to clouermli. ih;;';;;;;ri;;h". friilirs area. Apart from reasons or economy, when sub-soil contlins. oornprcssibre po.ket., unequauy roaded columns and boundary columns, a combined footing is useJto *itrri'r",i""r*,. These footings are usualry recta-ngurrr.in ,r*p" uui^aj ue moaified to a trapezbidal one to accommodate unequar column loa(iigs (or to.prope*y with a strap to accommodate wide "urr,,n "toJ property Iines.rinas) and provided o;;;;;;

"orrnli.lr*ings

37.What factors are considered in th^c structural design ofspread The3]an dimensions (B x L) ora ,pr"rJ-r;";;;;l;l"."ia.a footings ? uur"a on the arowable soir pressure The depth of foundation a"p.n,tr on (basement floor, etc.) and environnlenrar faators of the location. Floting it'i.il"rr.'i, g.*rary controlred by the shear stress' Diagonal tension shear ur*uv, ;il;;;il';;rt;."trally Ioaded square footing. "Jioi! may conrror ,r," oip,r, ti" wrren the LlB ratiois grearer

(

38'whaterattors

t I

_

ii,;"*r.*"r

,..tr;;H:'irfi;

Hil""*f,ri".

l,:?i,LT,ilt ;,"."t::llt::-9"''*l'

or rccta':rgutar rootings

,pu."u,iiuiio'",.Hil:i:i:"'#";H,"H:J:il,*T:,f CE 1305

-

?

:iffi :il"lii,?J.Tf,i;;H:,:i

Folndatio0 Engj,leerilg

l0

I

t

i

4'

fuiil

rhe ii;,:':;;r,;: ]i':,:i";ll'"'".::::.p:::,y**oting il square lootlng' The deDlh is

ii",l"x[1ff,1,*"1J"s*:*,'i, controlied by the shear excepr that y,,iLle-L,.oi"

-i,

,,.,i., ,riii'/ much greatir i""r .,; ;,;" consideration for rectangular ".;'.;,rr-* footirrg:r iu i,, rt.," ru..*,,,*i.,r,ii tl,e 1, ,cinforccmsnt.

;;;;;,

i;J;:J'?:"i,,L::lr-!'lJt:,il:

:fl

:;;

39.Clas_sify piles based on

installitiou liretlrods. Based on instalation t""r,riq*. pjil'r-irLc ciassifie<.I as crriven pires and cast-in-situ piles' Driven piles rnay be concrete, steel or timbo,. con.."t. piles are crassified as driven ,iH:l;,::I?:J*[iJl',1i1-'.:'u",";t"

*qri."ii*ii"rlrrvrw'v

'*''''i'

iii"J"'"a r'o'"a

vIIe rs the or)e casted in it casting yard and .-ur"qr""try "o.t-in-.jiu-l#;;i1., J.ir;,;';.

Driven cast-in-situ niles are lbrrrrecr rvitrrirr thc eround by driving a crosed boftom ,u:iir, ::,rjll^T1 ,subsequently'iirting so rbrmed wirh adequate "o,,.r.,"-,"i,.,.,i#.rr"re pirc is r.ourrci *;ir,i"'ir.. s19.yJui f,,ff:Tffi:1,,?:T*:Tl;,",,, mporary casing and subsequeilly-filling it *i"."1"Jil;.J;H;, f, pf^i, ."ir#."A concrete.

"i

40. Classify piles based

or functions.

Where the topsoil is so.ft.or too lveak to support the super_structure, piles are transmit the toad to the underlying used to b"d,.";il ui.. end_bearing piles or poinr bearing piles. Ifthe bedrock is noi"*ir,irg "u,,.a ri ,l"rrl,,"irl'i"r,,,, berowtheground surfaci, the Ioad is transferred throuqh piles ,ir""Jr,;fi".:rln are cailed friction pires. Transmission rowers. ofr--shore platfonnsind'bi;;r;;;;r;; subjected to uptift forces and piles are used to resisr the unrift'force., rnliia "r. oin. or tension pile. In order to resist horizontar and inclinei ror"". i,, *ui.. u,ii batter pires are used. Apptication of piles forproviding an;i,ri*,"'.i,,I,?ip,,lfl1ll"*,*o

;;#;iil,

rri"ti"".[rI,i,"

iiil;;i;i ";;;;ilhg

Under this classification piles, ntay be further. ciassifie
,"a"

liil'[:il*ff:ror

'

"rrcrures *"hor piles.

"["ri.utConcrete "ouiing'.

.^

piles are

i, .orJr"i"'o.'iy

o*IiL,,:,,rp*jlecl

Ierrgths ancl shapes

i,",i'#HL"lH#:l:t'J:,,"J:iJ;,,[:tiif,:{*::|;J"',i.i,g

wjth reinforcemenr. The

,o,n"nt

deveroped during

42. Classify piles based on ground cffccr.s: rttes are also used to r

rererred.to.as dispracement compaction pires. rhese ,il";"If;;'.:":'-.lill,::ill,,::1:::: - I1""'-" !' J(r('rL"rrrrrirr Y()lullle ol soil during installation. or granular soils there is a In t"n,l", orlen results. Driven piles l""r.i?l--]9'compat:ti'''r; hrtt i^ clays t,,"""i"g

m m:f

l;"H:H'ii,x1il'[::11 ];:T;1[iffi Jj:T"lf "ith,r;;ri'1,:';f"ll :]*;:',Thffi::::iH: ,;,r'

Cij

I

j0-q

-

l:oundalion Enginee.ilS

t (:.,-

l,l l

43.

List rhc udva ntages of costjli-situ cuocrcie pilcs

)il (ii)

(iii)

lir) (v)

:

t tles ot any size and length rnay lre consnrrctecl at the sirc.

iffi;:'

precast drive-n

pil.s, rl,"r"

i,

no;ffiil'f

danrage

or problern or

Suitable in location where vibr.ations oiauy type or noise are to be avoided. Suitable also in soils with ' cosr-in-siru pires tike ura."r"o,,,"J'pi";;;;;;;;';;**, bearing capaciry.

p""r';;;i;;;;;;1ffi

44. Give.typical length and capacities of various pilo types, Various pile types, their lengths and capacitics are iabulated below. Pile fype Max. pitc lcngth (nr) Iifaximum Dcsign toad Timber 30 300 Driven precast concrete 30 900 Driven prestressed concrete 60 900 Cast-in-situ concrete 40 900 Cast-in-situ under-reanued 45 90c0 Steel Pile Unlimited 10000. Composite 60 2400 45,List the advantages ofdri

Pli;ffi ;,;:x,ffi:.,t:?fi l"ox,lliL,,""" ,tl, (rr) 0,,* are t" rir.--*q,Iir"n,"iii'ni" _;;

(iiD (rv) ("1 (vi)

lt"tT

precasr

piles driven in ueuring

capa"ityg#tll:!f,!"

