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The role of numerical simulation for geosynthetic-reinforced soil structures – from laboratory tests to full scale structures -
Atsushi IIZUKA, Kobe UniversityMasafumi HIRATA, Toyo Construction Co. Ltd.Hideki OHTA, Tokyo Institute of TechnologyKatsuyuki KAWAI, Kobe UniversityYoshihiro YOKOTA, Maeda Kohsen Co. Ltd.
Contents Contents
Question: What is ‘Geosynthetic-reinforcement’ ? Where does ‘Geosynthetic-reinforcement’ come from?
Initial-boundary value problem
1. Full scale model tests
・ ‘Soil Bridge’, ‘Overhanging criff’ (strong and rigid structure & weaker
reinforcement), ‘Pre-stressed’ geosynthetic-reinforced soil structure,
‘Formative arts of geosynthetic-reinforced earth
2. Mechanical properties of compacted soil and geosynthetics
・ Similarity between compacted soil and OC clay
3. Numerical modeling of compacted soil and geosynthetics
・ mechanical interaction between compacted soil and geosynthetics
= geosynthetic-reinforcement effect
4. FE simulations of ‘Soil bridge’, ‘Overhanging criff’ & ‘Pre-stressed soil
5. Further targets
・ more realistic modeling of compacted soil
inconventional plasticity, suction effect
・ application in the engineering practice
2
Experiments
‘Model tests in labo. (preparatory model tests)’ To ‘Full scale model test’
‘Experiment’ To ‘Analysis’ ε
σ 0>Λ
0<Λ
0>Λ
0<Λ
loading (yield)
unloading
L＞0 strain hardening
L＜0 strain softeningunloading
loading (yield)
0 5 10 150
20
40
60
80
G-6
axial strain rate: 50%/min
strain (%)
load
(kN
/m)
Theory
Analysis
3
42,500
10,0006,000 6,0008,250 8,250
2,000 2,000
10,000 6,0006,000
22,000
A B
reinforcement(geosynthetics)
1,25
01,
500
2,75
0
12 3
4
6 5811 7 9
1012
14 1316 1519 17
20 18A B
Soil bridge 1992
Simple beam shaped soil structure reinforced by geosynthetics
‘Soil bridge’ was realized by removing steel H piles in number order,
which supported the geosynthetic-reinforced soil structure
Soil bridge
1/41/4
Construction of ‘soil bridge’
The notice board at the site of the 1992 field experiment
Placement of the geo-synthetics Installation of the displacement markers
The final appearance of the reinforced earth structure prior to the experiment
Appearance of the soil bridge in the end of the experiment
A student being disappointed by the regrettable appearance of the fill
2/4
4
0 5 10 150
20
40
60
80
Geosynthetics (ADEM G-6)
67.3 kN/m
axial strain rate: 50%/min
strain (%)
load
(kN
/m)
specific gravity of soil particle ρs (t/m3) 2.71grain size distribution
gravel fraction 2mm～75mm (％) 0.2sand fraction 75μm～2mm (％) 89.3silt fraction 5μm～75μm (％)clay fraction less than 5μm (％)
10.5
uniformity coefficient Uc 1.60coefficient of curvature Uc’ 1.23maximum grain size (mm) 4.75
15 20 251.40
1.45
1.50
1.55
1.60
1.65
1.70
ρdmax=1.631wopt=19.1
water content , w (%)dr
y de
nsity
, ρ d
(t/m
3 )
Materials
cross-sectional areaA (m2)
5.25×10-4
Young’s modulusE (kN/m2)2.55×106
Geosynthetics Compacted soil
sandy soil named ‘Omma sand’Unsaturated, compacted sand
aramid and polyethytene woven fabric coated by vinyl chloride resin
3/4
Experiment result of ‘Soil bridge’ 1992
step removed H pile settlement (m)1 No.1 0.000
2 No.1～No.2 0.160
3 No.1～No.3 0.319
4 No.1～No.5 0.438
5 No.1～No.6 0.590
6 No.1～No.7 0.770
7 No.1～No.8 0.880
8 No.1～No.9 ＞1.200
9 No.1～No.10 ＞1.200
It happened to cut the geosynthetics,
when #7 steel H pile was removed.
