Nicoll Highway Incident WONG Kai Sin 1 1 Lessons Learned from The Nicoll Highway Incident 20 th April 2004 Nicoll Highway 2 Nicoll Highway
Nicoll Highway Incident
WONG Kai Sin 1
1
Lessons Learned from The
Nicoll Highway Incident
20th April 2004
Nicoll Highway
2 Nicoll Highway
Nicoll Highway Incident
WONG Kai Sin 2
3
Golden Mile Tower
Golden Mile Complex
The Concourse
Plaza Hotel
Site Plan
Merdeka Bridge
Station Area
X-over Box
Area K Area I Area J Area H Tunnel Box
Collapsed section of NCH
Collapse Area
Nicoll Highway
4
Picture of the affected site
Before Collapse on 20 April 2004
Nicoll Highway
Nicoll Highway Incident
WONG Kai Sin 3
5
Picture of the affected site
After Collapse on 20 April 2004
Nicoll Highway
6
Picture of the collapse
Around 3:30 p.m. on 20 April 2004
Nicoll Highway
Nicoll Highway Incident
WONG Kai Sin 4
7
Picture of the collapse
Around 3:30 p.m. on 20 April 2004
Nicoll Highway
Nicoll Highway 8
Nicoll Highway Incident
WONG Kai Sin 5
9 Nicoll Highway
10 Nicoll Highway
Nicoll Highway Incident
WONG Kai Sin 6
11
66 KV Cable
Layout Plan
TSA
Nicoll Highway
Soil Conditions
Nicoll Highway 12
LMC
F2 lower
F2 upper
UMC
E
Fill
JGP1
JGP2
RL (m)
103.0
63.7
69.4
Soft Clay
Sand Fill
Stiff Clay
Stiff Clay
Upper
Marine Clay
Lower
Marine Clay
Dense
Silty Sand OA
100.0
98.0
85.5
82.5
Nicoll Highway Incident
WONG Kai Sin 7
13
Construction of Jet Grout Slab
14
Sacrificial JGP
JGP
FILL FILL
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
MARINE
CLAY
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
Ground Level Ground Level
Construction Sequence
D/WALL D/WALL
1ST STRUT
2ND STRUT
5TH STRUT
6TH STRUT
8TH STRUT
9TH STRUT
3RD STRUT
4TH STRUT
7TH STRUT
PILES
PILES
10TH STRUT
Nicoll Highway
Nicoll Highway Incident
WONG Kai Sin 8
9:30 a.m. April 20th 2004
Nicoll Highway 15
Photo taken at S338 Level 9 between 10 to 10:30 a.m.
waler
swayed
downward
Nicoll Highway 16
Nicoll Highway Incident
WONG Kai Sin 9
Strut Forces of S335
at Level 9
17
Strut S335 - Level 9
0
1000
2000
3000
4000
5000
Str
ut
Fo
rce
(k
N)
Strut S335 - Level 8
0
1000
2000
3000
4000
5000
Str
ut
Fo
rce
(k
N)
20/4, 10 a.m.
Strut Forces
8th
9th
Nicoll Highway 18
Nicoll Highway Incident
WONG Kai Sin 10
Strut Forces
Strut S335 - Level 6
0
1000
2000
3000
4000
5000
6000
Str
ut
Fo
rce
(k
N)
Strut S335 - Level 7
0
1000
2000
3000
4000
5000
Str
ut
Fo
rce
(k
N)
20/4
20/4 6th
7th
Nicoll Highway 19
Deflection of South Wall (Seaside)
Wall Deflection at I104
50
55
60
65
70
75
80
85
90
95
100
105
0 50 100 150 200 250 300 350 400 450 500
Wall Deflection (mm)
Re
du
ce
d L
ev
el (m
)
Preload Strut 9
17 April 04
20 April 04
Level 9 Strut
Nicoll Highway 20
Nicoll Highway Incident
WONG Kai Sin 11
Warnings prior to Collapse
• Wall deflections
• Strut forces
• Pore pressures
• Ground settlements
• Field observations
Nicoll Highway 21
Wall deflections
Inclinometer I104 – sea side Inclinometer I65 – highway side
Nicoll Highway 22
Nicoll Highway Incident
WONG Kai Sin 12
Wall Deflections
23
Maximum Wall Deflections at S335
Nicoll Highway 24
Nicoll Highway Incident
WONG Kai Sin 13
0
50
100
150
200
250
300
350
400
450
500
1/4/04 1/19/04 2/3/04 2/18/04 3/4/04 3/19/04 4/3/04 4/18/04
Wall D
efle
ctio
n (
mm
)
Changing Goal Posts!
