The 2nd Bishop Lecture

Advanced laboratory testing in research and practice

Paris ICSMGE, 2nd September 2013

Richard Jardine

Legacy

TC-101 honouring Prof A W Bishop1920-1988

Analyst, Experimentalist,Equipment designer

Life, work and archived papers:ww.cv.ic.ac.uk/SkemArchive/index.htm

Bishop’s 1950s laboratory at IC

Sampling & Advanced Laboratory testing:

Equipment & techniques

Rigour, meticulous attention to detail, engineering application

Bishop’s last keynote: Stockholm ICSMFE 1981:With 70 former and current IC group members

Alan Bishop

Lecture themes

Following Bishop & TC101: special capabilities & practical value of Advanced Laboratory Testing

Contributions: Author, colleagues & French co-workers

Integration of laboratory & field research with analysis

Example of application considered fully resistant to ‘theoretical refinement’: Piles driven in sand

For clays: see Jardine et al 2012

Sungai Perak, Malaysia: 160m central span

Mainstream Civil Engineering: see Williams et al 1997

Page 6

Offshore Energy applicationsOil and gas platforms

Piled tripods for Wind-turbines:Borkum West II German N. SeaMerritt et al 2012

Overy 2007

Research agenda: set by field experience

Axial capacity - improved after field research in France: Lehane et al 1993, Chow 1997, ICP-05 (Jardine et al 2005)

Installation stresses? Tip buckling

Other observations revealed by large-scale Dunkerque tests

Creep & ageing: affects axial capacity & stiffness

Non-linear stiffness: axial, lateral & rotational

Cyclic loading: potential impact

Page 8

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 2006Jardine & Standing 2012

1st tension tests varying with age

Ageing, creep & non-linear axial shaft stiffness, 235 days

81 days

9 days

Creep important at Q > 1MN

QRef = 200 kN

Non-linear axial stiffness: first time tension tests

Head loads Q, displacements δ

Pile stiffness k = Q/δ

QRef = 200 kN

kRef = stiffness at QRef

0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

k l/kR

ef

Q/QRef

R2 - R6

Rimoy et al 2013

End points refectage after driving

Creep increments

No ‘linear-elastic’ plateauStiffness falls with Q/Qref

Creep & ageing: very significant

Impact of axial cyclic loading

Load controlled T = 60s

One-Way: tension Two-Way: tension & compression

Plus: tension tests to failure

Failure depends on N, Qcyclic, Qmean & static tension capacity QT

Loads normalised Qcyclic/QT & Qmean/QT to allow for age & pre-testing

Impact of axial cyclic loading: can halve capacity

-0.2 0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

3

20624

13

1

12

41 1

927

345

>221>200

No cyclic failure First failure Cyclic failure after previous cyclic or static failure

Qcy

clic/Q

T

Qmean/QT

>1000

Unstable

Meta-stable

Stable

Failure Nf < 100

100 < Nf < 1000

Stable to N > 1000Shaft capacity grows Cycling adds to ageing

Research to improve understanding & predictive scope

1. Non-linear stiffness from advanced laboratory tests

2. Lab-based FE predictions & field trends

3. Stress path studies of creep & ageing

4. Installation soil stresses: laboratory model

5. Interface-shear & grain-crushing experiments

6. Lab results & ‘breakage’ FE analysis

7. Cyclic loading: towards lab-based design

Stress-path experiments

Pluviated Dunkerque, Ham River (Thames Valley) & Fontainebleau NE 34 sands

Sub-angular, 0.2< d50 <0.3mm, silica media

Theme 1

Stress path test: Kuwano 1999

‘Bishop & Wesley’ cell: 200 x 100mm specimens

Automated stress & strain options

High resolution local strain gauges multi-axial Bender Elements (BE)

Elasticity & kinematic yielding

Non-linearity & anisotropy

Time dependency

Elasticity & Kinematic Yield Surfaces: KYSStrain incrementdirections

0

0

0

0

1.0

1.0

q

p’

p’

p’

p’

Y1 Y2 Y3

Stiffness

ds dvol

dp’dvol

dqds

Y1

Y2(significant plasticstraining)

(elastic limit) Y3(large scale yielding)

Plastic strainTotal strain

Y1 Y2 Y3

volp

sp

Strain incrementdirections

0

0

0

0

1.0

1.0

q

p’

p’

p’

p’

Y1 Y2 Y3

Stiffness

ds dvol

ds dvol

dp’dvol

dp’dvol

dqds

dqds

Y1

Y2(significant plasticstraining)

