1 Sustainable Reclamation Initiatives and Geotechnical Issues on Land Supply for Future Development K K Yin Ove Arup & Partners Hong Kong Limited Reclamation History in Hong Kong Total reclaimed area 6824ha 2. Reclamation The Good Old Days .. 3. Fully Dredged Reclamation Method Existing Profile Sea Marine Deposits Alluvium/CDG. Dredging of Marine Deposit at Seawall and Main Reclamation Area Original seabed Sea profile Dredged Level Marine Deposits Marine Deposits Alluvium/CDG. Construction of Seawall and Filling at Main Reclamation Area Seawall Reclamation Area Sea Reclamation Fill Sea Marine Deposits Sandfill/ Rockfill Sandfill/ Rockfill Marine Deposits Alluvium/CDG. 4. Fully Dredged Reclamation Methods MD within the Reclamation area was dredged Sandfill was used to fill the dredged trench and Reclamation filling Vibro-compaction of sandfill 5. Dredging and Disposal of Marine Sediment Dredging Disposal A) Open Sea Disposal of Dredged Sediment Sea floor disposal areas at South Cheung Chau and East Ninepin or other empty marine borrow pits have been used for disposal of uncontaminated mud.
2 B) Confined Disposal of Dredged Contaminated Sediment Contaminated mud is being disposed of at East Sha Chau. Compliance on environmental monitoring and until 2. years after closure of all the pits to ensure that there is no adverse impact on the environment. Guide Boat Leading the Barge to the Target Area for Contaminated Mud Disposal 6. Sandfilling 7. Vibro-compaction of Sandfill Compaction of granular soils by depth vibrators. Reclaimed sands can be compacted to a depth of 70m and the intensity of compaction can be varied to meet need of various projects. Its improvement effect includes reduction of creep settlement, increase of shear strength of soils and reduction of permeability of soils. Penetration Compaction Completion The Vibroproble The Vibroproble is After compaction, the penetrates by vibration retracted from the working platform needs and aid of compressed maximum depth in to be levelled and air or water to the intervals.
3 The in- eventually roller required depth. situ sand or gravel is compacted. flowing towards the Vibroproble 8. Historical Projects with Dredged Reclamation Hong Kong International Airport Reclamation Container Terminal No. 9 Reclamation Area of Reclamation is approx. 950 hectare Area of Reclamation is approx. 120 hectare Dredging volume is approx. 70 million m3 Dredging volume is approx. 18 million m3. West Kowloon Reclamation Penny's Bay Reclamation Stage 1. Area of Reclamation is approx. 330 hectare Area of Reclamation is approx. 200 hectare Dredging volume is approx. 32 million m3 Dredging volume is approx. 42 million m3. 9. Fully Dredged Reclamation Advantages Good for fast tracking Settlement risk is lower Disadvantages Large amount of marine deposits to be disposed Large amount of sandfill and rockfill is required Adverse environmental impact due to dredging work and filling works 10.
4 Reclamation Not too long ago . 11. Reclamation with Fully Dredged Seawall Existing Profile Sea Marine Deposits Alluvium/CDG. Dredging of Marine Deposit at Seawall Area Original seabed Sea profile Dredged Level Dredged Level Marine Deposits Marine Deposits Marine Deposits Alluvium/CDG. Construction of Seawall and Filling at Main Reclamation Area Reclamation Area Seawall Sea Reclamation Fill Sea Marine Deposits Sandfill/. Sandfill/ Rockfill Rockfill Marine Deposits Sandfill/. Sandfill/Rockfill Rockfill Marine Deposits Alluvium/CDG Band drains 12. Reclamation with Fully Dredged Seawall Only MD under seawall is dredged Sandfill is used to fill the dredged trench for seawall No dredging is required for main Reclamation Sandfill is used for main Reclamation filling Ground treatment (mainly band drain and surcharging) is applied to accelerate the left- in-situ soft marine deposit and reduce long term settlement Dredging would still be significant particularly when the area of Reclamation is small 13.
5 Band Drain and Surcharge Typically used in soft ground to accelerate Marine-based Band Drain Installation consolidation of the compressible soils for the drained Reclamation . In Reclamation areas with thick soft marine clay/silt, long term consolidation under Reclamation loads can continue for many years. With band drains and surcharge load, the soft compressible soils can be pre-consolidated prior to development in a matter of weeks or months. Land-based Wick Drain Installation Band Drain 14. Past Reclamation with Fully Dredged Seawall Penny's Bay Reclamation Stage 2 (for Disneyland Theme Siu Ho Wan MTR Depot Park). Area of Reclamation is approx. 60 hectare 15. The Change o j ec ts ir pr g gin the lan ed ll p ha lace Dr t s s n p nen ud i r o m fo pro p the t g le c e proj e epin na k e t h of tio n io n o mpt Ra s u as ge Dumping at Sea Ordinance Cap. 466 (DASO).
