load carrying capacity of piles

8/12/2019 Load Carrying Capacity of Piles

1/24

LOAD CARRYING CAPACITY OF PILES

Load carrying capacity of a single pile can be determined based on:

(1) Static Pile Capacity Equations: These equations are based on parameters obtained from

field and laboratory testing. The static formulae are applicable to bored cast in-situ pile and

driven piles, especially in cohesionless soils

() Dynamic Formulae: These formulae are applicable to driven piles only

(!) Empirical meto!sbased on SPTblo"s,DMT,PMTand CPT

(#) Full scale Pile Loa! Testfor all types of piles

Static Pile Capacity Equations

The load carried by a pile is e$pressed in equation form as:

bfult QQQ +=. (1)

"here,

Qult% ultimate bearing capacity of a single pile

Qf% bearing capacity furnished by friction or adhesion bet"een the sides of the pile and the soil.

Qb% bearing capacity furnished by the soil &ust beneath the base of the pile.

The term Qfin equation (1) can be evaluated by multiplying the unit s'in friction or adhesion

bet"een the sides of the pile and the soil (f) by the surface area of the pile (As). The term Qbin

equation (1) can be evaluated by multiplying the ultimate bearing capacity of the soil at thetipbase of the pile (q) by the area of the base of the pile (Ab). ence equation (1) can be

e$pressed as:

bsult AqAfQ += ()

*quations (1) and () are generali+ed and therefore applicable for all soils. The manner in "hich

some of the terms of equation () are evaluated differs, ho"ever, depending on "hether the pileis driven in sand or in clay. t is convenient, therefore, to consider separately piles driven in sand

and piles driven in clay.

Piles in sand

The net ultimate bearing capacity of the pile is:

bqvsv

bsult

ANAK

AqAfQ

+=

+=

tan

here,

1


2/24

v % effective overburden pressure at the pile tip for end bearing part and average effective

overburden pressure in the layer for s'in friction part.

Nq% a bearing capacity factor based on angle of shearing resistance, andDBratio

K% a coefficient of earth pressure dependent largely on the relative density of the soil.

% angle of friction bet"een the pile and the soil.

The base and shaft friction resistances do not develop linearly "ith depth belo" certain depths.

This is probably mainly due to arching effects in the soil related to its relative density and

compressibility. t is therefore recommended that the effective overburden pressure in the above

equation should be calculated linearly "ith depth only do"n to a limiting depth (Dc) and then

assumed to remain constant belo" this. Tests indicate that the critical depth ranges from about

1 piles diameter for loose sand to about pile diameters for dense compact sand.

The limiting value of pile end bearing capacity in sands and gravels is 1/ 0mand that of

unit s'in friction is 11 '2a.

D/B = 20

D/B = 5

D/B = 70

26 28 30 32 34 36 38 40

175

150

125

100

75

50

25

0

Angle of shearing resistance, o

(After Tolinson!

Bearing

ca"acit#

factor,

Nq


3/24

"alues o# A#ter $S Army Corps o# En%ineers&2ile material

3teel .45to .6!

7oncrete .8to 1.

Timber .6to 1.

"alues o#K A#ter $S Army Corps o# En%ineers&

3oil Type 9alues ofK

In compression (Kc) In Tension (Kt)

3and 1. to . ./ to .5

3ilt 1. ./ to .5

7lay 1. .5 to 1.

ote: The above values do not apply to piles that are prebored,

&etted or installed "ith a vibratory hammer. 2ic'ing Kvalues at

the upper end of the above ranges should be based on local

e$perience.

!


4/24

AMERICAN PETROLEUM INSTITUTE 1993 DESIGN RECOMMENDATIONS* FOR

PILES IN COHESIONLESS SILICEOUS SOILS

Densit# $oil

%escri"tion

$oil/"ile

friction

angle (!

&iiting

s'in friction

al)es

('*a!

