A Complex Eco-friendly Geotextile Container Used in the Dredging and Disposal of Contaminated Materials at Victoria Harbor Felix Tseng 1 Clark Chu 1 Amy Tang 1 1 ACE Geosynthetics, No.33, Jing 3 Rd., C.E.P.Z. Wuchi, Taichung City, Taiwan, R.O.C.

Outline Case Introduction Design Concept Result Conclusion

Case Introduction - Trial location Limited capacity for disposing dredged sediment in Hong Kong Unpolluted sediment was dumped in the disposal site of high seas: South Cheung Chau, East of Ninepin, North Lantau, East Tung Lung Chau, Tai Mo To and South Tsing Yi Polluted sediment was stored in confined disposal site: East Sha Chau

Case Introduction - Sediment type It’s estimated that 50,000 cubic meter among the total dredged sediment, around 1.15 million cubic meter, was classified as Category H (>10xLCEL) which required special treatment of Type 3 contaminated dredged sediment Note: Marine sediment is classified as Category L, Category M, Category H by polluted level based on ETWB TCW No. 34/2002 LCEL – Lower Chemical Exceedance Level

Case Introduction - Monitoring work A complex geotextile container prefabricated with geotextile retains Type 3 sediment to avoid spread of suspended solid during disposal operation. In this trial test, the geotextile container was designed for the dredging and disposal work, and the water quality monitoring was performed during the operation.

Case Introduction - Geotextile Container Big geotextile container of volume of 100 to 1000 m 3 for filling sand or slurry can be transported and dumped by split barge. Geotextile container of 28m in circumference and 12m in length was designed for this project. Compared with previous design, the new one saved 18% usage amount of fabric, moreover, the filling volume reaches 300 m 3.

Design Concept - Mathematical Calculation With following input, the required tension of geotextile container is shown below: – Dumping depth, h=20m – Width of hopper gate, b 0 =2.0m – Length of each chamber, L=11m – Depth of hopper, h b =4.92m – Unit weight of sediment, γ =12kN/m 3 Tension while geotextile container goes through hopper  T 1 =83.08kN/m Tension while geotextile container impacts the seabed  T 2 =86.38 kN/m ACETex ® GT200-II PP, 200x200kN/m and seam strength of 140kN/m can meet required design tensile strength. Description of ACETex ® GT200-II Test Standard MaterialPolypropylene (PP) Nominal tensile strength - MDkN/m ≧ 200 ASTM D4595 Nominal tensile strength - CDkN/m ≧ 200 ASTM D4595 Elongation at nominal strength - MD% ≦ 23 ASTM D4595 Factory seam strengthkN/m ≧ 140 ASTM D4884

Design Concept - Hydraulic Trial Hydraulic trials were conducted to a scale of 1:20 for imitating the dumping process: – Dry dumping – Dumping in water with 1m depth (Actual dumping depth is about 20m) PrototypeModel Length of split barge (m) Depth of water (m)201 Tensile strength (kN/m)20010 Factory seam strength (kN/m) In-situ seam strength (kN/m)

Design Concept - Dry Dumping Trial Main Purpose – Measuring the dimension of geotextile container – Checking dumping damage Trial Condition – Metal case was made as split barge model – Same filling volume and materials (silica sand) – Different opening speed

Design Concept - Dry Dumping Trial Result – Filling volume: m3 – Filling rate: 66% – Results is shown as below table: ItemD1D1 D2D2 Hopper open time (s)3224 Hopper gate width (cm)1720 ACEContainer Avg. height (cm)11.38 ACEContainer Avg. width (cm) Filling rate (%)66

Design Concept - Dumping in Water Trial Main Purpose – Observing dumping behavior – Checking dumping damage Trial Condition – Metal model case in water tank with 1m depth water – Excluding the in-situ influence of current and wave

Design Concept - Dumping in Water Trial Result – Filling rate: 75~78% – Observing if there any leak in the dumping procedure – Result is shown as below table: ItemW1W1 W2W2 W3W3 W4W4 Hopper open time (s) Hopper gate width (cm) ACEContainer Avg. height (cm) ACEContainer Avg. width (cm) Filling rate (%)

Design Concept - Water Quality Monitoring Seven monitoring stations located around 200~600m from disposal location were selected, two at the upstream and five at the downstream. Monitoring was undertook at around 30-minutes interval for 2 hours after dumping.

Result - Dissolved Oxygen Monitoring Disposal Zone Monitoring Stations: Baselin e Post Impact Baselin e Post Impact Upstream & Downstream Monitoring Stations:

Result - Turbidity Monitoring Disposal Zone Monitoring Stations: Upstream & Downstream Monitoring Stations: Baselin e Post Impact BaselinePostImpac t

Result Water quality monitoring was continued for 5 days after disposal operation at East Sha Chau Baseline conditions was took 2 hours prior to disposal operation No pollution was found at upstream and downstream monitoring stations Exceeded result of DO in the monitoring record was due to natural wave fluctuation

Conclusion Mathematical computation and hydraulic trial can be reference info. for designing geotextile container for different conditions. High tensile strength, excellent permeability and fitness to configuration of hopper barge makes ACEContainer a effective solution for this project. Actual disposal operation proved ACEContainer is applicable to disposal of dredging material: a speedy solution without influencing navigation operation and avoiding possible pollution.

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