Design of Temporary Excavation and Lateral Support …1 Asia HKIE Technical Talk – ELS Design for SWSPS – 18 June 2008 Design of Temporary Excavation and Lateral Support System

1

Asia HKIE Technical Talk – ELS Design for SWSPS – 18 June 2008

Design of Temporary Excavation

and Lateral Support System

for the DSD Sheung Wan

Stormwater Pumping Station

By Eric Li - GCG (Asia)

Presented to the HKIE Geotechnical Division

18th June 2008


Sheung Wan Stormwater Pumping Station (SWSPS)

2


Project Set Up

� DSD Contract DC/2006/10

� Contract Sum : HK$ 78 million (approx)

� Designer : Drainage Services Department

(with GEO as in-house geotechnical consultant)

� Site Supervision : DSD Drainage Project Division

(with the engagement of an IGE)

� Contractor : China National Chemical Engineering Group

� ELS Designer : Geotechnical Consultant Group (Asia) Ltd.


43m

57m

Pile Cap Layout Plan

~ -5.9mPD

~ -7.1mPD

3


43m

Retaining Wall

Pile Cap / Base Slab

Typical North-South Section

~ +4.0mPD

~ -5.9mPD~ -7.1mPD


Selection of Retaining Wall Type

Wall Types Considered:

• Diaphragm Wall

• Bored Pile Wall

• Pipe Pile Wall

• Sheet Pile Wall

• No wall (open cut)

Design Objectives:

• Approximate max. 10m deep excavation

• Effective control of settlement due to excavation and groundwater drawdown

4


Reclamation and Seawall Dredging Plan

Approx. Location of Site


Typical Cross Section

Vertical Seawall (Indicative) Approx. Extent of SWSPS

Victoria Harbour

5


Pre-Contract Borehole Location Plan

Pre-Contract Ground investigation

• 2 series in 2002 & 2006 (32 holes)• Common sampling, field and laboratory tests• In situ vane & pressuremeter tests


North-South Geological Section

Sand Fill

Rock Fill

CDG

Marine Deposits

Alluvium

Fill

6


East-West Geological Section (away from Seawall)

Marine Deposits

Fill

CDG

Alluvium

Existing Salt Water PS


Isopach of Soft Marine Clays

Seawall Cope Line

7


Seawall Cope Line

Small sink hole at sea wall


5m3 sink hole

8


15m3 sink hole


-0.300

-0.200

-0.100

0.000

21

/8/0

6

31

/8/0

6

10

/9/0

6

20

/9/0

6

30

/9/0

6

10

/10

/06

Se

ttle

me

nt

(m)

SS1

SS2

SS3

SS4

Settlement near Seawall-0.300

-0.200

-0.100

0.000

21

/8/0

6

31

/8/0

6

10

/9/0

6

20

/9/0

6

30

/9/0

6

10

/10

/06

Se

ttle

me

nt

(m)

GS20

GS21

GS24

GS25

‘SS’ Markers on Seawall

‘GS’ Markers on Ground Adjacent to Seawall

9


Design Considerations

� Reclamation Site

� Sensitive Structures nearby, i.e. WSD Pumping Station

� High water table, i.e. 1.2m below existing ground level

(+3.0mPD)

� Presence of thick layer of variable FILL

& soft MARINE DEPOSITS


Design Methodology

� Drained and Undrained Conditions

� Lateral Stability

� Global Slope Stability

� Base Stability

� Hydraulic Stability

� Dewatering

� Ground Deformation / Settlement

� Structural Capacities

10


Plot of SPT-N against Elevation


Plot of Undrained Shear Strength (Cu) against Elevation

11


Adopted Shoring Layout Plan

FSP IV Sheet Pile Walings & Struts(3 levels)


Longitudinal Cross Section further from Seawall

12


Longitudinal Cross Section nearest Seawall


Transverse Cross Section

13


Elevation of Wall D(Showing Grouting Ground Improvement)

Penetration (T.A.M.) Grout Jet Grout

Sheetpile (not shown for clarity)


Fill

Marine DepositAlluvium

CDG

EastWestCulvert

Grout A

Grout B

Finite Element Analysis

(East-West Section)

14


Wall Deflection (East-West Section)

East WallWest Wall

δmax = 60mm

δmax = 115mm


Ground Settlement (East-West Section)

West WallEast Wall

δmax = 18mm

δmax = 82mm

15


Wall Deflection (North-South Section)