(elastic limit) Y3(large scale yielding)

Plastic strainTotal strain

Plastic strainTotal strain

Y1 Y2 Y3

volp

sp

Stiffness

Strainincrementdirections

Plastic strainTotal strain

dεs /dεvol

dp′/dεvol

dq′/dεs

εvol

εs

Y3 Large scaleyield surface

Δp′

Δp′

Δp′

p′

q

Y1 Y2 Y3

Y1 Y2 Y3

Stiffness depends on σ′ level Usually anisotropic

Plastic & non-linear if Y1 engaged

KYS dragged with q, p′Conforms to outer Y3

Scales with p΄

Intermediate Y2 KYSStrain increment direction changes

Onset of time/rate dependency

Cyclic threshold: sharp increase in permanent strain accumulation

and/or undrained p′ drift

.

Elastic Y1 KYS

Elastic property measurement techniques

Bender Element shear wave velocities:Vertical, polarised horizontally – Svh

Horizontal, polarised vertically - Shv

Horizontal, polarised horizontally - Shh

And vertical P-Waves

Vertical & radial static probing testsRange of conditions, keeping within Y1

Full cross-anisotropic elastic parameters set,assuming rate independence

© Imperial College LondonPage 18

HRS & Dunkerque sands: h =170, di = 38 & do= 70 mm

Correlated with BRE’s field seismic CPT & DMT Gvh tests at Dunkerque

Nishimura 2006

Resonant column & static Torsional Shear (TS) HCA tests

Porovic 1995 & Connolly 1998

Dynamic & static Gvh

Wide range of conditions

Cross anisotropic behaviour within Y1 KYSKuwano 1999, Jardine & Kuwano 2003

Stiffnesses vary with σ′ components & void ratio (e)

Eu = f (e). Au . (p′ /p′r) Bu

E′v = f (e). Av . (σ′v /p′r) Cv

E′h = f (e). Ah . (σ′h /p′r) Dh

G′vh = f (e). Avh . (σ′v /p′r) Cvh . (σ′h /p′r) Dvh

G′hh = f (e). Ahh . (σ′v /p′r) Chh . (σ′h /p′r) Dhh

f (e) = (2.17 – e)2/(1 + e)

pr is atmospheric pressure

Aij, Bij, Cij & Dij non-dimensional material constants

Stress level exponents Bu and [Cij + Dij] ≈ 0.5 to 0.6

Page 20

Anisotropic Y1 stiffness profiles: Dunkerque

0 100 200 300 400 500 600 700Elastic stiffness, MPa

0

5

10

15

20

25

Dep

th, m

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

Elastic stiffness MPaD

epth

m

Field seismic & laboratory Gvh measurements agree within ≈ 10%

At OCR = 1 K0E'v/E'h ≈ 1.7

Anisotropy post Y1 in non-linear range:Secant shear stiffnesses: dense Dunkerque sand

0.001 0.01 0.1 1s, %

0

200

400

600

800

1000

1200

1400

1600

G/p

'

Legend:Curve used for FE analysisTC test curve OCR=2TE test curve OCR=2TS test curve for OCR=2

0.001 0.01 0.1 1s, %

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

OCR = 1, K0 consolidation OCR = 2, K0 consolidation

G/p′

G/p′

Shear strain invariant εs Shear strain invariant εs

Lab-based ICFEP predictions for Dunkerque tests

Theme 2

Predictive tools: ICFEP; Potts and Zdravkovic 1999

Elastic pile displaced axially to failure

Sand: non-linear & σ′ dependent tangent stiffness between Y1 & Y3yield surfaces

G = f(p΄, εs) fitted to OCR = 1, Gvh trends

K΄ = g(p΄, εvol)

Y3 : non-associated Mohr-Coulomb, depth-variable φ′ & Ψ

Interface: effective-stress Coulomb, δ from interface shear tests

Can be extended: anisotropy, stress reversals or ‘bubble’ models…

Non-linear predictions for 81 day tension test 19m, 457mm OD, steel pipe pile

0 5 10 15 20 25 30 35Pile cap displacement, (mm)

0

500

1000

1500

2000

2500

Pile

res

ista

nce,

Q (

MN

)

Legend:predicted - ICFEPobserved

Shaft σ′rc from ICP-05 approach

Estimates for other soil σ′components…

Pile ageing: adjustment from field trends…

Creep & time – not modelled

Jardine et al 2005b

Pile

hea

d lo

ad,

Q (

MN

)

Pile head displacements, δ (mm)