6 Ne con ric wa side guide p r o p osals r sel ste c ing w lines / e x c a vation e c ha a fo f d r e d ging ass tio e n rac ste t m r a p p r o val o xc a va ted op ssm , eriza an ged/e tion a f d r e d s, p ent o tion ge m and i sp o sal o , du en arine d erm f po m t m it is tent p s opti d im ent. sue ial e i te o ns, s e an ffec d m ts on of d itor isp ing osa l 16. Diver of Change - Increased Environmental Concerns Enforcement of Environmental Impact Assessment Ordinance (1 April 1998). Air Quality Water Quality Noise Control Waste Management Nature Conservation Marine habitats & associated fauna marine mammals, fish, corals, & others Increased Public Concerns 17. Driver of Change - Lack of Contaminated Sediment Disposal Facilities Sha Chau Existing disposal facilities The Brothers Proposed disposal facilities (last mud pit). Hong Kong International Airport 18.
7 Driver of Change - Lack of Sand Borrow Area in HK. Legend: Borrow areas worked out Borrow areas sand remaining Tap Shek Kok Brothers South of Tsing Yi South of East of Tung Victor Rock Lung Chau East Lamma Channel Po Toi 19. And the Mitigation . Systematically manage impacts that our works may have on the environment for the benefit of community 20. Available of Advanced Technology Advanced technology of ground treatment methods have been developed overseas in recent years Successful application of various ground treatment method for Reclamation in overseas projects Innovative seawall schemes have been developed in overseas projects in recent years 21. Recent Implementation of Innovative Ideas . 22. Stone Column 23. Stone Column Typically used in soft soil applications in order to accelerate consolidation of the compressible soils for the drained Reclamation Increase the shear strength of the soil dealing Achieved by the use of vibro-displacement or vibro-replacement method Involve the installation of gravel compacted piles commonly referred to as stone columns.
8 24. Stone Column Installation Process 25. Vibroprobe 252 384. 23mm amplitude 26. Sand Compaction Pile 27. Use of Sand Compaction Pile Install large diameter compacted sand piles in soft clay/ mud. Diameter of sand piles is to Non-dredged method for seawall base Improve bearing capacity, slope stability and consolidation settlement by replacing the soft clay/ mud by the compacted sand piles Widely adopted in Japan and Korea SCP at Busan Visit Reclamation Sea Wall Sea Soft Marine Mud Soft Marine SCP Clay Provide drain path for consolidation settlement Improve slope stability Stiff Soil Improve bearing capacity 28. Installation cycle of SCP. Step 1 Step 2 Step 3 Step 4 Step 5 Step 6. Step 1 - Casing driving Sand fill Step 2 - Pour the sand inside the Sand fill casing Step 3 - Drive the casing to the required level Step 4 - Extract the casing by a fixed distance and fill up the bored hole by sand Step 5 - Re-drive the casing to compress the sand pile.
9 Supply the sand continuously Step 6 - Repeat Steps 4 and 5 until the sand pile is built 29. Operation of SCP plant 1 Delivery and store the sand on SCP barge Sand Transportation Barge Sand Storage Tank 2 Conveyor to send the sand to travelling bucket 1 2. 30. Operation of SCP plant 3 Travelling bucket to send the sand in vertical direction 4. 4 Load the sand to the hopper at top of casing 1 2. 3 Hopper 31. Operation of SCP plant 5 Discharge of sand into ground via the casing 4. 5. 1 2. 3. 32. Casing Driving Vibrator Hopper 33. Installation Control Top and bottom level of SCP piles measured by Auto-electronic Sand Level System Casing Toe Level Actual Sand Top Desired Sand Top Level Level Water Pressure Meter Auto-electronic Sand Level System Pressure inside the casing controlled by Pressure Control System Casing Pile Pressure Pressure Control System 34. Up-heaving of Soil after SCP Installation In case of marine mud 20 to 25m thick, specialist contractor advised based on their experience that the thickness of up-heaved soil after SCP.
10 Installation could be: 1) For SCP replacement ratio of 70%. Thickness of up-heaved soil could be 7 to 8m 2) For SCP replacement ratio of 40% Thickness of up-heaved soil could be 4 to 5m 35. Height of SCP Plant Surely the minimum height of the SCP plant is based on the envisage maximum thickness of marine mud, depth of water plus a bit Xm Xm Soft Marine Soft Marine Deposits Deposits (to be treated). 36. Original Height of SCP Plant Original Height ~50 60m advised by Specialist Contractor 37. Reduced Height of SCP Plant Spec ia SCP list cont pla n racto o ut t t r op fr can be m advised ame odifi that if h e ight ed by cut is a p t Rem roble ing ov m e 40m (Min height that could be reduced by specialist contractor). Mean Water Level ~ + mPD. 38. Possible SCP Application for Seawalls in Recent Large Scale Reclamation Project Airport Height Restriction Constraint Legends AHR above +45mPD.