Transcript
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Drag Load and
DowndragWhat We Know and How
to Design for It
2
3
& DECOU RT 235
4
Interpretation of a series of tests
performed at different times
0 10 20 30 40 50 60 700
10
20
30
40
50
60
70
Movement (m m)ChangeofHorizontalStress(KPa)
5 Da ys
1 Day
8 Da ys
4 Months
22 M onths
Cell D1
Results thought dueto set-upexplained as Increase inHorizontal Effective Stress
Felle nius 200 2
Results plottedAccording toMovement Path
0 50 100 150 200 250
0
10
20
30
40
50
60
70
Movement ( mm)
5 D ays
1 Day
8 D ays
4 Months
22 M onths
5
A. Distribu tion o f residual load in Piles DA
and BC beforestart of the loading test
Sand
Tests on instrumented 280 mm square precastconcrete piles in Drammen, Norway
0
2
4
6
8
10
12
14
16
18
0 50 100 150 200 250 300
LOAD (KN)
DEPTH
(m
Pi le DA
Pile BC,Tapered
0
2
4
6
8
10
12
14
16
18
0 100 200 300 400 500 600
LOAD (KN)
DEPTH
(m) True
Residual
T rue minusResidual
B. Load and resistance in Pile DA
fo r th e ultimate load ap plied in the test
Data from Gregersen et al., 1973
6
Result on a test on a 2.5 m diameter, 85.5 m long pile at
My Thuan Bridge, Vietnam
0 50 1 00 150 200 250
0
10
20
30
Movement (mm)
Load
(MN)
LEVE L A Do wnward, STAGES1 and 5
Test Data
FE analys is
Does unloading/reloading add anything of value to a test?
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True 50 years ago and true today: when something newis proposed, people try to incorporate it into the old.
Especially for loading tests on instrumented piles,
occasional unloading/reloading will add nothing ofvalue, but might severely impair the evaluation of the
test results. As will holding the load levels for differentlengths of time. Each lo ad should be kept on the pile anequal length of time!
The unloading/reloading cycle is an atavist, a remnantof a distant past!
Engineers of today are unaware of that the concept offactor-of-safety applied to an ultimate resistanc e
(capacity) was once a novel approach.
Before that approach was brought into practice, testingwas by measuring load-movement and the net
movements after unloading (several cycles) wasthought to show the pile toe load-movement response.
8
9
Distribut ion of soil stress, excess pore pressure, soil s ettlement, and
pile shorte ning. Hery a site. (Data from Bjerr um et al., 1969).
0
5
10
15
20
25
30
35
0 10 0 20 0 300 4 00
EFFECTIVE STRESSAND PORE PRESSURE (KPa)
DEPTH
(m
)
'z
afterfull
dissipationof
excess porepressure
'zu
Marine
Clay
FILL
Start o f
BedrockGrav el
0
5
10
15
20
25
30
35
0 30 0 60 0 900 1 ,2 00 1, 500
PILELOAD ( KN)
DEPTH
(m)
Bitumen
coated
uncoated
Distribution
calculatedfrom
=0.3times 'z for
actual excess u
Measureddistributio n
Notice the dis tinct ForceEquilibr ium, the Neutra l Plane
0
5
10
15
20
25
30
35
0 5 10 15
PILE SHORTENING (mm )
DEPTH
(m)
Bitumen
coated uncoated
10
Compilation of Norw egian results
0
cm cm
Dragload
11
Profile of test site and piles
Closed-toe, Open-toe, Inclined, and short pile
Study in Japan (Endo et al., 1969)
12
Soil profile and pore pressure distribution
Data from En do et al. 1969
0
10
20
30
40
50
0 20 40 60 80 100
CONSISTENCY LIMIT S (%)
DEPTH
(m)
Sandy
Silt
C lay
S ilt
Fil l
Sand
S ilt
0
10
20
30
40
50
0 50 100 150 200
PORE PRESSU RE (KPa)
DEPTH
(m)
Ju ne
1964
April
1966
Hydros tatic
D istribution
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Loads from shortening of closed-toe pile
June 1964 through March 1967(Data from Endo et al., 1969)
0
500
1,000
1,500
2,000
2,500
3,000
3,500
0 200 400 600 800 1,000
DAYSA FTER START
LOAD
(KN)
#2
#3
#4
#5
#6
#7
#
#3
#4
#5
#6
#7
0
5
10
15
20
25
30
35
40
45
50
0 5 0 0 1,0 00 1 ,50 0 2,0 00 2 ,50 0 3,0 00 3 ,50 0
LOAD (KN)
DEPTH
(m)
29DAYS
124DAYS
275DAYS
400DAYS
672DAYS
#2
#3
#4
#5
#6
#7
14
Combining the Pil e cE43 distributions of load and of settlement
measured June 1964 through March 1967
N.P.
Soil
Pile
Load Distribution Settlement Distribution
(Endo e t al., 1969)
Notice the
increasing
mobiliz ation of toe
resistance
Notice the
increasing
movement of th e
pile to e
15
0
5
10
15
20
25
30
35
40
45
50
0 5 00 1,00 0 1,500 2,000 2,500 3,000 3,500
LOAD (KN)
DEOTH
(m)
Close d-toe
P iles
Open-toe
Pile
Sandy
Silt
C
l
a
y
S
a
n
d
S
il
t
0
5
10
15
20
25
30
35
40
45
50
0 50 100 15 0 2 00
SETTLEMENT (mm)
Soil
P ile
Closed -toe PileToePenetration
Neutral plane
Load distribution in the t hree long piles t ogetherandsettlement of soil an d pilesmeasured March 1967 672 days after s tart. (Da ta from Endo et al., 1969).
16
0
5
10
15
20
25
30
35
40
45
50
0 2,000 4,000 6,000 8,000
LOAD ( KN)
DEPTH
(m)
Measured
load
Calculate d
Curve
= 0.40
= 0.35
= 0.30
= 0.25
Measured load distribution and distribution matched to measured
valu es in effective stress analys is. (Data from Endo et al., 1969).
17
Study of two instrumented, precast concrete piles driven throughmarine clayand into sand at Bckebol, Gteborg, Sweden (Fellenius 1972)
18Measured loads in piles versus time after driving
0
200
400
600
800
1000
1200
1400
1600
1800
0 500 1,000 1,500 2,000 2,500 3,000 3,500
DAYS AFTER END OF DRIVING
FORCEATGAGE
(KN
Firstload plac ed
on piles
Secondload
placed onpiles
2m thickfi ll
placed over siteM1 & M5
M2 & M
M3 & M7
M4
M4
M1 & M5
M2 & M6
M3 & M7
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0
10
20
30
40
50
60
0 500 1000 1500 2000
FORCEAT GAG E (KN)
2,650
19881923
Distribution of load in Piles I and II
Note, the
dragload was
eliminated by
the live lo ad
= L IVE LOADS
Neutral
Plane
That th e toe
resist ance is s mall is
due t o t hat t he
move ments are not
large enough t o
mobiliz e any la rger t oe
resistance
Placing the fill
20
Distribution of measur ed and calculated consolidation settlement
The settl ement
measured at d ept h
amount ed to o nly
a few millim eters,
but t his was
enou gh to fully
mobilize th e
nega tive s kin
friction
0
5
10
15
20
25
30
35
40
0 5 0 1 00 150 200 2 50
STRESS (KPa)
DEPTH
(m)
( 'Z) f
('Z)iPRECONSOLI DATION
STRESS, 'c
0
5
10
15
20
25
30
35
40
0 100 200 300 400 500
S ETTLEME NT (mm)
DEPTH
(m)
MEASURED
CALCULATED
FINAL (after80
year s)
Force gage locations
21
Leung, C.F, Radhakrish nan, R., and Siew-Ann Tan (1991) presented a c ase history on
instrumented 28 0 mm s quare precast c oncrete piles driven in marine clay in Singapo re
Neutr al Plane
Note, the distribution of nega tive
sk in friction is linear (down to the
beginning of the trans ition zone)
indica ting the proportionality to
the effective o verburden stress
CASE #7
22
Data from Leung, Ra dhakr ishnan, and Tan (1991)
0
5
10
15
20
25
30
0 200 400 600
LOAD (KN)
DEPTH
(m
)
OldS ilt
&
Clay
Fill
MarineClay
Weak
Shale
Bedrock
and
Residual
Soil
Clay
= 0.5
Two
months
after start
( 57days )
Two years
later
(745 days)
Variable load
Inoue, Y., Tamaoki, K., Ogai, T.,1977. Settlement of building due to
pile downdrag. Proc. 9th I CS MFE,
Tokyo, Vol.1, pp. 561 564.