layer water contentw (%)
dry densityρd (g/cm3)
1 15.8 1.462 18.1 1.403 16.8 1.52
4/4
5
13,23110,000 2,000
28,2318,887 10,000 2,000 5,000
5,00
0
60°
reinforcement(geosynthetics)
‘Overhanging cliff’ 1993
Remove the supporting fill then realize the ‘overhanging cliff’
1/5
Construction of ‘overhanging cliff’
The notice board at the site of the 1993 field experiment
Start of the construction Installation of the displacement markers
The final appearance of the overhanging cliff of reinforced earth in the end of the experiment
2/5
6
0 2 4 6 8 10 12 140
20
40
60
80
100
120
geosynthetics(ADEM F-10)
111.1 kN/m
axial strain rate 50%/min
load
(kN
/m)
axial strain (%)
cross-sectional areaA (m2)
3.76×10-4
Young’s modulusE (kN/m2)3.72×106
specific gravity of soil particle ρs (t/m3) 2.69grain size distribution
gravel fraction 2mm～75mm (％) 0sand fraction 75μm～2mm (％) 82silt fraction 5μm～75μm (％) 9clay fraction less than 5μm (％) 9
uniformity coefficient Uc 23.4coefficient of curvature Uc’ 12.3maximum grain size (mm) 2.0
15 20 25 301.40
1.45
1.50
1.55
1.60
1.65
ρdmax=1.561wopt=23.1
water content , w (%)dr
y de
nsity
, ρ d
(t/m
3 )
Materials
Geosynthetics
aramid and polyethytene woven fabric coated by vinyl chloride resin
Compacted soil
sandy soil named ‘Omma sand’Unsaturated, compacted sand
3/5
layer water content
w (%)
dry densityρd (g/cm3)
1 25.2 -2 26.2 1.413 26.9 -4 24.1 1.455 26.4 -6 25.7 1.417 26.5 -8 26.3 1.399 26.2 -
10 16.9 1.37
Experiment result
The experiment began with gradually removing the base embankment supporting the overhanging portion.
When all supporting portions were removed, little deformation amazingly occurred.
4/5
7
5/5
60°
30,031
5,913 5,000 5,000 5,000
5,0008,8001,000
8,887
5,00
0
reinforcement(geosynthetics)
60°70°
Another ‘Overhanging cliff’ 1994
Remove the supporting fillthen realize the ‘overhanging cliff’
We asked it a geosynthetic manufacture to offer the geosynthetics much weaker than their usual products. Then, in the summer of 1994, another ‘overhanging cliff’ was carried with much weaker geosynthetics at the same site in 1993.
7,000
cutter 950× 7
cutte r
120
40 405
poly
uret
hane
geosynthetics
4040
40
Cutting the geosyntheticsalong the 60 deg. and 70 deg. lines from the top layer
1/2
8
Experiment result
The experiment began with removing the fill supporting the overhanging cliff.
The remaining part of the fill was brought to failure by mechanically cutting the embedded geosyntheticsalong the 60 deg. and 70 deg. lines from the top layer
The ‘nose’ dropped down accompanied by an unexpected breakage of the geosyntheticsthat was made intentionally weak.
