Sample preparation

• sand sample

-LCPC sand sample

-UCAM sand sample

• Clay sample

-LCPC clay sample

22

Sand sample preparation

Objectives (Ternet, 1999):

-Reproducibility

-Spatial homogeneity of the density

-Organisation of the the sand grain comparable to in-situ sample

Longitudinal gaxis of the particles

(Ternet, 1999)(Ternet, 1999)

Methods:

-Manual ⇒ poor reproducibility and homogeneity

( , )

p p y g y

-Vibration of the box ⇒ poor homogeneity, small box

-Layer rodding ⇒ controled unit weight, poor homogeneity, poor reproducibility

-Layer tamping ⇒ poor homogeneity

33-Raining ⇒ reproducibility (automatic device), homogeneity (Mullis et al, 1977), comparable organisation of the sand grain (Miura & Toki, 1984)

Sand sample preparation

Sand raining Parameters: Controlled parameters (Garnier 2002):Sand raining Parameters:

-Falling heigth : 0.4m (0.57m) to 2m

-Hooper aperture : 2 – 3 - 4 mm (aperture > 2x maximum grain size)

Controlled parameters (Garnier , 2002):

-Relative density or void ratio

-State of geostatic stress (σv, σH, KO)

-Mechanical characteristics (evaluated by q )

44-Horizontal velocity

-Mechanical characteristics (evaluated by qc)

Sand sample preparation

y = 0,3x + 90,5R2 = 0,9

y = 0,0x + 94,6R2 = 0,5

94,03mm hp=60cm

y = 0,9x + 77,8R2 = 1,0

y = 0,5x + 86,2R2 = 1,0

84,0

89,03mm hp=80cm

3mm hp=90cm

y = 1,4x + 64,2R2 = 1,0

y = 0,8x + 75,3R2 = 1,0

74,0

79,0

(%)

4mm hp=60cm

4mm hp=75cm

3 7 26 6

y = 2,2x + 54,1R2 = 1,064,0

69,0

Id

4mm hp=90cm

2mm hp=60cmy = 3,7x + 26,6

R2 = 1,0y = 2,9x + 40,0R2 = 1,0

54,0

59,0 2mm hp=75cm

2mm hp=90cm

49,05 7 9 11 13 15 17 19

Vh (cm/s)

55(Thiriat, 2009)

Sand sample preparation

Calibrate density box

Dense sand (16kN/m3)

Medium dense sand (15kN/m3)

Direction of the horizontal displacement of the hooper Density increases with

(Ternet, 1999)

the depth(Ternet, 1999)

66

Sand sample preparation

(Ternet, 1999)

77

Sand sample preparation

Homegeneous area

(Ternet, 1999)

88

Sand sample preparation

European collaboration ( LCPC, Brunel University, Lyngby University) ⇒ prototype ll f l i lpressure cell for granular material

Installation tool + standardised procedure ⇒ stress measurement in sand better than 5% (Ternet, 1999)sand better than 5% (Ternet, 1999)

99

Sand sample preparation

-silo effect

coefficient of horizotnal pressure at rest: K-coefficient of horizotnal pressure at rest: K0

H=

720

=80

0

H

W=

Top view transversal view

L=1200

Ratio

H/W=0.87

1010

H/L=0.58 (Ternet, 1999)

Sand sample preparation

-silo effect

Top view Transversal view

Depth of the ESB box

1111(Ternet, 1999)

Sand sample preparation

-coefficient of horizontal pressure at rest: K0

unloading

Variation of KO during the spin up and the spin down of the centrifuge

unloading

loading

Loading phase: K0constant for N>15g

g

G-level (g)(Ternet, 1999)

Variation of KO with the soil density

k 1303721212

Relative density Drdk γ13.037.20 −=

(Ternet, 1999)

Sand sample preparation

-Mechanical properties of the sand sample : qc

Scatte ing of abo t

(Ternet, 1999)