Good for capacity & working load stiffness

Under-predictstime-dependentfinal movements

Creep and time effects

Need: stable high resolution instruments, careful calibrations,

accurate stress path & temperature control

Theme 3

Isolating elastic, plastic & medium-term creep strains K0 test on med. dense HRS

C

C

C

C

C

p′ (kPa)

Void

rat

io e

Ratios ofdεelastic/dεconsolidation

= 0.30

= 0.28

= 0.26

= 0.23

On unloading = 0.85

dp′/dt≠0 ‘consolidation’ sectionsεconsolidation = εelastic-plastic

Elasticity from stiffness functions

dεelastic/dεconsolidation falls with p′, increases on unloading

Creep from dp′/dt=0 pauses Kuwano 1999, Jardine & Kuwano 2002

‘Consolidation’ and medium term creep

εcreep/εconsolidation grows large with p’ & time

Falls with K = σ′h/σ′v

Falls with ID

Falls on unloading

Ratios of εcreep/εconsolidation

Kuwano & Jardine 2002

Stress path & creep stages Early creep-time curves

Creep: HRS under undrained triaxial shearing

Fig 14• Two

• Three» Four

Five

Creep negligible until Y2 engagedIncreases steadily post Y2 Stabilises after phase transformation - Y4

p′ (kPa)

Y4

200 x 100mm, dense TVS

New ‘Bishop and Wesley’ cell

Higher resolution strain gauges

Accurate cyclic loading

Longer term creep tests

Interactions with cycling

Rimoy’s tests: updated equipment

Rimoy & Jardine 2011

Medium dense TVS tests: K0 paths, OCR = 1‘True’ creep and ‘Creep plus low-level cycling’

Extended ‘creep’ p′ = 200, 400, 600 kPa

Extended cycling: qcyclic/p′ = 0.015 to 0.05

0

200

400

600

800

1000

0 200 400 600 800 1000p' (kPa)

q (k

Pa)

CSL 1.33

0.87

Ko line

True creep or cyclic loading with constant p'

True creep

Cyclic loading with constant p'

Rimoy & Jardine 2011

Mcritical state

Creep straining patterns

Invariant shear strains:εs increases monotonically, dεs/dt increases with p′

Volume strains: K0 pattern initially: dεvol/dεs= 3/2

Then reverses, negative dεvol/dtless dilatant at higher p′

Y2 KYS: Moving/changing with time

0 1000 2000 3000 4000 5000 60000.00

0.04

0.08

0.12

0.16

0.20

s (

%)

Minutes

True creep p' 600kPa p' 400kPa p' 200kPa

0 1000 2000 3000 4000 5000 6000-0.04

0.00

0.04

0.08

0.12

0.16

0.20True creep

p' 600kPa p' 400kPa p' 200kPa

vol

(%

)

Minutes

Adding low level cyclic perturbations

Applying qcyclic/p′ = 0.015 to 0.05 Augments straining

Creep & yielding: affected by stress state, time & background cycling

0 1000 2000 3000 4000 5000 60000.00

0.05

0.10

0.15

0.20

0.25

0.30p' = 600kPa

qcyc, 0.05p' = 30kPa qcyc, 0.025p' = 15kPa qcyc, 0.015p' = 10kPa

cyc

cre

ep -

cr

eep

(%)

Minutes

0.00 0.05 0.10 0.15 0.20 0.25 0.300.00

0.05

0.10

0.15

0.20

0.25

0.30

s (

%)

Yield points

vol (%)

P' = 600kPa q

cyc/p' = 0.05

qcyc

/p' = 0.025

qcyc

/p' = 0.015

True creep at 600kPa True creep at 400kPa True creep at 200kPa

k 0 lin

e

Also changes straining pattern: Reduces & retards dilation

Distributions of σ΄r σ΄z & σ´θ around piles?

Important to modelling ageing, cyclic response, group effects..