Nq &iiting )nit en%+

earing al)es

(-./2!

er# loose

&oose

-e%i)

$an%

$an%+silt

$ilt

15 478 8 1

&oose

-e%i)

Dense

$an%

$an%+silt

$ilt

20 67 13 2

-e%i)

Dense

$an%

$an%+silt

25 813 20 48

Dense

er# %ense

$an%

$an%+silt

30 57 40 6

Dense

er# %ense

rael

$an%

35 1148 50 120

The "araeters liste% in this tale are inten%e% as g)i%elines onl# here %etaile% inforation s)ch as

in+sit) cone tests, strength tests on high )alit# sa"les, o%el tests, or "ile %riing "erforance is

aailale, other al)es a# e )stifie%

$an%+silt incl)%es those soils ith significant fractions of oth san% an% silt $trength al)es generall#

increase ith increasing san% fractions an% %ecrease ith %ecreasing silt fractions

#


5/24

Piles in Clay

#cN!cs

AqAfQ

c

bsult

+=

+=

"hereAs% area of pile shaft

Ab% area of base of pile

c % average undrained shear strength along the pile

c% average undrained shear strength at base of pile

Nc% bearing capacity factor % 8

s% shape factor % 1. for a plain shaft and % 1. for a tapered pile

% diameter of pile

!% length of pile

% adhesion factor "hose value depends on unconfined compression strength, % 1 for soft

clay and 1 for stiff clay.

Recommen!e! "alues o# an!f#or Estimation o# Drille! Sa#tSi!e Resistance in Coesi'e Soil (Reese an! O)Neill* +,--&

Location along drilled shaft 9alue of Limiting value of loadtransfer,f('sf)

;rom ground surface to depth alongdrilled shaft of / ft < -

=ottom 1 diameter of the drilled shaft

or 1 stem diameter above the top of

the bell (if s'in friction is being used)

-

>ll other points along the sides of the

drilled shaft

.// /./

The depth of / ft may need ad&ustment if the drilled shaft is installed in e$pansive

clay, or if there is substantial groundline deflection from lateral loading.

Limitin% "alues o# $nit En! .earin% an! Si!e Resistance

7ohesive 3oil on-7ohesive 3oil

?nit 3ide @esistance ('sf). /./ #

?nit *nd =earing ('sf) 6 1.Nor 8 forN5/

/


6/24

To" fie feet

noncontri)ting

Botto one %iaeter

noncontri)ting

Straight Shaft

*eri"her# of Bell

noncontri)ting

Botto one %iaeterof ste

.oncontri)ting

Bee! Shaft

To Diaeter in stiff fiss)re% cla#

I!e"tifi#ati$" $f %$rti$"& $f !rie! &haft& "ege#te! f$r e&ti'ati$" $f

!rie! &haft &i!e re&i&ta"#e i" #$he&i(e &$i )Ree&e a"! O*Nei+ 19,,-

>llo"able pile capacity can be calculated using overall load factor often ta'en as . i.e.

bs"

QQQ

+=

or 1./ in s'in friction and ! in end bearing, i.e.

.!/.1

bs"

QQQ +=

The lo"er safety factor in s'in friction is because the pea' value of s'in friction on a pile in clay

is obtained at a settlement of only !-6 mm, "hereas the base resistance requires a greater

settlement for full mobili+ation. The frictional resistance on the shaft develops rapidly andalmost linearly "ith settlement and is generally fully mobili+ed "hen the settlement is about

./A of the shaft diameter. Thereafter, it either remains sensibly constant, or decreases slightly

as the settlement is increased further. Bn the other hand, the base resistance is seldom fully

mobili+ed until the pile settlement reaches 1 to A of the base diameter.

4


7/24

FACTOR OF SAFETY

(@ef: ;oundation Cesign, 2rinciples and 2ractices, by C.2. 7oduto)

The design factor of safety depends on many factors, including the follo"ing:

Te type an! importance o# te structure an! te consequences o# #ailure D

;oundations for critical structures, such as ma&or bridges, should have a higher factor ofsafetyE those for minor uninhabited structures could use a lo"er factor of safety.

Te soil typeD ?se a higher factor of safety in clays

Te spatial 'aria/ility o# te soilD *rratic soil profiles are more difficult to assess, and

therefore &ustify use of a higher factor of safety.

Te torou%ness o# te su/sur#ace e0ploration pro%ram D ntensive subsurface

e$ploration programs provide more information on the subsurface conditions, and

therefore can &ustify a lo"er factor of safety.