A three-storey building with a foot print of 15 m by 100 m founded on500 mm diameter open-toe pipe piles driven through sandand silty clayto bearing in a sand layer at about 35 m depth. The piles had morethan adequate capacity to carry the building. Two years afterconstruction, the building was noticed to have settled some 150 mm.Measurements during the following two years showed about 200 mmadditional sett lement. The building was demolished at that t ime.
CASE #10
A Downdrag Case
FINE SAND
S ILTY CLAY: w= wL
= 40% - 60%; u
= 40
SILTYCLAY: w = wL = 40% - 60%; u = 80
FINE SAND
SANDFILL
FINE SAND
SILT &
SAND
Pile Toe Depth Inoue 1977
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Sett lement between piles in Row6 and Row10from Sep. 1967 throughMay 1969 = 150mm.
Slope 1 : 100(Sep 67 Apr 71)
FINE SAND
SILTYC LAY: w= wL= 40%- 60%; u = 40
SILTYCLAY: w = w L = 40% - 60%; u = 80
FINE SAND
SANDFILL
FINE SAND
SILT &
SAND
Inoue 1977
-5
0
5
10
15
20
25
30
35
40
45
0 200 400 600 800
Stress and Pressure (KPa)
Depth(m)
SAND
S AND
SAND
CLAY
CLAY
SAND
silt
SettlingLaye r
"Curr ent"Ef fecti ve
Stress
FinalEf fecti ve
Stress
PoreP ressu re
LOAD SETTLEMENT
Depth(m)
S oilset tlement
Load in Pile
Building
Speculative distribution
Data f rom Inoue 1977
27
Two case historieson
Damaging Drag Loadand
Damaging Downdrag
28One Bridge Two foundations
30 mlo ng
piles driven
to bedrock50 mlong
pilesdrivento
sh aft bea rring
Provinc e A Prov ince B
?
Marineclay onbedrock
XXXXNEUTRALPLA NE
Highly loaded(max allowedby code)
Lightly loaded
29Limestone bedroc k providing good bearing
A CAS E HISTOR Y OF A STRIP-MALL FOUNDE D ON PILE S
GROUND
SURFACE
The so ils invest igation revealed 54 ft (16 m)
of no-s trength "muck".
Design called for 54 ft long piles. Desig ner
discounted all s haft r esistance contribution.
54 ft( 16 m)
30
54 ft (16m)
of "muck'
Limestone bedrock providing good bearing
GRO UNDSURF ACE
Strip-Mall as designed
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A real DOWNDRAG case
X x X x X x X x X x X x X x X
54 ft (1 6m)of "muck"
Limestone bedrock providing good bearing
ORIGINAL
GROUND
SURFACE
5 ft (1.5m) of
fill adde d
before thepiles were
drive n
5 ft (1.5m ) of "muc k"
32
The distribution of load at the pile cap is governed b y the
load-transfer beh avior of the piles. The design pile can
be said to be the ave rage pile. However, t he loads can
differ considerably between the piles depending on toe
resistance, length of piles.
The location of the neutral plane is Natures compromise
in finding the equili brium. If the end result by design
or by mis ta ke is that the neutral plane li es in or above
a compressibl e soil layer, the pile group will settle even
if the total factor of safety appears to be acceptable.
33
The princip les of the mechanism are ill ustrated
in the following three diagrams
The mo bilized toe resista nce, Rt, is a f uncti on of the
Net Pil e Toe Movem ent
34
Pile toe response for where the settlement issmall (1) and where it is large (2)
0
0 1,50 0
LOAD an d RESISTANCE
DEPTH
0
0
SETTL EMENT
21
1 2
NEUTRAL PLANE 1
NEUTRA LP LANE 2
Utimate
Resistance
Toe Penet rations
Note, t he magnitu de of settlement affects not only the magnitudeof toe resistance but also the length of the Tran sition Zone
= Movement into the soil
35
Pile toe res ponse for where the settlement is small (1)and where i t is large (2), showi ng toe pene tration
Note, the magnitude of settlement affects not only the m agnitude oftoe resistance but a lso the lengt h of the Transition Zone:
0
-50 0 1, 000
LOAD and RESISTANCE
DEPTH
0
0 200
SETTLEMENT
2
1
1 2
NEUTRAL PLAN E 1
NEUTRAL PLANE 2
U timate
Resistance
ToePen etrations
0
0
TOE PENETRATION
TO
ERESISTANCE
C
a b
a b
1
2
ToeResistances
A B
3
3
c
c
36
Load-movement relationsPile shaft by t-z relationPile toe by q-z relat ion
0 2 0 40 60 8 0 100
0
2 0
4 0
6 0
8 0
10 0
Movement (%)
Resistance
(%)
Exp. =0.75
Exp. =0.05
R = MVM NT Exp
Exp . = 0.50
Exp.= 0.33
Exp. = 0.20
Exp. =0.10
TOE
SHAFT
exp
2
1
2
1)(
=
R
R
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Alternative
expression
b = Constant =about 0.04 0.15
w = Penetration, 0
100
200
300
400
500
600
0 5 1 0 1 5
MOVEMENT (mm)
LOA
D
(KN)
exp
2
1
2
1)(
=
R
R
bw
eR
R
= 12
1
38
A quote from a textbook *) assigned to 4th Year students at
several North American Universities
Piles located in settling soil layers are subjected to negative skinfriction called downdrag. Thesettlement of the soil layer causesth e
friction forces to act in the samedirection as the loading on the pile.Rather than providing resistance, the negative skin friction i mposesadditional loads on the pile. The net effect is that the pile load
capacity is reduced and pile settlement increases. The allowableload capacity is given as:
neg
S
ultallow Q
F
QQ =
If you thi nk this ghas tly recommenda tion is c orrect, you
have not been pa ying attention!
*) Compassionperhaps misdirectedcompels me not to identify the author
39
0
5
10
15
20
0 500 1,000 1,500 2,000 2,500
LOAD(KN)
DEPTH
(m)
ALLOWABLE
LOAD- (Fs = 2.5 )
CAPACITY
DRAG LOA D
0
5
10
15
20
0 500 1,000 1,500 2,000 2,500
LOAD (KN)
DEPTH
(m)
ALLOWABLE LOADminus
DRAG LOAD*1.0
CAPACITY
DRAG LOA D
Do not include the dragload when determining the allowable load!
Drag load not sub trac ted fr om t he allowa ble l oad Drag l oad su btr acte d!
40
Similarly for the LRFD:
Do not include the dragload when determining thefactored resistance!
Drag load not subtracted from the factored resistance Drag load factored and subtracted!
0
5
10
15
20
0 500 1,000 1,500 2,000 2,500
L OAD (KN)
DEPTH
(m
)
FACT OREDRESISTANCECAPACIT Y
DRAG LOAD
0
5
10
15
20
0 500 1,000 1,500 2,000 2,500
LOAD(KN)
DEPTH
(m)
FACTORED RESISTANCE
minus FACTOREDDRAGL OAD
Factors =0.6and 1.5, respectively
FACTORED RESISTANCE
CAP ACI TY
DRAGLOAD
The locationof the neutral plane (i.e., thelocation of theforce equilibriumand the settlement equilibrium) cannot be determined using factoredloads and resistances! Mother Nature does not do factoring.
