session 3 - presentation 1 - r jardine - imperial college - axial design of driven offshore piles -...

8/10/2019 Session 3 - Presentation 1 - R Jardine - Imperial College - Axial Design of Driven Offshore Piles - DGF Seminar 201

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Imperial College LondonPage 1

Recent developments in axial design

of driven offshore piles

DGF Copenhagen

April 1st2014

Richard Jardine


Themes:

Changed API, ISO axial capacity recommendations

for sands, including ICP-05

Research background leading to new methods

Applications, case histories, some surprising results

New research: ageing, cyclic and lateral loading

Next set of issues: clay methods & improving load-

displacement predictions


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New rules for static axial capacity in silica

sand: 2011 API recommendations

Before: had = K vo tanfor shaft, qb= Nqvofor base.Limits to , qband values for , Nqdepend on D50and Dr

Now:modified to = K tan, no loose sand case

Recognises:API main text methods significant bias andpoor reliability:

Qcalculated/Qmeasuredratios = Qc/Qmsubject to CoV ~ 65%

Recommend:completely different CPT based methods,including ICP. Note need for different SI & specialist staff


The axial capacity prize:

Feedback from one UK

wind-farm design team

Critical economies through

ICP-05 or UWA-05 sand

axial capacity methods

Also applied in onshore civil

engineering: Williams et al 1997

Derived from field ICP research

Lehane et al 1993

Chow 1997

Jardine et al 2005


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Research background:

Critique of conventional approach &

how new CPT methods were derived


MTD and ICP methods

First proposed in 1996,

extended in 2005 to cover:

Group action

Pile shape

Seismic effects

Special and problem soils

Factors of safetyRing shear test methodology

Ageing

Cyclic loading

Databases: mini-to-mega piles


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Shaft capacities from 81 tests in sand; Jardine et al (2005)

0 10 20 30 40 50 60 70 80 90 100

Relative densi ty,Dr(%)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Qc

/Qm

DK

EU

EU EUEU

H

H

BD

GDK

EU EU EUEU

H

SP

SP

SP

Pile type & test direction

Steel, closed-ended, tension

Steel, closed-ended, compression

Concrete, closed-ended, tension

Concrete, closed-ended, compression

Steel, open-ended, tensionSteel, open-ended, compression

Concrete, open-ended, tension

0 20 40 60 80 100

L/D

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Qc/Qm

DK

EU

EU EUEU

H

H

BD

DK

HOEU EU EUEU

H

SP

SP

SP

0 10 20 30 40 50 60 70 80 90 100

Relative densi ty,Dr(%)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Qc

/Qm

DKEU EU

EU

EUH

HBD

DK

EU

EU

EU

EUEUEU

DK

HSP

SP

SP

0 10 20 30 40 50 60 70 80 90 100

L/D

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Qc/Qm

DKEU EU

EU

EUHH BDEU

EU

EU

EUEUEU

DK

HSP

SP

SP

API: skewed for relative density, pile length and tension loading

APIAPI

ICP ICP

Pile failures atHound Point andSungai Perak BridgeWilliams et al (1997)

ICP shows no skewing (tension solid) Average pile age = 25 days


Critical review of conventional theory

What controls shear () and normal stress rfat failure?

How does rf vary with v0and local Dr?

What controls the friction angle ?

Any missing key variables?

Is tension loading different to compression?

Does shallow foundation Nqapply to end-bearing?

Do any limits apply to and end bearing pressure qb?


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Background IC

research with

instrumented piles

Closed-end, 102mm

OD; up to 20m long

SSTs measure local

rand

Bond, Jardine and

Dalton (1991)

Intensive testing at 2

sand and 4 clay sites0

1.0

2.0

3.0

4.0

Distancefrom

piletip,h(m)

surface stress transducer

pore pressure probe

axial load cell

leadinginstrumentcluster, h/R=8

followinginstrumentcluster, h/R=27

trailinginstrumentcluster, h/R=50

lagginginstrumentcluster, h/R=72

ICP Configuration for Labenne tests, SW FranceDefinition of stresses and tip parameter - h


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Geotechnical profile: Labenne, after Lehane (1992)

Loose dune sand, including thin organic layer

Labenne end bearingMeasured base resistance qb and CPT qc


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Page 15

Denser North Sea Marine sand Dunkerque France,

Chow (1997)

Borehole log

Very dense, light brown, uniform, fine tomedium, subrounded SAND withoccasional shell fragments (Hydraulic fill)

GWL

Dense with shell fragments(Flandrian Sand)

Organic layer

Dense, green-brown and grey-brown,uniform fine to medium, subroundedSAND with some shell fragments(Flandrian Sand)

Becoming very dense

Depth(m)

CPT q (MPa) CPT f (kPa)C C

0 10 20 30 40 0 100 200 300 4000

2

4

6

8

10

12

14

16

18

20

22

24


Influence of CPT qcand pile tip position on r

Dunkerque, after Chow (1997)

API

For fixed depth r falls with h/R

rvaries with qc


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Possible

causes for h/R

influence onlocal stresses

along pile

length;

Chow (1997)

After Chow (1997)

Heave

Whip

Extreme

driving

cycles

Relaxation as

tip stress

concentration

moves away

Friction fatigue?