Removing the support fill The ‘nose’ dropped down
Cutting the embedded geosynthetics
2/2
Pre-stressed geosynthetic-reinforced soil structure 1996
Cantilever (span: max 2.0m)
4×0.53.75
①②④ ③
geosynthetic
styrene formnon-woven fabric
2nd layer
1st layer
0.30.4
0.5
ABCD
pre-stress
5.75
0.51.0
0.5
pre-stress (98.0kN) pre-stress (29.4kN)
Type A: pre-stressed in the interval of 1.0m
② ①
4×0.53.75
③④
geosynthetic
styrene form
non-woven fabric
2nd layer
1st layer
0.40.5
0.5
ABCDE
pre-stress
5.75
0.51.0
0.5
pre-stress (76.4kN) pre-stress (29.4kN)
pre-stress (29.4kN)
Type B: pre-stressed in the interval of 0.5m
max 2.0membankment steel bar
nut
steel plate
geosynshetics
chloroethylene pipe
1/3
9
embankment steel bar
nut
steel plate
geosynshetics
chloroethylene pipe
layerwater
contentw (%)
dry density
ρd (t/m3)1 14.9 1.385embankment A2 15.0 1.3401 14.0 1.300embankment B2 15.1 1.345
pre-stressing
Initial support of pre-stressed soil cantilever
2/3
Type A（when span: 1.5m) Type B (when span: 1.5m）
Experiment result
Buckling occurred Well maintaining the shape of cantilever
3/3
10
8,886.8 5,113.2 2,000
5,00
0
2,0003,000 11,350
polystyrene
cutting line pre-stress
geosynthetic
60°
cutting line
cutting line
6 ×1,
000=
6,00
050
0
3,00
04,
000
500
pre-stress56.8kN
pre-stress28.4kN
Combination: ‘Formative arts of reinforced earth’ 1996
Support (fill) Support (fill)
Overhanging cliff
Tightening by pre-stress
Simple beam & Cantilever
Cutting embedded geosynthetics
1/5
Experiment sequence of ‘Formative arts of reinforced earth’
Support for overhanging cliff Steel H pile
Styrene form A ① ② ③ ④
② ① ③ ④
⑤
① ② ③ ④ ⑤ ⑥
① ② ③ ④ ⑤ ⑥
⑦ ⑧
⑨ ⑩
Styrene form B
① ②
Geosynthetics E
Geosynthetics D Geosynthetics C
1. Remove the support embankment for overhanging cliff → ‘Overhanging cliff’
2. Remove Steel H piles and melt (remove) styrene form A → ‘Soil bridge’
3. Melt (remove) styrene form B → ‘Soil cantilever’
4. Cut geosynthetics C
5. Cut geosynthetics D → lead the failure of ‘Soil cantilever’
6. Cut geosynthetics E → lead the failure of ‘Overhanging cliff’
2/5
11
layer water contentw (%)
dry densityρd (g/cm3)
1 19.7 -2 14.7 1.293 13.7 -4 16.2 1.305 13.0 -6 12.4 1.287 15.1 -8 12.4 1.319 14.6 -
10 17.5 1.37
The ‘nose’ dropped, approx. 0.32m
Settlement approx. 0.11m
Experiment result (1/2) 3/5
When the 6th geosynthetic was cut in the order from the top
Experiment result (2/2) 4/5
12
cut the geosynthetic-reinforcement downward from the top
5/5
・ mechanical interaction(compacted soils vs. geosynthetics)
・ shear characteristics of soils(dilatancy)
Field Test
F.E.Simulation
compacted soilsgeosynthetics
compacted soils
geosynthetics
Lab．Model Test
geosynthetic-reinforcement mechanism
confining dilative deformation of compacted soils by geosynthetics
+
Reinforcement mechanism by geosynthetics 1/4
13
Compacted soil
1. Dilative deformation
2. Strain-hardening to
Strain-softening
Elasto-plastic model (Sekiguchi and Ohta’s model) for compacted soils
0 200 400 600 8000
200
400
600
800
C.S.L
K0-line
devi
ator
icst
ress
, q
(kP
a)
effective mean stress , p' (kPa)
plane strain and undrained compression shear
lowhigh OCR
lowhigh OCR
initial yield surface
0 10
200
400
600
800
devi
ator
icst
ress
, q
(kP
a)
vertical strain , εy
low
high
OCR
0 200 400 600 800-100
0
100
200
300
400
pore
