Hybrid Drain Geosynthetics for fine-grain soil improvements
description
Transcript of Hybrid Drain Geosynthetics for fine-grain soil improvements
Hybrid Drain Geosynthetics for fine-grain soil improvements
Chandan GhoshProf. & Head [Geohazards]
National Inst. of Disaster ManagementMinistry of Home Affairs, Govt. of India
PWP-3
PWP-2
PWP-1
H
CONSOLIDATION PRESSURE (P=20,50,100,200,400 KPA)
DR
AIN
FA
CE
U
150MM DIAMETER
Kanto loam slurry
Drain layer
Large strain slurry consolidation
• Do slurry behave similar to normal soil?• Do PWP in slurry different from normal
Terzaghi soil?• Can internal PWP be measured?• Do k, Cv, Cc, mv are constant with
consolidation pressure?• Permeability –direct and from Consolidation
theory differ much?
3
Typical application/troubles!! 様々な工法や問題
Important!!!Drain flow capacity
Local soils being excavated to construct road
Prepared foundation base
(a)
(b)Permeable high strengthgeocomposite
Rains
Imposed load
Geocomposite drain/reinforcement Details "b"
Drained water dueto consolidation
Settlement
Traffic load
Soft soil
In-plane flow
Problem domain
Local/problematic soils
Load types
Drain/reinforcement
Time dep. Sett.?
Clogging…flow capacity changes under confinement
Geosynthetics as drain
• Drain – clogging and efficiency in flow under pressure
• In-plane and x-plane flow be measured?• Index properties of geosynthetics• International codal practice• Evaluation of clogging – from slurry stage• Drain efficiency – hybrid drain system
6
AIM of present research
To recommend suitable drain system for field application
To assess nature of clogging and flow capacity of drains confined in fine-grained soil
7
Research needs
Flow capacity of synthetic drains placed in-situ
Assessment of clogging and its prevention
Recommending design flow capacity of drains based on available hydraulic index test data
Use of synthetic materials for improving fine-grained soils
8
Geosynthetics used
Geocomposite-AGC-A
Nonwoven –ANW-A
Nonwoven –BNW-B
Nonwoven –CNW-C
Nonwoven cover
Woven fabric
0
20
40
60
80
100
0 10 20 30 40 50 60 70 80
Elongation (%)
Tens
ile lo
ad (k
N/m
)
Nonwoven -A (EX-60)
Nonwoven-B (EX-80)Geocomposite-B (RD-15)
Geocomposite-A (RD-40)
Geocomposite-C (RD-80)In-air Tension test Width = 50mmGage length=100mmStrain rate = 20%/minTest done as per JIS L 1908
9
Grain size distribution
0
20
40
60
80
100
0.001 0.01 0.1 1 10 100Grain size (mm)
Perc
ent f
iner
(%)
Toyoura sand
Silty clay Kanto loam
Imposed load
Geocomposite drain/reinforcement Details "b"
drained water dueto consolidation
Settlement
In-plane flow
X-plane flow
10
Clogging mechanism
tg
Clogged particles
Piped particles
Randomly oriented geotextile fibres
Interface
Blinding
Woven-nonwoven type geocomposite
Woven fabricParticle deposition
Fine-grained soilswater flow with fines
Geosynthetic clogged by Kanto loam
Consolidation of soil – ideal vs natural
• Can we measure excess PWP directly?• Can excess PWP exceeds applied load increment?• What if load increment ratio varies from 0.5 to 3?• What if applied pressure is increased in steps or
in one go - say from p=0 to 400kPa?• How Excess PWP varies with H or with r?• How different is “k” – if measured in a
large specimen?
