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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
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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
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"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.
!
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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 $trength al)es generall#
increase ith increasing san% fractions an% %ecrease ith %ecreasing silt fractions
#
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Piles in Clay
#cN!cs
AqAfQ
c
bsult
+=
+=
"hereAs% area of pile shaft
Ab% area of base of pile
c % average undrained shear strength along the pile
c% average undrained shear strength at base of pile
Nc% bearing capacity factor % 8
s% shape factor % 1. for a plain shaft and % 1. for a tapered pile
% diameter of pile
!% length of pile
% adhesion factor "hose value depends on unconfined compression strength, % 1 for soft
clay and 1 for stiff clay.
Recommen!e! "alues o# an!f#or Estimation o# Drille! Sa#tSi!e Resistance in Coesi'e Soil (Reese an! O)Neill* +,--&
Location along drilled shaft 9alue of Limiting value of loadtransfer,f('sf)
;rom ground surface to depth alongdrilled shaft of / ft < -
=ottom 1 diameter of the drilled shaft
or 1 stem diameter above the top of
the bell (if s'in friction is being used)
-
>ll other points along the sides of the
drilled shaft
.// /./
The depth of / ft may need ad&ustment if the drilled shaft is installed in e$pansive
clay, or if there is substantial groundline deflection from lateral loading.
Limitin% "alues o# $nit En! .earin% an! Si!e Resistance
7ohesive 3oil on-7ohesive 3oil
?nit 3ide @esistance ('sf). /./ #
?nit *nd =earing ('sf) 6 1.Nor 8 forN5/
/
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To" fie feet
noncontri)ting
Botto one %iaeter
noncontri)ting
Straight Shaft
*eri"her# of Bell
noncontri)ting
Botto one %iaeterof ste
.oncontri)ting
Bee! Shaft
To Diaeter in stiff fiss)re% cla#
I!e"tifi#ati$" $f %$rti$"& $f !rie! &haft& "ege#te! f$r e&ti'ati$" $f
!rie! &haft &i!e re&i&ta"#e i" #$he&i(e &$i )Ree&e a"! O*Nei+ 19,,-
>llo"able pile capacity can be calculated using overall load factor often ta'en as . i.e.
bs"
QQQ
+=
or 1./ in s'in friction and ! in end bearing, i.e.
.!/.1
bs"
QQQ +=
The lo"er safety factor in s'in friction is because the pea' value of s'in friction on a pile in clay
is obtained at a settlement of only !-6 mm, "hereas the base resistance requires a greater
settlement for full mobili+ation. The frictional resistance on the shaft develops rapidly andalmost linearly "ith settlement and is generally fully mobili+ed "hen the settlement is about
./A of the shaft diameter. Thereafter, it either remains sensibly constant, or decreases slightly
as the settlement is increased further. Bn the other hand, the base resistance is seldom fully
mobili+ed until the pile settlement reaches 1 to A of the base diameter.
4
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FACTOR OF SAFETY
(@ef: ;oundation Cesign, 2rinciples and 2ractices, by C.2. 7oduto)
The design factor of safety depends on many factors, including the follo"ing:
Te type an! importance o# te structure an! te consequences o# #ailure D
;oundations for critical structures, such as ma&or bridges, should have a higher factor ofsafetyE those for minor uninhabited structures could use a lo"er factor of safety.
Te soil typeD ?se a higher factor of safety in clays
Te spatial 'aria/ility o# te soilD *rratic soil profiles are more difficult to assess, and
therefore &ustify use of a higher factor of safety.
Te torou%ness o# te su/sur#ace e0ploration pro%ram D ntensive subsurface
e$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
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o *rratic >verage !./ 4.
ote: f the static load testing program is very e$tensive and the subsurface conditions are
"ell-characteri+ed, the factors of safety for do"n"ard and uplift loads might be
reduced to about 1.5 and ./, respectively.
The actual factor of safety for both do"n"ard and up"ard loading (i.e., the real capacity dividedby the real load) is usually much higher than the design factor of safety used in the formula.
This is because of the follo"ing:
e usually interpret the soil strength data conservatively
The actual service loads are probably less than the design loads, especially in buildings
other than "arehouses
The as-built dimensions of the foundations may be larger than planned
3ome (but not allG) of the analysis methods are conservative.
6
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LOADING CONDITIONS )After US Ar'. C$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
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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
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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
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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
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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
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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
$teel 20
oncrete 3/4
Tier 3/4
&iit to 28if etting is )se%
(a! Jn case a ailer or gra )c'et is )se% elo gro)n% ater tale, calc)late en%
earing ase% on not e;cee%ing 28
(! 9or "iers greater than 24+inch %iaeter, settleent rather than earing
ca"acit# )s)all# controls the %esign 9or estiating settleent, ta'e 50< of the
settleent for an e)ialent footing resting on the s)rface of co"arale
gran)lar soils
1#
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RECOMMENDED 0ALUES OF ADHESION )NA0FAC DM24-
2L* TF2* 7B33T*7F
B; 3BL
7B*3B, 7,
23;
>C*3B, 7> (%
7), 23;
T0=*@ >C
7B7@*T*
9ery 3oft D / D /
3oft / D / / D #6
0edium 3tiff / D 1 #6 D 5/
3tiff 1 D 5/ D 8/
9ery 3tiff D # 8/ D 1!
3T**L
9ery 3oft D / D /
3oft / D / / D #4
0edium 3tiff / D 1 #4 D 5
3tiff 1 D 5 D 5
9ery 3tiff D # 5 D 5/
Bere8a"t8e( et a )191- The$r.: Reati$"&hi% ;et
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D/NAMIC FORMULA
The E"gi"eeri"g Ne
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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
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>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
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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
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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
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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
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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
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@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
!
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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