Te type an! num/er o# soil tests per#orme! D *$tensive laboratory andor in-situ

tests also provide more information on the soil conditions and can &ustify a lo"er factorof safety.

Te a'aila/ility o# on1site or near/y #ull1scale static loa! test results D These tests

are the most reliable "ay to determine load capacity, and thus provide a strong basis for

using a lo"er factor of safety.

Te anticipate! le'el an! meto!s o# construction inspection an! quality control D

Thorough methods can &ustify lo"er factors of safety.

Te pro/a/ility o# te !esi%n loa!s actually occurrin% !urin% te li#e o# te

structureD 3ome structures, such as office buildings, are unli'ely to ever produce the

design live loads, "hereas others, such as tan's, probably "ill. Thus, the later mightrequire a higher factor of safety

t is good practice to use higher factors of safety for analysis of up"ard loads (uplift

capacity) because uplift failures are much more sudden and catastrophic.

Table belo" presents typical factors of safety for design of drilled shafts that "ill support

ordinary structures.

Typical Factors o# Sa#ety #or Desi%n o# Drille! Sa#ts (Cast in1situ Piles&

Cesign nformation ;actor of 3afety

3tatic Load

Test

3oil 7onditions 3ite 7haracteri+ation

2rogram

Co"n"ard

Loading

?p"ard

LoadingFes ?niform *$tensive . !.

Fes *rratic >verage ./ #.

o ?niform *$tensive ./ /.

o ?niform >verage !. 4.

o *rratic *$tensive !. 4.

5


8/24

o *rratic >verage !./ 4.

ote: f the static load testing program is very e$tensive and the subsurface conditions are

"ell-characteri+ed, the factors of safety for do"n"ard and uplift loads might be

reduced to about 1.5 and ./, respectively.

The actual factor of safety for both do"n"ard and up"ard loading (i.e., the real capacity dividedby the real load) is usually much higher than the design factor of safety used in the formula.

This is because of the follo"ing:

e usually interpret the soil strength data conservatively

The actual service loads are probably less than the design loads, especially in buildings

other than "arehouses

The as-built dimensions of the foundations may be larger than planned

3ome (but not allG) of the analysis methods are conservative.

6


9/24

LOADING CONDITIONS )After US Ar'. C$r%& $f E"gi"eer&-

(1) Usual

These con%itions incl)%e noral o"erating an% fre)ent floo% con%itions Basicalloale stresses an% safet# factors sho)l% e )se% for this t#"e of loa%ing con%ition

(2) Unusual

igher alloale stresses an% loer safet# factors a# e )se% for )n)s)al loa%ingcon%itions s)ch as aintenance, infre)ent floo%s, arge i"acts, constr)ction, orh)rricanes 9or these con%itions alloale stresses a# e increase% )" to 33 "ercent&oer safet# factors for "ile ca"acit# a# e )se% as %escrie% elo:

(3) Extreme

igh alloale stresses an% lo safet# factors are )se% for e;tree loa%ing con%itionss)ch as acci%ental or nat)ral %isasters that hae a er# reote "roailit# ofocc)rrence an% that inole eergenc# aintenance con%itions after s)ch %isasters9or these con%itions alloale stresses a# e increase% )" to 75 s)al

>n)s)al

?;tree

20

15

115

20

15

115

Theoretical or e"irical"re%iction to e erifie% # "ile%riing anal#@er

>s)al

>n)s)al

?;tree

25

1

14

30

225

17

Theoretical or e"irical

"re%iction not erifie% # "ileloa% test

>s)al

>n)s)al

?;tree

30

225

17

30

225

17

8


10/24

Recommen!e! Factor o# Sa#ety on $ltimate Geotecnical Capacity .ase! on Speci#ie!

Construction Control2 (Re#3 AAS4TO Speci#ication #or 4i%5ay .ri!%es&

ncreasing 7onstruction 7ontrol

3ubsurface e$ploration H(1) H H H H

3tatic 7alculation H H H H HCynamic ;ormula H

ave equation H H H H

Cynamic measurement and analysis H H

3tatic load test H H

;actor of safety !./ .5/ ./ .() 1.8

H(1)% 7onstruction control specified on 7ontract 2lans

H()% ;or any combination of construction control that includes an approved static load test,

a factor of safety of . may be used.

