Session 4 How to reduce wall deflection November 2009 Reducing Wall Deflection

November 2009
Reducing Wall Deflection
Session 4
How to reduce wall deflection
Time
Session Topic
p
09:00 – 10:30
1
Overview
Coffee Break
10:30 – 11:00
11:00 – 12:30
2
Design (Part 1)
12:30 - 01:30
01:30 – 03:00
3
Mohr-Coulomb Soil Model &
Design (Part 2)
Coffee Break
03:00 – 03:30
03:30 – 05:00
4
How to reduce wall deflection
Reducing Wall Deflection
How to reduce
wall deflection?
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Options:
1. Change to circular shape
2. Increase wall stiffness
3. Increase
3
c ease no.
o of
o struts
s us
4. Increase preloads
5. Increase wall penetration
6. Install cross-walls
7. Ground improvement
• JGP - Jet grouting
• DCM - Deep cement
mixing
8. Improved soil slab with
tension piles
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Ring Beam System
Central at Clarke Quay in
Clarke Quay in Singapore
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The Sail at Marina Bay in Singapore
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Effect of
Penetration &
Wall Stiffness
Sheetpile Wall
Diaphragm Wall
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Effect of Number of Level Struts
2
3 struts
struts
Diaphragm Wall
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4
5
struts
struts
struts
Sheetpile Wall
6
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Diaphragm Wall with Cross-Wall
Cross-wall
Sand
Cross-wall
Marine Clay
Diaphragm
wall
Old Alluvium
Diaphragm
wall
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TERS Design with Cross‐Walls
DW
DW
Cross‐Wall
Cross‐Wall
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Main applications of JGP in deep excavation are:
1. To reduce wall deflection & ground settlement
2. To minimize effect on adjacent structures
3. To improve basal heave stability
4. To improve toe kick‐in stability
5. To control seepage
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JGP – Jet Grouted Piles
Ground Level
Ground Water Table
FILL
FILL
MARINE
MARINE
CLAY
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
JGP
MARINE
MARINE
CLAY
CLAY
D/WALL
D/WALL
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OLD ALLUVIUM
Completed JGP Slabs prior to Excavation
10
Slide 10
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How does it work?
It acts as a compression member to reduce wall deflection
deflection.
In addition, it can also act as an anchored slab to minimize bottom heave
minimize bottom heave. Reducing Wall Deflection
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No JGP/DCM δH,max = 361 mm
3m JGP/DCM δH,max = 141 mm
3m JGP/DCM with tension piles δH,max = 37 mm
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Full Penetration Wall
Floating Wall
1.2mD
W
1.2mD
W
5m JGP
5m JGP
δmax = 90 mm
Tmax = 1600 kN/m
Mmax = 350 kNm/m
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No Sacrificial JGP
1.2mD
W
5m JGP
δmax = 90 mm
Tmax = 1600 kN/m
Mmax = 350 kNm/m
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δmax = 101 mm
Tmax = 1580 kN/m
Mmax = 439 kNm/m
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2m Sacrificial JGP
2m JGP
1.2mD
W
5m JGP
δmax = 58 mm
Tmax = 1590 kN/m
Mmax = 371 kNm/m
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No Piles
7 Piles
2m JGP
1.2mD
W
5m JGP
δmax = 58 mm
Tmax = 1590 kN/m
Mmax = 371 kNm/m
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1.2mD
W
2m JGP
5m JGP
δmax = 442 mm
Tmax = n.a.
Mmax = n.a.
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Factor of safety without JGP = 0.45 to 0.6
Clark Quay Station Entrance
(Shirlaw et al., 2005)
This is one occasion where modeling of piles is a must.