41
If afactor of safety of 2.0 is applied alsoto the dragload and the drag load
is subtracted from theallowable load . . . , then?
Imagine that same pile designed for uplift: Logically, if onesubtracts the
drag load for the push case, should one not add it for the pull case ??!!??
The allowable load becomes zero!
Imagine a shaft-bearing pile (no toe resistance) with acertain capacity and
an allowable load for a factor of safety of 2.0.
Do you think that t here is a dif ference in bearing capacity between an
ordinary precast and a prestressed pile? The stress in the pile has
nothing to dowith the bearing capacity.
42
Negative-skin-friction/drag-load does not diminish capacity.
Drag load (and dead load) is a matter for the pile structural
strength, and the main question is if there is settlement that
can cause downdrag. The approach is expressed in The
Unified Design Method.
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The Unified Design Method is a
three-step approach
1. The deadplus live load must be smaller thanthe pile capacitydivided by an appropriate factor of safety. The dragload is not included
when designing against t hebearing capacity.
2. The deadload plus the drag load must be smaller than thestructural strength divided with a appropriate factor of safety. Thelive load is not included because live load and drag load cannotcoexist.
3. The settlement of the pile (pile group) must besmaller than a limitingvalue. The live loadand drag load are not included in this analysis.
44
Construing the Neutral Pla ne and
Determining the Allowa ble Load
45
Settlement analysis by theEquivalent Footing Method
Thec ompressibili tyinthis
zonemustbe of soil and pilecombined
Equivalent Footing
placedat the Location
of the NeutralPlane
2:1 distri bution2:1 dis tribution
G.W.
FILLS ,etc.
Settlement of thep iledfoundation isc aused
by the compres sion of the soil due to i ncreaseof effective stress below the neutralplane
frome xternallo ad applied tothep iles and , for
example, fromf ills, embankments,loadson
ad jacent foundations, andlo wering ofgro undwater table.
soilpile
soilsoilpilepile
combinedAA
EAEAE
+
+=
46Sandpoint, Idaho
Exampleof wherepile length is governed by settlement as opposed to capacity
0
10
20
30
40
50
0 1,000 2,000 3,000 4,000
Axia l Load (KN)
Depth(m)
0
10
20
30
40
50
0 100 200 300
Settlement (mm)
With outwick drains
Primary and
Seco ndary
After wick
drain effect
Axialdesign forseismiccondition
48
Liquefaction (Adapazari, Turkey)
Photo courtesy of Noel J. Gardner, Ottawa
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Photo courtesy of Noel J . Gardner, Ottawa
Liquefaction (Adapazari, Turkey)
0
5
10
15
20
25
30
35
0 1,000 2,000 3,000 4,000
LO AD and RESI STANCE (KN)
DEPTH
(m)
Liqu efiable zone
The Unified Method Applied toSeismic (Liquefaction) Design
0
5
10
15
20
25
30
35
0 1,000 2,000 3,000 4,000
L OAD and RESISTANCE (KN)
DEPTH
(m)
Liquefie d!
Liquefacti on in q li mited thickness zo ne
occurring above the neutral pl ane i s of
no practical c onsequence fo r the piles.
0
5
10
15
20
25
30
35
0 1,000 2,000 3,000 4,000
LOADa nd RESISTANCE (KN)
DEPTH(m)
L iquefied!
What about liquefaction occurring below the neutral plane?
0
5
10
15
20
25
30
35
0 1,000 2,000 3,000 4,000
LOAD and RESISTANCE (KN)
DEPTH
(m)
Liquefied!
Increase in toe
penetrat ion
Pile toe load-movement curv e
0
5
10
15
20
25
30
35
0 1,000 2,000 3, 000 4,000
LOAD and RES ISTANCE (KN)
DEPTH
(m)
Liquefied!
Increase in toe
penetration
Pile toe load-
movement curv e
0
5
10
15
20
25
30
35
SETTLEMENT
DEPTH(m)
Sudden increased
settlement
CASE HISTORY EXAMPLES
The New Internati onal Airport,Bangkok T hai land
Data fro m
Fox, I., Du, M. and Butt ling,S. (2004) and
Buttling, S. (200 6)
54
THAILAND
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Cur rent and Future ( long-term)
Pore Pressure Distribution
0
5
10
15
20
25
30
35
40
45
50
0 100 200 30 0 400 500
Pore Pres sure (KPa )
Depth
(m)
Long-Term
Shor t- Term
( Current)
0
10
20
30
40
50
60
70
1 975 1 98 0 1 98 5 1 99 0 19 95 20 00 20 05 2 01 0
YEAR
Depth
toGraounwaterTabl
e
(m)
Design
Phase
Co nstruction
Phase
Nearby Observations of Groundwater Tab le
Pumping (mining) of groundwater has reduced the pore pressures. In 1996during the beginning of the design process, pumping in thearea was stopped.Pore pressure measurements indicate that thedesired eff ect is being reached;the porepressures arerising.
The clay is soft and normally consolidated with amodulus number smaller t han10.
All foundations thet rellis roof, terminal buildings, concourse, walkways, etc. are placed on piles. The stress-bulbs from the various foundations will overlap eachothers areas resulting ina complicated sett lement analysis.
Several static loading tests on instrumented piles were
performed to establis h the load-transfer conditions at the
site at the time of the testing, i.e., short-term conditions.
Effective stress analysis of the test results for the current
pore pressures established the coefficients applicable to
the long-term conditions after water tables had stabil ized.
A total of25,000+ piles were installed.
The design employed the unified pile design met hod.
The extensive test ingand theconservative assumption on future porepressures allowed anF
sof 2.0. The structural strength of thepile is more than
adequate f or the loadat the neutral plane: Qd+ Q
n 1,500 KN1,800KN
The design (resis tance distri bution) for 600 mm diameter
bored pile i nstalle d to a 30 m embedment de pth.
0
10
20
30
LOAD (KN)
DEPTH(m
)
Qn =
770 KN
Qd = 1,040 KN RULT= 2,870 KNFs = 2.0
Short-Term
Fs = 2.0on long-
term capac ity
0
10
20
30
LOAD (KN)
DEPTH(m)
Long-Term
Qn =
500 KN
Qd = 1,040KN RULT = 2,160 KNFs =2.0
Clay
Sand
Settlementoccurringbelowthisdepthisthekeyto thedesign
Data fro m Fox, I., Du, M. and But tling,S. (2 004)
The settlements for the piled foundations were calculated to:
Construction Long-term Total
Trellis Roof Pylons 20 mm 90 mm 110 mm
Terminal Building 30 15 45
Concourse 35 20 55
* * *
60
0
5
10
15
20
25
30
0 500 1,000 1,500 2,000
LOAD (KN)
DEPTH
(m)
Neutral plane
CAPACITYDEAD
LOAD
DRAG
LOAD
LIVE
LOAD
TOE
RESISTANCE
C
L
A
Y
S
A
N
D
FIL L
A B
Examplefrom an actual p roject somewhere in Europe
A 30 0 mm diameter pile installed to a depth of 25 m through a surficial 2 m thick f illplaced on a 20 m thick layer of soft clay deposited on a thick sa nd layer.
A static loading test has been performed and the
eva luation of the test data has established thatthe pile capacity is 1,400 KN. Applying a factor
of safety of2 .0 results in an allowable load
of700 KN (dead load 600 KN and live load
100 KN). The drag load is 300 KN.
The designer insis ted on subtrac ting the d rag load
from the ca pacity ( considered available only from
below the neutral plane) before determining the
factored resistance (then = 900 KN). The ac tion
load was considered to be the su m of dead load,
live loa d, and drag load, whic h sum already before
multiplication by the load factor w as la rger than the
factored resistance! The tes t results w ere s tated to
show that the 1,400 KN c apacity pile piles was
inadequate to sup port the 700 KN load . The
des igner required longer piles and a considerably
incr eased number o f piles.