1


11/24

E0ample

>s sho"n in the figure and no ground "ater encountered, appro$imate a$ial capacity of the

concrete pile if the coefficient of lateral pressure (K) is assumed to be .8/ and the ;o3 % .

Solution:

7ritical depth,Dc% dia. of pile % 1 % ft

Nq% / for % !/ tan% tan I(!/) % .#8!

( ) ( )

'ips1/5lbs1/44651/!18.165165.!5#!5

1#

//4/1#8!.8/./41#8!.8/.

/4

tan

==++=

+

+

+=

+=+=

bqvsvbsult ANAKAqAfQ

Qdesign% Qult;o3 % 1/5 % 56./ 'ips

E0ample3

3ame conditions as in the e$ample above, e$cept that JL is located 1 ft belo" the 3L.

Solution:

( )

( ) 'ips1!.#/lbs1!#/545#516545#4.18461464#

1#

/18!41#8!.8/./18!41

18!4161

16

tan

==+=+++=

+

+

++

+=

+=+=

bqvsv

bsult

ANAK

AqAfQ

Qdesign% 1!.#/ % 41./ 'ips

11

25 ft

%esign=

-e%i) %ense to

%ense san%

= 128 "cf

= 35o

K= 05 (ass)e%!

12C

0

20

25

riticalDe"th,

Dc=

20

128 ; 20 = 2560 "sf

2560 "sf

De"th,

ft

Eer)r%en "ress)re, "sf

0

10

20

25

128 ; 10 = 1280 "sf

1280 F 10 ; (128 + 624! = 136 "sf

136 "sf

De"th

&

Eer)r%en *ress)re, "sf


12/24

E0ample3

> 1diameter concrete pile is driven at a site as sho"n in the ;igure. The embedded length of

pile is !/ ft. ;ind out the design capacity using a ;o3 % .

E0ample3

> 1diameter concrete pile is driven at a site as sho"n. ;ind out the design capacity of the pile

using a ;o3 % .

Qult% 8.# K 1#.1 % 14./ 'ipsQdesign% 14./ % /!./ 'ips

1

35 ft

%esign=

.orall# consoli%ate% cla#

= 104 "cf

qu = )nconfine% co"ression

strength = 1400 "sf

= 0 for 07 tsf (qu!

12C

Solution:

c% qu % 1# % 5 psf

'ips5#.lbs5#16/.#8#/485

156/.85!/158.

#

==+=

+=

+=

+=

cN!c

AqAfQ

c

bsult

Qdesign% 5#. % !5.1 'ips

20 ft

A%esign= B

.orall# consoli%ate% cla#

= 105 "cfqu= 1400 "sf

1= 0 for 07 tsf (qu!

12C

15 ft

Eerconsoli%ate% cla#

= 126 "cfqu= 4000 "sf

2= 056 for 20 tsf (qu!

Solution:

tipfrictionult QQQ +=

'ips8.#lbs8!4!/558!8/6#

1/1/4.18.5111

11

==+=

+=+=

+==

!c!c

AfAfAfQsurf"cesurf"cesurf"cefriction

'ips1#.1lbs1#1!5

1#

8

==

=

=

tipctip ANcQ


13/24

E0ample3

> 1#square pre-stressed concrete pile is to be driven in a clay soil as sho"n in the figure. ;ind

the required length of pile if ;o3 % .

1!

& =

%esign= 80 'i"s

&AG

= 115 "cf

qu= 2400 "sf

= 076

14C s)are

Solution:

Qult% ;o3 Qesi#n% 6 % 14 'ips

c% qu % # % 1 psf

Qtip% cNcAtip

% 1 8 (1#1#)(11)M

% 1#5 lbs % 1#.5 'ips

tipfrictionult QQQ +=

'ips!.1#/5.1#14 === tipultfriction QQQ

Qfriction%fAsurf"ce% cAsurf"ce

1#/.! % .541(1##1) !