Page 18

Load cyclesdegrade shaft

capacity

Can recover with time

Not true fatigue

See recent keynotes

on cyclic design:

Jardine et al (2012)

Andersen et al (2013)

-0.2 0 0.2 0.4 0.6 0.8 1

Qaverage/ Qmax static

0.2

0.4

0.6

0.8

1

Qcyclic

/Qmaxstatic

First failureCyclic failure after previous cyclic or static failureAged pile, no previous failureAged pile, after previous failure

13

31

345

24

27221

>200

1241

10

20

50

100

200

400

1

Nf

>1000

2069

Datapoint number = Nf> indicates unfailed by cycling

Field tests on 457mm OD,

19m long steel pipe piles, Dunkerque


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Delft University photoelastic particulate test rig

Tip installation stress focus and bearing failure



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Dunkerque: loading response & ICP effective

stress paths, similar patterns to Labenne

Base qb qc not relatedlinearly to v0

rvaries under load

Tension compression

rd= 2G r/R

Draffects responsethrough G

cvnot affected by Dr

cvangles: sand-on-steel interface ring-shear tests

Ho et al (2010)Steel interface

Crushed sand

Intact sand


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10/04/2014

Interface shear cv: silt-to-fine gravel,

Interfaces with roughness of industrial piles

Direct & ring shear: Barmpopoulos et al (2009), Ho et al (2010)

Direct shear trend

Ring shear


Full ICP design principles: closed ended piles Radial shaft stresses r= A qc(v0)

a(h/R)b

Loading to failure alters r by factor that varies with 1/R

Differences in tension and compression responses

At failure f /r= tan cv with cv from interface lab tests

Base capacity qblinked to CPT qcdiameter dependent

No upper limits to f or qb- care needed in variable profiles

How to deal with open ended piles?


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Generalisation of ICP

shaft expressions toopen ended piles

Choices considered by

Chow (1997)

B2: R* = (R2oR2i)

0.5


Assessment by Chow (1997)

Five hypotheses checked

with instrumented open-

ended (325mm)

Dunkerque pile

B2 choice considered

most practical

Re-checked against full

scale data base, adopted

for MTD-96

Later UWA-05 follow

alternative A2 route

-200 -150 -100 -50 0 50 100 150 200

Peak shear stress (kPa)

0

2

4

6

8

10

12

Depth(m)

Pile CST'89aC'89aPrediction

-200 -150 -100 -50 0 50 100 150 200

Peak shear stress (kPa)

0

2

4

6

8

10

12

Depth(m)

Pile CST'89a

C'89aPrediction

A2Scalar reduction based on IFR

B2h/R term revised with R*

defined by solid area of pipe pile


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Full ICP: checks for possible wall thickness ratio bias

Shaft capacity of open piles in sand: IC data base

0 10 20 30 40 50 60 70 80 90 100

D/t

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Qc/Qm

Pile type & test direction

Steel, open-ended, tension

Steel, open-ended, compression

Concrete, open-ended, tension


Pile plugs and open-end bearing: diameter dependence

Plug qb falls with

diameter D

ICP qb/qc= f(D)

IFR rises

sharply with D

Because of

interface shear

scale effect


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Debate over new API/ISO recommendations

Agreement: CPT based methods offer great potential

Debate over how to scale up from closed ended

model piles to full scale

API (2011) cites four approaches: ICP, Fugro, NGI

and UWA

What are the differences? Practical evidence that thefull ICP and other methods work?


2011 API commentary methods: NGI-05

Sliding triangle approach to capture h/R effects, z = depth

= z/ztipPatmosphericFDFsFtFl Fm

z/ztipterm not normalised by D or affected by Length L

F factors depend on: Dr; v0; loading sense; pile type

Base qbdoes not vary with D, unaffected by L/D

Terms fitted from NGI data base, checked against 28 high

quality load tests


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UWA-05 & ICP-05 end bearing for plugged piles vary with D

UWA qb/qc depends on Final IFR, which varies with D

Open ended piles in sand, taking D/t = 30

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 0.5 1 1.5 2 2.5 3

Outside diameter, m

qb/qc

ICP-05

UWA-05


UWA data base study: Lehane et al (2005)

74 high quality tests after 30 days, silica sands, CPT profiles

New CPT methods greatly reduce bias and scatter (CoVs)