Fellenius 2006
!! $$$ !!
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61
0
5
10
15
20
25
30
0 500 1,000 1,500 2,000
LOAD (KN)
DEPTH
(m)
Neutral p lane
Force
equilibrium
0
5
10
15
20
25
30
0 50 100 150 200
S ETTLEMENT ( KN)
DEPTH
(m)
Pile toe penetrations
Neutral planeEqual settlement
Pile-head
settle ments
Groundsurface
settlement
GraphicIllustration of the Case
62
0
5
10
15
20
25
30
35
40
45
0 500 1,000 1,50 0 2,000 2,50 0 3,000
LOAD and RESISTANCE ( KN)
DEPTH
(m)
0
5
10
15
20
25
30
35
40
45
0 1 0 20 30 4 0 50 60 70 8 0
SETTLEMENT (mm)
DEPTH
(m)
NEUTRAL PLANE
TOE MOVEM ENT THAT
MOBILIZES THE TOERESISTANCE
SETTLEMENT OF
PILE HEAD
TOERESISTANCE
PILE
"CAPACITY"
DEAD LOAD
DRAGLOAD
*)Portiono fthe toe
res istance will ha ve
developedf romthe driving
*)
TheUnified Method (repeated Illustration)
63
Factors of safet y and LRFD
FOR YOUR SAFETY, PLEASE
HOLD ON TO THE HAND RAILS
I KNOW, I KNOW, . . .
BUT HAVE Y OU EVER
T RIED TO EXPLAIN
T HE REAL WORLD
T O THE CODE
WRITERS?
64
Piled foundations in current codes
The Canadian Building Code and Highway Design Code ( 1992), as well as the Ho ng KongCode (Geo Guide 2006) app ly the Unified Design method. That is, the drag load is only of
concern for the struc tural s trength of the pile. Indeed, the Ca nadian H ighway Code even
states that for piles shorter than aspect ra tio (b/L) than 80, the des ign does not have to
check for drag load. However, the des ign must alwayscheck for downdrag.
The Manual of US Corps of Engineers indicate a similar approach (but less explicit), s tating
that the dr ag load constitutes a settlement problem.
The ASCE Prac tice for the Design and Installation on Pile Foundations (2007) in cludes thefollowing d efinitions and statements:
DOWNDRAG:The s ettlement due to the pile bein g dragged down by the settling ofsurrounding soil;
DRAG LOAD:Load imposed on the pile by the surrounding soil as it tends to movedownward relative to the pile sha ft, due to s oil consolidation, surcharges, or other c auses.
And: In some cas es, the allowable load, as well as the pile e mbedment depth, is governedby concerns for settlement and d owndrag, and by c oncern for structural s trength for de ad
load plus drag lo ad, rather than by capacity.
65
The FHWA has produced one of the most extensi ve r ecent g uidelines docum ent. The f ull refe rence is:
Report N o. FHWA-NHI-0 5-042, Design and Construction of D riven Pile Foundations - V olume I and II.
National Highway Institute, Federal Highway Ad ministration, U.S. Department of Transport ation,
Washingto n, D.C. , April 2006. 1,450 pages.
The issue of dr ag lo ad and dow ndrag, is cover ed i n a bout 20 of the tot al numb er of p ages. I n all
essential parts, th e FHWA docu ment ad heres to t he princi ples of the Unified Design Met hod.
The FHWA doc ume nt i ndicates t he followi ng c riteria f or i dentifying a drag lo ad and /or dow ndrag
pro blem. If any one of th ese c riteria is met, drag load and downdr ag s hall be considered in the design.
The crit eria are:
1. The settl ement of t he gro und sur face (afte r the piles are i nstalled) will be larger th an 1 0 mm (0. 4 in ).
2. The piles will be l onger than 25 m (82 ft).
3. The compr essible soil laye r is thicke r th an 10 m ( 33 f t).
4. The water table will be lowered more than 4 m (13 ft) .
5. The height of the emb ankment to be plac ed o n t he gro und sur face exceeds 2 m (6.5 ft).
Note however, that negative skin f riction is usua lly f ully mobilized a t amovement between the p ile an d the soil of about 1 mm, not 10 mm.
Where settlement is smal ler than 10 mm, downdrag is not the problem.However, for piles longer than 30+ m (100+ ft), the drag load p lus dead loadmight be of concern for the structural strength o f the pile.
66
The most recent AASHTO LRFD Specifications has applied the requirement ofthe Eurocode 7 in that the drag load (factored) is added to the factored serviceload (dead plus live) and the condition is applied that the resistance is the pilecapacity minus the drag load (factored):
)( negultrnegnfq QRfQfQf +
?!?
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67
5.0 m
SOFT CLAY
SILTY CLAY
11.5 m
FILL
Ave rage unit shaft r esistance, rs =20 KPa
Rs =9 4.2 KN; Rs =Q n
Average rs =5 0 KPa
Rs = 543 KN
"The sett lement due to the fill is sufficie nt to develop maximum negative skin fri ct ion in the soft clay ".
fq*300 + fn*94 543/fr
1.35*300 + 1.35*94 543/1.0
532 543
(Alternative: If fr= 1.1, the lengthin the silty clay becomes 12.4 m)
Q (unfactored) =3 00 KN
Eurocode Guide , E xample 7.4 (Bored 0. 3 m diameter pi le)
Rt =0 KN ?!
CALCULATIONS
The Gui de states that the neutral plane lies at the i nterface o f the two clay layers,
which based on the infor mati on given in the example, cannot be correct. Bu t there is a
good deal mor e wr ong with this desi gn ex ample.
The Gui de st ates that the tw o rs-values are from effective stress c alcul ation. The
values correl ate to s oil unit weights of 18 KN/m3 an d 19.6 KN/ m3, -coefficients of 0.4
in both layer s with groundwater tabl e at ground surface, and a fill str ess of 30 KPa.
68
If the settlement is acceptable, there is room for shortening the pile or increasingthe load. That would raise thelocation of the neutral plane. Would then the pilesett lement still be acceptable?
Analysis using the same numerical values for the pile shaf t,
but including the benef it of a small toe resistance
0
5
10
15
20
0 200 400 600 800 1,000
LOAD (KN)
DEPTH
(m
)
Maximum
Load = 500 KN
Q = 200 KN not 94KN
Rf
=760/1.35 KN >1. 35*300 KN
Rf= 560 KN >405KN
Rt125 KN
= Factored resistance
Fs
=2.50
5
10
15
20
SETTLEMENT (m m)
DEPTH
(m)
Toe
Movem ent
Neutr alPlane
THE KEY QUESTION:
is the settle ment accept able?
?