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d = 1.5 m
d = 3 m
d = 6 m
Effect of Grout
Layer Thickness
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Presence of JGP slab can reduce the number of strut levels. Reducing Wall Deflection
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JGP
Jet Grouted Piles
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Jet Grouting
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Construction
of Jet Grout
Slab
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Jet grouting on land
Jet grouting over a canal
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Bulk density of JGP 2
1.9
Bulk Density (Mg/m3)
1.8
1.7
1.6
1.5
1.4
1.3
Triple Tube
1.2
Double Tube
1.1
1
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Unconfined Compressive Strength qu (kPa)
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JGP Strength & Density (Shirlaw et al., 2000)
qu = 2 cu
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JGP strength (14 days) Design qu
(kPa)
Mean
Measured qu
(kPa)
Singapore River
Double
tube
500
1225
Chia & Tan (1993)
Geylang River
Single
tube
500
1843
Liang et al. (1993)
Clarke Quay MRT
Station
-
600
2520
Shirlaw et al. (2000)
Tunnel at Race Course
Rd
-
600
2024
Shirlaw et al. (2000)
Tunnel at Race Course
Rd
-
600
1290
Wen (2005)
C824 – Nicoll Highway
Double
tube
900
5826
This study
C824 – Nicoll Highway
Triple
tube
900
3584
This study
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Source
JGP
Method
Project
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JGP strength from C824 at Types C to M3 8
7
Specification: qu = 0.9 MPa
No. of Samples
6
5
4
3
2
1
0
<0.9
0.9-1
1-2
2-3
3-4
4-5
5-6
6-7
7-8
8-9
9-10
Unconfined Compressive Strength of JGP (MPa)
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JGP Modulus 1400
Eu / qu ~ 100
Eu/qu ~ 100
Eu / c
/ cuEu/Cu
~ 200
200
~ 200
1200
Modulus (MPa)
1000
800
600
400
Triple Tube
200
Double Tube
0
0
2000
4000
6000
8000
10000
12000
14000
Unconfined Compressive Strength (kPa)
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Deep Cement Mixing ‐‐ DCM
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Deep Cement Mixing
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Strength & Modulus of DCM samples in Marine Clay
External measurements
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σ−ε curves from local and external strain measurements
(Tan et al., 2002)
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Modulus and Strength of DCM Samples in Marine Clay
(Tan et al., 2002)
External Measurements
Local Measurements
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Curing Time of DCM Samples in Marine Clay
(Tan et al., 2002)
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Adverse Effects of Jet Grouting
Double Tube Method
1. It pushes the wall outward away from excavation area
away from excavation area.
2. It causes ground heave.
Esplanade by the Bay
I-5D
I-6D
I-12D
I-9D
I-10D
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How to model JGP slab in FEA?
1. Wall and JGP slab are wished‐in‐place.
2. Step‐by‐step simulation of p y
p
excavation sequence
qu = ? Eu = ?
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Deep Excavation
Shallow Excavation
H
H
JGP strength not critical
JGP strength critical
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qu (core) = qu (mass) ?
3D view of core sample
Plan view of JGP slab
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Eu (core) = Eu (mass) ?
3D view of core sample
Plan view of JGP slab
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Other Issues: (1) Initial Stresses in JGP
σ1 – σ3
Initial state of stress
ε
Assumptions commonly adopted in practice: (1) JGP slab is wished in‐place.
(2) φu = 0 Æ Ko = 1.0 Æ (σ1 – σ3) = 0
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Other Issues: (1) Initial Stresses in JGP
σ1 – σ3
Initial state of stress
ε
Actual condition in field:
σ1 >> σ3
Æ (σ
( 1 – σ3) > 0 ) 0
What Ko value should we use in analysis?
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Other Issues: (2) Field Construction Sequence
1. Construction of DW panels
• Reduction in σh
2. Installation of JGP slab
• Increase in σ
Increase in σh
• Rotation of principal stress direction
p = ?
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Other Issues: (2) Field Construction Sequence
3. Step‐by‐step excavation
• Reduction in σh
Each soil element goes through a different stress path
Each soil element goes through a different stress path.
Can the soil model produce the correct response at each element?
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Other Issues: (3) Wall Deflection Profile
Wall Deflection at I104
105
RL (m)
Fill
E
Fill
E
90
UMC
UMC
85
F2 upper
F2 upper
100
95
80
85.4
LMC
LMC
75
LMC
70
69.4
65
60
63.7
61 2
61.2
59.2
55
50
0
50
100
150
200
250
300
350
400
F2
lower
OA N = 20
OA N = 30
OA N = 70
F2
F2 lower
OA N = 20
OA N = 30
OA N = 70
72.1
66.