1st Goal Post
3rd Goal Post
2nd Goal Post
Maximum Wall Deflections at S335 Nicoll Highway 25
Ground Settlement at L111
-300.0
-250.0
-200.0
-150.0
-100.0
-50.0
0.0
50.0
5/24/02 9/1/02 12/10/02 3/20/03 6/28/03 10/6/03 1/14/04 4/23/04
Sett
lem
en
t (m
m)
Nicoll Highway Incident
WONG Kai Sin 14
Pore Pressure at GW(V)25
GW(V)25
Pore Pressure Measurements
29/1/04
GW(V)-25 at 17.5 m in Upper Marine Clay
Nicoll Highway Incident
WONG Kai Sin 15
29
What caused the failure?
Nicoll Highway
1. Basal heave instability
2. Uplift instability
3. Removal of JGP slab
4. Inadequacy of JGP
5. Shifting of JGP slabs
6. Wall kick-in – insufficient wall penetration
7. Wall failure – formation of plastic hinges
8. Curvature of tunnel alignment
9. Presence of the utility gaps
10. Short Waler & Eccentric Strut Loading
11. Settlement of diaphragm wall
12. Strut failure
13. Waler/stiffener failure
What caused the failure?
Nicoll Highway
30
Nicoll Highway Incident
WONG Kai Sin 16
Basal Heave Stability
Nicoll Highway 31
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
U
W
W < U
MARINE
CLAY
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
JGP
D/WALL D/WALL
Ground Level Ground Level 1ST STRUT
2ND STRUT
3RD STRUT
4TH STRUT
5TH STRUT
6TH STRUT
7TH STRUT
8TH STRUT
9TH STRUT
10TH STRUT
Ground Water Table
Ground Water Table
FILL FILL
Uplift Failure
Slide 32
Nicoll Highway 32
Nicoll Highway Incident
WONG Kai Sin 17
Uplift Failure
Ground Level Ground Level
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
D/WALL
FILL FILL
MARINE
CLAY
D/WALL
W < U
Nicoll Highway 33
Is Old Alluvium a Sand or Clay?
Predominantly classified as sand but behaves like clay
High fines content (typically 20 to 30%)
Low permeability k ~ 10-6 to 10-8 m/s based on field measurements
Nicoll Highway 34
Nicoll Highway Incident
WONG Kai Sin 18
Clean Sand Pockets and Lenses in OA
Fill
E
UMC
F2
LMC
RL (m)
102.9
98.2 96.4
85.6
83.4
68.3
61.6
E / F2
Fill
E
UMC
F2
LMC
JGP
RL (m)
102.9
98.2
96.4
85.6
83.4
68.3
61.6
E / F2
Old Alluvium
Sand pocket
Nicoll Highway 35
Removal of JGP
JGP
FILL FILL
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
MARINE
CLAY
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
Ground Level Ground Level
D/WALL D/WALL
1ST STRUT
2ND STRUT
5TH STRUT
6TH STRUT
8TH STRUT
9TH STRUT
3RD STRUT
4TH STRUT
PILES
PILES
7TH STRUT
10TH STRUT
Removal of this JGP layer
Nicoll Highway 36
Nicoll Highway Incident
WONG Kai Sin 19
Fill
E
UMC
F2 upper
LMC
F2 lower F2
LMC
LMC
F2 lower OA N = 20
OA N = 30
OA N = 70
OA N = 100 OA N = 70
OA N = 30
OA N = 20
F2 upper
UMC
E
Fill
JGP1
JGP2 JGP3
RL (m)
85.4
72.1
66.8
64.7
60.0
55.0
59.2
61.2
63.7
69.4
Inadequacy of JGP Slab
16 rigs
24 hrs / day