South Wall North Wall

δmax = 102mm

δmax = 88mm


Ground Settlement (North-South Section)

North WallSouth Wall

δmax = 53mm

δmax = 75mm

16


Exaggeration scale: 30

Tilt = 1/650 Seawall

Fill (Sand)

Fill (Rock)

Seawater

Deformation of Seawall


Slope Stability Analysis

(South Wall)

17


Instrumentation Layout Plan

Principal Instrumentation :

- Ground settlement markers (SS, GS, SA)

- Inclinometers (IN, INX)

- Standpipe Piezometer (SP, PZ, PP)

- Building Tilt Marker

East Wall

West Wall

North Wall


Outline Construction Programme for Key Activities

18


Settlement against Time

-0.350

-0.300

-0.250

-0.200

-0.150

-0.100

-0.050

0.000

0.050

01-A

ug-06

01-S

ep-06

01-O

ct-06

01-N

ov-06

01-D

ec-06

01-Jan-07

01-F

eb-07

01-M

ar-07

01-A

pr-07

01-M

ay-07

01-Jun-07

01-Jul-07

01-A

ug-07

01-S

ep-07

01-O

ct-07

01-N

ov-07

01-D

ec-07

01-Jan-08

Date

Settlement (m

)

SS3 SS2 SS1 SS4


-0.600

-0.500

-0.400

-0.300

-0.200

-0.100

0.000

01-A

ug-06

01-S

ep-06

01-O

ct-06

01-N

ov-06

01-D

ec-06

01-Jan-07

01-Feb-07

01-M

ar-07

01-A

pr-07

01-M

ay-07

01-Jun-07

01-Jul-07

01-A

ug-07

01-S

ep-07

01-O

ct-07

01-N

ov-07

01-D

ec-07

01-Jan-08

Date

Settlement (m

)

GS23 GS24 GS20

Ground Settlement Time Plot behind North Wall (Seawall)

‘SS’ Markers on Seawall

‘GS’ Markers on Ground Adjacent to Seawall

ExcavationH-Piling, Sheetpiling, Ground Improvement Grouting

Pile Cap



-0.500

-0.450

-0.400

-0.350

-0.300

-0.250

-0.200

-0.150

-0.100

-0.050

0.000

01

-Au

g-0

6

01

-Se

p-0

6

01

-Oc

t-0

6

01

-No

v-0

6

01

-De

c-0

6

01

-Ja

n-0

7

01

-Fe

b-0

7

01

-Ma

r-0

7

01

-Ap

r-0

7

01

-Ma

y-0

7

01

-Ju

n-0

7

01

-Ju

l-0

7

01

-Au

g-0

7

01

-Se

p-0

7

01

-Oc

t-0

7

01

-No

v-0

7

01

-De

c-0

7

01

-Ja

n-0

8

Date

Se

ttle

me

nt

(m)

GS31 GS34 GS28

Ground Settlement Time Plot behind East Wall

Excavation

H-Piling, Sheetpiling, Ground Improvement Grouting

Pile Cap

19


Ground Deformation behind East Wall(due to excavation only)

GS28 (6.2m) GS31 (9.6m) GS34 (15.6m)

Inclinometer IN2 (1m)

Predicted δδδδmax = 115mm




-0.070

-0.060

-0.050

-0.040

-0.030

-0.020

-0.010

0.000

0.010

01

-Au

g-0

6

15

-Au

g-0

6

29

-Au

g-0

6

12

-Se

p-0

6

26

-Se

p-0

6

10

-Oc

t-0

6

24

-Oc

t-0

6

07

-No

v-0

6

21

-No

v-0

6

05

-De

c-0

6

19

-De

c-0

6

02

-Ja

n-0

7

16

-Ja

n-0

7

30

-Ja

n-0

7

13

-Fe

b-0

7

27

-Fe

b-0

7

13

-Ma

r-0

7

27

-Ma

r-0

7

10

-Ap

r-0

7

24

-Ap

r-0

7

08

-Ma

y-0

7

22

-Ma

y-0

7

05

-Ju

n-0

7

19

-Ju

n-0

7

03

-Ju

l-0

7

17

-Ju

l-0

7

31

-Ju

l-0

7

14

-Au

g-0

7

28

-Au

g-0

7

11

-Se

p-0

7

25

-Se

p-0

7

09

-Oc

t-0

7

23

-Oc

t-0

7

06

-No

v-0

7

20

-No

v-0

7

04

-De

c-0

7

18

-De

c-0

7

01

-Ja

n-0

8

Date

Se

ttle

me

nt

(m)