wat
er p
ress
ure
, Pw
(kP
a)
effective mean stress , p' (kPa)0 1
-100
0
100
200
300
400
pore
wat
er p
ress
ure
, Pw
(kP
a)
vertical strain , εy
low
high
OCR
2/4
0ln1 00
=−++−
= ∗ pvD
PP
ef εηκλ
''
( )GPD
PDX 3
''2*
2
2* ++= κββ
( ) ijijijijG
PDL εκδβηη
η
+−= *0*2
3'
−
−=∗
'''' 0
0
0
0
23
PS
PS
PS
PS jijijijiη
XL
hnCnεCn
Λst
epqstpq
mneklmnkl =
+=
klkl
fn∂σ∂
= （h：plasticity coefficient by Hill ）
( )0**
23
klklkl ηηηη
β −−Μ='P
Sijij =η '
00 P
Sijij =η
ε
σ 0>Λ
0<Λ
0>Λ
0<Λ
loading (yield)
unloading
L＞0 strain hardening
L＜0 strain softeningDACSAR
,
Yield function of SO model
, ,
incorporate to F.E.program,unloading
loading (yield)
SO model 3/4
14
DACSAR– open to the public –
France – LCPC
Bulletin Laboratoires des Ponts et Chaussees, 232, pp.45-60, 2001
Soil and water coupled Elasto-(visco)plastic F.E. code
SO model is incorporated into DACSAR
4/4
Evaluation of mechanical characteristics of soils
Unsaturated compacted soil
Like saturatedover-consolidation (OC) clay
VS
K0-consolidation
CV-SBT
disturbed loose sample
Adjust water content101 102 1030.6
0.8
1.0
1.2
5th layer w = 23.4% w = 20.6% w = 21.0% w = 23.2%
void
ratio
, e
effective normal stress ,σv' (kPa)
0 100 200 300 400 500 6000
100
200
300
400
w = 23.4% w = 20.6% w = 21.0% w = 23.2%
5th layer
shea
r stre
ss , τ (
kPa)
effective normal stress ,σv' (kPa)
101 102 103
0.8
1.0
1.2
1.4
1.6
w = 20%
39.2kPa 78.4kPa 156.8kPa 313.6kPa
void
ratio
, e
effective normal stress ,σv' (kPa)
0 50 100 150 200 250 300 350 4000
50
100
150
200Su/σvf' (at peak) Su/σvf' (at kink)w = 20%
shea
r stre
ss, τ
(kP
a)
effective normal stress, σ'v (kPa)
Unsaturated disturbed & loosened soil
Like saturatednormally-consolidation (NC) clay
compressibility
shear
shear
compressibility
Soils used in experiment
1/8
15
Disturbed samples Undisturbed samples
Undisturbed samples Disturbed samples
Test embankment 1994 at ‘Yuhidera’
Test embankment 1996 at ‘Taiyogaoka’
Soil sampling and laboratory tests
shear box
load cell
motor
screwed jack
measurement of verticaldisplacementmeasurement ofhorizontal displacement
measurement ofshear load
loading plate
specimentest equipment consolidation
pressure（kPa）
initial water content
(%)
numberof
testDisturbed Conventional 39.2 , 78.4
156.8 , 313.620, 23, 25,
27, 3020
Yuhidera(1994) Undisturbed Conventional 39.2 , 78.4
156.8 , 313.618.0 ~ 29.1 20
Conventional 39.2 , 78.4156.8 , 313.6
5 , 7 , 12 , 15 ,18 , 21 , 25
34Disturbed
Mikasa’s 39.2 , 78.4 7 , 25 4Taiyogaoka
(1996)Undisturbed Conventional 39.2 , 78.4
156.8 , 313.68.4 ~ 17.6 20
Labo. tests
・compaction tests
・SBT
Ko-consolidation
&
shear under constant volume
2/8
101 102 1030.6
0.8
1.0
1.2
5th layer w = 23.4% w = 20.6% w = 21.0% w = 23.2%
void
ratio
, e
effective normal stress , σv' (kPa)101 102 103
0.8
1.0
1.2
1.4
10th layer w = 16.8% w = 14.6% w = 16.0% w = 16.1%
void
ratio
, e
effective normal stress , σv' (kPa)
0 100 200 300 400 500 6000
100
200
300
400
w = 23.4% w = 20.6% w = 21.0% w = 23.2%
5th layer
shea
r stre
ss , τ (
kPa)
effective normal stress , σv' (kPa)0 100 200 300 400 500 600
0
100
200
300
400
w = 16.8% w = 14.6% w = 16.0% w = 16.1%
10th layer
shea
r stre
ss , τ (
kPa)
effective normal stress , σv' (kPa)
Compacted soils: mechanical properties
B sample (1996）A sample (1994）
Similar to OC clays
Key:
How much is OCR?