AIM
• what happens inside slurry when loaded upto 400kPa
• How different are all parameters?• Drained water and settlement – how are
they related?• To check soil bevaviour and looking into
gap – theory and practice
Leh cloud burst - 2010
• Slurry formation• Mud slides• Prevention of mud slides
• Measuring in-plane flow and drain efficiency using a large dia consolidation apparatus
• Measuring internal PWP during test• Validation of consolidation theory
NEW BUS STAND
SONAM NORBOO MEMORIAL HOSPITAL
BSNL OFFICE
HIGHLY POPULATED COMMERCIAL AREA
Cloud burst at Leh, 4-5 Aug 2010Boundary Wall of DIHAR Broken by slurry
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Apparatus developed
Local soils being excavated to construct road
Prepared foundation base
(a)
(b)Permeable high strengthgeocomposite
Rains
Imposed load
Geocomposite drain/reinforcement Details "b"
Drained water dueto consolidation
Settlement
Traffic load
Soft soil
In-plane flow
Basis of developingexperimental methods
coarse sand
LVDT
Air pressure chamberPlexiglasscylinder
O-ring
150mm 350mmSoil slurry
20 channel data logger
Weightbalance
Weightbalance
Porous stone affixed withflexible tube
PWP-1 PWP-3
3.15flexible tube
Data cable
Air pressure vent
PWP-2
Geosyntheticdrain layer
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Test procedure
PWP-3
PWP-2
PWP-1
Data logger
Airpressure regulator
Silty claysample
Setting PWP tipsCompacting sand base Geocomposite
as boundary drain filter
Silty clay slurry
Blinding of Geocomposite filter
Particle blinding
(a) (c)(b) (d)
(f)
(g)(e)
Silty clay
220 mm150mm
18
Flow tests in drains placed within Kanto loam and silty clay
during consolidation
Soil slurry
Drain (120x50mm)
Consolidation pressure
Drain pipe
Kanto loam slurry
Drain layer
19
Local soils being excavated to construct road
Prepared foundation base
(a)
(b)Permeable high strengthgeocomposite
Rains
Imposed load
Geocomposite drain/reinforcement Details "b"
Drained water dueto consolidation
Settlement
Traffic load
Soft soil
In-plane flow
Various in-plane flow tests carried at in-situTest situation – double layer drain system
Double layer drain and in-situ state
Geocomposite-AGC-A
Nonwoven –ANW-A
Nonwoven –BNW-B
Nonwoven –CNW-C
2.7mm thick4mm thick 5.5mm thick 6.2mm thick
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Various drains tested in-situ during consolidation of slurry
Water flow in Flow out
Soil slurrySand
Perspex cylinder wall
Sectional plan 120mmX50mm drain sample
PWP device
Conso. pressure
Multilayer drain system
120mmPorous stone tip
Hybrid drains
(a) Basic sample - BA
(b) Horiz. sand drain - HSD
(c) Geocomposite drain - GCA
(d) GCA+HSD = HB1
(e) GCA+HSD = HB2
(f) GCA+HSD = HB3
150mm
100
GCA
HB1
HB3
HB2
NWA
HSD
NWB
NWC
Toyoura sand
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Status of drains after test
(a) Geocomposite drain susceptible to clogging
KL-GC drain
(b) HYBRID drain less susceptible to clogging
KL-HB2
(c) Geocomposite drain susceptible to clogging (d) HYBRID drain less susceptible to clogging
CS-GC drain CS-HB2
Clogging by Kanto loam Almost no clogging due to sand mat
Thin sand mat used in HYBRID drain
120mm
50mm
Clogged geocomposite drain sampleplaced within silty clay
Nearly clean geocomposite drain found after test in HYBRID system
22
Permeability factor – in-situ
0
5
10
15
20
25
10 100 1000Consolidation pressure (kPa)
Perm
eabi
lity
k x
10-9
(m/s
) Silty clayKanto loam
k-values by water flow test
k-values from consolidation test
0
5
10
15
20
10 100 1000Consolidation pressure (kPa)
Perm
eabi
lity
fact
or x
105 =
k-G
C d
rain
/k-s
oils
Kanto loamSilty clay
Flow factor w.r.t. no clog GC drain
