Design of Temporary Excavation and Lateral Support System for the DSD Sheung Wan Stormwater Pumping Station

8/10/2019 Design of Temporary Excavation and Lateral Support System for the DSD Sheung Wan Stormwater Pumping Station

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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 StormwaterPumping Station (SWSPS)


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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


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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 excavationand groundwater drawdown


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Reclamation and Seawall Dredging Plan

Approx. Location of Site


Typical Cross Section

Vertical Seawall (Indicative)Approx. Extent of SWSPS

Victoria Harbour


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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


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East-West Geological Section(away from Seawall)

Marine Deposits

Fill

CDG

Alluvium

Existing SaltWater PS


Isopach of Soft Marine Clays

Seawall Cope Line


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Seawall Cope Line

Small sink hole at sea wall


5m3 sink hole


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15m3 sink hole


-0.300

-0.200

-0.100

0.00021/8/06

31/8/06

10/9/06

20/9/06

30/9/06

10/10/06

Se

ttlemen

t(m

)

SS1

SS2

SS3

SS4

Settlement near Seawall-0.300

-0.200

-0.100

0.00021/8/06

31/8/06

10/9/06

20/9/06

30/9/06

10/10/06

Se

ttlemen

t(m)

GS20

GS21

GS24

GS25

SS Markers on Seawall

GS Markers on Ground Adjacent to Seawall


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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


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Plot of SPT-N against Elevation


Plot of Undrained Shear Strength (Cu) against Elevation


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Adopted Shoring Layout Plan

FSP IV Sheet PileWalings & Struts(3 levels)


Longitudinal Cross Section further from Seawall


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Longitudinal Cross Section nearest Seawall


Transverse Cross Section


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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)


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Wall Deflection (East-West Section)

East WallWest Wall

max = 60mm

max = 115mm


Ground Settlement (East-West Section)

West WallEast Wall

max = 18mm

max = 82mm


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Wall Deflection (North-South Section)

South Wall North Wall

max = 102mm

max = 88mm


Ground Settlement (North-South Section)

North WallSouth Wall

max = 53mm

max = 75mm


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Settlement against Time

-0.350

-0.300

-0.250

-0.200

-0.150

-0.100

-0.050

0.000

0.050

01-Aug-06

01-Sep-06

01-Oct-06

01-Nov-06

01-Dec-06

01-Jan-07

01-Feb-07

01-Mar-07

01-Apr-07

01-May-07

01-Jun-07

01-Jul-07

01-Aug-07

01-Sep-07

01-Oct-07

01-Nov-07

01-Dec-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-Aug-06

01-Sep-06

01-Oct-06

01-Nov-06

01-Dec-06

01-Jan-07

01-Feb-07

01-Mar-07

01-Apr-07

01-May-07

01-Jun-07

01-Jul-07

01-Aug-07

01-Sep-07

01-Oct-07

01-Nov-07

01-Dec-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-Aug-0

6

01-Sep-0

6

01-Oc

t-06

01-Nov-0

6

01-Dec-0

6

01-Jan-0

7

01-Fe

b-0

7

01-Mar-

07

01-Apr-

07

01-May-0

7

01-Jun-0

7

01-Ju

l-07

01-Aug-0

7

01-Sep-0

7

01-Oc

t-07

01-Nov-0

7

01-Dec-0

7

01-Jan-0

8

Date

Se

ttlemen

t(m)

GS31 GS34 GS28

Ground Settlement Time Plot behind East Wall

Excavation

H-Piling, Sheetpiling, Ground Improvement Grouting

Pile Cap


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Ground Deformation behind East Wall(due to excavation only)

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

Inclinometer IN2 (1m)

Predicted max = 115mm




-0.070

-0.060

-0.050

-0.040

-0.030

-0.020

-0.010

0.000

0.010

01-Aug-0

6

15-Aug-0

6

29-Aug-0

6

12-

Sep-

06

26-

Sep-

06

10-Oc

t-06

24-Oc

t-06

07-

Nov-0

6

21-

Nov-0

6

05-

Dec-0

6

19-

Dec-0

6

02-Jan-0

7

16-Jan-0

7

30-Jan-0

7

13-Fe

b-0

7

27-Fe

b-0

7

13-Mar-

07

27-Mar-

07

10-Apr-

07

24-Apr-

07

08-May-0

7

22-May-0

7

05-Jun-0

7

19-Jun-0

7

03-Ju

l-07

17-Ju

l-07

31-Ju

l-07

14-Aug-0

7

28-Aug-0

7

11-

Sep-

07

25-

Sep-

07

09-Oc

t-07

23-Oc

t-07

06-

Nov-0

7

20-

Nov-0

7

04-

Dec-0

7

18-

Dec-0

7

01-Jan-0

8

Date

Se

ttlemen

t(m

)

SS13 SS9 SS10 SS14

Ground Settlement Time Plot behind West Wall



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-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)

Eleva

tion

(mPD)

"+" 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 withinjected cement

Disturbed clay is displaced to surface in slurryform

Jet nozzle is typically 1.4mm to 3mm dia.

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


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Typical Set up of Jet Grouting

(Double Tube Method)

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

Jet Grout Zone

Soil Overburden

PVC tubing to assist spoilreturn. (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 androtation of grout string to next level4. Commence Jetting

Sequence of Jet GroutingRef. : CNCEC


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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



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Hole S2Hole S5

Jet Grout Core Sample

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


T.A.M. Grout Core Sample


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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


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Augering to assist penetration


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Alignment out-of-line whenencountering obstructions


Groundwater leaking throughretaining wall


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Excavation in progress


Disposal by barge


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Installing waling and strut


Excavation completed


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Concreting in progress


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


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Foundation Completed


Ref. : DSD


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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


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Documents

Design of Temporary Excavation and Lateral Support System for the DSD Sheung Wan Stormwater Pumping Station