the 2 bishop lecture advanced laboratory testing in research ...the 2nd bishop lecture advanced...
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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