IC-Grenoble laboratory model & particle scale studies

Theme 4

© Imperial College LondonPage 34

Model experiments with Prof. Pierre Foray

1.3 x 1.5m chamber with close temperature & pressure controlDense pluviated Fontainebleau NE34 sand; CPT: 20< qc <25 MPaTests over months under 150 kPaUp to 36 stress sensors in sandMultiple tests with instrumented Mini-ICP

Jardine et al 2009, Zhu et al 2009

Mini-ICP model pile

Stainless steel: 1.4m x 36mm

Cyclic jacking installation

Traces shaft effectivestress paths and tip loads

Local measurements of:

– Axial load

– Surface τrz & σr

At three h/R levels

h, h

eigh

t abo

ve p

ile ti

p: m

m

Jardine et al 2009

Installation σ´r trendsin sand mass:

End of push End of pause

0.25

0.50

0.75

0.75

0.50

1.0

0.50

1.5

2.03.04.08.0

0 5 10 15 20-30

-20

-10

0

10

20

30

40

50

r / R

h / R

0

2.0

4.0

6.0

8.0

10

0 .2 5

0 .5 0

0 .7 5

0 .7 5

1 .0

0 .5 0

1 .5

2 .03 .0

4 .06 .01 4

0 .5 0

0 .2 5

0 5 1 0 1 5 2 0-3 0

-2 0

-1 0

0

1 0

2 0

3 0

4 0

5 0

r / R

h / R

0

4 .0

8 .0

1 2

1 6

2 0

1000s data contoured

σ´r/qc = f(h/R, r/R, σ´zo)

Intense tip concentration Unloading above tip

Sharp changes over each jacking cycle

Corresponding σ´z & σ´θ trends

Jardine et al 2013b

Radial profiles of σ´r /qc and σ´θ /qc shortly after installation

σ´r and σ´θ profiles interlinked, peaks in at 2 < r/R < 4

Critical to shaft capacity ageing theories

Compared later to advanced analysis

Radial stresses measured on pile face – far below installation maxima

Interface shear zone; Yang et al 2010

Pile edge

Grey dense fractured shear zone ‘crust’0.5-1.5mm thick, growing with h Not present if qc < 6 MPa

10 mm

36 mm

Side view of verticalsample from shaft

Shaft view fromabove during excavation

1

2

3

Breakage Zones 1, 2 & 3

Breakage starts under tip σ′v > 20 MPa

Fractured sand displaced & spread over shaft: Zone 1

Further abrasion on shaft

Partial fracturing in outer Zones 2 & 3

Yang et al 2010

Micro analysis of progressive grain crushing

(a) Fresh (b) Zone 1

(c) Zone 2 (d) Zone 3

Qic-Pic laser analyses of small samples: Progression from fresh sand to Zone 1 ‘crust’

Breakage most severe in Zone 1, less in Zones 2 & 3

Matching pile conditions in lab tests

Oedometer, interface ring-shear & high-to-low pressure stress path experiments

Theme 5

High pressure oedometer compared to Zone 1Void ratios, limits & sand states

Fresh NE34e = 0.63

Average Zone 1e = 0.36

High pressureoedometer

Yang et al (2010)

Wide range of silica sands: coarse example

Abrading steelinterface

Crushed sand

Intact sand

Replicating shear zones: ‘Bishop’ ring-shear interface tests

Sands sheared against steel for metres σ′n up to 800 kPa; Ho et al 2011

Interface shear angles vary with shear displacement

Large displacement δ angles: independent of ID and vary less with d50 & interface configuration

‘5mm’ shear box

50mm D, 100mm L Dense NE 34 specimens

Cuccovillo and Coop 1998 test system

High-to-Low Pressure Triaxial tests

High-to-Low pressures,without dismantling & changing soil fabric

Matching model pile installation stress paths

High-to-Low pressure stress-path tests

0 4000 8000 12000 16000Mean Effective Stress, p', kPa

0

4000

8000

12000

16000

Dev

iato

ric S

tress

, q, k

Pa

K0 CompressionStage

Axial compression Stage

Unloading Stage

Isotropic unloading

Second shearing stage

K0 compression: tip advancing from above

Active shearing: tip arrival with σ´v > 20MPa

Unloading, tip advancing to greater depth

Re-shearing, in compression or extension at high ‘OCR’

Effects on angle of shearing resistance?

High pressure 1st shearing:

0 10 20 30 40

External Strain%0

10

20

30

40

50

', D

egre

es

P-T1 Cell'= 6500kPaP-T2 Cell'= 6500kPaP-T3 Cell'= 6500kPa

0 10 20 30 40

External Strain%0

10

20

30

40

50

', D

egre

es

P-T1 Cell'= 6500kPaP-T2 Cell'= 6500kPaP-T3 Cell'= 6500kPaP-T1 Cell'=500 kPaP-T2 Cell'= 300kPaP-T3 Cell'= 150kPa

Ductile response low peak φ′

Brittle and much higher peak φ′Critical to pile test interpretation

Low pressure re-shear:

