sandra escoffier soil characterization.ppt - series characterization.pdf•liquefaction potential 3....

Soil characterization

• CPT test

• Shear vane test

• T-bar test

• Air hammer test

• Bender element test

• Soil characterization from accelerometer measurements

22

Cone penetration test

⇒ Characteristics of CPT in centrifuge (Bolton et al 1999) : ⇒ Characteristics of CPT in centrifuge (Bolton et al., 1999) :

• repeatability of interlaboratory tests

• size effect B/d50 (in sand)

• side boundary effect S/B

• Initial penetration Δz/B effect - interface effect

i i f i f⇒ Determination of specimen parameters from CPT (Robertson & Campanella, 1983):

• soil strength

• deformation modulus /Vsdeformation modulus /Vs

• liquefaction potential

33


2 main objectives: - check the uniformity reproducibility of the specimen2 main objectives: - check the uniformity, reproducibility of the specimen

- obtained an indirect characteristic profile

Hydraulic CPT Electric CPT

At the prototype scale : Ø 38 mm ⇒ scaling of the cone penetrometer can not be achieved

44

Most of the miniature CPT : Ø around 10 mm (IFSTTAR 12 mm)

Cone penetration test • Reproducibility of interlaboratory tests (sand)• Reproducibility of interlaboratory tests (sand)

European Program of Improvement in centrifuging (EPIC)

Normalized cone Normalized cone

resistance Qh

Z

Variation within a ± 10 % band width

lize

d d

ep

tN

orm

a

(Bolton et al 1999)

55

(Bolton et al., 1999)


• size effect B/d50 (in sand)

Modeling of modelsModeling-of-models

z B z Bzm Bm

Prototype scale

zp Bp zm Bmzm Bm

Prototype scalen1 < n2 < n3

66B/d50 > 20(Bolton et al., 1999) (Bolton et al., 1999)


• side boundary effect S/B (sand)


77At least 10B away from any hard boundary



• Initial penetration Δz/B effect - Interfaces effect (sand)

- Boundary fringe 10B where Q increases with depth like shallow foundation (Bolton et al., 1999)

- Depending on relative density, boundary fring may lie between 5B

( , )

Normalized cone boundary fring may lie between 5B and 20B (Gui & Bolton)resistance Q

dep

th Z

No

rmali

zed

88(Bolton et al., 1999)(Gui & Bolton, 1998)


• Initial penetration Δz/B effect - Interfaces effect

(Gui & Bolton, 1998)

99


• Shear strength in sand (Rayhani & El Naggar, 2008)

1010(Robertson & Campanella, 1983)


• Shear strength in clay

Correlation between CPT tests and shear t t f h l

Empirical relationshipvane test for each clay

uc ASq =

1000

1200

c

vcu N

qS σ−=

800

1000

inte

qc

(kPa

)

Nc : cone factor that depends on OCR

400

600

resi

stan

ce e

n po

i

conteneur A (melange kaolinite-chaux a 1%)

0 10 20 30 40 50 60 70 80cohesion non drainee Su (kPa)

0

200 regression linéaire : Y= 17.33 X

Conteneur B (melange kaolinite-chaux a 2%)

regresion lineaire : Y= 17.04 X

rapport conventionnel qc/Su : 18.5

(Rault 2009)

1111

cohesion non drainee Su (kPa)

Determination d'une relation Qc et SuEssais preliminaires a 1G - fevrier & mars 2009

massifs A (KC01 (1%)) & B (KC02 (2%)] (conteneurs diametre 300mm) SOLCYP01.grf

(Rault, 2009)


• Deformation modulus (E, Gmax)

(Rayhani & El Naggar 2008)(Rayhani & El Naggar, 2008)

Around 10B

1212


• Liquefaction triggering (Sharp & al, 2010)

qc1N – CRR correlation b d hi i

Scaling of the diameter cones ( i i i i f ff )based on case histories (minimize interface effect)

Modeling of modelsØ12mm - n=3 ⇒ Ø36mmØ8mm - n=4 5 ⇒ Ø36mm

sandformwithPqpq

a

c

m

v

aNc 8.03.0'

01 −=⎟⎟

⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛=

σØ8mm - n=4.5 ⇒ Ø36mmØ4mm - n=9 ⇒ Ø36mm

garCSR

v

vd

v

av max'0

'0

65.0σσ

στ

==

1313(Idriss & Boulanger, 2004)

(Sharp et al., 2010)


• Liquefaction triggering (Sharp & al, 2010)

