Sample preparation
• sand sample
-LCPC sand sample
-UCAM sand sample
• Clay sample
-LCPC clay sample
2
Sand sample preparation
Objectives (Ternet, 1999):
-Reproducibility
-Spatial homogeneity of the density
-Organisation of the the sand grain comparable to in-situ sample
Longitudinal
g
axis of the
particles
(Ternet, 1999)
((Ternet,, 1999))
Methods:
-Manual ⇒ p
poor reproducibility
p
y and homogeneity
g
y
-Vibration of the box ⇒ poor homogeneity, small box
-Layer rodding ⇒ controled unit weight, poor homogeneity, poor reproducibility
-Layer tamping ⇒ poor homogeneity
-Raining ⇒ reproducibility (automatic device), homogeneity (Mullis et al, 1977),
comparable organisation of the sand grain (Miura & Toki, 1984)
3
Sand sample preparation
Sand raining Parameters:
Controlled parameters (Garnier , 2002):
-Falling heigth : 0.4m (0.57m) to 2m
-Relative density or void ratio
-Hooper aperture : 2 – 3 - 4 mm
(aperture > 2x maximum grain size)
-State of geostatic stress (σv, σH, KO)
-Horizontal velocity
-Mechanical characteristics (evaluated by qc)
4
Sand sample preparation
y = 0,0x + 94,6
2
R = 0,5
y = 0,3x + 90,5
2
R = 0,9
3mm hp=60cm
94,0
3mm hp=80cm
89,0
y = 0,9x + 77,8
2
R = 1,0
y = 0,5x + 86,2
2
R = 1,0
3mm hp=90cm
84,0
y = 0,8x + 75,3
2
R = 1,0
Id (%)
79,0
4mm hp=60cm
y = 1,4x + 64,2
2
R = 1,0
74,0
4mm hp=75cm
4mm hp=90cm
69,0
y = 2,2x + 54,1
2
R = 1,0
64,0
2mm hp=60cm
y = 3,7x
3 7 + 26
26,6
6
2
R = 1,0
y = 2,9x + 40,0
2
R = 1,0
59,0
2mm hp=75cm
54,0
2mm hp=90cm
49,0
5
7
9
11
13
15
17
19
Vh (cm/s)
(Thiriat, 2009)
5
Sand sample preparation
Calibrate density box
Dense sand (16kN/m3)
Medium dense sand (15kN/m3)
(Ternet, 1999)
Direction of the horizontal
displacement of the hooper
(Ternet, 1999)
Density increases with
the depth
6
Sand sample preparation
(Ternet, 1999)
7
Sand sample preparation
Homegeneous area
(Ternet, 1999)
8
Sand sample preparation
European collaboration ( LCPC, Brunel University, Lyngby University) ⇒ prototype
pressure cell
ll for
f
granular
l
material
i l
Installation tool + standardised procedure ⇒ stress measurement in
sand better than 5% (Ternet, 1999)
9
Sand sample preparation
-silo effect
W=
=800
H=720
H
-coefficient
coefficient of horizotnal pressure at rest: K0
L=1200
transversal view
Top view
Ratio
H/W=0.87
H/L=0.58
(Ternet, 1999)
10
Sand sample preparation
-silo effect
Top view
Transversal view
Depth of the ESB box
(Ternet, 1999)
11
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
Loading phase: K0
constant for N>15g
loading
g
(Ternet, 1999)
G-level (g)
Variation of KO with the
soil density
k0 = 2.37 − 0.13γ d
(Ternet, 1999)
Relative density Dr
12
Sand sample preparation
-Mechanical properties of the sand sample : qc
(Ternet, 1999)
(Ternet, 1999)
Scattering
Scatte
ing of abo
aboutt
12%
13
Sand sample preparation
(Zhao et al., 2006)
(Zhao et al., 2006)
(Madabushi et al., 2006)
(Zhao et al., 2006)
14
Sand sample preparation
(Madabushi et al., 2006)
(Zhao et al., 2006)
Flow rate is the
major parameter
15
(Zhao et al., 2006)
Sand sample preparation
(Zhao et al., 2006)
16
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 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
(Khemakhem, 2011)
(Garnier, 2001)
17
Clay sample preparation
• Methods of clay sample reconstitution
Methods
References
Hydraulic gradient
Hamilton et al, (1991)
L
Luong
& Rivière
Ri iè (1999)
Rahman et al. (2000)
Hydraulic actuator
Mc Namara et al. (2010)
Begag Qerimi et al
al. (2010)
In fligth consolidation
Ilyas et al. (2004)
Hydraulic actuator +In fligth
consolidation
Kitazume & Miyajima (1994)
(Khemakhem, 2011)
IFSTTAR centrifuge
18
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
Draining layer (sand +
geotextile or geotextile)
Kaolin powder + water
Clay slurry
Cl
l
w = 90 %
(about 2 time wl)
Preparation of the following layer
Consolidation
(Khemakhem, 2011)
19
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)
20
(Khemakhem, 2011)
Clay sample preparation
• Evolution of Cu profile at Ng – limitations
Su near surface
decreases rapidelly
Low Su near surface
(offshore conditions)
Normally consolidate sample clay
(Khemakhem, 2011)
Overconsolidate sample clay
(Khemakhem, 2011)
21
Clay sample preparation
• Selection of σv for consolidation at 1g versus the request Su profile
Expression of Su versus OCR (Ladd et al, 1977)
⎡S ⎤
= ⎢ u' ⎥ OCR m
'
σ v ⎣ σ v ⎦ nc
Su
with OCR =
σ v'
max (σ v' )
Experimental determination for Su=f(OCR) for the kaolinite clay
1g
550 kPa
0 kPa
Test at 100g
135 to 550kPa
qc measurements
q
at different σ’v
qc = 3.5σ v' OCR 0.59
with S u = 18.5qc
qc measurements
at different σ’v
(depths)
(Garnier 2001)
(Garnier,
22