(kN)

p,og."r, of the work wiil

|

be

ton,,oott the adjacent soil and therebv increase the

Thesupervision of the work ai the site is less cumbersome as the work is neat The spaoe for storage ofmaterials In places wher ground water isisless. al pressure, driven'piles can be used advantageously.

46. I-ist rlrc disadvantages gf drivcn precast concrcic pilcs

:ll

(ii)

(iii)

lffil"',,|nJ}ii ff"6**'"i"ra"'i"iii*r'r,stand

hancrins stress during

proper advance ,funningi. required for casring the piles. Heavy equipmerit js req-uirea i.L,

iranaii,rg'"ra,iilrirg (rv) be p'"di",.d.''fl; ;;ethod invorves cauing off extra .not ffi;T: }!:fli "outd more Jengths, rhis ieacls ro addirional cost. (v) ri;;;;;il;j;'i rvhere the drainage conditions u-foor. i"il il;;;';# f;"Jltrors ot. adjacent structures are to ji.ti"U"a, these be should not O" r.#,o,,, piles .(vii) Not suitable in,location whcro noisc is pruvefitcd,

47. List the disadvantages of cast-in_situ concretc DilcsThese piles auring instaltaiio^.r.qr,.rJ,]?rr"n,r ofall the materials used rn the

(i)

l;1,

, l:pe;"vision

and quality control construction. i,u;';;;.;" rvirr not be neat and crean. fl:,';:11?'J.Tt"^"u,u",*,. nctlon derived by driven pit"s ln cot esion. j!ri."*if . i, no, feasible here. CIi I305 - trbundrtion Bnginccr.irrg

t2

: r+,rii+:,r:'-,.:- i,;r ';: ii '-:..,ri'::;r'**uir*'**i'xai-;;tsii1vlaa+r}qri6x$;#i'{A'

(iv)

)f

(v)

constluction may be riiilic,it in iocation rvherc there is ground water flow or

artesian prcssurc,

Norr-homogeneity r:l.pile marerial rnay be possible due to segregation.

48. What are the uses of piles ? Transfer roads througrr son soil o'v/ater to a suitabre bearing stratum by means ofend beaiing of the piles (oalled cnd _ bearug pues.1 ,o1o:,1:-o retari,.,ery weak Uy ,.un, of friction atong the 1l.qjn ,"i: lengtll of the piles (callccl l.riction oiles.t compact granular soir trrus ;ncr"asing trreir density and in trun bearing capacity (callcd cornptrction pilcs) Tie down the structures to uplift due to hydrostatic pressure or ' ove urning rnonrcrrt (callerl.subj.ect upiift uii,;s). Resist large horizonral r:r inclinerl ibrces (calied baner piles) Provide ancrrorage against horizonrai prii ti.o," sheet-pfung werlls or other pulling forces (called anchor pii:s). Protect water fi'ont stiLrctures irueinsr inrpact from ships or other floating objects (called fcndcr piles and dolphins)

(t)

(iD t*rr",

iir

(iii)

'

(iv)

!"). (vi) . (vii)

49.

What are the_design proce.
(D (i0

(iii) (iv) (vJ (vD

!rii) (viii)

(ix) (x) 50.

Calcr.llate loacls

-

tn, other for settlement. "natl," soit stratinJion, -ana sketch the soil profrre or proflies ,tlo*,iint on trris ' profile superimpose the outiine_ of the propo-sed f*nduti;; ;;J;;&;tu;;. Establish the pennanent water level ani fiuctration levels.

DeoidetherypeofpiteandrlletfroO.,fiiiiafr"tt";.'''''.Dotcrmlne the lengflr of edch pile. Establish pile spac-ing.

Determini pire capaclry. Check streri in lo*"..t to. Analyse for pile settle[.]enr Design the pile cap.

W lt lhctors arc to bc r:ousirlcrcrl

(i)

iii)

(iiil !il) (v) (ril

?

one for bearing capacity

Size, weisht

i;;i;"

:

il

lhc sclcciiou of nilc

fff :::"11,;xi..:.li Il it

l,:, ?;

?

JIIjj*""l,, *

Location of water tobte .,,,i iri ri,"ir.il",i. "t. Types ofstructur.s in ttre ,lci,riLy oi,ir" ,it" or"onr,.u"rion. Environmentat conditions pr;;;il site location. Depth to which trrc pire rraiio rie

;;;;;;posed

r;il;.,,'*, ffXlklfl,i",'T,:ll,f*m*il l[; et:l|''* fiiii, (r,(., Llre span of.proposed pile

which the p,e has ro so

lcruntlation.

51. What factors decicle the

rh"

b"u;;;;;;.j;ji:

j:?[iliHJ,l.,:'::':#,::,?uctu.ur

st.ength of rhe pi,e and the.oiiona tn, ,,iruif", oi:ri.,],*o *nools the design load. The first criteria is satisfied when thc pif" rora lr'*.iri.t"i,Jo o, to avoid i,.1 damage from over driving' (ii) to avoid over stressing ofthe,rir. ,na"r,ririin toad and (iii) to avoid buckrinp faiture of the pire. These ru",o,=ilr*'L,rr.,; il.1l";il;?1 properry depending material and pire dimension u'a uo"o.cinjii on the piie irt-. ,rrr"t ,rur. srress ln a particurar type ofpile tne supporting strensth of

CIj l30i - Fourdrtiur [ngineer;ng

lo-s t t1

t

"-+;_+iis fixed 6y the code. lJur tjro supporting stl.engthen

of

standard

by rire second criter.ion .i.i.e.. the ;he llj;,i:-i:,],rii,,,rl"nrrcJlcd sort .nli:js :i:c

f.ili: ;:r:,te.ial o,. ,1,"

52. How a load on a pile is car.r.icC

?

:ed

l:)'s]'ir: lli:rion,

a,rrJ

:TF.it":FU:J'"';3['c:rr rffi:rli,i;il?:,i: r f *;li[lfii{.i..l:j,'li:['1,,,", Qr.= Resistanco duc to sriin vp l(cslstallue due lo point iiictlorr

lriction

-

Q, = Q, l (]r,

A. = El"Gctivc surface .:rea ol,rt,. ,.,,^ S,-: fl,*rrlf u1:i'l*".'ilif'1

q, = Bearing p.essure ofsc

Ap

- ,,ea ns are"

r-- average unit skin "rr,,".;?111il"'' friction or ",rl^.;^.-

,'j",,:i,ffi

iill,i

"o,.,rr*.iirr

r

oanry]y rhc resisrance ofrered

ffi

by

g*rrr"L:[*x

soil along the ernbedded shaft length

_,

fi,fijllHl,",ffi ffi

:,ghbearingrheu,,ima,e

Values of K arrd reconrmended ""t" by brous and used. Meyerrcops varue ofoan based on angre be used which is "rti.].ii"r.

ffiT,$;E:}ffi

ft;fr

iffi *T* ::r,,.ss

Ii;J:ilffi#ffi l,fi :,ji,rJ#i"itil":11i,.:,,,:.,':,;xffi ii;rY.ffj

is rhe principre on rvlrictr l,ilc-Ilriving fonnirta

"#r".rii,irr; rri

,t?;,I*;;:i j",i**

r*$*",*l,,lt***,****4*ujill,*-,,u

,i 1

(

(

Cl, I30j

-

I ooNdiliol i.:itginocring

t4

t e

Whcre E = driving

en$tliy. j.;.r-.ii,::,iif

taken as the;rile peneuaticr;:s (

.