Overall: Mean Qc/QmCoV

API-93 0.81 0.67

NGI-05 1.11 0.37

Fugro-04 1.11 0.38

(full) ICP-05 0.95 0.30

(full) UWA-05 0.97 0.27 (measured IFRs)

Similar data-base results to Jardine et al (2005)

New studies in hand: IC & ZJU, UWA and new NGI JIP


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Applications:

all with full ICP approach


Sungai Perak, Western Malaysia;Williams et al 1997

Pile tests

1&2 3 4

Balanced cantilever bridge on 1.5m OD driven steel piles

API design 33m penetration had to be doubled after tests

Medium-dense

gravelly sands

Average results

API: Qc/Qm= 1.99

ICP: Qc/Qm= 1.10


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760mm OD heavilyinstrumented steel

tubulars

Average results:

API: Qc/Qm= 0.58

ICP: Qc/Qm= 0.97

ICP predictions (thicklines) fit tests at 3 L/D

values, no skew or bias

with L/D

Dense North Sea sand

EURIPIDES - HollandKolk et al (2005)

Page 38

Now widespread wind energy applications

Piled tripods for Borkum West II

German N. Sea Merritt et al 2012

Overy 2007


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North Sea track record since 1996

13 installations of ICP designed foundations reported

Overy (2007)

Encouraging correlations with driving SRDs and stress

wave matches in sand, clay and mixed profiles

Substantial variations from conventional API, depending

on soil profile, pile details etc

Engineering potentialfacilitated new low-cost marginal

field options: Sayer & Overy (2007)

Borkum West II wind-turbine tripods: see Merritt et al 2012


If conventional API is so unreliable, why areoffshore failures rarely reported?

Almost no offshore static testing, limited driving monitoring

Problems revealed by tests performed for near-shoreprojects: Hound Point, Sungai Perak, Jamuna Bridge etc

Systematic conservative bias in some conditionssuch as

very dense marine sands

Unrecognised positive factors: shaft ageing characteristicsin sand


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Page 41

Dunkerque

programme:

Dense marine sand

Eight steel pipe piles

457mm OD, 19m

Static & cyclic loading

9 days to 1 year after

driving

Jardine et al 2006

Jardine & Standing

2012

1sttime tension tests at Dunkerque

235 days

81 days

9 days

Creep importantat Q > 1MN

ICP capacity after 9 days

EoD shaft 0.63 ICP

Low driving base capacity

Ageing disrupted by pre-testing

Pile age after driving: a missing parameter


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New and ongoing research

Pile installation and stress system it creates

Ageing in laboratory and field

Cyclic axial loading

Layering and base capacity

Lateral loading response

Extending the field database


Long term calibration chamber tests in Grenoblewith new 36mm OD mini-ICP: Jardine et al (2009)

1.2 m ID, 1.5 m deep chamber

On pile stress measurements

Multiple soil stress cells installed in sand mass


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Experiments on NE34 Fontainebleu sand:

Yang et al (2010)

CPT cone resistance, qc

Critical depth

Shear zone

Crushing zone

Shear zone developed around the pile shaft,Yang et al (2010)

Plan view Side aspect

Zone 1 material 0.5 to 1.5mm adheres to pile shaft


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Schematic

development of

Zones 1 to 3

Related to stress

regime in:

Crushing area

beneath tip

Degradation overshaft length

1

2

3

Microscope images: progressive grain crushing

(a) Fresh sand (b) Zone 1 sand

(c) Zone 2 sand (d) Zone 3 sand


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Stresses in soil

mass during

penetration(and at rest)

rnormalised

by CPT qc, %

Similar plots for

and z

Jardine et al (2013)

0.25

0.50

0.75

0.75

1.0

0.50

1.5

2.0

3.04.06.0

14

0.50

0.25

0 5 10 15 20-30

-20

-10

0

10

20

30

40

50

r /R

h/

R

0

4.0

8.0

12

16

20

0.500.75

1.0

1.5

2.0

2.0

1.5

3.0

1.0

4.0

6.01012

16

0 5 10

-10

-5

0

5

10

r /R

h/

R

0

4.0

8.0

12

16

20

30

Local stress paths at Leading pile instrumentOne cycle towards end of installation

0 50 100 150 200 250 300

-150

-100

-50

0

50

100

150

o

2nd

P.T.

end point

S

hearstress(kPa)

Radial stress (kPa)

start point

1stP.T.

o

peak load

(c)Peak load

Start of push

Unloading

End Point


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Interim conclusions from field & laboratory

Driving analyses highly variable. Base capacity well belowstatic estimates

Shaft capacities build over time from low EoD values to farexceed full ICP or UWA Qsestimates

Installation stress regime promotes ageing, as may interfacecrust and physiochemical effects

Base resistance very sensitive to local variationstake lowerbound CPT profile for qbdesign