- Modeling of models - Good correlation between qc1N and Lateral displacement & thickness of liquefied layer

(Sharp & al, 2010)(Sharp & al 2010)

- Results consistent with the field liquefaction chart based on case histories(Sharp & al, 2010)

(Sharp & al, 2010)

1414

Shear vane test

• Determination of Su for soft soil

⇒Determination of the Su value

kMS t

u =

Drawback : discrete values

Advantage : peack value and strain softening behaviour

⇒ Parameters that affect Su(D i t l 1989 & W t t l 1998)

g

(Rault, 2008)(Davis et al., 1989)

(Davis et al, 1989 & Watson et al., 1998)

-delay between insertion and rotation

-rate of rotation

-vane geometry

⇒ Centrifuge test : variation of σ’ along the vane heigth

1515

of σ v along the vane heigth

Shear vane test


Correlation with CPT – 1g test(if D i l 1989)

Infligth determination of cu(W l 1998)(ifsttar – Davis et al., 1989) (Watson et al. 1998)

NF P94-072 (1995) NF P94-112 (1991)

vane geometry

NF ⇒ aspect ratio h/d=2

Centrifuge modeling ⇒ variation of σv’ along H ⇒ decrease of the aspect ratio

Infligth test(Watson et al. 1998)

1g test(Davis et al. 1989)

Vane H (mm)

D (mm)

H/D

A 28 19 1.47

Vane H (mm)

D mm)

H/D

A 10 15 0 67

A 28 19 1.47

B 14 18 0.78

C 14 27 0.52

D 14 36 0.39

1616

A 10 15 0.67

B 10 10 1

C 15 10 1.5

Shear vane test


Correlation with CPT – 1g test(if D i l 1989)

Infligth determination of cu(W l 1998)(ifsttar – Davis et al., 1989) (Watson et al. 1998)

NF P94-072 (1995) NF P94-112 (1991)

Rate of rotation (linked to the vane geometry) : undrained conditions

Both NF : 18°/min ⇒ rate of shearing at the end of the blade 0.026-0.04mm/s and 0.18mm/s

Centrifuge modelling ⇒ scaling factor for dynamic time and diffusion time

04.002.02 totc

T fv ≤=(Davis et al., 1989) Tf : time to failure0.00.02 to

D

Vane H (mm) D (mm) Shear rate

Cv consolidation coefficient

Vane H (mm) D (mm) Shear rate (mm/s)

(mm/s)

B 14 18 0.18

(Davis et al., 1989)

A 10 10 0.09

B 13 13 0.11

C 20 20 0.17

D 30 30 0 26

1717

D 30 30 0.26

E 40 40 0.34

IFSTTAR

Shear vane test

• Determination of the CU for soft soil

Correlation with CPT – 1g test0.0 0.1 0.2 0.3 0.4 0.5

resistance en pointe Qc (MPa)

0

-60

-40

-20

(mm

)

-26.5

-65.5

-Consolidation of a clay layer at a given σ’v-under σ’v shear vane test at different depth and qc profile ⇒ (cu, qc) for a given σ’v

14

16

18

20

men

t (kP

a)

-120

-100

-80

ofon

deur

mod

ele

zpc

(

-104.51200

4

6

8

10

12

ista

nce

au c

isai

llem

essais scissometriques pale de 13 x 13 mm ( c = - 82.70 mv/v)(conteneur A : melange kaolinite-chaux 1%)

essai KC01V01 (cote -26.5 mm/TN) : Su = 14.68 kPa

essai KC01V02 (cote -65.5 mm/TN) : Su = 16.51 kPa

essai KC01V03 (cote -104.5 mm/TN) : Su = 18.79 kPa-200

-180

-160

-140prof

-143.5

-182.5profil penetrometrique PA01(kaolinite pure) - contrainte 102 kPa (W = 39.5 %)

800

1000

nte

qc

(kPa

)

0 10 20rotation (degre)

0

2res essai KC01V04 (cote -143.5 mm/TN) : Su = 15.85 kPa

essai KC01V05 (cote -182.5 mm/TN) : Su = 16.18 kPa Determination de Qc et Su(Essais preliminaires a 1G - 16.03.2009)

Conteneurs A (KC01) & B (KC02) - (diametre 300mm)

200profil penetrometrique KC01P01 (melange kaolinite-chaux a 1%) - contrainte 119 kPa (W = 72.2 %)

400

600

resi

stan

ce e

n po

in

conteneur A (melange kaolinite chaux a 1%)