., : ,..:. ,,:,.;.:;r.:ri

). i.lccor,,',,,, 1,,.,.';;

,icrn tirt lest fevz drivirrg hlow: ':.i,,11,r,,.,.i .or.,on,. c,r..,

is

C,= 2:54 x l0 ..2 ( ) lirr.rfu.olr hiiiirriieri. ,0.2t,4 r lt) 2( .

(:

)

56.

l

i

r

r

r; t

,. : r

i r r

r IrIIiiI;rrr:r.rl

Wlrtt are the limitaiiors ol.lrile tlri,rllg

,.,r ;;r..rl;c i, Dynamic forrnutae ay.e ori,t.,,i,, ,,,;;.;i;;, uf irirpa,:r of two tiee bodies. "b,ricc{ Bur oiie is not a lree bodv and is rcsirrin:rr drrc :c, Lr,: ,,r. :,.,;,:i,., soir r..,hich kcc rs on increasins with thc incteasu in deprh ol' pilc lro,crrxrio;; i': ,,i,,r,1',i,,,,"t'r.i uflccrrcirty about the rerati&snip betwe.n the static load fesistance and dyr.mic I"u,l'.".'rrun"r. Ari dle formurae are based on the premise t'at the soir resistaucc i"o artcr driving operation. This is to some extent true in coarse-g.ainc,l ;;;;';'i,."rr,,. formulae may be used "' ",L,uri,, ;ron_cohesive soils. Dynanric ur. not likety to yield usetul 'Dr.;,;,;;';,;;;;;rl; results in cohesive soirs "onr,-a",iii,deoosits. ,ll',i", yierd any information abour pile settlement.

.#;';r;,;;;"r,," ,"iil;;; i; .o;:.;;i".i;"

57,Explainabouttypesofh8rnrnetsusetIi']?)iiijijl'i\,i!tl, The most comnrontv us"a r,unrr",' ;. Tliis hanrmer is ,ifted up and tripped, falling freely on the cap block n,,J"rrr,rr,, ,,,*,,i,*a on ,tr" pile head. This tvpe of ',r"oi,i"i hammers are quite satisfactory ior.ligi;, *;.k: i.ua rorrrges are the srow iate of blows and length ofleads reqJired duiing .;;ii. ,,i;:--"*'"^ in.adequate fall to drive the pile. For rapid driving ani tr;ct er crfi";,,cr ,;r,gii'"r"il,5,. acting sheam h.ammers are emptoyed. In the single acting hirrnnrers, .h;;; is u;ed to Iift the ram up to the required height and rhe rarn aiops

ii,.:';;;I;,i,,;rr.

"il,

una"r

;;:;;;_;re

groJii;;;,;#iil"od

which pushes the pire inside. In the case of double *trg.r,u*r"r, iu", e'#ir,'i,ri;ig'"ird drlving process steam or air pressure is used. steam harirrners are more eijiciunt thanirop hsurmer,s t' but needs additional devices like piessure, g"n".utoi on;-i o.;;.""'""' "'"" .gas

llrrr

trfl [:.'-ffi _-,- i':;:l;.]: __ "vi!,pv,4.r,r!; l,Tl'll,x) l:i:';:'U i(.!i{ s \r-r (}. 1l.,.Ii"r lrg dffi' I tlr:j rs econOmicali'.compared hammlrS.

Steanr

r

igh,, havc to

vibmtory drivcr is uscrl irr t;ilc rlriyirrp tr Vibratory drivers arc. use^tl-.r.".',rr4 ;,, iiil rlrir,in6. lt consists ofa variable soeed oscillator having two counter-rotating ecccnrr.ic'*,i isilt,. rlhe ec"entric weights produce two unbalanced vertical imoulses.d,,,ir;"t,;.t -;;;;r,,i;"r,"'iii"ll r. ith the weight of rhe pile the downward impurse incrlases the cicrvnrv:lid IL,.,r, i;, 1,.,n .,1.'.-rr eq uency of vibration of the pire is almost equal to the natural ,iequerrcv .;ii;r,I,J,i,, ,..urn amplitude which helps rapid pcnetr.ation "ho,n,r"r, .. occurs causing high trf p;ii. V li,roii,:, jrave several advantases tvpe orha,inre* u;,.., t..i.,r.',;, 58. Hou,-n

;il;';;,.

i;;':i;;;;;;;;'l;;,il.ilf,irh

;iTi:l'"t#;ii"r

59.Uuder rvhat condition a poinl_bc:rrirrg pi j; i-r r.rrJ Point

-

#J.,lt:;

,.,

bearing Oiles nray h.',,

is ,virr,in a reasonabre depth ,,Jtr,r** i,i,5;i,";:i;iliff,lji,i,,:lixill ;:ijl ;,;;,:;;,;:",, :::;:'i,",ilfl-,":"Xii;'ir"-,.,.i,'1;,ll:0.rn,u,,,.'::i''. r.],u,,r,'..,:oi,l"'i'ffi[:i':l il:'r:Ti::

'ri'"poi,t-r,"o,iig'riti,ll,""il,llXli,.,,ljl,:'if:'l:l"lll":t,i:iidequrrcto,i,e-iJlir.ilffi""a: devetop ttre required capaciry

,, ..r;.';;;.;;i,-:r,,',,,'"'ir]',,'..I,11"ffi Cl'j

I :,i0:i

-

i:,,r:r:.jxiiojr Lnirir-ocrir)L{

Jlj:r|l:rr,,f*m

so as ro

I5

/,5,j 1,, l

.J*

::EGT

t. 60.Untler rvhat filcrI conttitions fricti'iii' piles urr'iii",i "! Friction piles are used when hard stra[urn or beti rocli is deep rvhich would require very long point-bearing piles. Tlre length of frictiorr pilc valics rvith the characteristics oi the soii, the magnitude of loads, and the size ofthe piirs, irrictiorr piles aie suitable in ariy deep deposit and in layered soils. In the case of cohesion less soils the skiir iiiction is computed based on the coefficient offriction between the pile surface and the soil. In cohcsive soils the skin friction is computed based on the adhesion factor between the clay oltire pilc sur.face. The nraximum value is iaken as that equal to the cohesion,

?