SS13 SS9 SS10 SS14

Ground Settlement Time Plot behind West Wall


20


-18.0

-16.0

-14.0

-12.0

-10.0

-8.0

-6.0

-4.0

-2.0

0.0

2.0

4.0

0 5 10 15Displacement (mm)

Ele

va

tion

(m

PD

)"+" toward excavation

Ground Deformation behind West Wall(due to excavation only)

Inclinometer IN5 (1m)



Jet grouting

• Jet grout cuts insitu soft clay and mixes that with injected cement

• Disturbed clay is displaced to surface in slurry form

• Jet nozzle is typically 1.4mm to 3mm dia.

• Applicable to more cohesive soils where T.A.M. grouting may not work

21


Typical Set up of Jet Grouting

(Double Tube Method)

Temporary casing for drilling through fill.Withdrawn prior to jetting. (optional)

Jet Grout Zone

Soil Overburden

PVC tubing to assist spoil return. (optional)

Ref. : CNCEC


1. Set up rig 2. Drill to toe level 3. Test jetting

6. Jet grout completed. Withdraw grout string

5. Simultaneously withdrawal and rotation of grout string to next level4. Commence Jetting

Sequence of Jet Grouting Ref. : CNCEC

22


Jet grout parameters

• Jet grout parameters adopted at SWSPS

Target grouted dia. = 1500 – 2000 mm

Grout pressure = 300 – 400 bars

Air pressure = 8 - 12 bars

Withdraw rate = 13 to 15 min/m

Rotation rate = 6 – 7 rev/step

• Target strength & stiffnessUCS = 600 kPa

Elastic modulus = 150 MPa


23



24



Jet Grout Core Sample

25


Hole S2Hole S5

Jet Grout Core Sample

(UCS: typically 7-10 MPa, sometimes >40 MPa)


T.A.M. Grout Core Sample

26


T.A.M. Grout Core Sample


Sheetpiling (by push-in method)

• Suitable in area where vibration is undesirable

• With limited penetration depth

• Difficult to overcome obstruction

• Tend to be more costly

27


Ref : Giken Seisakusho Co. Ltd

Sheetpiling by push-in method

At SWSPS

• Giken rig with special tool to overcome obstruction (up to 1m)

• Maximum 24m long sheet pile

• Limited to Type IV sheetpile


Sheetpiling by push-in method

28



Augering to assist penetration

29


Drilling through Obstructions


Cutter Head for Rock Obstructions

30


Alignment out-of-line when encountering obstructions


Groundwater leaking throughretaining wall

31


Excavation in progress


Disposal by barge

32


Installing waling and strut


Excavation completed

33


Concreting in progress


Concreting in progress (3 concrete pumps & 13 concrete trucks)

34


Foundation Completed


園林景觀工程設計散石徑散石徑散石徑散石徑／／／／太極區太極區太極區太極區散石徑散石徑散石徑散石徑／／／／太極區太極區太極區太極區

遮雨蓬

長椅

小型廣場小型廣場小型廣場小型廣場小型廣場小型廣場小型廣場小型廣場

方形花園方形花園方形花園方形花園方形花園方形花園方形花園方形花園

觀賞園林觀賞園林觀賞園林觀賞園林觀賞園林觀賞園林觀賞園林觀賞園林

海濱長廊

海濱長廊

海濱長廊

海濱長廊

海濱長廊

海濱長廊

海濱長廊

海濱長廊

海濱長廊海濱長廊海濱長廊海濱長廊海濱長廊海濱長廊海濱長廊海濱長廊

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散石徑

裝飾性街燈Ref. : DSD

35


Before Commencement After Completion

Ref. : DSD


Summary

Issues to be considered in ELS design

• Site history

• Site characterization

• Design parameters (drained or undrained)

• Design objective and constraints

• Retaining wall installation effects

• Economy and construction programme

36


Acknowledgement

• Drainage Services Department

• China National Chemical Engineering Corp

• Hyder Consulting Limited


Thank You !

Documents

Design of Temporary Excavation and Lateral Support …1 Asia HKIE Technical Talk – ELS Design for SWSPS – 18 June 2008 Design of Temporary Excavation and Lateral Support System