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 18 th June 2008 Sheung Wan Stormwater Pumping Station (SWSPS) 1
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. 57m ~ -7.1mPD 43m ~ -5.9mPD Pile Cap Layout Plan 2
43m ~ +4.0mPD Retaining Wall Pile Cap / Base Slab ~ -5.9mPD ~ -7.1mPD Typical North-South Section 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 3
Approx. Location of Site Reclamation and Seawall Dredging Plan Approx. Extent of SWSPS Vertical Seawall (Indicative) Victoria Harbour Typical Cross Section 4
Pre-Contract Ground investigation 2 series in 2002 & 2006 (32 holes) Common sampling, field and laboratory tests In situ vane & pressuremeter tests Pre-Contract Borehole Location Plan Fill Rock Fill Marine Deposits Sand Fill Alluvium CDG North-South Geological Section 5
Existing Salt Water PS Fill Marine Deposits Alluvium CDG East-West Geological Section (away from Seawall) Seawall Cope Line Isopach of Soft Marine Clays 6
Small sink hole at sea wall Seawall Cope Line 5m 3 sink hole 7
15m 3 sink hole 0.000 21/8/06 31/8/06 10/9/06 20/9/06 30/9/06 10/10/06-0.100 Settlement (m) SS Markers on Seawall SS1 SS2-0.200 SS3 SS4-0.300 0.000 21/8/06 31/8/06 10/9/06 20/9/06 30/9/06 GS20 10/10/06 GS21 GS24 GS25-0.100 Settlement (m) -0.200-0.300 GS Markers on Ground Adjacent to Seawall Settlement near Seawall 8
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 9
Plot of SPT-N against Elevation Plot of Undrained Shear Strength (Cu) against Elevation 10
FSP IV Sheet Pile Walings & Struts (3 levels) Adopted Shoring Layout Plan Longitudinal Cross Section further from Seawall 11
Longitudinal Cross Section nearest Seawall Transverse Cross Section 12
Penetration (T.A.M.) Grout Jet Grout Elevation of Wall D (Showing Grouting Ground Improvement) Sheetpile (not shown for clarity) Culvert West East Fill Marine Deposit Alluvium CDG Grout A Grout B Finite Element Analysis (East-West Section) 13
δ max = 115mm δ max = 60mm West Wall East Wall Wall Deflection (East-West Section) δ max = 18mm δ max = 82mm West Wall East Wall Ground Settlement (East-West Section) 14
δ max = 102mm δ max = 88mm South Wall North Wall Wall Deflection (North-South Section) δ max = 53mm δ max = 75mm South Wall North Wall Ground Settlement (North-South Section) 15
Seawater Fill (Sand) Seawall Tilt = 1/650 Fill (Rock) Exaggeration scale: 30 Deformation of Seawall Slope Stability Analysis (South Wall) 16
Principal Instrumentation : - Ground settlement markers (SS, GS, SA) - Inclinometers (IN, INX) - Standpipe Piezometer (SP, PZ, PP) - Building Tilt Marker North Wall West Wall East Wall Instrumentation Layout Plan Outline Construction Programme for Key Activities 17
Settlement against Time 0.050 0.000 H-Piling, Sheetpiling, Ground Improvement Grouting Excavation Settlement (m) -0.050-0.100-0.150-0.200-0.250 SS Markers on Seawall Pile Cap -0.300 SS3 SS2 SS1 SS4-0.350 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 against Time 0.000-0.100-0.200 Settlement (m) -0.300-0.400-0.500 GS Markers on Ground Adjacent to Seawall GS23 GS24 GS20-0.600 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 Ground Settlement Time Plot behind North Wall (Seawall) Settlement against Time 0.000-0.050-0.100-0.150 H-Piling, Sheetpiling, Ground Improvement Grouting Excavation Pile Cap Settlement (m) -0.200-0.250-0.300-0.350-0.400-0.450 GS31 GS34 GS28-0.500 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 Ground Settlement Time Plot behind East Wall 18
GS28 (6.2m) GS31 (9.6m) GS34 (15.6m) Predicted δ max = 82mm Inclinometer IN2 (1m) Predicted δ max = 115mm Ground Deformation behind East Wall (due to excavation only) Settlement against Time 0.010 0.000-0.010-0.020 Settlement (m) -0.030-0.040 Predicted δ max = 18mm -0.050-0.060 SS13 SS9 SS10 SS14-0.070 01-Aug-06 15-Aug-06 29-Aug-06 12-Sep-06 26-Sep-06 10-Oct-06 24-Oct-06 07-Nov-06 21-Nov-06 05-Dec-06 19-Dec-06 02-Jan-07 16-Jan-07 30-Jan-07 13-Feb-07 27-Feb-07 13-Mar-07 27-Mar-07 10-Apr-07 24-Apr-07 08-May-07 22-May-07 05-Jun-07 19-Jun-07 03-Jul-07 17-Jul-07 31-Jul-07 14-Aug-07 28-Aug-07 11-Sep-07 25-Sep-07 09-Oct-07 23-Oct-07 06-Nov-07 20-Nov-07 04-Dec-07 18-Dec-07 01-Jan-08 Date Ground Settlement Time Plot behind West Wall 19
4.0 Displacement (mm) 0 5 10 15 2.0 0.0-2.0-4.0 Elevation (mpd) -6.0-8.0-10.0 "+" toward excavation Predicted δ max = 60mm -12.0-14.0-16.0 Inclinometer IN5 (1m) -18.0 Ground Deformation behind West Wall (due to excavation only) 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 20
Temporary casing for drilling through fill. Withdrawn prior to jetting. (optional) Soil Overburden PVC tubing to assist spoil return. (optional) Jet Grout Zone Typical Set up of Jet Grouting (Double Tube Method) Ref. : CNCEC 1. Set up rig 2. Drill to toe level 3. Test jetting 4. Commence Jetting 5. Simultaneously withdrawal and rotation of grout string to next level Sequence of Jet Grouting 6. Jet grout completed. Withdraw grout string Ref. : CNCEC 21
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 & stiffness UCS = 600 kpa Elastic modulus = 150 MPa 22
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Jet Grout Core Sample 24
Hole S5 Hole S2 (UCS: typically 7-10 MPa, sometimes >40 MPa) Jet Grout Core Sample T.A.M. Grout Core Sample 25
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 26
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 Ref : Giken Seisakusho Co. Ltd Sheetpiling by push-in method 27
Augering to assist penetration 28
Drilling through Obstructions Cutter Head for Rock Obstructions 29
Alignment out-of-line when encountering obstructions Groundwater leaking through retaining wall 30
Excavation in progress Disposal by barge 31
Installing waling and strut Excavation completed 32
Concreting in progress Concreting in progress (3 concrete pumps & 13 concrete trucks) 33
Foundation Completed 散石徑 / 太極區 園林景觀工程設計 海濱長廊 綠化天台 小型廣場 方形花園 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 觀賞園林 遮雨蓬 長椅 散石徑 裝飾性街燈 Asia HKIE Technical Talk ELS Design for Ref. SWSPS : DSD 18 June 2008 34
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 35
Acknowledgement Drainage Services Department China National Chemical Engineering Corp Hyder Consulting Limited Thank You! 36