61,Horv piles are useful irr a sandy strBturii , lf.the soil prollle show that tho upp.r'straruln is a soft or compressible materiir overlying a lower dense sand stiatum, then piles are used io carry the load through the upper layer to the dense sand stratum. Ifthe soil profile shov/s that th? lnaterial is roose sand, p es are used to compact the sand deposit in o'der to incrcasc its riensity ar:rJ trenie its bearing capacity. If sandy river,beds are objected to scour, piles are used to ourry thi toad oi ttre super structure to dense sand layers below the rnaximum depth ofscour.

(i) (i,

(iii)

Explain the bearing capacity of piles irr dcep cohcsive depositsj deposit pire deverops friction a[ arong iis surface and acts as a friction Il a.deeq-cl1y -. A. t,ctron rre. pile in a cray deposit is supported by adhesion between the soil and the surface of the pile. Soft clays came in direct conarct rvith the surface of the p e *a ir,, ,"y be equal to the cohesion ofthe clay. In stiffcrays, usuaUy a gap "arrirl"" is criated between the soir ani the pile surface. Thus the adhesion will be less ihern that ofti'e cohesion oftho olay. 62.

63, Ifow an under reamed pile is construclod ? under reamed pile isconstructed by making a hole ir': the ground by making use of .'hand An a operated auger. An under remernber dcvicc ii then lowere
required depth' The under rsamer device has sha'p oiades and when pressed tates the shape of a bulb.ultimately and is provided with a i:uckei to collect the cut soil. If is pressed aow,i ana rotated. under pressure, the blades open up aird due ro rotar] action, the soiiis cut and falls in the bucket' when the bucket is ful the Jnder reamer is pulled out and cleaned. The under rgamel i-s lowered again and the process is rcpcated, After ihe urtirnate enrarged end is rormea, the reinforcement oage is lowered and concr&s i: done.

64.What is an under reassured pile ? . Under reamed piles are ofbored cost-i*-siru and bored compaction concrete p es with is rermecl a ,bulbs or una"r_oiu*. rhe bul6s'p;;;J;; ::lT.g:1 :ni1c"d baseil aoequare bearrng or anchorage. An under_rcaineJ pile ruey have one, t*o o. *orc bulbr, accordingly they are referred to as singre, doubre or m uiri-unter-reamed pires. under-re.med piles should satisfy all the design ,"qrlr.,i.,.rtr.r,' n.onr.*tional pite. Under_reamei pll*;; used,for a.variety of field applicatiorr, ru oirraiu acte,;,,ate'caiacity for downw*d:il;; and lateral loads and moments as in traninrissicr, ".g., ,otr". iuiiniu,ion, to take the foundation io d€eper stratum in order. to prevent the effecr nt",.rrurri'.t .ffi as in expansive soirs, to reach trrm strata and to take the foundation belorv :i;urrr. Iei,el. .

lT_:-]t

65. lVhat is a pile group ?

Driven piles, when used as a foundction, ar.e alli,lys uscd in a group. This is to ensure that the structurar load of a coium. or , rvirri liss. wit'in the zone of influence of the CE I30i

-

Iirrltdatiotl Ijogiricr:riog

l6

I foundation. A rninimurn of thr gurroll.ii) 'r:{j(i llthotrgir rirc lord rnay nor dcmand the ol tlrlcc Pilcs. lluikliIu .::.1'l:: 't

tusu

,u;o..or,,,1:o,,j

r;',#,;#"l"l|l,,r"]i; i;,i;.;li:j,,;ll],,il$:i*.,*;:llfil :lr"-iir.

that rhey are symmetrical with 1s5pss1 ro trie road ;.".. centroid orthe pit".rp. rr,i,

."r1,X,ijfi:.:l-

",.

,;;

.r *ting

;;';ii*"

roarJs

of resurtant struct;al

coming on the pire are

66, What is a.pile group capacity ? The pire group capac-itv is-not

ln

rnE

the surn rcrai ofthe individual pile capacities of the piles group. Soil disturbance caused by pil" i;;,;lt;;i;;1;;,

between adjacent piles, inav *dllT ffi,[,,J:.,.rr:1ir:'#ffil:f:]i: capacities' other possibiri& is that lp;;i.,; tie ."ir r"i*"",, pir"s may get deunfied or with adhesion and th" g.orp rnay tend to behave as : LTf:.-"d

."*_, iriiiii*r

lllclrlyr

strow rrishei

s,;il ;+rrry:

;;;,"#J[,:::yJ:T:y, l, t]:l

Where

q, :

#rir"'r?i;,,T"::1ff:fi:;,;ij; ltrf:,i# :*i,:[l,ff i;o ], ;#:fi[#lf,i #::;:i#

.sp*r,,e

;lli

number of piles in a group.

*nfijflTi}j"3it"fl,'""1-"^::::g":ed i, rreciding ple spacing ? iviir,,uffi,iff:Hfi:"j;;::ir"j'XJr'ilJi'.lriverop-ed in the soir as resistance :u-Tr6 "r"c":.rr"ry.' rioii"? to_u,oia ;h. ;;;,k,; il;,#i,l;,1i.".j;iL.:il"ol,f"fl:XJrXfl

'' wiu ov"irai.

l}if ;fr:l',1ilff ,T"f i' i: ""'1""0' *" ii' pii " i#i'J' ar"*"ii.,p."i"e;i,il:,ffil*-ljf;iT:;lff lil.t:i1l1J.1tfi i

it:-f;ifi,iiIllfr ti:i,:j,,',1#::u..f #jill$:"i{*iilii1,r*,,,**t#iiL:#,},.*l":,8};;,,: -vi.Pqv!'url Jnraller spacing may also be when negative skin friction

exisis.

advantageous

67, What is a pile load test ? The pile load test is the onl.,, rtir-^+

*^.r_ r .

