lessons learned from the nicoll highway...

Nicoll Highway Incident

WONG Kai Sin 1

1

Lessons Learned from The


20th April 2004

Nicoll Highway

2 Nicoll Highway


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


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


WONG Kai Sin 4

7

Picture of the collapse

Around 3:30 p.m. on 20 April 2004

Nicoll Highway

Nicoll Highway 8


WONG Kai Sin 5

9 Nicoll Highway

10 Nicoll Highway


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


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


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


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)


0

1000

2000

3000

4000

5000

Str

ut

Fo

rce

(k

N)

20/4, 10 a.m.

Strut Forces

8th

9th

Nicoll Highway 18


WONG Kai Sin 10

Strut Forces


0

1000

2000

3000

4000

5000

6000

Str

ut

Fo

rce

(k

N)


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


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


WONG Kai Sin 12

Wall Deflections

23

Maximum Wall Deflections at S335

Nicoll Highway 24


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)


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


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


Nicoll Highway

30


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


WONG Kai Sin 17

Uplift Failure


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


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


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


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


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


D/WALL D/WALL

1

2

5

6

8

9

3

4

7

Yielding of Diaphragm Wall

Nicoll Highway 40


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


D/WALL D/WALL

1

2

5

6

8

9

3

4

7


50

55

60

65

70

75

80

85

90

95

100

105

0 50 100 150 200 250 300 350 400 450 500


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


D/WALL D/WALL

1

2

5

6

8

9

3

4

7

Insufficient Wall Penetration

Toe kick-in?

Nicoll Highway 42


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


WONG Kai Sin 23

I104

Toe kick-in?

Nicoll Highway 45

66 kv Cable

Presence of Utility Gaps

TSA

Nicoll Highway 46


WONG Kai Sin 24

Curvature in Tunnel Alignment

MC3008 AC3

MC3007

M2064 47

Short Walers & Eccentric Strut Loading

Nicoll Highway 48


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


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


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


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


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


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


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


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


WONG Kai Sin 30

Waler/stiffener Failure due to Wall Rotation


72

74

76

78

80

250 300 350 400 450 500


Re

du

ce

d L

ev

el (m

)

Preload Strut 9

17 April 04

20 April 04

Level 9 Strutº º

º


50

55

60

65

70

75

80

85

90

95

100

105

0 50 100 150 200 250 300 350 400 450 500


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


WONG Kai Sin 31

Stiffener Plate

Stiffener Plate

Slide 61

Nicoll Highway 61

Behaviour of Waler with Stiffener Plates

62


WONG Kai Sin 32

C - Channel

C-channel as Stiffness

Slide 63

Nicoll Highway 63

Behaviour of Waler with C-channels

64


WONG Kai Sin 33

Testing of Real Specimens

Nicoll Highway 65

Testing of Real Specimens

Nicoll Highway 66


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


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


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


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


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


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


WONG Kai Sin 40

1st Back-Analysis by NLC (5 March 2004)

Wall Stiffness

Reduced 50% from Step 11 onward

JGP Strength and Modulus


Upper Marine Clay Strength and Modulus


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


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


WONG Kai Sin 41


Be careful of any novel ideas or unproven methods.

Nicoll Highway 81

82

Thank You

for your attention!

Nicoll Highway

lessons learned from the nicoll highway...

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