Theme 6

Simulating crushing and pile installation stresses

‘ALE’ Finite Element method; Zhang et al 2013a, b

Monotonic penetration with ‘Breakage’ mechanics model from standard lab tests

End bearing and breakage: Zhang et al 2013’s predictions

Predicted and measuredpile tip stresses qc

Contours of breakage parameter B:Fresh sand B = 0, fully fractured B = 1

1200

1000

800

600

400

200

0

0 5 10 15 20 25

Pene

tratio

n (m

m)

50mm ID top membrane Numerical simulation

qc (MPa)

0 5 10 15 200.0

1.5

3.0

4.5

6.0

h/R=3

h/R=6

' r /

qc:

%

r /R

h/R=9

(a) Numerical results by Zhang et al. (2013)

Fontainebleau sand

σ´r /qc and σ´θ /qc profiles predicted during installation

Encouraging agreement with cyclic penetration model pile tests

But predictions steady at h/R > 10, while shaft σ´r/qcmeasurements keep falling with h/R

Improve by modelling shaft abrasion & cyclic penetration?

Maxima within 30%of measurements

Cyclic axial loading

Model pile lab tests extending Dunkerque field experiments

Parallel cyclic lab element testing

Integration into practical design

Theme 7

Stable Mini-ICP cycling: interface stress paths Load-controlled to N > 1000Stresses remain within Y2 shaft capacity rises

Tsuha et al (2012)

Unstable stress paths Mini ICP tests failing with N < 100

Displacement-controlledTwo-Way tests engage Y3 and Y 4Phase transformation at interface

Load-controlledOne-Way tests engage Y2

Drift towards interface failure

Shaft capacity falls markedly

Tsuha et al (2012)

Cyclic failure interactions: model & field casesMini-ICP & NE34 Dunkerque full scale

es

Comparable trends; field response marginally more robust

-0.2 0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

3

20624

13

1

12

41 1

927

345

>221>200

No cyclic failure First failure Cyclic failure after previous cyclic or static failure

Qcy

clic/Q

T

Qmean/QT

>1000

Unstable

Meta-stable

Stable

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

Nf = 1

Nf > 1000

Nf = 100

Nf = 5

580

300

2X104104

300

1000

100

5

1

74

4760

7000

1000*

1050

50*

4040

One w

ay

Qcy

clic

/QT

Qaverage/QT

Two way

Stable

Meta-Stable

Unstable

Qcy

clic/Q

T

Qmean/QT Qmean/QT

Qcy

clic/Q

T

Displacementcontrolled

Load controlled

Matching cyclic conditions in lab element tests

γrz shearing dominatesεθ = 0, εz is small εr constrained by soil mass

Interface δσ′r/δr = 2G/R Constant Normal Stiffness?G ≠ constant, R = variable

 

 r

z

z

r

 r 

zr

r

z 

τzr

τrz

Apply undrained CNS = ∞Cyclic Triaxial CTX or Simple Shear CSS tests

CSS tests in HCA?

Pre-cycling stress path?

Undrained cyclic element tests: NE34 & Dunkerque sands

1500 cycle CTX tests from OCR = 4

Y2 yielding and p′ drift rates depend on:

qcyclic/p′ and N

CTX or HCA CSS mode

OCR & pre-cycling

Creep & ageing pauses

Sim et al 2013

Practical Application:

Jardine et al 2012Andersen et al 2013SOLCYP – Puech et al 2013

Borkum West II; Merritt et al 2012

www.heavyliftspecialist.com

Wednesday TC-209 workshop

Bishop Lecture: Summary and Conclusions

• Challenges posed by field experience & observations

• Advanced Lab testing: permits scrutiny of Elastic, Plastic, Anisotropic, Kinematic Yielding, Time-dependent and Cyclic soil behaviour in precise experiments

• Also critical to investigating pile installation stresses, grain-crushing, interface-shear & cyclic behaviour

• Endorse Bishop’s approach: integrate laboratory experiments with field & analytical research - and help apply the results in practice

AcknowledgementsCurrent & former IC colleagues, particularly: S. Ackerley, A. Aghacouchak, F. Altuhafi, R. Kuwano, F. Chow, T. Ho, S. Rimoy, WW. Sim, J. Standing, Z. Yang, and B.T. Zhu

Co-workers and collaborators, particularly: C. Dalton, I. Einav, P. Foray, J. Powell, A. Puech, M. Siva and C. Tsuha

Funding from: Atkins, French CNRS, Chinese NSF, Commonwealth Commission, UK EPSRC, HSE, Royal Society, Shell, Total and others