,

-t-:i*r,l#** lt*ffi *#+aft rtrf,$,*,tififfi ;'J,i:H,::l,j:HlH;:r,10:1."J, ,*,ti*r pll *'.;;u,""; L,,"',, road test is

"ona,.t"Jio

l'*:irti;:rhg""#,lr,,11ffi ll,l,ffi i#Ii:,lim*f#t1;tif 68, Distinguish. between a test pilc and a ryr.rlkius uile .A test pile is one

superstructure.

whic

r"ri rii"r'.,:Jlllt,

:

used in the I":rJ icst only

:,*:,Jr.5j:ffi x#11{id:1T' j:#31ur CE i305

-

j*t,it,:*;ffi

Foui:cjalic.-r

ii*

ar

;#I: jr[J:{

hgirecrirg 11

165i

!..

t'

A t,,/uriiipr J1:i. ;!.-,tj,. ,,

^ rr..,.in :i\rtcr srrrrciur.c. j-1,,j !1,i, I,,,,;'1,};,'

;.iii,,;.1 ir,r;r,L,ll)(:r'piles ro car.ry load ,l ;..,,;]. .f:f ,,d: dicj+rl one anrj halltimes rhe ,",.,''..], : .::',':r:

.;,:

e.sijnilicli jrr'e !ca(; ,-r; r;:.i. ri:r: icr:i a:

,.., ,,

l

srlrglcpiterr)d40r;:rrr:.rrr(:,or;;..,i:.,;:,

,.: .,.j,

1,.,,,iri..,,1;r;;,rYatucol"l2rnrnforar

,ir, ', :,i, "')l.l';"J'l:J':li:'il'i'1"""11.'l:::r:r:jr:'.ij ''li'\rwrure ioiri': ': rii'i":i i''i :'';

,iic ii,;rrr-s,:rirc:ncnrcurvc ? il:.' l"::i: .,',;,. n Ll.i",-ing -filrn a pile Ioad

ret.re,nfri .,,iu.ll'r'v (i)

(iD

(iiD

The^straighr portions of

thr; ;.r: "..'.:;t ciLt'tderj rind the irltimate load is found. A iactor ol- sa.ferv ," ,r,, .,.....) .ir( ire s:lio load against shear failure is dclcrnrincd.

Two+hirds of the linar

.

loerd at

"vrric'

th$ iotrii dispracerrent attains a value

Fiff1,_percent ofthe finai ioad a1 t'" rotal displacernent equals I0% prle dra:r)etcr in casc ]);]:"ii piles of urrifo:.ir, (llrlrrr)j'T or'7.5% of bulls o1'undcr-rcamcd

;il;r:'

70.

""""""

of

r

(D

;,1'"ffi il'"',"

ofthe

? ,ffd::t5*i"'i;;J:'ii";i;*;*iffi;1i,j J;;fll,

A cohesive fi

":kilfi'u"t' u '"#f 'fi:';"T'l':H v\4rsuuu'*es ple is in process downwafit f^,-w!rl1 tlme with time and during durino tt ' ,-- , :": li;::;'::ll '"*l'and this (ii) e,on-.or,",rulx111a*#:td1filliffif;:' 'il;;J:H:Tl,'":."-1t^?31*ir: a

a

ins0arred

:^

Iaver and a pire is insraued in ro the overburden pressure

such a meaium.

(,ii) ffi'l;##il::l' " ;;;,;ii;;''#iil"T;.1:' j j::,Tlti;:i,iil",.:,1,:::_fl*::,.,1,?j"":;:$_"ffi "**;il;r,;

,r. r"-1,,,,,:rj"l]lr, ioarled pircs a rc r u :r i-r strl : !aill(t toads and seismic t.lr.^-;,. , ,...i,-,

#"enective

.

in rehining wail and l",Jl?"",ljx"if..f.i,l,i",i;:::,*:;;j,;l;, ii::j;llll..*,,*,,t: r,..'.,,,= rer.l ioacls and momenh

on nile n".,'.tr r;,,,ili r',,:';:r iesist arty Ioad in bendinq '':"^'.:t,,'lor ro*'ol resrst load and moment i, ""dlii-xbld' Pilcs are th" us'"tJ ti "in'*'it""i'"'l o' resrst lateral loads t o"t"u't' vertical piles can not l31'l:*in' but or,,,".i:l':^i? ,nli p;r"t, c,:iir-l ""''io'' uonveurronar approacrr *s'r,li*l'[f; i. ;".J,1.:::1 -..,_alasric, nelv r,,,,,,.;.r"i,,u*j"lrjpjil:,ij:fil?j.rfj",i:fl:;*:*: inro ano rhe soir reacrion ro

,,,."

'1.111b':it

use.

,, *nflr*I"":

understand by b:rffcr ;:itui

;;"rfl[l,1,',i,!:ffi"iil

y,::filt"t

.r

lill, iil;;;;] ?::ll 1:r pcr pi,c, i, may be more

ffi,-qffitr+--*ifi$**;;ltffi C

ij

j :ii).i

2

biur.t.rlr..r.

What is [egative skin I rt'hat ilet
3iffi

-

- Ioi;lii::rj-rl ril.r:ri;;"",,r, I8

_=-rr-

-='

i.;"'

What are the.requirement of I pilc r:;, ,, ; rttes are combined h" n grt] at tic ro;,'r,,:rel, is relerrcd tu as the pile cap. pile r;uos are most invariably nrade oi rciniorced .",,"r.,. i],,u"."rp"i, a"rign.a as individual subjected to the corumn loads prus fioting tm risir'rr i" o],. ""!, ,ra the soir above rhe cap. Under " concentrated load alr pires in the sanie gr.,-"p ,,r' ,,..r,j,,,,.ji" equar 4xial loads. Embeddeo plle cap contributes sienificruitry'r1,," "r.. {br ri e p;;'.1 , piie group stiffness is increased by 5 to 15% when the pir-e cap rests 1."fir. in conraci ,.,ir;r i:re soir-anir.also the.settrement is reduced to l5%. Following are the reoommendatic;:s by ,,,r,.f" Uy i.i.'ioa* for a pile cap, 73.

rd a

(i)

t.

(iD

s

(iii)

!iy) (rl (vi)

The depth of pile. gap shoul
anchorage ofthe column ancj pir" ."1,lfoi""*Jnt, shourd be ,igi,i l,,ougi,'io a-i;ibrrte

3-r I:l "1,equitably. tn a group The ove*ani ofrhe pile cap shallnor.rnally

,re

necessary

irnposed road on the pires

be 100 to rhe pite shoild p,;j;;id;;;;r',r,"'JX.l'".,r," 150 rnm. The cap is cosr ovei o tereti,,g * mm and rn rhe casc o'rargc r:ap, *r,.i'Jiritr.,,,i.l'riiii-rriii, "or., "iifli.rir.* "f 75i,r,iv'Lr ii:pose
should be given.

"onr"qrJnti;i

;;;;;,

74. How

will you estimate the setflelncnt of :i trile sroun ? orocedlre ,r.,ri if,"" pill'g.up acts as a single large deep cassurnes foundation.such as a piie or.a raft. For end-bearing pite-'iroup the load is assumed to be applied at the pire tips as a unifonn toua or..,r," ur"'of ,f,;;;rp. The stress distribution berow the tips can be evaruated using the ,pp.o*irioi" :o o;2,;-.il., distribution . For friotion piles in olay, tho load is assumed," u" ,;;f;; ;il;, a depth of about two-thirds rength of the piles. rhe 30 0rar "pifi"J ". " - - ----- the "..i aisiiruuaoi

A widely used

i.;;;;;i;

iy"iiri*

r"*.r.