Flow factor w.r.t. clog GC drain
In-situ state
Permeability factor = ‘k’-no clog drain/’k’- soil1. Permeability factor >105, which is satisfactory2. With increasing pressure this factor increases, which is also a good indication
23
Flow tests in drains placed within Kanto loam and silty clay
during consolidation
Soil slurry
Drain (120x50mm)
Consolidation pressure
Drain pipe
Kanto loam slurry
Drain layer
24
Average in-plane flow capacity 平均水平流動量
0
0.05
0.1
0.15
0.2
0.25
0.3
10 100 1000Consolidation pressure, (kPa)
Tran
smiss
ivity
x 1
0-5,
(m2/
s)
Silty clay
No clog GC
(b)
Hybrid-2
0
0.05
0.1
0.15
0.2
0.25
0.3
10 100 1000Consolidation pressure, (kPa)
Tran
smis
sivi
ty x
10-5
, (m
2 /s)
No clog GCHSDGCDHB1HB2HB3
Kanto loamNo clog GC
(a)
0
1
2
3
4
5
10 100 1000
Consolidation pressure p, (kPa)
Ave
rage
flow
rate
q (m
l/min
)Hyd. Grad. i=1
Silty clay
(b)
Hybrid -2
0
1
2
3
4
5
10 100 1000
Consolidation pressure p, (kPa)
Ave
rage
flow
rate
q (m
l/min
) NWANWBNWCHB2
Hyd. Grad. i=1
Kanto loam
(a)
Soil
Drain
Consolidationpressure
In-situ state
1. Flow in HYBRID drain is the highest2. Without sand mat flow is the low, NWC drain is the lowest3. Confining pressure causes 70 to 80% reduction in GC drain
Clogging of drains
• How to evaluate clogging?• How to remove clogging of drains? –
ultrasonic removal• Hybrid drains – combination of geotextile
and sand mat
26
Clogging of geocomposite
Inner woven part
Kanto loamSilty clay
Nonwoven cover
Large dia – 1D consolidation
• Can PWP be measured directly?• Slurry and normal soil states – at 50 kPa• Variation of internal excess PWP – with height ?• Do excess PWP attains 100% immediately after
applied pressure?• Direct and indirect permeability – are they same?• k, p, mv, Cc, Cv – are these constant with p?• Can we measure Drained water during
consolidation?
Consolidation from slurry stage
• Kanto loam – slurry (is there a relation between LL and slurry water content?)
• Why p=50 kPa?- transition from slurry to Terzaghi soil
Kanto loam slurry
Drain layer
At p=400kPa (dia =150mm, H=57mm)
0 5 10 15 20 250
20
40
60
80
100
120
140 PWP-2PWP-3PWP-4
Time, hrs
PWP,
kPa
0 0.1 0.2 0.3 0.4 0.5 0.6 0.70
0.25
0.5
0.75
10.10 hrs0.281.55.511.521.55
PWP ratio, u/del p
Sam
ple
heig
ht, z
/H
Kanto loam – local soil and silty clay - commercial
Material Kanto loam (local soil)
Silty clay (commercial)
Plasticity LL % 108.1 37.7 PL % 82.3 16.4 PI 25.8 21.3Natural water content (%) 101 3
Particle density, s (Mg/m3) 2.687 2.612
d max (kN/m3) 7.66 11.96Optimum w% 82 17Initial void ratio of slurry 6.70-8.00 2.30-3.30
Grain size –Clay, Silt, Sand 10%, 27%, 63% 43%, 55%, 2%
Triaxial (UU), uu, cuu 40, 19.6 kN/m2 - - -
(CU), cu, ccu 250, 5.9 kN/m2 - - -
0 100 200 300
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Kanto loamSILTY CLAY
Time (hrs)
Verti
cal s
trai
n
0.01 0.1 1 10 100 1000 10000
0.00
0.03
0.06
0.09 0.0 0.2 0.4 0.6 0.8 1.0 1.2
p=400 kPa
(e)
0.01 0.1 1 10 100 1000 100000.00
0.03
0.06
0.09 0.0 0.2 0.4 0.6 0.8 1.0 1.2
p=200 kPa
(d)
0.01 0.1 1 10 100 1000 100000.00
0.03
0.06
0.09 0.0 0.2 0.4 0.6 0.8 1.0 1.2
p=100 kPa
(c)
0.0 1 0. 1 1 10 10 0 1 00 0 10 00 00. 0 0
0. 0 5 0. 1 0
0. 1 5 0. 2 0 0.0
0.2 0.4 0.6 0.8 1.0 1.2
p= 5 0 k P a
(b )
15 0m m di am e ter
P WP-3P WP-2P WP-1
H
C on so li da ti on p res su re , p
Drain
face
u
0.01 0.1 1 10 100 1000 100000.00 0.10 0.20 0.30 0.40 0.50 0.0
0.2 0.4 0.6 0.8 1.0 1.2 Vertical strain vs time
PWP-2 at mid height vs time
Consolidation time, min
p=20 kPa
Kanto loam (a)
Exce
ss p
ore
wat
er p
ress
ure
ratio
(u/d
el
p)
Verti
cal s
train
of s
lurr
y sa
mpl
e
t50 at p=400kPa
0 5 10 15 20 25 30 35 40 4587
89
91
93
95 400 T50,T10...