Nicoll Highway 37
Weak joint at JGP slab along the power cable alignment
Nicoll Highway 38
Nicoll Highway Incident
WONG Kai Sin 20
Weak joint at JGP slab along the power cable alignment
AC-3 S
335
Nicoll Highway 39
JGP
JGP
FILL FILL
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
MARINE
CLAY
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
Ground Level Ground Level
D/WALL D/WALL
1
2
5
6
8
9
3
4
7
Yielding of Diaphragm Wall
Nicoll Highway 40
Nicoll Highway Incident
WONG Kai Sin 21
Yielding of Diaphragm Wall
JGP
JGP
FILL FILL
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
MARINE
CLAY
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
Ground Level Ground Level
D/WALL D/WALL
1
2
5
6
8
9
3
4
7
Wall Deflection at I104
50
55
60
65
70
75
80
85
90
95
100
105
0 50 100 150 200 250 300 350 400 450 500
Wall Deflection (mm)
Re
du
ce
d L
ev
el (m
)
Preload Strut 9
17 April 04
20 April 04
Level 9 Strut
41
Yielding of strut lead to
yielding of wall?
Yielding of wall lead to
yielding of strut?
JGP
JGP
FILL FILL
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
MARINE
CLAY
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
Ground Level Ground Level
D/WALL D/WALL
1
2
5
6
8
9
3
4
7
Insufficient Wall Penetration
Toe kick-in?
Nicoll Highway 42
Nicoll Highway Incident
WONG Kai Sin 22
43
Elevation Contour of Top of OA
(Ishihara & Lee, 2008)
Before
After Nicoll Highway
44
Comparison of Top of OA Level
Nicoll Highway
Nicoll Highway Incident
WONG Kai Sin 23
I104
Toe kick-in?
Nicoll Highway 45
66 kv Cable
Presence of Utility Gaps
TSA
Nicoll Highway 46
Nicoll Highway Incident
WONG Kai Sin 24
Curvature in Tunnel Alignment
MC3008 AC3
MC3007
M2064 47
Short Walers & Eccentric Strut Loading
Nicoll Highway 48
Nicoll Highway Incident
WONG Kai Sin 25
Settlement of D Wall
MARINE
CLAY
OLD ALLUVIUM
JGP
Ground Level
1ST STRUT
2ND STRUT
3RD STRUT
4TH STRUT
5TH STRUT
6TH STRUT
7TH STRUT
8TH STRUT
9TH STRUT
FILL Ground Level
MARINE
CLAY
FLUVIAL
CLAY
Nicoll Highway 49
Settlement of Diaphragm Wall
JGP
JGP
FILL FILL
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
MARINE
CLAY
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
Ground Level Ground Level
D/WALL D/WALL
1ST STRUT
2ND STRUT
5TH STRUT
6TH STRUT
8TH STRUT
9TH STRUT
3RD STRUT
4TH STRUT
PILES
PILES
7TH STRUT
10TH STRUT
Nicoll Highway 50
Nicoll Highway Incident
WONG Kai Sin 26
STRUTS
INEFFECTIVE
NO SUPPORT
TO NORTH WALL
20th APRIL 2004
~ 3.30pm
OLD ALLUVIUM
Buckling of Struts ?
NICOLL HIGHWAY ORIGINAL GROUND LEVEL
40m
30m
20m
10m
0m
DEPTH
0 10 20m
SCALE
VERY SOFT
CLAY
Slide 51
51
Fill
E
MC
F2
LMC
F2
LMC
F2 OA N=20
OA N=30
OA N=70
OA
N=100 OA N=70
OA N=30
OA N=20
F2
MC
E
Fill
JGP
55.
59.2
61.
2
63.