75. Whatare the cqllses.ofpile group settlcrneat ? lret'ement ofa pire group is due to the compression of pire from the loading prus settlement occurring in the soirsupporting ihe ,i," pil.."Th""toiul ,.ttr.-"rt rnay be attributed the pite. The total settlement mrv ue-attriuuieJ;[;;,;;;*;auses : (i) the axial deformation of the pile, (ii) the deformatiJn rr,"'r"ii"ti"r.,"",ir" "lr"Il,i*face, (iii) the compression of the stratum below the tiDs of "r

the.pile. rf,_ ,"iif,i1,r.r,r"iue, to 1i; ana (ii) are very small

f""tr'f[",::?lT;;:i#jr,1;r':.t;-;",;i;;'i;ri;,'uTi,:"ij,,t" expressed as the total

and

evaruate. Hence onry the -vxvv v,,r L,,E settjernent ofa pile lroup.

76. What do you understanrt bJ a statc of pltstic A mass ofsoir is said to.b€ in a stare,ir"i"rti"equilibrium ? ll,,irii.-irm when the stress invorved and rne corresponding strain a.e within erastic i;,";,r.

.

plastic equilibrium.

if

faitrrre

n-,irr., of soir is said to be in a state of ir rlrou, tn o".,rl';;,,,,i,i;,';;; at a, points within

this mass. :Hl'1ffi':,:i"AXJ:;'ff:i},::r'"rv ".,"*:u"" i"'i"il;;Ji:."",. -Normarrv, the yierding on tt" *tot".,,urr.'}",;#;l:::1"':lll"u.^t (bricl< fill) produces.flailureo;1;l;Jilili;i

l,:,,::ilt[kff

orpurti.

;:;jffi l tl*as;ffii#r:

il;;-,:il"j*1,U"':J:,",:'[:X#11']#fi,fl a part of thii Inass undergoes failure is ierered

"quiiiurii,."*r,'vrr

CE l3C5 .. Lb{ir{taiion lr8inecrirg

;.1,,"

19

(/-l-

":*+€i

7'i. lirplair the effect

,#;+--.€

ill']lllil,"."::"1i1displacernen,.s.

If

t'

rvali

ot,

n wt.u o wuri-;.".i;i;ffi",'""J[,:iljl,' '.l.'' 1It:'tirrr ]:

ril1,,;;;j,,.;,,

"s:;:,)f.

,l;l:',,,1,;,1,^,1-'l"r!.oi,"rlundthereareto

the wall

rolates or rr,6.r.,r... ,, ,,i:.i,l;{.:::].;:i ,l"rrr rire.backnrr, ,".,rting'r;;l':;,"T.i,:filll;_ il:,. f)1,,,,r1., !vl:!ii il'i(: t'ull shear

*r"l,,,r', l;10.r.:irvL'presslrre. i.-,rrnirit",,,l

the soir mass in Iaterai p...uu-r" i i -. ir. r,lr", i.1",':: .;::.,",,.. -'ii...;:or;i;i l.erlsuio lbr rt ;.

.r*"

',

"oniiiionlJ*lf"O

Onthe otherhand if the rvall jr:ol,c:i ,

.

,ar'ue

ilX,,;;:iiff..j,J'axi'num

,*

i

i

,

, i

ji.

;

,:

;rr

. jij.

*:r,*

;;":i,,;;.;i,:;i ;,,,,,';,::'il;'H,I"'j*lll::.i:. :ic ;t>; rhis condition is called

the

'78, DcfiIrc

ro nl

Farth Pressure :lt rcst. ln tts nalufal stBte. atn eiernenl

s;l.min

-

the elertrgit

ol.suil i:l :l ii,jt1ji

r,"1

tf **i:*:;',i+.r,11.1,:ffi:;i1i;nffi i,nr3T"#,,ilpf, ry rrrrr"tJliitl"rl::"illjr''

infinite exrcnr

"t*nn';rtj."r,l:lllr;3;t'ntest""atresra^ri

i'rt;r i:;

irorr.zonhi directio^ and ar rest condition,

ir;:1-,

1;,1-:.islioarrcriscalrcdtheco-efticienr

79. Give.typical values of Ct I

heoretically the

of ''",'irl' i lr t r';r t j: , i c"-";,"^1*'.t-'i ucrenf of earrit tl:.rr.,I; '

. .{ proper choice of poissotr,s ratio lir,. lili rr:):l 1,.1s

Soil

Ko

berorv.

Typc

Loose

it

to

Choice is^no rvuv r,""-..,,,1,i,i"nr:,ntade' ",,i r:.,,. ;iriJn,l.o,i.iJ'111h '*'tres orr" our,;,,.,i

;:i'i;.*[:"J1,::'"ffi.'# -"'-

given

rc:i r

c i,i, ;s gi,,,en try

Sand

0.4

ii'il.rllill,,ll

Dense

.

or rorthe soir

Sand "

..

srn,.i ci.)riiliiri)i,r,:i , r3i1;r ^.....

iI layers .

;;"'

ffifltfi##f;iffi

Soft

clay

0.6

f

}Iard clay

0.5

r;ir,1iilq#il,ii#ifl$t

CIi l.lC:! - :;ruri.j,rilDrr li,giii.,..r.irU 20

-====-E

t If the same wa, moves towards the.soii, iir o.crcr to maintaih stabirity the resistance and.in this process soil wi, ofrer of ollerirg ;,.;r.;;;,':,,,riitt aru"top due movehent of the wa, ( o. to the inward ..hir.:.io,, ; is calted the passive earrh pressure. This passive pressure is more "_p"]t_.i.r', ttrin

to

*".li"ill,

ed

is ie

d

tf,",,"tiu. fr.lrur".

,-

81. Establish relationshins between vertic:i!

:r.d iatcral car,r pressures at failure. Mohr's circte reorlsenting trr. rtut. or: rill.rrJJ,. i,,,.'JJiroi,r* is shown in Fig. point the srress condition-ar th. tir; f-ri;; l-."p::."nj. tiu.e plane inclined at an angle lrom the plane on *r,i"ri in" ,u;o, ";: pri::cipal srr.ess

I

;;;; acrs.

^

_

The radius of Mohr,s circle is origin. From Fig.l

ard tl']e center is located at a distance

trorn the

Rearanging Where 82.

List the assumptions made.in Rankinc,s Earth pressurc theory. rhe soit mass ir."mi_innrit", cohesion less rhe ground surface is. a. plane, or incrinea. The back of the wa, ii there are no shearing stresses -ii,r,,"r between the walr and the".ru.oi backfi, r"ir. i, *ords, the stress rerationship for to the wall is the .urn" u, io. ury other element for away irom "Oj""ent

(i) !il). (iii) (iv)

io;;;lr:fi;;d ;;;;;;;;iiltar

,ri'.,irfri:"'il

ffi;fii:*r

The walr yields about the base and thus satisfies the deformation condition for plastic equilibriurn.