69
Conventional piled foundati ons with f loor suppor te d on the piles or as a gr ound slab
Piled Raft and Piled Pa d Foundations
70
Piled raft foundation with loads supported by contact stre ss and piles
Remaining load on raft evenly distributed as con tact stress
Evenly distributed load on the r aft supported by evenly distr ibuted piles (Fs = 1.0)
Uneven load on raft
supported by the piles
(Fs = 1.0)
71
Piled pad foundation with loads supported by co ntact stress and piles
Enginee red Backfi ll
Conventional raf t or mat Geotextile
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Jorj Osterberg2001
The Bi-D irectional
Static Loading Test
The O-cell Test
2
Schematics of the Osterberg O-Cell Test(Meyer and Schade 1995)
Upward L oad
Downward Load
THE O-CELL
Telltales
and
Grout Pipe
Pile Head
3
Three O-Cells inside the reinforcing cage(My Thuan Bridge, Vietnam)
4
5
The O-cell can also be installed in a driven p ile. Here in
a 600 mm cylinder pile with a 400 mm central v oid
6
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7
Results of an O-cell test on a 2.8 m by 0.8 m,24 m deep barrette in Manila, The Philippines
- 60
- 50
- 40- 30
- 20
- 10
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
0 5,000 1 0,000 15,0 00 20,00
M
ovement(mm)
Load (KN)
Upward
Downward
Upward
Approximate
extension of
the toemovement to
the zero
conditions
EXAMPLE 1
8
O-Cell test on a1,250 mm
diameter, 40 m
long, bored pileat US82 Bridge
in Washington,Mississippi
installed into
dense sand-80
-60
-40
-20
0
20
40
60
80
100
120
0 2,0 00 4 ,00 0 6,0 00 8 ,00 0 1 0, 00 0
LOAD (KN)
MOVEMENT
(mm)
UPPER PLATE
UPWARD MVMNT
LOWE RPLATE
DOWNW ARD MVMNTWeight
of
Shaft
Residual
Load
Shaft
Toe
EXAMPLE 2
9
Resistance Distribution
0
5
10
15
20
25
30
35
40
0 2, 00 0 4 ,0 00 6 ,00 0 8 ,0 00 1 0, 00 0
LOAD (KN)
DEPTH
(m)
Stra in -Gag e
L eve l#4
Strain-Ga ge
Le vel # 3
Strain-Gag e
Lev el # 2
Strain-Ga ge
Le vel # 1
O-Cell Level
PileT oe
ClaySilt
SandySilt
Dens eSand
withGravel
The unit she ar resis tance a t shaft
failureco rresponds to a beta
coe fficient of abou t 1.0.
0
5
10
15
20
25
30
35
40
0 100 200 300 400
AVERAGE UNIT SHAFT RESISTANCE ( KPa)
DEPTH
(m)
G.W.
10
Load-Movement Curves
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
0 2 0 40 6 0 8 0 1 00 12 0
MO VEMENT (mm)
LOAD
(KN)
Strain-Gage
Level #4
Stra in -Gag e
Level #2
Strain-Gage
Level #1
O- Cell
11
Searching for the Residual Load
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
0.0 0.5 1.0 1.5 2.0
P ILE C OMPRESSION (mm)
LOAD
(KN
INDICATED RESI DUALLO AD
0
1,0 00
2,0 00
3,0 00
4,0 00
5,0 00
6,0 00
7,0 00
8,0 00
9,0 00
0 . 0 2 5. 0 50 . 0 7 5 . 0 1 0 0. 0 1 25 . 0 15 0 .0
PLATESEPARATION (OPENING) (mm)
LOAD
(KN) O-Ce ll Load
O-Ce ll Load
12
From the O-Cell results, one can produce the load-movement curvethat one would have obtained in a routi ne Head-Down Test
Head down
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13
14
O-Cell Results Shown Two Ways
-80
-60
-40
-20
0
20
40
60
80
100
120
0 2 ,0 00 4, 00 0 6 ,0 00 8, 00 0 1 0,000
LOAD (KN)
MOVEMENT
(mm)
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
0 2 0 4 0 60 80 1 00 1 20
M OVEM ENT (mm)
LOAD
(KN)
Sha ft
Mo veme nt
Toe
Move ment
Weight ofShaft
Re sidua lLo ad
15
Finding a Soft Pile Toe
0 2 4 6 8 1 0 1 2 14 16
- 80
- 70
- 60
- 50
- 40
- 30
- 20
- 10
0
10
20
APPLIED L OAD (MN)
MOVEMENT
(mm
)
REBOUND
WHEN
UNL
OADING
COMPRESSION OF
SOFT SOILAT T O E
Toe load-movement for a pile witha soft toeat Albuquerque, NewMexico(Data from Osterbergand Hayes, 1999)
EXAMPLE 3
16
Kahuku Bridge acr ossKamehameha Highway, Hawaii
Test on 600 mm, 17 m long, bor ed pile
0
10
20
30
40
50
60
70
80
0 100 200 300 400 500 6 00 700 800
LOAD (kips)
DEPTH
(ft)
DATA FRO MO-CEL L TEST
O-cell
Shaftandtoeresist ances
arenot fully mobilizedb elowt he O -cell
0
10
20
30
40
50
60
70
80
0 100 200 3 00 400 5 00 600 700 800
LOAD (k ips)
DEPTH
(ft)
CONVERT ED TO
HEAD- DOW N"TEST"
APPROXIMATED
SPECUL AT IVE
FULLY
MOBILI ZED
O-cell
EXAMPLE 4
17
EXAMPLE 5
Test at Bangkok Airport
18
Stage 1Lower Cell activated
Upper cell closed
Stage 2Lower Cell openUpper Cell activated
Stage 2Lower Cell closedUpper Cell activated
Data fromFox, I., Du, M. an d Buttling,S. (2004)
Buttling, S . (2006)
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19
Downward movements during test phases 1, 2, and 3
Concern was expressed (Buttling 2006)t hat the toe resistance (Phase 1) was3,000KN and
the shaf t resi stance for the lower segment was 5,000 KN (Phase 2), while in Phase 3 the
combined shaft and toe resistances were only 6,000 KN. Should not the Phase 3 resistancebe 8,000 KN rather than 6, 000 KN (i.e., the sum of the values5,000 KNand 3,000)?
0
25
50
75
100
125
150
175
0 2,000 4,000 6,000 8,000 10,000
LOAD (KN)
MOVEMENT(m
m)
Active CellInactive, Open Cell
Inactive, ClosedCel
P1 P2P 3
1 2 3
20
Downward toe mov ements
0
2 5
5 0
7 5
100
125
150
175
0 2 ,000 4,000 6,000 8,000 10,0 00
LOAD (KN)
MOVEMENT(mm)
Active Cell
Inactive, Open CellInactive, Closed Cell
P1 P2P3
1 2 30
25
50
75
1 00
1 25
1 50
1 75
0 2,00 0 4,000 6,0 00 8,000 10 ,000
LOAD (KN)
DOWNWARDMOVEMENT(mm)
Active Cell
Inacti ve, Open CellInacti ve, Closed Cell
P2
P1 and P2
datacombined
P3
1 2 3
are best plott ed per sequenc e of testing
21
0
5
10
15
20
25
30
35
40
45
0 2,00 0 4,0 00 6 ,000
Load (KN)
Depth(m)
Stage 1
101 mm toe
0
5
10
15
20
25
30
35
40
45
0 2,000 4 ,000 6,000
Load (KN)
Depth(m)
Sta ge 2
62 mmDow nw ard
Movement
0
5
10
15
20
25
30
35
40
45
0 2,000 4 ,000 6,000
Load (KN)
Depth(m)
Sta ge 2
Stage 3
Load Distri butions for the Bangkok Airport Test
22
0
5
10
15
20
25
30
35
40
45
0 2 ,000 4,0 00 6,00 0
Load (KN)
Depth(m)
Stage 3
48 mm
DownwardMovement
0
5
10
15
20
25
30
35
40
45
0 2, 000 4,0 00 6 ,00 0 8, 00 0 1 0,0 00 1 2,0 00
Load (KN)
Depth(m)
St age 2 St ag e 3Stage 1
?
?