Sqrt. T(min)
t50=55mint100=264min
Is there a unique transitional stage at p=50kPa?
1 10 100 10000
50
100
150
200
250
Si lt y clayKan to lo am
Consol id ation pr essur e, k Pa
Slurr
y he
ight,
mm
H5 0=57m m
H50 =110m m
H50=23m m
No rm al soi l s tat e
Slur r y s tat e
P WP- 3
P WP- 2P WP- 1
H50
Co n so li da tio n p res su re (p = 50 k P a)
Drain
face
u
1 50 m m di am e te r
1 10 100 10000.0
0.5
1.0
1.5
2.0
2.5
0
20
40
60
80
100 110mm thick at 50 kPaSeries357mm thick at 50 kPa
Consolidation pressure, kPa
Void
ratio
, e0-
e
Indi
cativ
e w
ater
cont
ent (
%)
Silty clayLL=37.7%PL=16.4%
Oeodometer specimen (60mm dia, 20mm height)
(a)
CcS=1.1
Normal soil stateSlurry state
Water content = 37%
CcN=0.31
1 10 100 10000
2
4
6
8
0
50
100
150
200
250
300 110mm thick t 50 kPaoedo-KL57mm thick at 50 kPa
Consolidation pressure, kPa
Void
ratio
, e0-
e
Indi
cativ
e w
ater
cont
ent (
%)
Kanto loamLL=108%PL=82%
Oedometer specimen(60mm dia, 20mm height)
(b)
CcN=1.1
CcS=3.1
Slurry state Normal soil state
Water content = 124%
1 10 100 10000.0
0.2
0.4
0.6
0.8
1.0
Consolidation pressure, kPa
Voi
d ra
tio (e
at p
=1 to
400
kPa
)/e
at p
=1 k
Pa)
Normal soilSlurry
Std. Oedometer specimen(60mm dia, H=20mm)
Silty clay slurry150 mm dia for
H50=23mm, 56mm, 110mm
(a)
1 10 100 10000.0
0.2
0.4
0.6
0.8
1.0
Consolidation pressure, kPa
Voi
d ra
tio (e
at p
=1 to
400
kPa
)/e
at p
=1 k
Pa)
Normal soilSlurry
Std. Oedometer specimen(60mm dia, H=20mm)
Kanto loam slurry150 mm dia with
H50=23mm, 56mm, 110mm
(b)
mv, Cv, k – are not constant
0 100 200 300 4000.0
2.0
4.0
6.0
8.0
10.0
0
2
4
6
8
10
12k-indirectk-direct
Consolidation pressure p, kPa
Perm
eabi
lity
k, m
/sX1
e-9
"k"
dire
ct X
1e-
6
10 100 10000.0
0.2
0.4
0.6
0.8
1.0
0
2
4
6
Consolidation pressure, kPa
mv(
p)/m
v(p=
20 k
Pa) a
nd
k(p)
/k(p
=20k
Pa)
Coeff
. of c
onso
lidati
on, m
2/yr
cv vs p (Oedometer)
cv vs p
mv ratio vs p
k ratio vs p
10 100 10000.0
0.2
0.4
0.6
0.8
1.0
0
2
4
6
Consolidation pressure, kPa
mv
(p)/
mv
(p=2
0 kP
a) a
nd
k(p)
/k(p
=20
kPa)
Coeff
. of c
onso
lidati
on, m
2/yr
cv vs p (Oedometer)
cv vs p mv ratio vs p
k ratio vs p
With more “p”, u/p reduces
0 25 50 75 100 125 150 175 200 225 250 275 3000
0.2
0.4
0.6
0.8
1
Kanto loam
Silty clay
Time (hrs)
Exce
ss P
WP
ratio
, u/p
Excess PWP (p=20 to 400kPa)
0 20 40 60 80 100 120 140 160 180 2000
20
40
60
80
100
120
1400
0.1
0.2
0.3
0.4
0.5
0.6
0.7
PWP-2, kPaPWP-3PWP-4
Cons. Time, hrs
Exc
ess P
WP,
kPa
Ver
tical
stra
in
Clay sand basic 100 mm
0 0.5 1 1.50.00
0.25
0.50
0.75
1.00
0.05 hrs0.23351.3168333335.79016666711.7901666723.79016667
PWP u/D p
z/H5
0
p=20 kPa
0 0.5 1 1.50.00
0.25
0.50
0.75
1.00
0.03hrs0.1951666670.57855.04516666711.9951666725.99516667
PWP ratio, u/D p
z/H5
0
p=50 kPa