compressibility
Shear characteristics
3/8
16
Disturbed & loosened sample : mechanical properties
10-1 100 101 102 1030.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
w = 25%
w = 25.9% w = 25.9% w = 25.2% w = 25.2%
void
ratio
, e
effective normal stress , σv' (kPa)101 102 103
0.8
1.0
1.2
1.4
1.6
w = 20%
39.2kPa 78.4kPa 156.8kPa 313.6kPa
void
ratio
, e
effective normal stress , σv' (kPa)
Cc = 0.45 Cc = 0.16～0.22
0 50 100 150 200 250 300 350 4000
50
100
150
200Su/σvf' (at peak) Su/σvf' (at kink)w = 20%
shea
r stre
ss, τ
(kP
a)
effective normal stress, σ'v (kPa)0 50 100 150 200 250 300 350 400
0
50
100
150
200
w = 6.8% w = 6.8%
w = 7%
shea
r stre
ss, τ
(kP
a)
effective normal stress, σ'v (kPa)
compressibility
shear characteristics Taiyogaoka sample (1996）Yuhidera sample (1994）
Similar to NC clays4/8
0 5 10 15 20 25 300.2
0.4
0.6
0.8
1.0
1.2
average of s u / σvf' (at kink)= 0.53
average of s u / σvf' (at peak)= 0.71
su / σvf' (at peak) su / σvf' (at kink)
water content, w (%)
s u / σ
vf'
15 20 25 30 35
0.4
0.6
0.8
1.0
1.2
1.4
average of s u / σvf' (at kink)= 0.64
average of s u / σvf' (at peak)= 0.81
su / σvf' (at peak) su / σvf' (at kink)
water content, w (%)
s u / σ
vf'
0 100 200 300 4000
20
40
60
80
100
Su/σv0' = 0.20
shea
r stre
ngth
, Su (
kPa)
effective normal stress, σv' (kPa)0 100 200 300 400
0
20
40
60
80
100
Su/σv0' = 0.23
shea
r stre
ngth
, Su (
kPa)
effective normal stress, σv' (kPa)
Critical State
Strengthincrease
‘Strength’ of soils
Yuhidera sample (1994） Taiyogaoka sample (1996）
5/8
17
unsaturatedcompacted soil
saturatedover-consolidation clay
equivalent
?
Evaluation of material properties : compacted soils
undisturbed sample of compacted soil
■ : converted▲ : experimental
1.2
1.4
1.6
10 2 10 3
300
200
100
γd
, (t/m
3 )Su
, (k
Pa)
○ ： 21.0%◇ ： 20.6%
◎ ： 23.2%
● ： 23.4%water content
Su/σv’=0.234
logσv’ , (kPa)
NCvOCiv
SuOCRSu
=
Λ
'' 0σσ
▲ ■
c
s
CC
−=Λ 1
σv0’=2058kPa～931kPa
6/8
Specification of φ’ and other input parameters
75.1Ｍ
=Λ
' sin10 φ−=Ｋ
(Karube 1975)
(Jaky 1944)
( )Λ−+
=
exp
3321 0
0
MK
NCz
zx
'στ
(Ohta et al.,1985)
with
NCvOCiv
SuOCRSu
=
Λ
'' 0σσ
0 20 40 60 800.00
0.05
0.10
0.15
0.20
0.25 Su /σV0 ‘ = 0.234
Su
/ σv0'
φ' (deg)
φ '=27.5 (deg)K0=0.447
constant volume shearbox test
shearingτ σ−
consolidatione v− log 'σ
γd～σ v’～Surelation
λ κ σ, , ,v e0 0'φ ' Λ
Μ DK 0v '( i )
( ii )
0
0
1')i(
KK+
=ν ( )01)ii(
eD
+ΜΛ
=λ
7/8
18
0 50 100 150 200 250 300 350 4000
50
100
150
200SO96C2 (w = 12%)
experimental data F.E result
shea
r stre
ss, τ
(kP
a)
effective normal stress, σv' (kPa)
0 50 100 150 200 250 300 350 4000
50
100
150
200SO96C1 (w = 12%)
experimental data F.E result
shea
r stre
ss, τ
(kP
a)
effective normal stress, σv' (kPa)
0 50 100 150 200 250 300 350 4000
50
100
150
200SO96C3 (w = 12%)
experimental data F.E result
shea
r stre
ss, τ
(kP
a)
effective normal stress, σv' (kPa)0 100 200 300 400 500
0
100
200
300 experimental data F.E.result
10th layer
shea
r stre
ss , τ (
kPa)
effective normal stress , σv' (kPa)
0 100 200 300 400 5000
100
200
300 :experimental data :Sekiguchi-Ohta :Drucker-Prager :elastic material
