3116 part 2 version 5
TRANSCRIPT
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National University of Singapore
Department of Civil and Environmental Engineering
CE3116 Foundation Engineering
Semester 2 20141!
Design of Deep Foundation "art 2
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#ntrodu$tion
A test pile has been installed into the ground location of the borehole
provided in Part 1. Shaft resistance data are obtained from the test pile under
dierent working loads. With the additional information, K SP values are
compared with the assumed values in Part 1. !urthermore, the settlement ofpile is e"amined. #astl$, with another set of pile resistance data obtained
from load tests, a new design is obtained.
1% Comparison of t&e ' S"( )alues
he K SP values calculated from the additional information are tabulated as
follow.
%epth &.'&('.)1m
*W# +
SP(
value
Kspt-+
SP(value
Kspt-+
SP(value
Kspt-+
SP(value
Kspt-+
/ /.//)0./
/ /.// &1.// /.// &.// /.// 23.// /.//)&/
/4.)
/)0./
/ 1.2 &1.// 1.4' &.// 1.)0 23.// /.014/
/'.&
/)0./
/ ).40 &1.// ).)4 &.// 1.'& 23.// 1.))'/
/03.)
/)0./
/ &.11 &1.// ).01 &.// ).4) 23.// 1.2&')/
/1/).
4/)0./
/ &. &1.// &.&/ &.// ).04 23.// 1.0/'/
/13.3
/)0./
/ /.& &1.// /.23 &.// /.4' 23.// /.&14/
/1).3
/)0./
/ /.42 &1.// /.41 &.// /.&2 23.// /.)))&/
/ ).2/)0./
/ /./' &1.// /./0 &.// /./3 23.// /./4
/
('.4
/)0./
/ ().40 &1.// ().)4 &.// (1.'& 23.// (1.))
Average 1.3) 1.2 1.&4 /.02
%epth '.)1(1).1'm*W# +
SP(value
Kspt-+
SP(value
Kspt-+
SP(value
Kspt-+
/ /.// 23.// /.// ).// /.// 44.// /.//)&/
/ 2).4/ 23.// /.') ).// )./) 44.// 1.1'
)
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4//
11&.'/ 23.// ).// ).// 4.&0 44.// ).2'
'//
12'./ 23.// ).0/ ).// .14 44.// &.&
')//
)14.4/ 23.// &.3 ).// 0.)2 44.// 4.03
'// '1.// 23.// 1./ ).// &.2/ 44.// )./3
4// )/.1/ 23.// /.&2 ).// /.33 44.// /.4
)&// 1).0/ 23.// /.)) ).// /.4' 44.// /.)'
/ 0.2/ 23.// 1.2) ).// &.&& 44.// 1.'3
Average 1. &.2 ).1
%epth 1).1'(12.1'm
*W# +
SP(value
Kspt-+
SP(value
Kspt-+
/ /.// 44.// /.// )3.// /.//)&/
/ &2.&/ 44.// /.0/ )3.// 1.&14/
/ 3.1/ 44.// 1.3& )3.// ).0)'/
/1/3./
/ 44.// ).4& )3.// &.'')/
/10.1
/ 44.// &.0) )3.// .)&'/
/1'3.1
/ 44.// 4.40 )3.// 3.&/4/
/1/&.2
/ 44.// ).&2 )3.// &.0&)&/
/ )'.3/ 44.// /.0 )3.// 1.1/
/ 0.4/ 44.// /.1' )3.// /.&1
Average ).&& &.3'
%epth 12.1'( 10.))m*W
# +
SP(
value
Kspt-+
SP(
value
Kspt-+
SP(
value
Kspt-+
/ /.// )3.// /.// )0.// /.// )0.// /.//
)&// 0.1/ )3.// /.&/ )0.// /.)' )0.// /.)'
4//
)4./ )3.// /.'1 )0.// /.00 )0.// /.00
'//
4'.)/ )3.// 1.0) )0.// 1.3 )0.// 1.3
&
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')//
4&.0/ )3.// 1.) )0.// 1.2 )0.// 1.2
'//
/./ )3.// ).)4 )0.// ).1 )0.// ).1
4//
1.1/ )3.// ).) )0.// ).10 )0.// ).10
)&// 1./ )3.// /./ )0.// /./ )0.// /./
/
(1)./
/ )3.// (/.44 )0.// (/.4& )0.// (/.4&
Average 1.&) 1.)3 1.)3
%epth 10.))()1.))m*W# + SP( value
Kspt-+ SP( value
Kspt-+
/ /.// )0.// /.// &.// /.//)&/
/)).1
/ )0.// /.3' &.// /.14/
/&/.2
/ )0.// 1./' &.// /.02'/
/43.3
/ )0.// 1.3/ &.// 1.&&')/
/22.'