23
0
50
100
150
200
0 500 1,000 1,500 2,000 2,500 3,000 3,5 00
LOAD FOR LOWEST STRAIN-GAGE (KN)
MOVEMENT(mm) Stage 1
Stage 2( Stage 3)
Stage 3
The lowest strain-gagevalues are very suspect
24
O-Cell tests for Hacienda ElenaDevelopment, Guay nabo, Puerto Rico
EXAMPLE 6
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25
Clayey Silt
Sapro lite
HardClay
Weathered
Bedrock
O-cell Test Results
- 80
- 70
- 60
- 50
- 40
- 30
- 20
- 10
0
10
20
0 1,0 0 0 2 ,00 0 3 ,0 00 4, 000 5 ,00 0
LOAD ( KN)
MOVEMENT(m
m)
26
Measured load-movements can besimulated (fitting) to t-z and q-z relations
Pile shaft by t-z relation; Pile to e by q-z relat ion
0 2 0 40 60 8 0 100
0
2 0
4 0
6 0
8 0
10 0
Movement (%)
Resistance(%)
Exp. =0.75
Exp. =0.05
R = MVM NT Exp
Exp . = 0.50
Exp.= 0.33
Exp. = 0.20
Exp. =0.10
TOE
SHAFT
exp
2
1
2
1)(
=
R
R
27
O-c ell Test Resultswith UniPile Simulation
0
5,000
10,000
15,000
0 10 20 30 40 50 60 70
MO VEMENT (mm)
LOAD
(KN)
Toe
Shaft
Exp.= 0. 20
Exp.= 0.55
O-c ell Test Resultswith UniPile Simulation
0
5,000
10,000
15,000
0 10 20 30 40 50 60 70
MO VEMENT (mm)
LOAD
(KN) Head
Toe
Shaft
Extrapolation of
O-cell dataExp.= 0. 20
Exp.= 0.55
Fitting Result s
O-c ell Test Resultswith UniPile Simulation
0
5,000
10,000
15,000
0 10 20 30 40 50 60 70
MO VEMENT (mm)
LOAD
(KN) Head
Toe
Shaft
Extrapolation of
O-cell dataExp.= 0. 20
Exp.= 0.55
Combining the
t-zand q-z
curves
Pensacola, Florida
410 mm diameter, 22mlong, precast concretepile driven into silty sand
EXAMPLE 7
Pensacola, Florida, USA
-10
0
10
20
30
40
50
60
0 500 1, 000 1,500 2,000 2, 500
LOAD (KN)
MOVEMENT
(mm)
Pensacola, Florida, USA
-4
-3
-2
-1
0
0 500 1, 000 1,500 2,000 2, 500
LOAD (KN)
MOVEMENT(mm)
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Pensacola, Florida, USA
0
1,000
2,000
3,000
4,000
0 2 4 6 8 10
DOWNWARD TO E MOVEMENT (mm )
LOAD
(KN)
0
1,000
2,000
3,000
4,000
0 2 4 6 8 10
DOWNWARD TOE MOVEMENT (mm)
LOAD
(KN)
Exp. = 0.45
CURVE FIT
TEST
Pensacola, Florida, USA
0
1,000
2,000
3,000
4,000
5,000
0 10 20 30 40 50 60
UPWARD SHAFT MOVEMENT (mm)
LOAD
(KN)
E xp. = 0.15
CURVE FIT
TEST
33
Bridge ove r Panama Canal, Paraiso Reach, Republic of Panama
O-cell test on a 2.0 m (80 inches) diameter, 30 m (100 ft) deep s haftdril led into the Pedro Miguel and Cuc aracha formations, February 2003.
EXAMPLE 8
34
O-cel l
Strain-Gage
Locations
-50
-40
-30
-20
-10
0
10
20
30
40
50
0 5,000 10,000 15,000 20,000
LOAD (KN)
MOVEMENT(m
m)
Downw ardMovement
Upward
M ovemen t
Load-Movements . Measured and Fitted to UniPile Calcula tion.
35
Test Results Processed for Design Analysis
0
5
10
15
20
25
30
0 5 ,000 1 0, 00 0 1 5, 00 0 20 ,00 0 25 ,000 30, 0 00
LOAD (KN)
DEPTH
(m)
0
5
10
15
20
25
30
0 5,000 10,000 15,000 20,000 25,000 30,000
LOAD (KN)
DEPTH(m)
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
0 1 0 20 30 4 0 50 6 0 70
MOVEMENT (mm
LOAD(KN))
Measured and Calculated
Load-Movement Curves
plus Simulated Pile HeadLoad-Movement
TOE
SHAFT
HEAD
Off set
Limit
0.30
0.45
0.30
___
1.20
Torre Chapultepec, Mexico City, Mexico
O-cell Tes t on a 700 mm diameter 34 m deep bored pi le
0 m - 26 m desiccated clayey silt
5 m 34+ m dense sandand silt
EXAMPLE 9
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Torre Chapultepec, Mexico City, Mexico
- 400
-350
-300
-250
-200
-150
-100
-50
0
0 500 1 ,000 1, 500 2,000 2,500
LOAD (KN)
DOWNWARDMOVE
MENT(mm) Toe-Up O-cell Test
Torre Chapultepec, Mexico City, Mexico
0
2,000
4,000
6,000
8,000
10,000
0 20 40 60 80 100 120 140
MOVEMENT (mm)
LOAD
(KN)
Head-Down Test
0
2,000
4,000
6,000
8,000
10, 000
0 20 40 60 80 100 120 140
MOVEMENT (mm)
LOAD
(KN)
Head-Down Test
Torre Chapultepec, Mexico City, Mexico
-400
-350
-300
-250
-200
-150
-100
-50
0
0 500 1,000 1, 500 2,000 2,500
LOAD (KN)
DOWNWARDMOVEMENT(mm) Toe-Up O -ce ll Test
- 400
-350
-300
-250
-200
-150
-100
-50
0
0 500 1 ,000 1, 500 2, 000 2,500
LOAD ( KN)
DOWNWARDMOVEMENT(mm) Toe-Up O-cell Test
40
O-cel l Tests on an 11 mlong, 460 mm square
precast concrete piledriven in silica sand in
North-East Florida
(Data from McVay et al. 1999)
A study of Toe and
Shaft Resista nce
Response to
Loading
41
CPT sounding next to an 11 m long, 460 mm square precastconcrete pil e driv en in s ilic a sand in North-East Florida
Data fromBullock et al. 2005, 1999
0
2
4
6
8
10
12
14
0 1 0 2 0 3 0 40
Cone Stress, qt (MPa)
DEPTH
(m)
0
2
4
6
8
10
12
14
0 1 00 2 00 30 0
Sleeve Friction (K Pa)
DEPTH(m)
0
2
4
6
8
10
12
14
0.0 0.2 0 .4 0 .6 0.8 1.0
Friction Ratio (%)
DEPTH(m)
PRES
2b
42
Load-mo vement curves for the pil e toe.The t wofirst cycles and beginning of the third cycleThe t wofirst cycles and beginning of the third cycle
0
200
400
600
800
1,000
1,200
1,400
1,600
-3 -2 -1 0 1 2 3 4 5 6 7 8
T OE MOVEM ENT (mm)
CELLLOAD
(KN
1
2
3
Toe Re sistance
Response
Data from
Bullock et al. 2005, 1999
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43
Load-mo vement cur ves
for the pile toe during all four load cycles
0
200
400
600
800
1,000
1,200
1,400
1,600
-5 5 15 25 35 45 55 65 75
T OE MOVEMENT (mm)
CELLLOAD(KN
Data fromBullock et al. 2005, 1999
44
0
2
4
6
8
10
12
14
0 10 2 0 3 0 40
Cone St ress, qt (MPa)
DEPTH
(m)
PRES
2b
Data fromBullock et al. 2005, 1999
45
0
200
400
600
800
1,000
1,200
1,400
1,600
0 5 10 15 20 25 30 35 40 45 50
CELLEXT ENSION (mm)
LOAD
(KN)
8 hours 4days
16days
SHAFT LOAD-MOVEM ENT DIAGRAM FROM O-CELL TEST S
PDA
CA PWAP
1 8 min.BOR
1 hBOR
EOD
Shaft
Resista nce
Response
UPWARD MOVEMENT (mm)
Data fromBullock et al. 2005, 1999
46
0
2
4
6
8
1012
14
16
18
20
0 500 1 ,000 1,50 0 2 ,000 2,50 0 3 ,000
Shaft Res istance, Rs (KN)
DEP
TH
(m)
E-F
LCPC
Schm ertmann