864.7
60 0
60.0
OA N = 100
55.0
WallDeflection(mm)
1. Are these deflection profiles correct?
2. Can they be used to determine the wall bending moments?
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Other Issues: (3) Wall Deflection Profile
Where is the reference line?
Profile A
(Initial)
Profile A
Profile B
(After JG)
Profile D
Profile C
Using Profile A as reference line.
Using Profile B as reference line.
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Profile B
Profile A
Profile A
Measured wall deflection of an excavation in Taiwan (Lin & Lin, 2008)
P fil D
Profile D
Profile C
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Case 17
Case 3
With simulation of jet grouting
Without simulation of jet grouting
δHmax = 14 mm
δHmax = 71 mm
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δHmax = 90 mm
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Case 17
With simulation of jet grouting
Relative Shear
Case 3
Without simulation of jet grouting
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™ Profile B is the more rational choice as reference line.
™ It gives the true deflection profile.
Profile A
(Initial)
Profile A
Profile B
(After JG)
Profile D
Profile C
Using Profile A as reference line.
Using Profile B as reference line.
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Other Issues: (4) JGP Slab Thickness
Design
• Reasonable to assume uniform thickness
• Need to conduct sensitivity study eed to co duct se s t ty study
Back‐Analysis
• Need to know variations of JGP thickness
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Other Issues: (5) JGP Post‐Failure Behaviour
σ
σ
σ3 = 0 kPa
σ3 = 500 kPa
ε
Unconfined compression test
ε
Confined compression test
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stress‐strain curves of clay‐cement mix under different confining pressures Reducing Wall Deflection
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Modelling of JGP Post‐Failure Behaviour
σ
σ
σ3 = 0 kPa
ε
σ3 = 500 kPa
ε
σ1 – σ3
FE simulation using Mohr‐
Coulomb Model
ε
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Cross‐section & soil profile adopted in the analysis
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Plastic points showing extensive yielding in JGP slab and surrounding soils at 7th strut level JGP1
Sacrificial JGP layer Reducing Wall Deflection
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Modelling of JGP Post‐Failure Behaviour
σ
σ
σ
50%
ε
ε
ε
(A) (B)
(C)
no softening
50% reduction
80% reduction
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80%
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Maximum wall deflections computed by Analyses A, B and C at 10th level
Analysis
Strain
Softening
Maximum Wall Deflection ((mm))
South Wall
North Wall
A
None
263
191
B
50%
reduction
318
220
C
80%
reduction
380
225
325
181
Measured
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Deflection profiles at the south wall at different stages of excavation 105
Level 3
100
Level 4
100
100
100
90
90
Level
e e 5
Level 6
95
Level 7
90
Level 9
75
70
Reduced Level (m)
Reduced Level (m)
Reduced Level (m)
80
Level 1
Level 2
Level 10
85
80
70
Level 3
Reduced Level (m)
Level 8
90
80
70
Level 4
80
Level 5
Level 6
Level 7
70
Level 8
Level 9
65
Level 10
60
60
60
60
55
0
50
100
150
200
250
300
350
400
Wall Deflection (mm)
Measured
(326 mm)
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-100
50
50
50
50
100
300
Wall deflection (mm)
500
-100
0
100
200
300
400
Wall deflection (mm)
-100
0
100
200
300
400
Wall deflection (m m )
(A)
(B)
(C)
no softening
50% reduction
80% reduction
(263 mm)
(318 mm)
(380 mm)
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Deflection profiles at the north wall at different stages of excavation 105
100
100
100
100
90
90
90
95
90
Level 1
75
70
80
70
Level 1
Level 2
Level 3
Level 4
Level 5
Level 6
Level 7
Level 8
Level 9
Level 10
65
60
55
50
0