83, \Ybat is the significance

ofthe as,sumptions of smooth wall in Rankine,s theory, In the Rankine's theo- tne warr is That is there are noshearinp stresses acting between th€ srrac" o,,ai;;;ffiflfi practice considerabre frictioi may be developed on the wa, material. Rantcin";;;l;;;;"ll assumption results in an overan

iss;;;i;t;;il#.

*r,

fi1XT:::.:fi:1,i",'#1ff:':::lo tne safe_sia-e.

"i*I"

d"p",i;i;;';"'ii,;.,,s,irud, orthe wal

and under_estimatioo of pas.-sive in rnaking this assumption

""onjltjllolved

""iX;'i.'i:;:[9Jfij:[1li't'c

*"rr i.

extenr

ii;;.il;;"fr"ssure

design based on this is no,

tn

ilii"il

prcssurc

potii;ffir',["}u,.;Xfl:"fij,ti'"

= lateral earth pressure = Vertical pressure on the elemerrt

rriciion.

G;;;, ;;i#;;

i, tig"lii..ri"ra ,r,.

orr

dav or moist cohesion ress backnrr ? orplasLic eqtrilibrium i'.""-urir-niJ*t", g,"

F*

=

CD 1305

-

I:oundation

ll

ginccring

i/ -)

I

":,

,,

The tttal active earih pl.essuic tnanguiar pressure disriil..rition.

ira

{ Fig. 2j ,icr l,r,ii

le;,gth r:i rlre r,,,all rs compured from the

actilg at i{/3 above the base of the q,srll. For dry backfill .use

and for. n.roisi b;rr:iil,ill

85. ltrow rvill you comDutc thc acriv. ^.^.-.,_... oI'a sub-ntct'gcrl cohcsiorr rcss backfis rhe u-e coinput'-'d i:sing Ilarikinei subrnerged *ith

J,i;-;;;;;;:'ll'"',:i]tn'ou*"ru i';in ';";;;"'ii,; ;;;;;;;il; J:[;?""' ":'#]: |:|'ifl; 5;;,;1

.

/ ? Th""t:-'H;; Ii"i.lm1 i,

i1itpff[',,Ti"::.iij;:f,,

m

Thus the pressure at the base ofthe wall. Then total pressure.

acting at x above the base.

vou computc tlrc p:rssive prcssurc of a cohesion tcss backfllt with uniform "'f;il;x*":"t Using Rankine,s the

.

[":i,li1tl*l;.{i#f },;/r;:lillri:,*,,.*,",'i,:iil::ilH. lffi l";',T'..'"1:f q. q . The increase in latera]-earth

pressure al rest is ko

-v

Hence the lateral passive pressure at any deptir of is given by,

At the base ofthe wall, the pressure indentnity is given

x

(Fig. 3)

acting at a height ofabove the base ofthe wail ( irig. ,i)

the pirssiy+ Fr*r;:iril'.j nr' :r baclifilt lyirh rwo rrifferent dry lJere ltankine,s earlh or rsr:ri. Jil{r anct l'i is the angte rr*.rr* ,".irij::t-t1l.:.:il'ber':spc('iiv; the height ofbackfill' then carm pressure"rcoefli"i.nt. ,;r;1;.'l;ire Kn' & Kpz are the passive rr;,".1.i,,, i-tl.' wnere is rhe unitweightu.r,l',",."^t.irt.ttre witn t't" soil iaver i' r''iii""'" l- J#rj'ojifisu'lnarse ";,i1':']:g,igl,t,"r'rirr,

:l;,*ffii=!:.,"1",Ir0'i"

The p'essure ar the base,, Ia)rer. Thar i,

pp;i#;;

or" to rveight. ol firsr layer piris i""

rhe la[eml pressure due to second

Then total pressure po is given as CE 1105

-

liruriCr,tion Eui,.irreei-irig

=r, -."':

I

acting at x above the base ofthe rval! (Fig. 5 )

88. What are conjugate planes al:d corjjirg*tc :iticj;i.rcr: :l In finding out the active earth pressurc iir' a sl;1:iug-; baokfill by Rankine's theory an additional assumption that the verticai an<] l;rtar;rl .iir.ss.rs arc conjr.rgate is made. It can be established that if the strcss on a gi.zen pla,c aL ir givun poirrt is pai.allel to another plane, the stresl on the Iatter plane at the san're rrcilt n'ritt t,;:--prr.llLi to thellrst plane. such ilun.i u," callsd the ooniugatc plancs and thc sr.resscs arrrirrg r>ri riilr.B ric calicrj conjugate stresscs, 'ln.l'rig. 6 ,_[, anrl aro conjugatc sllcsscs anil ihc p,ilurrs on lvlricir these stt esses are acting are called conjugate planes. The iatio = k, is,":aiicci the conjugate ratio.

will you compute the acfive pressr:re of a cniir:sive backfill ? As per Rankine's theory for a srnooih, r,ci.ticai vllll with horizontal cohesive backfill

89, triow

for an active condition is

Frorn the pl'incipal stress relat.ionship, substirulir),r

Thus there is a tension at

90. Explaln

crlticat depth

ji-,!-

lve have

and decieases to zero at a depth

ir

a cohesive.fill

:

,

As per Rankine,s earth preisure tlreory under aotive condition, up to a depth of soil will be at a sate of tension, where . Thisiensile ,Gr;";"d;;;te"

, the com.prcssive stress equal to a dopth

smaller than

Hc

of

. Tliis meani that,a vertical bank ofcohisive soil should be able to siand without any fut.rul ,rppoJ H"-i,

called the critical depth. This condition is not stricrly irr"-in p.,,"t"", ,;;;;,iil;.il;; against the wall increascs lronr a valuc of whereas on a vertical unsupported fabe ofa banl.. thc norurll stless is zero at every point. As a result, the greatest depth up to, which a vertical li"na" rnrupported is a little H".

"u,

"u,r

less than

For a saturated clay, the angle of internal {iictioii is zeiu and he.ce = l.Then H" Thus the sreatesr depth of which-a cut ,,ii,i,irt rot".ur support of its vertical sides can be slightly less than the critical tieprh,

; t;;;;;;;;;

:

I.1".

How-willyou cgmlru.te the passivc pressrre ol n cohr:;ive back{ill ? rne case oI passive pressure .rn the rur antj . , Substituting these values principal stress relationship, 91,

we get

Hence the total pressure

p, is given

as

The pressure distribution is shown in Fig.