5th layersh
ear s
tress
, τ (
kPa)
effective normal stress , σv' (kPa)
Performance of constitutive modelsdisturbed loose soils
undisturbed compacted soils
8/8
FE simulation of ‘Soil bridge’ 1992
126 5
4
3 158 137 9
12 10 18
17141619 11
20
side view of soil structure (:mm)
supporting portion (H steel)
reinforcement(geosynthetics)
22,00010,0006,000
6,0006,000
6,000
10,00042,500
8,000 8,0002,000 2,000
2,75
0
1,25
01,
500
A
step No. of steel pile to be
removed
maximum deformation
（m）
1 No.1 0.000
2 No.1～No.2 0.160
3 No.1～No.3 0.319
4 No.1～No.5 0.438
5 No.1～No.6 0.590
6 No.1～No.7 0.770
7 No.1～No.8 0.880
8 No.1～No.9 ＞1.200
9 No.1～No.10 ＞1.200
Step in experiment and results
1/5
19
1st layer
3rd layer2nd layer
geosynthetics
1 3 4 6 8 10 12 142579111315supporting portion
No.8 No.6 No.2 No.3 No.5 No.7
FE mesh used in simulation
number of H-steel piles removed
FE model of ‘Soil bridge’ 1992
SO94C1
1st layer 2nd layer 3rd layer
Coefficient of earth pressure at rest : K0 0.47 0.47 0.47
Critical state parameter : Μ 1.73 1.73 1.73
Preconsolidation vertical pressure :σv0' (kPa) 1730 858 2660
Effective overburden pressure :σvi' (kPa) 17.9 10.9 3.7
Input parameters
102 1031.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2nd layer
3rd layer1st layer
w=27%w=30%
w=25%w=23%
w=20%
dry
dens
ity, ρ
d (t/m
3 )
effective normal stress, σv' (kPa)
ρd (t/m3) w (%)1st layer 1.46 15.82nd layer 1.40 18.13rd layer 1.52 16.8
Determination of pre-consolidation pressure, 0vσ ′
2/5
Material properties : Geosynthetics
0 5 10 150
20
40
60
80
G-6
axial strain rate: 50%/min
strain (%)
load
(kN
/m)
uniaxial extension test
Polyethylene polymer grid
Aramid fiber Linearly elastic material
3/5
20
deformation
deviatoric stress distribution
shear strain distribution
volumetric strain distribution
εｖ(%)0.110.060.01
-0.04-0.09
γ(%)30.023.015.08.00.0
q (kPa)530400265137
0
FE simulationResult (1/2)
4/5
-1.5
-1.0
-0.5
0.00 5 10
No.3
step number
disp
lace
men
t (m
)
G1 G2 G3 co
mpu
ted
mea
sure
d
-1.5
-1.0
-0.5
0.00 5 10
No.5
step number
G1 G2 G3 co
mpu
ted
mea
sure
d
-1.5
-1.0
-0.5
0.00 5 10
No.7
step number
G1 G2 G3 co
mpu
ted
mea
sure
d
Vertical displacement (m)
-2 0 2 4 6 8 10 12 14 16 18 20
0
30
60layer 1
0
30
60layer 2
axia
l for
ce (k
N)
0
30
60 measured F.E.result
layer 3
-2 0 2 4 6 8 10 12 14 16 18 20
0
30
60layer 1
0
30
60layer 2
axia
l for
ce (k
N)
0
30
60 measured F.E.result
layer 3
Axial force working in geosynthetics (kN)
step=3 step=8
1st layer
3rd layer2nd layer
#8 #3 #5 #7#6 #2
step=3step=8
#3 #5 #7
FE simulationResult (2/2)
5/5
21
FE simulation of ‘overhanging cliff’ 1993 & 1994
60°70° geosynthetics
supporting potion FE mesh used in simulation
Cut the embedded geosynthetics along the lines (1994)
Overhanging cliff 1993
(geosynthetics F-10)
Overhanging cliff 1994
(weaker geosynthetics F-3)0 2 4 6 8 10 12 14
0
20
40
60
80
100
120
geosynthetics(ADEM F-10)
111.1 kN/m
axial strain rate 50%/min
load
(kN
/m)
axial strain (%)0 5 10 15
0
20
40
35.6 kN/m
Geosynthetics(ADEM F-3)
axial strain rate: 50%/min
strain (%)
load
(kN