0 10 20 30 40 50 60 70 80h i d i S (kP )

0

200

conteneur A (melange kaolinite-chaux a 1%)

regression linéaire : Y= 17.33 X

Conteneur B (melange kaolinite-chaux a 2%)

regresion lineaire : Y= 17.04 X

rapport conventionnel qc/Su : 18.5

1818

cohesion non drainee Su (kPa)

Determination d'une relation Qc et SuEssais preliminaires a 1G - fevrier & mars 2009

massifs A (KC01 (1%)) & B (KC02 (2%)] (conteneurs diametre 300mm) SOLCYP01.grf

T-bar test

D b k f CPT d h t t (St t & R d l h 1991)Drawbacks of CPT and shear vane test (Stewart & Randolph, 1991)

- CPT : interpretation largely based on empirical relationships

- shear vane test : physical size VS sample height

T-bar : continuous profile – results can be analysed directly in terms of yield shear strength

- relative rough cylindrical surface- relative rough cylindrical surface

- smooth end surface

- rate of penetration :few mm/s

- penetration resistance measured just behind the T-barpenetration resistance measured just behind the T bar

- hypothesis : full closure of the soil behind the cylinder

- Theory plastic solution for limiting pressure acting on a cylinder moving laterally through cohesive soil (Randolph & Houlsby 1984)Houlsby, 1984)

dSNP ub=

(Stewart & Randolph, 1991)P: force per unit length acting on the cylinder

D: diameter

N : bar factor (recommended value 10 5 Randolph &

1919

Nb: bar factor (recommended value 10.5 Randolph & Houlsby, 1984)

T-bar test

2020

T-bar test

R li bilit f th T b i ith th t t (St t & R d l h 1991)Reliability of the T-bar : comparison with other tests (Stewart & Randolph, 1991)

- CPT (in flight)

- shear vane test (1g)

triaxial tests- triaxial tests

1g test – normally consolidated sample1g test – normally consolidated sample

2121

(Stewart & Randolph, 1991)(Stewart & Randolph, 1991)

Air-hammer test

• Shear wave velocity

(Arulnathan et al., 2000 ; Ghosh & Madabhushi, 2002)

Air hammer AccelerometerAir hammer Accelerometer

(Arulnathan et al., 2000) (Ghosh & Madabhushi, 2002)

-requiered properties

- well-define and repeatable shear wave pulsep p

- usefull range of frequency

- magnitude of the soil distorsion

2222

Air-hammer test


Cambridge Davis

Hollow cylinder Brass 42mm long Aluminium 47mm longHollow cylinder Brass 42mm long Aluminium 47mm long

Piston Teflon 19mm long Teflon 25mm long

valve 3 ways solenoid 4 ways solenoidvalve 3 ways solenoid 4 ways solenoid

Outer surface of the cylinder Sand (glued) Sand (glued)

(Arulnathan et al., 2000)(Ghosh & Madabhushi, 2002)

2323

Air-hammer test


frequency content

Vs wavelength /distance between accelerometer as small a possible (Arulnathan et al., 2000)

(Arulnathan et al., 2000)

Increase of the sampling frequency

λ (cm) < d

d λ Vs

Model scale1 2 3 4

150 30kHz 15kHz 10kHz 7 5kHzacc1

acc2

2424Vs (m/s)

150 30kHz 15kHz 10kHz 7.5kHz

300 60kHz 30kHz 20kHz 15kHz

acc1

Air-hammer test


Amplitude – shear strain level

Gmax ⇒ γ ≅ 10-6 to 10-5

(Arulnathan et al 2000)(Ghosh & Madabhushi 2002) (Arulnathan et al., 2000)(Ghosh & Madabhushi, 2002)

γ Estimated from the double integration of the

accelerometer measurements

γ Estimated from maximum acceleration, a0, and hypothesis of

an equivalent sine wave, ωaccelerometer measurements a equ a e t s e a e, ω

Maximum displacement

20

ωaMaximum distorsion

⎟⎞

⎜⎛ −∫∫ ∫∫ 12 accacc

a02Maximum distorsion⎟

⎟

⎠⎜⎜

⎝ −= ∫∫ ∫∫

12max max

accacc zzγ

2525ωπ sV

Bender element tests

• Bender element = piezoelectric transducer

Receiver : series bender

Transmitter: parallel bender

(Brandenberg et al., 2006)

• Configuration of bender element system

Wave generatorOscilloscope

(data acquisition)

amplifier amplifier

2626transmitter receiver


• Centrifuge application: some challenges-Large specimen : shear wave attenuation