Clj

i. 1305 ..

lbxrx,ill:0ir l.:, .:::\:rr-ide

k-( ii

l:,

"::'"'r:fi q) liil

:Ht,i",, j[i{:1iii","1,,*;;l,J"Tl,ffi .,, The soit is isotropic and f,o,,riogol.;l;".." ','. il:,li,,ilfl

r{

o,,n",n"oo,

c

The soil is dry and cohesion r.i..'--'11,,.) I he ruprurc surlace is a plane surl"acc. -'"' The failure wedge is u ,;ci.j Uo,lu. I he lressure surface is iplnn" r*f".". There is wall fri"tio, o,iti"llor,r" sI."A*. Faiture is two-dimensionat.

!iO 1yl !"il lyjjl ^^

ilf;XllT*'to" "#ii;Iil: lf wall friction is considered

or^ear.th resistanc"

c _-_ a

irr

an-i,,^^,:^-

._._,

...r,, ,;.'oflil;:^,.::r:::::"_l l]i]!,pr*"

surface of failure unsafe values

;:ff :J,1?'J:il1,o*.'"ifjllj"*l:,i1"-;",ii"li:""'"",x'#ffi

:rl#'*#';,il};*

n:i*ir:n*;,ru:,,mT*J:l{,ti*:*:#:i[:..,J.,H]u:::**,.#fl ,0. *ni.,::J"^:_understand by arching in pd,r or a suDport retaining soits ? soil

yields whita rnass y,"rds while rhthe

posirion, the soit near ,t

,iifair" part of the suppo.rinoves i.l"ti"" nro"#"";;,ffi. vreldrng "r,i,:F,i:,:.::::._. is opposed

surrace ( or

o d

assu*ption orp!anc ruprure surrace in couromb,s

by the shear

,;;;;;, jo,'::;;:^:?rr.

ilt

.--. of ^r:.ir remains in res

riom its original position, The

kansferof

pressu;i.;;.jffird*xr*:J*.,mJtf:f

'*''ufff

:ffi

?:,:il,::"$Trii:;ii:.ff :

l:n:.;t*x*,r"t*:r:1,:l*d{*g:1",.ir,*Hil;i,":,:::;

waus that yield about rhe lower and rather than the upper end. 95. What are retaining

9

structurcs ? Jlructures which are use.i r^ h^t,r r.-^r_ , hold back a soil mass exampres of retaining arr ,,ru"rj::1l: excavatloll.!3s:meiit '"rining wars, _

"' *''

L rr

ffil:iHffi.'i5f;:ffit1*:,il:;H;L,]H

:1T,*::ir']'**ffi1,1?TJ:,il:':fili!ff f;iiXlX::.I:: ilffi il: :l'Jl;::il:?"i",iil"1#lt :,r,mili

a

at differenr erevations ,in

tt

ilt#ii::iii{t!;;,;*.lln ( Fig.g Dunressed types

96. What are gravity-type rctaining 'ryalls

mn-* ::i, il""','J:;

97.

,

1

ar

[i*[:,,."Tul;ifi l#.]iiftt;:in:ilt'*:ii

IIow will you proportio

a

c

).

:rffiffii#Hil*#t"#ffiffi

Massive gravity walls

fl

?

T

gravity-type rehini g rvili

T:i:t?j

l;:,,r;f;

j,

j

c

( t. h

c

E ?

CE I305 .- louodation Engircering 24

:.h

i)

'1ljJ,]. i'rr iii.:'':;:

,

::

!.,':

A prclinrinary dirlcnsiou h s to [;c .sr;unr*rr jirr lhc dcsign oIa rotaining walr. .r.his is rcl'crrcd to as proportior)ing wrrich crrabjcs rt," .t".ig,,.* io ,r"cid-c trru basic wall for analysis. If trre uieriminariry serectcd ".r1rr"r",,,, ,iii,i.".rrr, "rin. '-nigurenot satisfactory after stabirity checks, then the'sections are modifiLd, un,r , sho vs the dimensions of various components of gravity-type walli i.or pr"iin,inury ".rr".il"a.

,*

.j"ition.

.

l

The top width of the stenr oi truy rctaining w.rll should not be less than 0.3m for construction activities. The bottom oithe base c,r tr[ *z,ii Jourd be berow the *""ir,.iJ and in n. case less than 0'6m. The counter fort rt;;dr" have sim ar dimensions of that of cantilever warrs. The co,nter fbrts sha[ b" of il.3r; are,spaced at cenrer-to,center distances of 0.3 to 0.7H where H is rhc heighi-rii;,. ,.irf ,lire *^lf .

Jr

;r.t

ii;;nd

98. What are.the

stallility require.ments of t gravity t1,pe rctahring wall. ? The following stability conditions should be siriified: _.. The maximum base-pressure .rt the roe of thE walr should be we, below the safe bearing capacity ofthe soil. As the materials used for the walr cannot take tension, and the same shoura not be allowed to develop in the base dr arrywhere in the. mater.iat. In particular, the base pressue should remain compressive over the entire base width. The walt should be rur" ueiinri .iioi;; .i,r," wa1 and the soil below. There shourd be arrequate safety agai.st over turning of the wall by rotation about its

(r) (ii)

(iii)

;;;#;,il;r,

(iv) . (v)

toe. Ap-art from safety

oftlre wall against the above fbu:.facr.ors, the rvall should also be

salb against overall stability. 99. What are the requirements

-

Iateral

ofa backfill material

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Baokfill'materiars for retaining structures should luve a property to transfer a minimrfr pressuro

on the

wall. A'g;oJ;;;ffi'li-ilu,Jriuiui,orro cl**d;:-

requirements, viz., high.long+erm streiglh and free

satisry two importBnr

general granular materiari make the best typc of backfifl sinci they maintain indefinite Cr"vL"iff f r. tend to creep. Further it is susceptibre;, r',""!rriuur*utting ano shrinkage based rrn the climatic ohanges' suoh soiis shoul
active stat' of srress and have free drainage.

ir"r;;;di;;';;._";iil;;;

100. What are.the joints provided in retaini[g walls ? A retaining wa[ is provided with construction,l0ntractio* or expansion joints. construction Joints are provided between two successive poi," oi and are verticar ancr horizontar joints' Each surface or the eoncrotc "o,i"i.t" u"ror. placing .r.ur,i,t u,r,r ,ougii.".i the next pour of .is Alt.f.*ivety a key. is provided b",;;;;;;i,.d;;."" L.nractron Joints arc verticar qrooves orjoints, B rnm wi,e arrd r2 to l6mnr deep, provided in thg fac€ ofthe wail. These ioiits ailow,h; *,i;;i;;;;ri,rt'."i,ni, permissibre

l"llfll

rimirs wirhout harming the concrete. Expansion joints are provided to withstand the effects of expansion due to temperature changes' These are verticar ioints extencling rro, ,t . ir,,i. ro tt e top ofthe wa, and are filled

with flexible joint fillers.

CE

I:ioi

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Foundnlioo L)rgilN..rring

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