20 40 60 80 100 120 140 160 180 200 220 240
Level 3
Reduced Level (m)
Reduced Level (m)
Reduced Level (m)
80
Reduced Level (m)
Level 2
85
80
70
Level 4
80
Level 5
Level 6
Level 7
Level 8
70
Level 9
Level 10
60
60
50
-40
0
40
Wall Deflection (mm)
80
60
50
-40 0
120 160 200 240 280
40
Measured
80
50
-40
0
120 160 200 240 280
Wall deflection ((mm))
Wall deflection ((mm))
40
80
120 160 200 240 280
Wall
a de
deflection
ect o ((m m))
(A)
(B)
(C)
no softening
50% reduction
80% reduction
(191 mm)
(220 mm)
(225 mm)
(181 mm)
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Comparison of Computed and Measured Strut Forces
100
100
100
95
90
85
95
90
85
80
80
0
500
1000
1500
2000
Maximum strut load (kN/m)
(A)
no Softening
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90
85
80
75
75
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Reduced Level (m )
105
Reduced Level (m )
105
Redu ced L evel (m )
105
75
0
500
1000
1500
2000
0
500
1000
1500
2000
M i
Maximum
strut
t t load
l d (kN/m)
(kN/ )
Maximum strut load (kN/m)
(B)
50% reduction
(C)
80% reduction
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Other Issues: (6) Adhesion between JGP and Pile
h
JGP
How can we determine ca between JGP and pile?
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Mixing of clay & cement
Roughen the surface
Completed
specimens
Specimen
and
moulds
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Compressive strength of specimen at different curing time
(Goh, 2005)
1600
Compressive Strength (kPa)
1400
1200
28 days
1000
14 days
800
7 days
600
400
200
0
0
10
20
30
40
Water added (%)
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Adhesion between concrete with clay‐cement mixture
(Goh, 2005)
700
y = 0.448x + 444.82
600
20%[email protected]
Shear Strength (kPa)
500
30%[email protected]
y = 0.3348x + 369.64
400
20%[email protected]
300
30%[email protected]
y = 0.7408x
200
y = 0.6273x
100
0
0
50
100
150
200
250
300
350
400
450
500
Normal Stress (kPa)
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PreliminaryTest Pile TP2
Max load
1750 Tonnes
1m diameter
Rod extensometers
(damaged on
installation)
SPT Blows per
mm penetration
Shear Transfer at maximum load
GL
(7)
Sandy
Made Ground
Pile Load Test at KPE
Typical
<10/300
Pile head settlement
at maximum load
=23mm
Residual settlement =4mm
10m
(Shirlaw et al., 2005)
(Shirlaw et al., 2005)
Marine Clay
(83)
Jet Grout Slab
(754)
20m
(197)
(52)
Measured adhesion = 754 kPa
Adhesion at failure >>754 kPa
30m
Marine Clay
65.5m
40m
(126)
Fluvial Sand
50m
Old Alluvium
46/300
25/300
(72)
44/300
55/300
100/220
100/260
(106)
(15)
100/280
100/220
60m
100/220
0
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500
Shear transfer (kN/m2)
1000
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Other Issues: (7) How to model the adhesion in FEA?
d
Qs on piles in field = ( π d h / s ) ca
Qs on piles in FEA = 2 h c
il i FEA 2 h a,FEA
ca,FEA = (π d ca) / (2 s)
s
h
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JGP
Pile
p
g
Spacing
2.5 d
3.0 d
3.5 d
4.0 d
ca,FEA
0.63 ca
0.52 ca
0.45 ca
0.39 ca
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Conclusions
1. Many uncertainties involving JGP:
• Strength
• Modulus
• Initial stress
• Slab thickness
• Post‐failure behaviour
2. Shallow excavations Æ JGP strength may not be important.
3. Deep excavations Æ JGP strength becomes critical. Proper modeling of post‐failure behaviour becomes important. 4. Use qu=600 kPa and Eu=150 MPa as reference case
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5. Conduct sensitivity studies on
‐ Modulus
‐ Strength
‐ Slab thickness
‐ Post‐failure softening
6. Do not zero the inclinometer readings at the start of excavation. Always base on the initial readings.
7. Exercise stringent quality control during jet grouting.
8 M it
8. Monitor performance closely during construction.
f
l l d i
t ti
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