!% 67ft


14/24

NA0FAC DM24 METHOD

BEARING CAPACIT/ FACTORSH N5

(%eg! 26 28 30 31 32 33 34 35 36 37 38 3 40

N

(Drien *ile

10 15 21 24 2 35 42 50 62 77 86 120 145

N

(Drille% *iers!

5 8 10 12 14 17 21 25 30 38 43 60 72

EART4 PRESS$RE COEFFICIENTS 84CAND 84T

PILE T/PE 6HC 6HT

Drien single +*ile 05 H 10 03 H 05

Drien single Dis"laceent *ile 10 H 15 06 H 10

Drien single Dis"laceentTa"ere% *ile

15 H 20 10 H 13

Drien Iette% *ile 04 H 0 03 H 06

Drille% *ile (&ess than 24

Diaeter!

07 04

FRICTION ANGLE 7 PILE T/PE

$teel 20

oncrete 3/4

Tier 3/4

&iit to 28if etting is )se%

(a! Jn case a ailer or gra )c'et is )se% elo gro)n% ater tale, calc)late en%

earing ase% on not e;cee%ing 28

(! 9or "iers greater than 24+inch %iaeter, settleent rather than earing

ca"acit# )s)all# controls the %esign 9or estiating settleent, ta'e 50< of the

settleent for an e)ialent footing resting on the s)rface of co"arale

gran)lar soils

1#


15/24

RECOMMENDED 0ALUES OF ADHESION )NA0FAC DM24-

2L* TF2* 7B33T*7F

B; 3BL

7B*3B, 7,

23;

>C*3B, 7> (%

7), 23;

T0=*@ >C

7B7@*T*

9ery 3oft D / D /

3oft / D / / D #6

0edium 3tiff / D 1 #6 D 5/

3tiff 1 D 5/ D 8/

9ery 3tiff D # 8/ D 1!

3T**L

9ery 3oft D / D /

3oft / D / / D #4

0edium 3tiff / D 1 #4 D 5

3tiff 1 D 5 D 5

9ery 3tiff D # 5 D 5/

Bere8a"t8e( et a )191- The$r.: Reati$"&hi% ;et


16/24

D/NAMIC FORMULA

The E"gi"eeri"g Ne


17/24

1) STANDARD PENETRATION TEST (SPT)

-e#erhof (176! has recoen%e% the folloing correlation eteen the a;ial ca"acit#

of a single "ile in gran)lar soil:

st DANnmNA& +=

here

R= *ile a"acit# (.!

m= 400103for %rien "iles

120 103for ore% "iles

N= $*T in%e; at the "ile toe otaine% # aeraging los oer length 6 + 10Baoe

an% 2 + 4Belo the ase

At= *ile toe area

n= 2103for %rien "iles

1103for ore% "iles

N

= Aerage $*T in%e; along the "ile

D= *ile ee%ent length

As= *ile )nit shaft area

The stan%ar% *enetration Test is s)ect to a )ltit)%e of errors an% )ch care )st

e e;ercise% hen )sing the test res)lts 9or this reason, a ini) factor of safet# of

4 sho)l% e a""lie% to the calc)late% ca"acit# (Kef: ana%ian 9o)n%ation ?ngineering

-an)al, 2n%e%ition!

Alternate Form of e!er"of (1#$%) met"o& for &r'en 'les

15


18/24

>ltiate earing ca"acit# at ase NB

DNq bb ## = ('./2!

here N= $*T resistance in the icinit# of the "ile ase

D= &ength of "ile ee%%e% in the san%

B= Diaeter of "ile

9or "iles %rien into non+"lastic silts, an )""er liit of 300Nis recoen%e%

Aerage $'in 9riction oer the length of "ile is %eterine% as

Nqs = ('./2!

here N is the aerage al)e of $*T resistance oer the ee%%e% length of the "ile

ithin the san% strat)

The al)e of qsotaine% aoe sho)l% e hale% in the case of sall %is"laceent

"iles s)ch as steel "iles

9or ore% "iles, the al)es of qan% qsare a""ro;iatel# 1/3 an% 1/2, res"ectiel#, of

the corres"on%ing al)es for %rien "iles

16


19/24

2* A+IA, -APA-IT. /ASED ON STATI- -ONE0PENETRATION TESTS

-ana&'an Foun&at'on En'neer'n anual

The ca"acit# of a "ile in gran)lar soil can e co")te% fro the res)lts of a static cone+