Limit qcto 100 MPa in North Sea sands, beware tip buckling

Address cyclic loading in design & consider ICP clay method


ICP effective-stress clay approach:

= rftan , analogous to sand: rf/v0= f (YSR, St, h/R*)

Good predictions for ICP data base, reduces CoV and bias

Applied since 1996, particularly in North Sea

Needs different SI approach. Key issues, including low IPclays, debated at OSIG 2007

Micro-fabric in shear zones is crucial, as in landslides. Alteredby driving, promotes progressive failure

Ring shear tests to measure ; qbrelated directly to CPT qc


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Microscope thin section

through clay around piles at

Pentre; Chow (1997)

Residual shearing mode,

unusually low for given Ip

More common with plastic clays

Pile shaft

Principal displacement shears

Reidel shears


Interface friction angles for piles driven in clayMeasure max, min in ring shear interface tests, can be surprising!


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Load-displacement behaviour

Axial, lateral and moment monitoring of Magnus and HuttonTLP foundations: errors of 400% in conventional T-z, P-y

predictive approaches

Far better fit with (Class A) non-linear small strain FE

predictions; Jardine and Potts (1988), (1993)

Central role in new DONG-led PISA lateral loading JIP

Widely used in onshore Civil Engineering: many conferencesand case histories


Advanced soil testing & non-linear modelling:Six TC-29/101 conferences since 1994

Lyon 2003 Atlanta 2008 Seoul 2011


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200 x 100mm samples

Accurate cyclic loading

Longer term creep tests

Interactions with cycling

Higher resolution strain gauges

Multi-axial BE systems

Advanced stress-path

triaxial equipment

Jardine 2013

Page 58

Or, IC Resonant column HCA

Static mode

1, 2, 3 and control

Dynamic mode

Torsional resonant column

38/71 mm hollow cylinder

71/101 mm hollow cylinder

Static loading ram

torque system

and hydraulic

pressures

Oscillator (RC)

Specimen sizes


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Predictive tools

FE code ICFEP, fully coupled includes range of possible

elastic-plastic soil models, can model progressive failure

Simulate small-strain behaviour by tangent stiffness

functions between (Y1) elastic and outer (Y3) yield surfaces

G/p= f(D)

K/p= g(vol)

Fitted from lab tests, applied in 100s of projects

Illustrate with simulations of tension tests on 19m long,

456mm OD Dunkerque steel piles driven in dense sand

Page 60

Dunkerque anisotropic stiffness profiles: lab and field

Anisotropic Y1stiffness profiles: Dunkerque0 100 200 300 400 500 600 700Elastic stiffness, MPa

0

5

10

15

20

25

Depth,m

Legend:Eu from TXC testsE`v from TXC testsE`h from TX testsGvh from TX BE testsGhh from TX BE testsGvh from field seism. CPT tests

Elastic stiffness MPa

Depthm

Field seismic & lab Gvhmeasurements agree within 10%


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Page 61 0.001 0.01 0.1 1

e s, %

0

200

400

600

800

1000

1200

1400

G/p'

Legend:Curve used for FE analysisTC test curve OCR=1TE test curve OCR=1TS test curve for OCR=1

Dense sand non-linear secant shear stiffness data

OCR=1, other tests at different OCRs

Non-linear ICFEP predictions for tension test

19m, 457mm OD, steel pipe pile at Dunkerque

0 5 10 15 20 25 30 35

Pile cap displacement, (mm)

0

500

1000

1500

2000

2500

Pileresistance,

Q

(MN)

Legend:

predicted - ICFEP

observed

Shaft rcfrom ICP-05

CPT approach

Estimates for other

soil components

Non-linear stiffness

and interface shear

from lab tests

Jardine et al 2005b

Pileheadload,

Q

(MN)

Pile head displacements, (mm)

Good for capacity &

working load stiffness


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Conclusions

Need for improved capacity methods highlighted

Background instrumented pile & data base researchreviewed

New API/ISO sand methods and practical applicationdiscussed

Case histories demonstrate full ICP is fit for purpose

New factors highlighted, including strong time effects, basecapacity in variable strata & cyclic loading


Conclusions

Recent research outlined and interim conclusions noted

Focus on stress regime and soil fabric around shaft

Greatest practical impact with sands

Key aspects of ICP clay effective stress approach outlined

Way to improve pile-soil deformation analysis reviewed andillustrated


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Acknowledgments

Sponsors & partners: BP,BRE, IFP, EPSRC, Exxon

HSE, Shell, INPG 3S-R

group, Total and others

Current and former co-

workers: Andrew Bond,

Fiona Chow, Reiko

Kuwano, Barry Lehane,

Siya Rimoy, Jamie

Standing, ZhongxuanYang, Bitang Zhu and

many othersPierre Foray

1949-2014

session 3 - presentation 1 - r jardine - imperial college - axial design of driven offshore piles -...

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