/ )0.// ).// &.// 1.22'/
/4.
/ )0.// ).&1 &.// 1.3'4/
/
2./
/ )0.// ).// &.// 1.2)&/
/43.2
/ )0.// 1.3/ &.// 1.&)
/).4
/ )0.// /.'4 &.// /.3&
Average 1.2 1.)'
%epth )1.))()4.)/m*W# + SP( value
Kspt-+ SP( value
Kspt-+ SP( value
Kspt-+
/ /.// &.// /.// 23.// /.// 1//.// /.//)&/
/ /.// &.// /.// 23.// /.// 1//.// /.//4/
/10.)
/ &.// /.21 23.// /.&) 1//.// /.10'/
/4'.0
/ &.// 1.&0 23.// /.03 1//.// /.2/')/ 0./ &.// ).&' 23.// 1.21 1//.// /.0
4
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/ /'/
/''.
/ &.// ).33 23.// 1.32 1//.// 1.//4/
/33./
/ &.// ).14 23.// 1.&2 1//.// /.33)&/
/24.4
/ &.// 1.21 23.// /.'2 1//.// /.24
/ /.1/ &.// /.// 23.// /.// 1//.// /.//
Average 1.2& /.' /.22Tables 1-6 K SPT values in each layer of soil.
Workings
he K SP values are calculated using the following formula5
K SPT =qs
N
Where +s is the shaft resistance obtained from pile load test and is the (
value obtained from borehole data.
Several representative (values in each la$er of soil are taken in order to
provide a more e"tensive comparison.
he calculated K SP values are compared against the assumed K SP value inthe part 1 design, which is ).2.
Discussions
he comparisons show that the K SP values calculated from the pile load tests
are generall$ lower than the assumed values in the previous design.
herefore, the e"act stiness of the soil is lower than what was e"pected in
the previous design.
6esides, it can be observed from the pile load tests that the shaft resistance
of the pile is dependent on the working load. 7owever, the shaft resistance as
calculated from the formula +s-K SP is an ultimate resistance without the
consideration of the e"act behavior of the soil. herefore, the results obtained
from the previous design ma$ be less conservative and partial factors are
thus important to factor down the resistance.
Also, it can be observed that there is no general trend or correlation between
the magnitude of the working load and the shaft resistance.
2% "ile *ase resistan$e
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6ase resistance of bored pile under drained condition at dierent level of soil
can be correlated to the SP( value at the corresponding level of soil b$ the
following e+uation.
6ase resistance per unit area,qb= K b N 89hang : 6roms, 1''1;
where
30 45b
K = −
b-1./
%esign base resistance 86;, RbB=( π 4 )×D2×30×N
1.0=3393kN
Case C
=93 partial factors5 >b-1.
%esign base resistance 89;, RbC =(π
4)×D2×30×N
1.6=1060kN
he e"pected base resistance will be the same as the previous design as the
K b has not been changed.
3% Settlements
At /.2 W#-4//k, settlement of pile- 4.'0mm
At 1./ W#-')//k, settlement of pile- 1/.4mm
?a"imum allowable settlement of pile- /.1 @ ominal diameter of pile
-/.1 @ 1)// - 1)/mm
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at ultimate compressive resistance as stated in =urocode 3.
ltimate compressive resistance - 11))4 k 8from Part 1;B')//k.
6$ e"trapolating, settlement at ultimate compressive resistance- 1).3 mm
C 1)/mm
7ence, the settlement is acceptable.
Discussions
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/ /4//./
/(
)&.&/ )0.// (/.0& &1.// (/.32 &.// (/.2 23.// (/.41
/.// 1/.&/ )0.// /.&3 &1.// /.&& &.// /.)' 23.// /.10
%epth '.)1(1).1'm
SP(value
Kspt-+
SP(value
Kspt-+
SP(value
Kspt-+
/.// 2.'/ 23.// /.1/ ).// /.)& 44.// /.1&4//./
/ 01.4/ 23.// 1.4& ).// &.1& 44.// 1.02')//./
/))1.&
/ 23.// &.00 ).// 0.21 44.// 2./&1&0//.
//104.3
/ 23.// &.)4 ).// 3.1/ 44.// 4.)/11//.
//
)44./
/ 23.// 4.)0 ).// '.&0 44.// 2.22104//.
//))&.2
/ 23.// &.') ).// 0./ 44.// 2./0)/3//.
//)&3./
/ 23.// 4.1 ).// '.1) 44.// 2.&'104//.