PWP-3
PWP-2
PWP-1
PWP-3PWP-2PWP-1 H
50
Consolidation pressure (p=50 kPa)
Dra
in fa
ce
u
150mm diameter
PWP inside specimen
0 0.5 1 1.50.00
0.25
0.50
0.75
1.00
0.02hrs0.23350.6501666674.95016666711.9501666725.95016667
PWP ratio, u/Dp
z/H5
0
p=100 kPa
0 0.5 1 1.50.00
0.25
0.50
0.75
1.00
0.05hrs0.23350.6501666671.4501666676.95016666725.95016667
PWP ratio, u/D p
z/H5
0
p=200 kPa
0 0 .5 1 1.50.0 0
0.2 5
0.5 0
0.7 5
1.0 0
0.10 hrs
0.281.55.511 .521 .5 5 01 66 67
P WP r atio , u /D p
z/H5
0
p= 400kP a
PWP-3
PWP-2
PWP-1
PWP-3PWP-2PWP-1
H 5 0
Co nsol i dat i on pr essure ( p=50 kPa)
Dra
in fa
ce
u150m m diam eter
PWP-3PWP-2PWP-1 H
50
Consolidation pressure (p=50 kPa)
Dra
in fa
ce
u
150mm diameter
Excess PWP is more than net increase in “p”
10 100 10000.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
PWP-3PWP-2PWP-1
Consolidation pressure, kPa
Peak
exc
ess P
WP
ratio
, u/p
Silty clay
u/Dp
u/p
(a)
10 100 10000.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Consol ida tion pr essur e p, kPa
Peak
exce
ss PW
P ra
tio
Kanto l oam
u/Dp
u/p
(b)
15 0 mm di am e ter
P WP -3P WP -2P WP -1 H
Co n so li da ti on p re ssu r e, p
Drain
face
u
Permeability - direct
0 50 100 150 200 250 300 350 4000
500
1000
1500
0
1
2
3
4
5
t50 vs pClay sand t50 vs p Cv vs pclaysand Cv vs p
p, kPa
t50,
min
Coeff
. con
solid
ation
, m2/
yr
sample100 mm
0 50 100 150 200 250 300 3500
1
2
3
4
5
6
p=50 kPa 100
200 400
Flow pressure, u (top) kPa
Dire
ct P
erm
eabi
lity,
k (m
/s)X
exp
-9
Kanto Loam
0 50 100 150 200 250 300 3500
0.5
1
1.5
2
2.5
3
3.5
4
4.5p=50 kPa 100 200400
Flow pressure, u (top) kPa
Perm
eabi
lity,
k (m
/s)X
exp
-9
Silty clay
1 10 100 1000 100000
1
10
100
1000
5010020040020
Consolidation time, min
Darc
y pe
rmea
bilit
y x1
0-9,
m/s
Kanto loam
e – p curve
0 100 200 300 400 500 600 7000
2
4
6
8
Consolidation pressure, kPa
void
ratio
, e Kanto loamCc=1.1Cc (Cal)=0.8 Silty clay
Cc=0.31Cc(cal)=0.25
Oedometer sample
11010010002.0
2.5
3.0
3.5
4.0
50 100
200 400
Darcy permeability x 10-9, m/s
Void
ratio
chan
ge, e
Kanto loam
55
New developments New multi-purpose test apparatus developed
– Flow capacity at in-situ state & increasing confinement
– Excess pore water measurement inside specimen
– Direct measure of ‘k”, vertical strain, drained water
Conclusions• Transition between slurry and normal Terzaghi soil
state occurred at consolidation pressure of 50 kPa. • Water content at this transition state found fairly
close to the respective liquid limits of the Kanto loam and silty clay.
• Peak excess PWP represents the state at which soil undergoes maximum rate of compression.
• ‘e-log p’ curves for slurry state and normal soil state are different and it has two separate Cc values.
Thank you