Dutch
Meyerhof
Beta
Tests
Distributions of unit and total shaft resistances
0
2
4
6
8
1012
14
16
18
20
0 50 100 1 50 200
Unit Sh aft Resistance, rs (KPa)
DEPTH
(m)
E-F LCPC
=1.60
=1.00
= 0.20
=0.80
Data fromBullock et al. 2005, 1999
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ShinHo and MyeongJi Housing Project,ShinHo and MyeongJi Housing Project,in the estuary of the Nakdong River, Pusan, Koreain the estuary of the Nakdong River, Pusan, Korea
Project Managers: Drs. Song Gyo Chung andProject Managers: Drs. Song Gyo Chung and
SSung Ryul Kim, Dongung Ryul Kim, Dong--A University, BusanA University, Busan
2
3
4
5
AIR VIEW
(Shinho Site)
SITE PLAN (SH Site)
6
Silty cl ay
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7
0
1 0
2 0
3 0
4 0
5 0
6 0
0 10 20 30
ConeStress, qt
(MPa)
DEPTH
(m)
0
1 0
2 0
3 0
4 0
5 0
6 0
0 25 5 0 75 100
Sleeve Friction,fs (KPa)
DEPTH(
m)
0
10
20
30
40
50
60
0 500 1, 000 1, 500
PoreP ressure (KPa)
DEPTH
(m)
0
10
20
30
40
50
60
0 1 2 3 4 5
Fricti onRatio,fR
(%)
DEPTH
(m)
SILT&CLA Y
VerydenseS AND
Profile
FILL
SiltyCLAY
(marine)
SAND
805-08-08 Myeongji Site C -block
0
10
20
30
40
50
0 10 20 3 0
Cone Stress, qt
(MPa)
DEPTH
(m)
0
1 0
2 0
3 0
4 0
5 0
0 2 00 400
Sleeve Friction (KPa)
DEPTH
(m
)
0
10
20
30
40
50
0 25 0 500 7 50 1,000
Pore Pressure (KPa)
DEPTH
(m
)
0
10
20
30
40
50
0 1 2 3 4 5
Friction Ratio (%)
DEPTH
(m)
Profile
Mixed
CLAY
SAN
Reduced porepressure (dilation)
SAND
9
0
5
10
15
20
25
30
35
40
45
0 500 1,000 1,50 0 2,000 2,50 0 3,000
LOAD and RESISTANCE ( KN)
DEPTH
(m)
0
5
10
15
20
25
30
35
40
45
0 1 0 20 30 4 0 50 60 70 8 0
SETTLEMENT (mm)
DEPTH
(m)
NEUTRAL PLANE
TOE MOVEM ENT THAT
MOBI LIZES THE TOE
RESISTANCE
SETTLEM ENTOF
PILE HEAD
TOE
RESISTANCE
PILE
"CAPACITY"
DEAD LOAD
DRAGLOA D
*)Portiono f the toe
res istance will ha ve
developed f rom the driving
*)
TheUnified Method for Design of Piled Foundations(typical only ; the numbers arenot applicable to this site)
10
The ques tions to resolve in the de sign
1. What is the capacity in the different layers?
2. What is the depth to the force equilibrium/settlementequilibrium, i.e. , the neutral plane
3. What will be themaximum load int he pile? Is thestructuralstrength adequate?
4. What is the sett lement of thepile as a function of thelocation ofthe neutral plane.
11
The shaft resistance: 10,000 KN
The toe resistance: 5,000 KN KN
Pile structural strength 12,000 KN
(when grouted) 16,000 KN
12
01A, 01B
12A, 1 2B,12C,1 2D
0
5
10
15
20
25
30
35
40
45
50
55
60
0 50 1 00 1 50 2 00 2 50 3 00
PRES (Bl/200m m)
DEPTH
(m)
0
10
20
30
40
50
60
0 10 20 30
Cone Stress,qt
(MPa)
DEPTH
(m)
PRES HEIGHT of
FALL
(cm)10
20
40
10
20
First Shinho O-cell test pile
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13
14
0
10
20
30
40
50
60
70
0 2 4 48 72 96 12 0 144 168 19 2 216 240
HOURS AFTER GROUTING
TEMPERATURE
(C)
Temperature a t various
depths in the gr out of a 0.4 m
center hole in a 56 m long,
0.6 m diameter, cylinder pile.
Temperature Records
15
-20 0
-15 0
-10 0
-50
0
5 0
10 0
15 0
20 0
25 0
30 0
0 24 48 72 96 120 144 168 192 2 16 24 0
HOURSAF TER GROUTING
STRAIN
()
Strain Records
16
0
5
10
15
20
25
30
35
40
45
50
55
60
- 300 -200 -100 0 100 200 300 400
STRAIN ()
DEPTH
(m)
9d
15d
23d
30d
39d
49d
59d
82d
99d
122d
218dDay of
TestAtan E- modulusof 30 GPa,this strai nchange corres ponds
to a load c hange of 3,200 KN
Strain measuredduring the 218-daywait-period betweendriving (grouting)and testing.
17
-90
-60
-30
0
30
0 1, 000 2,000 3,000 4,000 5,000 6,000
LOAD T OE-UP TEST (KN)
MOVEMENT(mm)
Breaking outthe O-cellbottom plate
Upper O-cell plate continuedupward during the unloading, butpile head did not move ?!?
The O-cell Toe-up Test
Plunging ?!?
18
0
5
10
15
20
25
30
0 1,00 0 2,00 0 3 ,000 4 ,000 5 ,000 6 ,000 7,0 00
LOAD TOE-UP TEST (KN)
UPWARDMOVEMENT(mm)
The pile head
did not move.
A 16 mm pile
shaft
compression is
not pos sible.
Pile must be
crushed above
(and below? )
O-cell plat e.
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19
0
10
20
30
40
50
60
- 5,000 0 5, 000
LOAD 2nd TOE-UP (KN)
DEPTH
(m)
0
10
20
30
40
50
60
-5,000 0 5, 000
LOAD 1st TOE-UP ( KN)
DEPTH
(m)
20
-1,000
-500
0
500
1,000
1,500
0 1,000 2,000 3,000 4,000 5,0 00 6,000
O-c ell Load 2nd Toe-up (KN)
Strain-GageLoad(KN)
SG-1
SG-2
3.0 mm mvmnt up
21
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
0 10 20 30 40 50 60 70 80 90
MOVEMENT (mm)
LOADHEAD-DOWNTESTS(KN)
Now The Head-down Test
22
We have got the strain.
How to we get the load?
Load is stress times area
Stress is Modulus (E) times strain
The modulus is the key
E=
23
For a concrete pile or a concre te-filled bored pile, the
modulus to use is the combined modulus of concrete,
reinforcement , and steel casing
cs
ccss
comb
AA
AEAEE
+
+=
Ecomb
= combined modulusE
s= modulus f or st eel
As
= area of steelE
c= modulus for concrete
Ac
= area of concrete
24
For a concrete pile or a concre te-filled bored pile, the
modulus to use is the combined modulus of concrete,
reinforcement , and steel casing
cs
ccss
comb
AA
AEAEE
+
+=
Ecomb
= combined modulusE
s= modulus f or st eel
As
= area of steelE
c= modulus for concrete
Ac
= area of concrete
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25
Themodulus of steel is 200GPa (207GPa for those weak at heart)
Themodulus of concrete is. . . . ?
Hard to answer. There is a sort of relation to the cylinder strengthand themodulus usually appears as avalue around 30GPa, or perhaps 20GPaor so, perhaps more.
This is not good enough answer and being vague is not necessary.
Themodulus can be determined from thestrain measurements.