1313

Scattering of about 12%

(Ternet, 1999)

Sand sample preparation

(Zhao et al., 2006)

(Zhao et al., 2006)

(Madabushi et al., 2006)

1414(Zhao et al., 2006)

Sand sample preparation

(Madabushi et al., 2006)

(Zhao et al., 2006)

Flow rate is the major parametermajor parameter

1515

(Zhao et al., 2006)

Sand sample preparation

(Zhao et al., 2006)

1616

Clay sample preparation

• Type of clay sample

- reconstituted sample ⇒ clay coming for the site or « well-known clay »

- undisturbed sample ⇒ clay coming for the site and carrefull samplingundisturbed sample ⇒ clay coming for the site and carrefull sampling

Use of undisturbed sample abandoned because of excessive local heterogeneities (Garnier, 2002)

“well-known clay” : IFSTTAR Speswhite clay (kaolinite)

“site clay” : Rion clay (Greece), Lysaker clay (Norway)

•IFSTTAR boxes for clay sample

1717(Khemakhem, 2011) (Garnier, 2001)

Clay sample preparation

• Methods of clay sample reconstitution

MethodsMethods ReferencesReferencesMethodsMethods ReferencesReferences

Hydraulic gradientHydraulic gradient Hamilton et al, (1991)Hamilton et al, (1991)L & Ri iè (1999)L & Ri iè (1999)Luong & Rivière (1999)Luong & Rivière (1999)Rahman et al. (2000)Rahman et al. (2000)

Hydraulic actuatorHydraulic actuator Mc Namara et al. (2010)Mc Namara et al. (2010)Begag Qerimi et al (2010)Begag Qerimi et al (2010)Begag Qerimi et al. (2010)Begag Qerimi et al. (2010)

In fligth consolidationIn fligth consolidation Ilyas et al. (2004)Ilyas et al. (2004)

Hydraulic actuator +In fligth Hydraulic actuator +In fligth consolidationconsolidation

Kitazume & Miyajima (1994)Kitazume & Miyajima (1994)

(Khemakhem, 2011)

IFSTTAR centrifuge

1818

IFSTTAR centrifuge

Clay sample preparation

• Consolidation at 1g with hydraulic actuator

• successive clay layers of about 10cm thick (at the end of the consolidation)

• 1 week per layer (kaolinite) – drainage at both end of the clay sample

• σv selected based on the request OCR and the σv at Ng

mixing

Cl l 90 %Kaolin powder + water Clay slurry w = 90 % (about 2 time wl)

Consolidation

Preparation of the following layer

Draining layer (sand + geotextile or geotextile)

(Khemakhem, 2011)

1919

Clay sample preparation

• Consolidation at Ng

• avoid desaturation during the fligth ⇒ water layer above the sample surface (few cm)

• consolidation indicator ⇒ pore pressure profile and surface settlement

• hydrostatic pore pressure distribution

• settlement stabilization : asaoka method (Magnan, 1980)

2020

(Khemakhem, 2011)

Clay sample preparation

• Evolution of Cu profile at Ng – limitations Su near surface decreases rapidelly

Low Su near surface (offshore conditions)

2121(Khemakhem, 2011)

Normally consolidate sample clay

(Khemakhem, 2011)

Overconsolidate sample clay

Clay sample preparation

• Selection of σv for consolidation at 1g versus the request Su profile

Expression of Su versus OCR (Ladd et al, 1977)

( )'

'

'' max v

vm

ncv

u

v

u OCRwithOCRSSσ

σσσ

=⎥⎦

⎤⎢⎣

⎡=

Experimental determination for Su=f(OCR) for the kaolinite clay

1g Test at 100g

550 kPa 0 kPa 135 to 550kPa

qc measurements qat different σ’v qc measurements

at different σ’v(depths)

qSwithOCRq 51853 59.0' == σ (Garnier 2001)

2222

cuvc qSwithOCRq 5.185.3 == σ (Garnier, 2001)