"enetroeter test The test is est s)ite% for silts an% san%s that are loose to e%i)

%ense Jt is %iffic)lt to carr# o)t this test in graels an% in %ense san%s

The ca"acit# of a single "ile in gran)lar soil a# e %eterine% fro:

DAfAq& sstc +=

here

qc= "oint resistance fro the cone+"enetration test (Jt is recoen%e% that for "iles

ith B L 500 , a %esign al)e of qcsaller than the eas)re% aerage qc, oreen e)al to the ini) eas)re% al)e e )se%! (Kef: ana%ian 9o)n%ation

?ngg -an)al!

fs= aerage )nit si%e shear eas)re% # the static cone+"enetroeter test

At= cross+sectional area of "ile at toe

As= $haft area "er )nit length of "ile

D= ?e%ent length of the "ile in soil

The 9E$ to a""l# to the ca"acit# fro static cone+"enetroeter testing sho)l% e

eteen 25 an% 3, %e"en%ing on the n)er of cone tests "erfore% an% on the

osere% ariailit# of the test res)lts

Ot"er Aroa"es

Tomlinson (2001)

*lot all releant qc/%e"th "rofiles together an% %ra an aerage line for the section

aro)n% the "ile ase A loa% factor of 20 H 25 is then a""lie% to the ase resistance

(Aq! %e"en%ing on the scatter of the "rofile

18


20/24

Practic in Nthrlan!s

9or en% earing ca"acit#, )se ean of to aerages qc1 an% qc2, for single "rofile,

%eterine%:

(1! eteen 07B an% 4B elo the "ile ase (c1! Jf qcincreases stea%il# elo the

"ile, the aerage is %eterine% onl# to %e"th 07B Jf a "rono)nce% %ecrease in qc

occ)rs eteen 07B an% 4B, the loest al)e ithin that range is ta'en as qc1

(2! 8B aoe the ase (qc2! The aerage al)e of qc2aoe the ase sho)l% e

%eterine%, or'ing )"ar% fro the ase, )sing onl# al)es, hich %ecrease

fro or e)al to that at the ase

The al)e of en% earing ca"acit# (q! sho)l% e restricte% to15 -*a

$haft resistance "er )nit area (qs! can e %eterine% fro al)es of local sleee

resistance (fs! oeer, fs)st e )lti"lie% # a factor to allo for the effect of "ile

installation on the %ensit# of the san% The factor %e"en%s on the aterial an% en%

sha"e of the "ileM s)ggeste% al)es eing 11 for a concrete "ile ith a "ointe% en% an%

07 for a steel "ile

$haft resistance can also e %eterine% fro %irect correlations ith cone resistance,

eg qs= 0012qcfor tier, "recast concrete an% steel %is"laceent "iles

The al)e of qssho)l% e restricte% to 012 -*a


21/24

3* A+IA, -APA-IT. /ASED ON PRESSUREETER TEST

The )ltiate en% earing ca"acit#, "", for close%+en%e% "iles is gien # the folloing

e)ation The ca"acit# for o"en+en%e% "iles is half of that:

[ ] v%lmep p'AQ +=(

here

A= "ile ase area

#le= e)ialent liit "ress)re

h= hori@ontal "ress)re at the ase leel

= total ertical "ress)re at the ase leel

$= earing ca"acit# factor%lm

vu

p

q

= here quis )ltiate earing ca"acit#, is total

ertical stress at the foration leel an% h is the total hori@ontal stress at the

"ress)reeter test leel ' al)es can e otaine% fro Tale elo

Beari"g Ca%a#it. Fa#t$r+ f$r A>ia. L$a!e! Pie& )After LCPCSETRA+ 19,?-

ro)n% t#"e "l('*a! ategor# Bore% "ilesan% sall

%is"laceent"iles

9)ll%is"laceent

"iles

la# 0 H 1200

J 12 18$ilt 0 H 700

9ir cla# or arl 1800 H 4000

JJ 11 32 H 42

o"act silt 1200 H 3000

o"ressile san% 400 H 800

$oft or eathere%roc'