7
69.4
NLC Design > Measured
Therefore, strut failure did not initiate the collapse.
Buckling of Struts ?
Nicoll Highway 52
Nicoll Highway Incident
WONG Kai Sin 27
53
Waler/Strut Connection
JGP
JGP
FILL FILL
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
MARINE
CLAY
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
Ground Level Ground Level
D/WALL D/WALL
1ST STRUT
2ND STRUT
5TH STRUT
6TH STRUT
8TH STRUT
9TH STRUT
3RD STRUT
4TH STRUT
PILES
PILES
7TH STRUT
10TH STRUT
Levels 1 to 6
54
Waler/Strut Connection
JGP
JGP
FILL FILL
MARINE
CLAY
MARINE
CLAY
OLD ALLUVIUM
MARINE
CLAY
MARINE
CLAY
FLUVIAL
CLAY
FLUVIAL
CLAY
Ground Level Ground Level
D/WALL D/WALL
1ST STRUT
2ND STRUT
5TH STRUT
6TH STRUT
8TH STRUT
9TH STRUT
3RD STRUT
4TH STRUT
PILES
PILES
7TH STRUT
10TH STRUT
Levels 1 to 6
Levels 7 to 10
Nicoll Highway Incident
WONG Kai Sin 28
9am 20 APRIL WALER STARTS TO FAIL
INCREASED WALL
MOVEMENT 17th TO 20th APRIL
17th/20th APRIL
VERY SOFT
CLAY
OLD ALLUVIUM
Yielding of Waler/Strut Connection with C-channel
NICOLL HIGHWAY
FILL
M
F2
M
BORED PILES
40m
30m
20m
10m
0m
DEPTH
0 10 20m
SCALE
Nicoll Highway 55
NICOLL HIGHWAY
COLLAPSES
OLD ALLUVIUM
WALL ROTATES
SOIL FLOW
20th APRIL 2004
~ 3.30pm
Yielding of Waler with C-channel
ORIGINAL GROUND LEVEL
BORED PILES
40m
30m
20m
10m
0m
DEPTH
0 10 20m
SCALE
VERY SOFT
CLAY
Slide 56
Nicoll Highway 56
Nicoll Highway Incident
WONG Kai Sin 29
Capacity of Waler with C-channel
C - Channel
Concrete Packing
D/Wall
Slide 57
Strut Waler
Nicoll Highway 57
Capacity of Waler with C-channel
WALL
ROTATION
ROTATION ANGLE OF WALL
Slide 58
58
Nicoll Highway Incident
WONG Kai Sin 30
Waler/stiffener Failure due to Wall Rotation
Wall Deflection at I104
72
74
76
78
80
250 300 350 400 450 500
Wall Deflection (mm)
Re
du
ce
d L
ev
el (m
)
Preload Strut 9
17 April 04
20 April 04
Level 9 Strutº º
º
Wall Deflection at I104
50
55
60
65
70
75
80
85
90
95
100
105
0 50 100 150 200 250 300 350 400 450 500
Wall Deflection (mm)
Re
du
ce
d L
ev
el (m
)
Preload Strut 9
17 April 04
20 April 04
Level 9 Strut
Nicoll Highway 59
Effect of Wall Rotation on Waler/stiffener Capacity
Waler (H400) with C-Channels at top & bottom
0
500
1000
1500
2000
2500
3000
3500
4000
0 1 2 3 4 5 6 7
Wall Rotation (degrees)
Wale
r C
ap
acit
y (
kN
)
Nicoll Highway 60
Nicoll Highway Incident
WONG Kai Sin 31
Stiffener Plate
Stiffener Plate
Slide 61
Nicoll Highway 61
Behaviour of Waler with Stiffener Plates
62
Nicoll Highway Incident
WONG Kai Sin 32
C - Channel
C-channel as Stiffness
Slide 63
Nicoll Highway 63
Behaviour of Waler with C-channels
64
Nicoll Highway Incident
WONG Kai Sin 33
Testing of Real Specimens
Nicoll Highway 65
Testing of Real Specimens
Nicoll Highway 66
Nicoll Highway Incident
WONG Kai Sin 34
67
3-D Numerical Modeling
Nicoll Highway
Capacity of Waler/Stiffener without Wall Rotation (Analysis with strain hardening)