/m)
F-10 F-3Very strong & stiff The ‘nose’ dropped down
SO94C1
1st layer 3rd layer 5th layer 7th layer 9th layer
K0 0.47 0.47 0.47 0.47 0.47
Μ 1.73 1.73 1.73 1.73 1.73
Λ 0.85 0.85 0.85 0.85 0.85
σv0' (kPa) 598 686 980 882 774
σvi' (kPa) 78.1 60.9 43.7 26.3 8.9
1/3
Weakergeosynthetics
1994
1993
2/3
22
8.8m
5.0m
X
Y
A-1 A-2
B-1
C-1
D-1
E-1 E-2
D-2
C-2
B-2
A-2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0 5 10 15 20
measured computed
step number
disp
lace
men
t (m
) C-2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0 5 10 15 20
measured computed
step number
disp
lace
men
t (m
) C-2A-2
Vertical displacement of markers installed in the 1994 embankment body 3/3
1. Introduce pre-stress to the steel bars installed at the interval of 0.5 m
(1) Load the pre-stress to the element(2) Install the bar element(3) Applied extension force to the bar element
2. Remove the support (plastic foam) in number order so as to realize the ‘soil cantilever (2.0m span)’
FE model used in simulation (type B)①②
2nd layer
1st layer
supporting portion
③④0.5m×4
pre-stressABCDE
1.4m
3.75m
・plane strain condition
・ total element number : 1106
・ total nodal number : 948
・ pre-stress : A-D 29.4 kNE 76.4 kN
steel bar(truss element)
pre-stressFE analysis of ‘Soil cantilever’
Type B
1/5
23
Input parameters for ‘Soil cantilever’
10 100 10001.1
1.2
1.3
1.4
1.5
1.6
1st layer
2nd layer
w=15-25%
w=10%
w=7%
w=5%
dry
dens
ity , ρ d
(t/m
3 )
effective normal stress ,σv' (kPa)
ρd (t/m3) w (%)1st layer 1.30 14.02nd layer 1.35 15.1
compacted sand
1st layer 2nd layer
Coefficient of earth pressure at rest : K0 0.49 0.49
Critical state parameter : Μ 1.41 1.41
Preconsolidation vertical pressure :σv0' (kPa) 87.6 180.7
Effective overburden pressure :σvi' (kPa) 9.7 3.0
0 2 4 6 8 100
20
40
60
80
100
120
geosynthetics(ADEM F-8)
93.9 kN/m
axial strain rate 1%/min
load
(kN
/m)
axial strain (%)
Compacted soil → elasto-plastic material
Geosynthetics → linearly elastic material
Cross-sectional area; A
3.2×10-4 (m2)
Young’s modulus; E
4.86×106 (kN/m2)
Estimate of pre-consolidation pressure
2/5
Deformation when the span reaches 1.5m
Shear strain distribution when the span reaches 1.5 m
Some difference between the monitored and the computed values, why?
point Bpoint A
-0.16
-0.12
-0.08
-0.04
0.00
0.0 0.5 1.0 1.5
point A
span length (m)
measured F.E.result
disp
lace
men
t, δ
(m)
-0.16
-0.12
-0.08
-0.04
0.00
0.0 0.5 1.0 1.5
point B
span length (m)
measured F.E.resultdi
spla
cem
ent, δ
(m)
Simulation result
γ(%)
22.9
17.2
11.5
5.7
0.0
3/5
24
0.1 1 10 100 1000 100000.0
0.2
0.4
0.6
0.8
1.0
PW / PI = 0.42
PW : Working prestress forcePI : Initial prestress force
P W /
P Itime (min)
0.1 1 10 100 1000 100000
20
40
60
80
100
120
No.1 No.6 No.2 No.8 No.3
forc
e (k
N)
time (min)
42.0PP IW =
Reduction of pre-stress
Measured the pre-stress force working in the steel bar with time
Pre-stressed barSide view
Plane view
1
2
3
4
No.5
6
7
8 No.6
No.1
No.2
No.7
No.8
No.3
No.4
Combination soil structure 1996
The pre-stressed force is reduced with time and only 42% remains at the end.
