A Complex Eco-friendly Geotextile Container Used in the ...
A Complex Eco-friendly Geotextile Container Used in the Dredging and Disposal of Contaminated Materials at Victoria Harbor
Felix Tseng1 1ACE
Clark Chu1
Amy Tang1
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 m3 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 m3.
T ype A. Factory Seam Work
T ype B. In-situ Seam Work
Type B. In-situ Seam Work Type A. Factory Seam Work
Design Concept - Mathematical Calculation •
With following input, the required tension of geotextile container is shown below: – – – – –
• •
Dumping depth, h=20m Width of hopper gate, b0=2.0m Length of each chamber, L=11m Depth of hopper, hb=4.92m Unit weight of sediment, γ=12kN/m3
Tension while geotextile container goes through hopper Æ T1=83.08kN/m Tension while geotextile container impacts the seabed Æ T2=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
Material
Polypropylene (PP)
Nominal tensile strength - MD
kN/m
ؤ200
ASTM D4595
Nominal tensile strength - CD
kN/m
ؤ200
ASTM D4595
%
أ23
ASTM D4595
kN/m
ؤ140
ASTM D4884
Elongation at nominal strength - MD Factory seam strength
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)
Prototype
Model
Length of split barge (m)
11
0.55
Depth of water (m)
20
1
Tensile strength (kN/m)
200
10
Factory seam strength (kN/m)
140
8.67
In-situ seam strength (kN/m)
82.5
5.04
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: 0.0275m3 – Filling rate: 66% – Results is shown as below table:
Item
D1
D2
Hopper open time (s)
32
24
Hopper gate width (cm)
17
20
ACEContainer Avg. height (cm)
11.3
8
ACEContainer Avg. width (cm)
58
63.7
Filling rate (%)
66
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: Item
W1
W2
W3
W4
Hopper open time (s)
18
25
33
34
17.5
22
21
20
ACEContainer Avg. height (cm)
7
7.1
6.75
6.9
ACEContainer Avg. width (cm)
59
57.7
61
62
Filling rate (%)
75
75
78
77
Hopper gate width (cm)
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:
Concentration, mg/L
•
Dissolved Oxygen (Surface & Middle) at Ebb Tide 10
Impact
Baselin e
8 6
`
4 2 14:24
14:52
15:21
15:50
16:19 M6
Upstream & Downstream Monitoring Stations:
16:48
17:16
17:45
18:14
M7
Turbidity (Depth-averaged) at Ebb Tide Concentration, NTU
•
Post
25
Impact
Baselin e
20 15
Post
`
10 5 0 14:24
14:52
15:21
15:50 M6
16:19 M7
16:48
17:16
17:45
18:14
Result - Turbidity Monitoring Disposal Zone Monitoring Stations:
Concentration, NTU
•
Turbidity (Depth-averaged) at Ebb Tide 25
Impact
Baselin e
20 15
`
10 5 0 14:24
14:52
15:21
15:50
16:19
M6
Upstream & Downstream Monitoring Stations:
16:48
17:16
17:45
18:14
M7
Turbidity (Depth-averaged) at Ebb Tide Concentration, NTU
•
Post
Baseline
25 20
Impac t
Post
17:16
17:45
15 10 5 0 14:24
14:52
15:21
15:50 M1
M2
16:19 M3
M4
16:48 M5
M6
18:14
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.
Thanks for your attention~
Felix Tseng1 1ACE
Clark Chu1
Amy Tang1
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 m3 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 m3.
T ype A. Factory Seam Work
T ype B. In-situ Seam Work
Type B. In-situ Seam Work Type A. Factory Seam Work
Design Concept - Mathematical Calculation •
With following input, the required tension of geotextile container is shown below: – – – – –
• •
Dumping depth, h=20m Width of hopper gate, b0=2.0m Length of each chamber, L=11m Depth of hopper, hb=4.92m Unit weight of sediment, γ=12kN/m3
Tension while geotextile container goes through hopper Æ T1=83.08kN/m Tension while geotextile container impacts the seabed Æ T2=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
Material
Polypropylene (PP)
Nominal tensile strength - MD
kN/m
ؤ200
ASTM D4595
Nominal tensile strength - CD
kN/m
ؤ200
ASTM D4595
%
أ23
ASTM D4595
kN/m
ؤ140
ASTM D4884
Elongation at nominal strength - MD Factory seam strength
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)
Prototype
Model
Length of split barge (m)
11
0.55
Depth of water (m)
20
1
Tensile strength (kN/m)
200
10
Factory seam strength (kN/m)
140
8.67
In-situ seam strength (kN/m)
82.5
5.04
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: 0.0275m3 – Filling rate: 66% – Results is shown as below table:
Item
D1
D2
Hopper open time (s)
32
24
Hopper gate width (cm)
17
20
ACEContainer Avg. height (cm)
11.3
8
ACEContainer Avg. width (cm)
58
63.7
Filling rate (%)
66
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: Item
W1
W2
W3
W4
Hopper open time (s)
18
25
33
34
17.5
22
21
20
ACEContainer Avg. height (cm)
7
7.1
6.75
6.9
ACEContainer Avg. width (cm)
59
57.7
61
62
Filling rate (%)
75
75
78
77
Hopper gate width (cm)
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:
Concentration, mg/L
•
Dissolved Oxygen (Surface & Middle) at Ebb Tide 10
Impact
Baselin e
8 6
`
4 2 14:24
14:52
15:21
15:50
16:19 M6
Upstream & Downstream Monitoring Stations:
16:48
17:16
17:45
18:14
M7
Turbidity (Depth-averaged) at Ebb Tide Concentration, NTU
•
Post
25
Impact
Baselin e
20 15
Post
`
10 5 0 14:24
14:52
15:21
15:50 M6
16:19 M7
16:48
17:16
17:45
18:14
Result - Turbidity Monitoring Disposal Zone Monitoring Stations:
Concentration, NTU
•
Turbidity (Depth-averaged) at Ebb Tide 25
Impact
Baselin e
20 15
`
10 5 0 14:24
14:52
15:21
15:50
16:19
M6
Upstream & Downstream Monitoring Stations:
16:48
17:16
17:45
18:14
M7
Turbidity (Depth-averaged) at Ebb Tide Concentration, NTU
•
Post
Baseline
25 20
Impac t
Post
17:16
17:45
15 10 5 0 14:24
14:52
15:21
15:50 M1
M2
16:19 M3
M4
16:48 M5
M6
18:14
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.
Thanks for your attention~