Stiffener Plate at top and bottom
C-channel at top
C-channel at top and bottom
68
Nicoll Highway Incident
WONG Kai Sin 35
Major factors contributing to the failure
1. Design lacks robustness and redundancy.
2. Inadequate wall capacity.
3. Inadequate wall penetration into hard stratum.
4. Missing splays in some struts.
5. C-channel strut-waler connection was
structurally inadequate.
strut
splay
waler
P = 2657 kN
(2/3)P
= 1771 kN
P/3
Nicoll Highway 69
Root of the problem
Improper Design!
Nicoll Highway 70
Nicoll Highway Incident
WONG Kai Sin 36
Original Design
Level 10
325 mm
Measured Computed
Formation = 118 mm
Final = 145 mm 71
Method adopted in Original Design
• Undrained analysis
• Mohr-Coulomb soil model
• Effective stress parameters:
c’, f’, E’ and n’
• Phreatic surface: Z-method
• Computer program: PLAXIS
This method over-estimated the undrained
shear strength of marine clay.
This is
known as
Method A.
Nicoll Highway 72
Nicoll Highway Incident
WONG Kai Sin 37
“Correct” Method
• Undrained analysis
• Mohr-Coulomb soil model
• Total/effective stress parameters:
cu, fu=0, E’ and n’
• Phreatic surface: Z-method
• Computer program: PLAXIS
This is
known as
Method B.
Nicoll Highway 73
74
Measured Computed using Method B
Nicoll Highway – Results of Undrained Analysis using Method B
Why is Method B giving the correct deflection? Nicoll Highway
Nicoll Highway Incident
WONG Kai Sin 38
Bending
Moment
in Wall
Method A
Method B
Nicoll Highway 75
0
50
100
150
200
250
300
350
400
450
500
1/4/04 1/19/04 2/3/04 2/18/04 3/4/04 3/19/04 4/3/04 4/18/04
Wall D
efle
ctio
n (
mm
)
Moving the Goal Post
1st Goal Post
3rd Goal Post
2nd Goal Post
Nicoll Highway 76
Nicoll Highway Incident
WONG Kai Sin 39
Root of the problem
Inappropriate
Back-Analysis?
Nicoll Highway 77
Full Mesh Half Mesh
Back-Analysis continued to use Half Mesh & Method A
Nicoll Highway 78
Nicoll Highway Incident
WONG Kai Sin 40
1st Back-Analysis by NLC (5 March 2004)
Wall Stiffness
Reduced 50% from Step 11 onward
JGP Strength and Modulus
Reduced 20% from Step 3 onward
Upper Marine Clay Strength and Modulus
Reduced 20% from Step 3 onward
Lower Marine Clay Strength and Modulus
Reduced 50% (i.e. f’ = 12° ) from Step 11
onward
Method “A”
Nicoll Highway 79
2nd Back-Analysis by NLC (19 April 2004)
Wall Stiffness
Reduced 55% from Step 9 to 17 and 70%
from Step 18 onward
JGP Strength and Modulus
Reduced 20% from Steps 3 to 8 and 40%
from Step 10 onward
Upper Marine Clay Strength and Modulus
Reduced 30% from Step 3 onward
Lower Marine Clay Strength and Modulus
Reduced 65% from Step 9 to 17 and 75% (i.e. f’ = 6° ) from Step 18 onward
Fluvial Clay (F2) Strength and Modulus
Reduced 30% from Step 3 to 8 and 40% from Step 9 onward
Estuarine Clay (E) Strength and Modulus
Reduced 45% from Step 18 onward 80
Nicoll Highway Incident
WONG Kai Sin 41
What caused the failure?
Be careful of any novel ideas or unproven methods.
Nicoll Highway 81
82
Thank You
for your attention!
Nicoll Highway