4/5
Deformation when the span reaches 1.5 m
Shear strain distribution when the span reaches 1.5 m
-0.16
-0.12
-0.08
-0.04
0.00
0.0 0.5 1.0 1.5point A
span length (m)
measured F.E.resultdi
spla
cem
ent, δ
(m)
-0.16
-0.12
-0.08
-0.04
0.00
0.0 0.5 1.0 1.5
point B
span length (m)
measured F.E.resultdi
spla
cem
ent, δ
(m)
Well agreement between the monitored and the computed values
point Bpoint A
Simulation result #2 (considering reduction of pre-stress)
γ(%)
22.9
17.2
11.5
5.7
0.0
5/5
25
after removal of supporting portion (1)
after removal of supporting portion (2)
after cut geosynthetics
Pre-stressed barSide view
Plane view
1
2
3
4
No.5
6
7
8 No.6
No.1
No.2
No.7
No.8
No.3
No.4
Combination soil structure 1996
Much difference, yet
1/1
( )
*
*
0
*
0
'ln'
' ln'
' ln ln 0'
ps v
y
pv
pv
pf D Dp
pD DRppD D D Rp
η ε
η ε
η ε
= Μ + −
= Μ + −
= Μ + − + Μ =
*
0
'ln 0'
pv
pf D Dp
η ε= Μ + − = 0 0*
0 0
32 ' ' ' '
ij ij ij ijS S S Sp p p p
η
= − − (Sekiguchi-Ohta model)
0
''''
yppRpp
= =
R : similarity ratio
f : normal-yield function
f s: subloading function
Subloading surface concept applied to SO model
(Hashiguchi et al. 1989)
q
(p',q)
(p',q)C.S.L
K0-Line
py' p0'
normal yield surface
subloading surface
1/2
26
Triaxial CU specimen
0 1 2 3 4 5 60
1
2
3
4 CU-Shear test , OCR=5
K0-Line
C.S.L
Original S O modelm=10.0m=1.0m=0.1
devi
ator
icst
ress
q
effective mean stress p' 0.0 0.2 0.4 0.60
1
2
3
4 CU-Shear test , OCR=5
m=0.0m=10.0m=1.0m=0.1
devi
ator
icst
ress
q
strain εa
0.0 0.2 0.4 0.6-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
m=0.0m=10.0m=1.0m=0.1
CU-Shear test , OCR=5
pore
wat
er p
ress
ure
P w
strain εa
Smoother change
from hardening to softening
Higher ability of expressing dilatancy characteristics
2/2
Considering suction effect in compacted soil
10 50 100 500 1000 50000
0.2
0.4
0.6
0.8
1
1.2
Effective normal stress σv (kPa)
Voi
d ra
tio e
s=170(kPa), w=11(%)
10 50 100 500 1000 50000
0.2
0.4
0.6
0.8
1
1.2
Effective normal stress σv (kPa)
Voi
d ra
tio e
s=60(kPa), w=18-21(%)
10 50 100 500 1000 50000
0.2
0.4
0.6
0.8
1
1.2
Effective normal stress σv (kPa)
Voi
d ra
tio e
s=85(kPa), w=17-21(%)
s=60kPa s=85kPa s=170kPa
possible bands of pre-consolidation pressure of compacted soils
1/2
27
Estimate of preconsolidation stress considering suction
dρ
dyρ
s1s2s3s4s5
s=0ρd
σvy3 σvy2σv
s
w
Sr =100(%)
Sr =90(%)
Sr =80(%
)
s1s2s3s4s5s6s7
Compression t est after soaking
s5
s3
s2
Compression t est , s3
Compression curve
Void ratio contours(Matyas et al.(1968))
Water retention curve model (Kawai et al.(2000))
Compaction curve
Suction distribution
50
100
0
(1)Boundingdrying curve
(2)Boundingwetting curve
Sr 0
Suction s
(%)
sW1 sA1 sA2sW2
Sr
Range of Suction ②
Range of Suction ①
suction
water content
dry density
vertical stress
2/2
WALL OF REINFORCED SOILWALL OF REINFORCED SOILWALL OF REINFORCED SOIL
A new method to prevent slope slide(soil structure with geosynthetics reinforcement confined by pre-stress)
Leading to
A new soil structure and a new construction method
50m high
slope 1:1