-High-g environment : superposition of mechanical vibrations

Maximizing the amplitude of the elastic waves

-maximizes signal to noise ratio

-increases the propagation distance

Staking of the signal


Signal processing


2727


• Some illustrations

V velocity in centrifuge : 50 250 m/sVs velocity in centrifuge : 50 – 250 m/s

Average frequency of the input signal : 5kHzWave length : around 1cm to 5cm

Distance between transmitter and receiver larger than 1 to 2 λ

Free type bender elementsfixed type bender elements

Protruding part 10x17X1.5mm

(Zhou et al., 2010)

12.5x8mm

(Brandenberg et al., 2006) (Fu et al., 2004)

2828(Rammah et al., 2006)


• Liquefaction triggering Liu G. (2009)

Cross section viewBender element ⇒ Vs(z)

( ) 5.0'5.0

02

max 321

197.23230

vK

ee

G σ⎟⎟⎠

⎞⎜⎜⎝

⎛ ++

−=

(Hardin & Drnevich, 1972)

2max sVG ρ=

25.0

'1 ⎟⎟⎠

⎞⎜⎜⎝

⎛=

vss

PaVVσ ⎠⎝

Acceleration measurements during earthquake ⇒ amax

garCSR v

dav max

'' 65.0σσ

στ

==

(Seed & Idriss, 1971) (Liao & Whitman, 1986)

CSRrd (z)gvv 00 σσ

Pore pressure measurements during earthquake ⇒ Δu

Top view'0vu σ=Δ

Liquefaction

or not

2929Liu G. (2009)


• Liquefaction triggering Liu G. (2009)

Liu G. (2009) Liu G. (2009)

3030

Soil characterisation from accelerometer measurements

(Zeghal et al., 1995)

One dimensional shear beam idealisationy

• τ-γ loops , G(γ )/Gmax , β(γ)/ βmax

One dimensional shear beam idealisation

( ) ( )dztzutzz

∫= ,, &&ρτ

( ) 0,0 =tτ ( ) HutHu &&&& =,

zH

Soil column with a vertical array of accelerometers

( ) ( ) zzz ∫0 ,, ρ

• U(0,t) : linear fit from the top pair of accelerometers

( )223

2321 0 z

zzuuuu −

−−

+=&&&&

&&&&

• Determination of (z t)• Determination of τ (z,t)

Few accelerometers

limited amplification/attenuation h

many accelerometers

significant amplification/attenuation h

(Z h l t l 1995)

phenomena phenomena

Trapezoidal integrationUse on the surface acceleration

3131

(Zeghal et al., 1995)(Zhegal et al., 1995)(Zhegal et al., 1994)



-determination of τ(z,t)

( ) ( )zuuzz &&&& += 121 ρτ ( ) k

i

kkk

i zuuz Δ+

=∑ −

=+1

11

2&&&&

ρτor

Z < λ/2

(Brennan et al. 2005)

(Zeghal et al 1995)

-determination of γ(z,t)

Only 2 accelerometersmany accelerometers

2nd order approximation(Zeghal et al., 1995)1st order approximation

2nd order approximation

(Zhegal et al., 1995)

⎤⎡( )z

uzuz 1)( −=γ ( ) ( ) ( ) ⎥

⎦

⎤⎢⎣

⎡ΔΔ

−+ΔΔ

−Δ+Δ

=−

−−

+− 1

11

11

1

i

iii

i

iii

iii z

zuuzzuu

zztγ

3232determination of u(z,t) from acceleration measurements



- determination of u(z,t) from acceleration measurements

Data processing : integration + filteringEffect of direct integration

Appropriate filter:

-frequency range of interest

-non dispersive filter or dispersive filter (limited dispersion in the frequency range of interest)

-adequacy between the required adequacy between the required sharpness of the pass band filter and the filter order

-filtfilt function in Matlab© to avoid phase h fshift

3333



Importance of the paccelerometers properties

(phase lag)

3434



loopAβ =

triangleAπβ

4=

γτ

ΔΔ

=G

(Hardin et al. 1972)

3535


Importance of the frequency range of the pass-band filter


Frequency range :

20-450Hz Frequency range :

20-70 Hz

3636

(Brennan et al., 2005)



3737(Rayhani & El Naggar, 2007) (Brennan et al., 2005)

sandra escoffier soil characterization.ppt - series characterization.pdf•liquefaction potential 3....

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