//&4./
/ 23.// .&' ).// 14.// 44.// 0.)31&0//.
//&2/.3
/ 23.// .12 ).// 1&.4' 44.// 3.'3')//./
/)'1.2
/ 23.// 2.11 ).// 11.)1 44.// .&4//./
/
&21./
/ 23.// .1 ).// 1&.2/ 44.// 3.'0
/.//
(1/).&
/ 23.// (1.3' ).// (&.'& 44.// ().&&
%epth 1).1'(12.1'm
SP(value
Kspt-+
SP(value
Kspt-+
/.// .&/ 44.// /.14 )3.// /.)&4//./
/ 22.1/ 44.// 1.)2 )3.// )./4')//./
/104.)
/ 44.// 4.1' )3.// .0)1&0//.
//10).2
/ 44.// 4.12 )3.// .311//.
//&)/./
/ 44.// 3.)3 )3.// 11.02104//.
//&41.
/ 44.// 3.3 )3.// 1).2
0
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)/3//.//
413.4/ 44.// '.4' )3.// 12.4
104//.//
1''.0/ 44.// 4.24 )3.// 3.4/
1&0//.// 4/.0/ 44.// /.'& )3.// 1.21
')//.// (03.4/ 44.// (1.'' )3.// (&.)4
4//.//
(123./
/ 44.// (&.23 )3.// (2.01
/.//
(14.)
/ 44.// (&.3& )3.// (./0
%epth 12.1'(10.))m
SP(value Kspt-+ SP(value Kspt-+
/.// 3.4/ )3.// /.)3 )0.// /.)4//./
/ &'.3/ )3.// 1.43 )0.// 1.4)')//./
/ 4.1/ )3.// 1.31 )0.// 1.21&0//.
// 3&./ )3.// ).3& )0.// ).&11//.
// 4.)/ )3.// ).&0 )0.// ).)'
104//.
// 2'.)/ )3.// ).1' )0.// ).11)/3//.
// 23.'/ )3.// ).14 )0.// )./3104//.
// (&.&/ )3.// (1.&4 )0.// (1.&/1&0//.
// (&4.)/ )3.// (1.)3 )0.// (1.))')//./
/ (44.0/ )3.// (1. )0.// (1./4//./
/ (&'.3/ )3.// (1.43 )0.// (1.4)
/.// (4&.'/ )3.// (1.& )0.// (1.23
%epth 10.))()1.))m
SP(value
Kspt-+
SP(value
Kspt-+
/.// &.3/ )0.// /.1& &.// /.1/4//./
/ &&.3/ )0.// 1.)/ &.// /.'4
'
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')//.// 1'.// )0.// /.0 &.// /.2&
1&0//.// ).&/ )0.// /.'4 &.// /.3&
11//.// )2.0/ )0.// /.') &.// /.3)
104//.// 1.2/ )0.// /.2' &.// /.4
)/3//.// 43.// )0.// 1.0 &.// 1.&1
104//.// (0).&/ )0.// ().'4 &.// ().)'
1&0//.//
(1/&.4
/ )0.// (&.' &.// ().03
')//./
/
(112.4
/ )0.// (4.1) &.// (&.)1
4//.//
(11'.4
/ )0.// (4.) &.// (&.&)
/.//
(11'.&
/ )0.// (4.) &.// (&.&1
%epth )1.))()4.)/m
SP(value
Kspt-+
SP(value
Kspt-+
SP(value
Kspt-+
/.//42.)
/ &.// 1.) 23.// /.3'1//./
/ /.424//.
//0.)
/ &.// 1.0' 23.// 1.)/1//./
/ /.0')//.
//13.
/ &.// 4.'1 23.// &.1/1//./
/ 1.331&0//
.//)).
3/ &.// 3.&/ 23.// 4.11//./
/ ).&11//
.//)02.
4/ &.// 3.'& 23.// 2./11//./
/ ).02104//
.//&/0.
1/ &.// 0.2 23.// 2.411//./
/ &./0
)/3//.//
&/0.4/ &.// 0.23 23.// 2.41
1//.// &./0
104//.//
&'0.3/ &.// 11./0 23.// .''
1//.// &.''
1&0//.//
&&'.3/ &.// '.44 23.// 2.'
1//.// &.4/
')//.//
)).3/ &.// 3.&/ 23.// 4.1
1//.// ).&
1/
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4//.//
)44.2/ &.// .3' 23.// 4.)'
1//.// ).42
/.//)4/.
// &.// .3 23.// 4.)11//./
/ ).4/
Kb of Pile 6ase Fesistance
#oad +6 SP( Kb
/ ))).1 23&.0'4'
1
4// '&& 231.&04
)
')//1)00.