Calculate first the
Values are known
=
tE
26
0 200 4 00 6 00 80 0
0
10
20
30
40
50
60
70
80
90
100
MICROSTRAIN
TANGENTMODULUS
(GPa)
Level 1
Level 2
Level 3
Level 4
Level 5
Best Fit Line
Example of Tangent Modulus P lot
27
First Head-down Test
0
10
20
30
40
50
60
0 500 1,000 1,500
STRAIN ()
CHANGEOFSTRESS/CHANGEOFSTRAIN,Mt
(GPa)
SG-12 CD
SG-12 AB
SG 11
SG-10
SG-9
SG-8
Q =A(-0.0035()2
+ 29 )
The Shinho te st pile head-down test
28
The Shinho te st pile head-down test
0
10
20
30
40
50
60
0 2,000 4,000 6,000 8,000 10,000
LOAD , 2nd HEAD-DOWN (KN)
DEPTH
(m)
ZEROLINE IS ATS TARTOF
2NDHEAD-DOWNTEST
Afte r
Unloading
0
10
20
30
40
50
60
0 2,000 4,000 6,000 8,000 10,000
LOAD, 2ndHEAD-DOWN (KN)
DEPTH(m)
ZERO LINEI SA TSTARTOF
2NDHEAD-DOWN TEST
= 1.0
= 0.4
(0.2
= 0.1
(0.1)
= 0.7
(0.2)
= 0. 3
(0.1
TRUERESISTANCE(fo r
max imum residual load)
RESIDUAL
(maximum)
Afte rUnloading
PRESUMED RESIDUALL OADATSTART OFO-CELL TEST
29
0
10
20
30
40
50
60
0 2,000 4,000 6,000 8,000 10,000
L OAD, 2nd HEAD-DOWN (KN)
DEPTH
(m)
ZEROLINE IS A TSTART OF
2ND HEAD -DOWNTEST
= 1. 0
= 0.4
(0.25
= 0.1
(0.1 )
= 0.7
(0.2 )
= 0.3
(0.1
TRUERESISTANCE(for
maxim um residual load)
RESIDUAL
(maxim um)
AfterUnloa ding
PRE UMED REI DUALL OAD ATSTARTOFO-CELL TEST
30
0
10
20
30
40
50
60
0 2,000 4,000 6,000 8,000 10,000
LOAD, 2nd HE AD-DOWN ( KN)
DEPTH
(m)
ZERO LINE IS AT STARTOF
2ND HEAD-DOWN TEST
= 1.0
= 0.4
(0.2
= 0.1
(0.1)
= 0.7
(0.2)
= 0.3
(0.1)
TRUE RESISTANCE(for
maximum residual load)
RESIDUAL
(maximum)
After
Unloading
Theshadedforcearea corresponds
to a shortenin g of just abo ut 3 mm
PRESUMED RESIDUAL LOADATSTARTOF O-CELL TEST
EstimatingResidual LoadDistributionat Start ofthe O-cellTest
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31
FHWA tests on 0.9 m diameter bored piles
One in sand and one in clay(Baker et al., 1990and Briaud et al., 2000)
0
2
4
6
8
10
12
0 10 20 30 4 0
Cone Str ess a nd SPT N-Index(MPa andbl/0 .3 m)
DEPTH
(m
)
Silty
Sand
Sand
Pile 4
0
2
4
6
8
10
12
0 1 0 2 0 3 0 40
Cone Stres s (MPa)
DEPTH
(m
)
Pile 7
N
qc
Clay
SiltySand Clay
32
RESULTS: True Load-transfer curves
0.0
2.0
4.0
6.0
8.0
1 0.0
1 2.0
0 1, 0 00 2 ,0 00 3 , 000 4, 00 0 5, 0 00
LOAD (KN)
DEPTH
(m)
PILE 4
SAND
Measu re d
Di stribu ti on
0.0
2.0
4.0
6.0
8.0
1 0.0
1 2.0
0 1, 0 00 2 ,0 00 3 , 000 4, 00 0 5, 0 00
LOAD (KN)
DEPTH
(m)
PILE 4
SAND
True
Dis t r ib utio n
Re sidua
Loa d
Measu re d
Di stribu ti on
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0 1 ,000 2 ,000 3,00 0 4,00 0 5, 00 0
LOAD (KN)
DEPTH
(m
)
PILE 7
CLAY
Me asured
Distribution
0.0
2.0
4.0
6.0
8.0
10.0
12.0
0 1 ,000 2 ,000 3,00 0 4, 00 0 5,00 0
LOAD (KN)
DEPTH
(m)
PILE 7
CLAY
TrueDistribution
Res idualL oad
33
Results of analysis of a Monotube pile in sand(Fellenius et al., 2000)
0
5
10
15
20
25
0 1, 000 2 ,000 3,0 00
LOAD (KN )
DEPTH
(m
True
Resistance
Measured
Resistance
Residual
Load
(Fellenius et al., 2000)
34
Note, just bec aus e a strain- gage has registered some strain
values dur ing a test does not g uarantee that the data are
useful. Unavoidable errors and natural variati ons amount to
about 50 microstra in to 100 microstra in. Therefor e, the test
must be des igned to achieve strain values at least of about 600
microstrain, preferably 1, 000 microstrain and beyond. If the
imposed strain are small er, the relativ e errors and imprecision
wil l be too large, a nd int erpretat ion of the test data becom es
uncertain, causing the inv estment in instrumentation to be less
than meaningful. The test should engage the pile material up
to at least half the strength. Preferably, aim for reac hing close
to t he material strength (structural strength).
35
Residual Load is the same as Drag Load . The
distinction made is that by residual loadwe mean the
locked-in load present in the pil e immediately before westart a static loading test. By drag loadwe mean the load
present in the pile i n the long-term
Residual load
Residual load as well as drag load can develop in
coarse-grained soil just as it does in clay soil
Both residual load and dragload develop at ve ry small
movements betw een the pile and the soil
36
0
200
400
600
800
1,000
1,200
0 5 10 15 20 25
MOVEMENT (mm)
LOAD
(KN)
HEAD
TOE
TOE TELLTALEA
Does not this shape of
measured toe movementsuggest that there is a
distinct toe capacity?
Toe Resistance
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37
0
200
400
600
800
1,000
1,200
0 5 10 15 20 25
MOVEMENT (mm)
LOAD
(KN)
HEAD
TOE
TOE TELLTALEA
0
200
400
600
800
1,000
,
0 5 10 15 20 25
MOVEMENT (mm)
LO
AD
(KN)
HEAD
"Virgin" Toe Curve
TOE
B
No, it onl y appears that way when we forget to consider the residualtoe load (also called the initial, or virgin toe movement)
38
Of course,
we must consider also other aspects:
39
Interpretation of a series of tests
performed at different times
0 10 20 30 40 50 60 70
0
10
20
30
40
50
60
70
Movement (m m)Changeo
fHorizon
talStress
(KPa
)
5 D ays
1 Day
8 D ays
4 Months
22 Mon ths
Cell D1
Results thought dueto set-upexplained as Increase inHorizontal Effective Stress
Fellenius 2002
Results plottedAccording toMovement Path
0 50 100 150 200 250
0
10
20
30
40
50
60
70
Movement ( mm)
5 D ays
1 Day
8 D ays
4 Months
22 Mon ths
40
Also the best field work can get messed up if the analysis and
conclusion effort loses sight of the his tory of the data
0
1,000
2,000
3,000
4,000
5,000
6,000
0 25 50 75 100 125 150 175 200
MOVEME NT (mm)
LOAD(
KN)
STATNAMICCAPWAP
STATIC
0
1,000
2,000
3,000
4,000
5,000
6,000
0 25 50 75 100 125 150 175 200
MOVE MENT (mm)
LO
AD
(KN)
STATIC
STATNAMIC
CAPWAP
41
The O-Cell test with a couple of straingages, judiciously placed, will provide:
1. Separate values of shaft and toe resistances
2. Estimate of residual load
3. Load-transfer for the pile
4. Pile-toe load-movement curves (q-z function)
5. Results that can be extrapolated to other piles
6. Data necessary for settlement analysis
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