1000 H 3000

$an% an% grael 1000 H 2000

JJJ 18 26Koc' 4000 H 10000

er# co"act san%an% grael

3000 H 6000 J 11 H 18 18 H 32

32 for %ense san% or graelM 42 for loose san% or graelliite% %ata ase

Li'it %re&&=re#lis %efine% theoreticall# as Nth ma%imum #rssur rach! !urin& a

#rssurmtr tst at 'hich th cait 'ill continu to %#an! in!finitlO Jn realit#,

1


22/24

this is not "ossile as the erane e;"ansion is restricte% The liit "ress)re can e

otaine% # e;tra"olating the test c)re to infinit# -Pnar% re%efine% the liit "ress)re

as the "ress)re re)ire% to %o)le the cait# %iaeter

The liit "ress)re is also %efine% "racticall# as the "ress)re reache% hen the soil

cait# has een inflate% to tice its initial ol)eM#lis the "ress)re at *c/*o= 1

NE@CASTLE FULLDISPLACEMENT PRESSUREMETER

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35 40 45 50

CA0IT/ STRAIN+

PRESSURE+BPa

&iitin *ress)re

The e)ialent liit "ress)re, #le%e"en%s on the %istance the "ile "enetrates the

earing la#er an% the %egree of hoogeneit# of that la#er A hoogeneo)s la#er is

%efine% as one in hich the a;i) al)e of #lis less than 15 of the ini) al)e

of#l(#l in! The a;i) al)e of#lis ta'en as 15#linfor a non+hoogeneo)s

la#er The e)ialent liit "ress)re,#leis ta'en as the aerage liit "ress)re ithin a

%istance "elo an% a %istance aoe the "ile ase leel, that is

[ ]+

= ilmilme (p"

p1

here#liis the liit "ress)re oer %e"th +i, hich is the thic'ness of a la#er at hich

#lis eas)re% s)ch that


23/24

@1F Q F@n= "

" an% are %istances %e"en%ing on the "ile %iaeter an% ee%ent length is

e)al to "or the %istance eteen the "ile ase an% the to" of the earing la#er hich

eer is sallest "is gien #:

" = 05 if BeR 1

= Be/2 if BeL 1

here

Be= 4ase area of "ile / ase "erieter of "ile

Jt is ass)e% that the "ile "enetrates the earing la#er s)ch that the e)ialent

ee%ent %e"th, e, is greater than 5B, here eis gien #:

= ilmilme

e (pp

1

'is re%)ce% to 'eif eR 5B, here 'eis gien #

+=

B

B

'' eee

1

/

6.6.

The )ltiate friction ca"acit#, "f, is gien #:

[ ]= isif (qQ

here

qsi= )nit s'in friction for soil la#er ian%iis the thic'ness of soil la#er i The )nit friction

is otaine% fro Tale elo rea% in con)nction ith 9ig)re elo

!


24/24

The &ee#ti$" $f !e&ig" #=r(e& f$r ="it fri#ti$" )after LCPC SETRA+ 19,?-

$oil t#"e #l(-*a!

Bore%concrete

Bore% an% line% Drien ro)te%

oncrete $teel oncrete $teel &o"ress)re

igh"ress)re

$oft cla# 0+07 A A A A A B

$tiff cla# 12+2 A, (B! A, (B! A A, (B! A B ?

er# stiff cla# L2 A, (B! A, (B! A A, (B! A, B ?

&oose san% 0+07 A A A A A B

-e%i) %ense san% 1+2 B, (! A, (B! A B, (! B ?

er# %ense san% L25 , (D! B, (! B , (D! D ?

o"letel# eathere% chal' 0+07 A A A A A B

*artiall# eathere% chal' L1 , (D! B, (! B , (D! ? ?

-arl 15+4 D, (9! , (D! 9 9 9

$tiff arl L45 9

eathere% roc' 25+4

9ract)re% roc' L45

)res in "arentheses onl# a""l# for ell+constr)cte% "iles

Jf#lR 15 -*a

load carrying capacity of piles

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