4 23))./&2
11&0/
/10.
1 23 &).3&011/
/
)1&).
0 23
&3.4132
4104/
/ )&22 2341.&123
')/3/
/)3''.
2 234'.114/
4104/
/)3''.
2 234'.114/
41&0/
/)44&.
' 234).0324
4
')// 1'22 23&4.)'0)
2
4//
13&).
0 23 &/.4
/13&).
0 23 &/.4
average
&).24210
Tables 7-13. New K SPT and K b values.
Workings
With the additional information, new K SP values can be calculated using the
same method as section 1.
With the new K SP values, new values of shaft resistance can be calculatedusing the formula +s-K SP.
he new average K SP values that are used for the new design are tabulated
as follow.
e!"h #$% K SPT #avera&e%&.'& ( '.)1 &.1/
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'.)1 ( 1).1' 4.431).1' ( 12.1' 4.'212.1' ( 10.)) ).1/10.)) ( )1.)) /.30)1.)) ( )4.)/ ).2Table 1'. esi&n values of K SPT in each layer of soil.
As larger K SP values are generall$ obtained from the additional information,
larger values of shaft resistance are obtained, thus the design length of the
pile can be reduced. his indicates that the soil behaviour is stier than what
was previousl$ assumed, thus providing more shaft resistance.
Also, using the additional information obtained from pile load tests, new
values of K b can be obtained using the formula K b-+b 8as shown in able
1&;, where is 23 at )4.)/m according to borehole data.
he obtained result of K b, &).242, is larger than the assumed value of &/. he
larger value of K b results in a larger base resistance. herefore, the pile lengthcan be further reduced as more load can be taken b$ pile base resistance.
he shaft resistance and base resistance can be determined using the
following formulas.
Rs¿∑(πD Li)× K SPT −i × N i
γ
Where #i, K SP(i, i are the length of pile, K SP, values respectivel$ in i(th soil
la$erG %-1)///mmG >6-1./G >9-1.&.
Rb=( π 4 )×D2×K b×N
γ
Where K b-&&.242G is the value at the pile baseG %-1)//mmG >6-1./G
>9-1..
Case B
# -) m
Fs6 -1/ ''4 k
Fb6 -& 01 k
F6 -14 32 k
he pile length has been reduced to )m from )0m in the previous design.
1)
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Case C
# -)0 m
Fs9 -' &)3 k
Fb6 -) &// k
F9 -11 )3 k
he pile length has been reduced to )0m from &4m in the previous design.
Furt&er Dis$ussions and Con$lusion
After some anal$ses of the data from Anne" 9, we found that there is load
redistribution when the load increases. !or e"ample, at the depth of &.'& H
'.)1m, the K SP value increases from substantiall$ from /.01 to .)) when the
load increases from ')//k to 1&0//k while at the depth of '.)1 H 1).1'm,
the K SP value decreases from &.00 to &.)4 when the load increases from
')//k to 1&0//k. his shows that when the load increases, the load is
redistributed to other level of soil when certain level of soil has reached its
ma"imum resistance.
he dierent K SP values when the same load is applied before and after the
ma"imum load implies that the stress strain curve of soil is non(linear and the
soil e"hibits plastic behavior. !rom the data, we can observe that the soil is
generall$ stier after the ma"imum load is applied. his is coincident with the
theor$ we have learnt in the class that the soil follows a dierent stress strain
curve when it loads be$ond its $ield stress.
6esides, from the new data, we can observe that K SP value can be up to
12.4 while in the previous design, we had chosen the K SP value to be ).2.
he chosen value of ).2 is +uite conservative as we can observe from the
data, nearl$ all la$ers of soil has a K SP value larger than ).2 e"cept the la$er
that is near to the base. Some of the reasons that the la$er near to the base
has a small K SP value are the e"istence of the base resistance at that la$er of
soil and also there is some anchorage length re+uired for the pile to build up
resistance that is similar to the case of steel in the reinforced concrete.
7ence, the chosen value of ).2 is +uite safe for design of pile but for most of the cases, this will result in over(designing of the pile and introduce large
economic cost.
!urthermore, it can be observed from the data in Anne" 9 that the higher the
working load, the higher the mobilised base resistance. his is due to the fact
that when working load e"ceeds the shaft resistance, more of the load will be
taken b$ the base.
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,eferen$es
=urocode 3 8)//';. (eo"echnical desi&n - Par" 1) (eneral rules.
!arrel : revor 81''';. (eo"echnical esi&n "o *urocode 7.
an I.9. : 9how 9.?. 8)//&;. esi&n and cons"ruc"ion of bored !ilefounda"ion.
12