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NTU-JTC I3C Seminar
Methods for Land Reclamation using Soft Soil and Waste Chu Jian
NTU-JTC I3C Seminar
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2 August 2012
Outline
• Part 1. Overview of land reclamation methodsP t 2 M th d f l d l ti i ft• Part 2. Methods for land reclamation using soft or dredged soil
• Part 3. Suggested reclamation and soil improvement procedure for using soft soil for large scale land reclamationP t 4 U f t f l d l ti
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• Part 4. Use of waste for land reclamation
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Part 1Part 1Overview of land Overview of land reclamation reclamation methodsmethods
According to fill materials usedAccording to fill materials used
• Granular materials, either dredged or excavated sand (Marina, Tuas, Changi East etc.)( , , g )
• Hill cut materials (Changi airport, Kansai Airport, etc.)
• Clay slurry dredged from seabed (Tianjin Port, silt pond at Changi, Shanghai Pudong Airport, Kita-Kyushu Airport, Tokyo International Airport, Brisbane Port Wenzhou etc)
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Brisbane Port, Wenzhou, etc)• Cement treated clay slurry dredged from
seabed (Central Japan Airport, Pasir Pajang etc)
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1). Use of sand fills
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One of the creations of HDB
Changi East Reclamation Project
Area = 2000 ha
Sand = 272 M m3
PVD = 140 Mm
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2). Use of hill cut materials
Kansai Airport
to settle 11.5 m over 50 yearsy
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3). Use of dredged soft soil3). Use of dredged soft soil
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Tianjin Port
Dongjiang 30 km2
Mainly over water depth of up to 5 m. Sometimes
Beijiang & Nanjiang 40 km2
Bohai Golf
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More than 190 km^2 of land has been reclaimed around the Tianjin Port in Tanggu using clay slurry
to 10 m.Lingang Industrial Area, 120 km2
Wenzhou, China
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88 km2
200 km2
land is being
reclaimed. Total 448 km2
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Port of Brisbane
Channel maintenance dredging materials consisting of river muds capped with sand was
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capped with sand was used. The thickness of the fill was up to 9 m. The seabed compressible clay was over 30 m.
New Kitakyushu Airport
1414 After Terashi and Katagiri (2005)
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4. Use of cement treated soil -Central Japan international airport
After Kitazume (2007)
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After Kitazume (2007)
Cemented soil placement
After Kitazume (2007)
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Part 2Part 2Methods for land rMethods for land reclamationeclamationusing soft or dredged soilusing soft or dredged soil
Difficulties in the use of soft soil for land reclamation
• Major difficulty: The top surface is too soft for workers and machines to go on top to carry out soil improvementand machines to go on top to carry out soil improvement works.
• Key technical challenge: how to form a work platform.
• Which method to use? The one with the lowest unit cost!
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lowest unit cost!
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Methods for creating a working platform
# Method Description / Mechanisms Advantages Limitations
1 Sun drying Reduce the water content of soil d f f d i ti l
Simple and i l
Very time consuming; Depth of improvement Sun drying and form of a desiccation layer economical p p
is shallow
2Capping with sand or good
earth
Place sand or good earth in thin layers
Relatively cheap
Slow and difficult to implement
3Use of
geotextile
Place a layer of geotextile to the top of soft soil before soil or fill
is placed.
Relatively expensive
Relatively quick and reliable
Lime or Use lime or cement mixing to Difficult in controlling the properties and
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4Lime or
cement mixing strengthen a layer of soil at the top to form a working platform
Expansive the properties and consistence of the
cement treated layer
5 Dewatering
Use special drainage method to dewater or consolidate the a
layer of soil at the top to form a working platform
Relatively cheap
Require special equipment and procedure. The
method needs to be further developed
1). Sun drying
0
10
20
30
40
60 70 80 90 100 110 120 130 140
m)
含水率(%)
40
50
60
70
80
90
100
深度
(cm
12月4日 11月20日 11月6日
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2). Sun drying + place sand or good earth as a cap layer – Brisbane port
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After Berthier et al. (2009)
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3). S3). Sand spreading for silt pondand spreading for silt pond
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Use of geotextile for silt pond at Changi East
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Use of geotextile and sand
25 After Kitazume (2007)
5). Use of cement mixed soil
In-situ treatment of dredged materials for Port of Valencia, Spain. Cement mixing was used toCement mixing was used to form a working platform on top of muddy deposit (cu=75 kPa)(Burgos et al. 2007)
After Allu, Finland (http://www.allu.net)
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5). Dewatering using PVD or circular drains
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Installation of short PVDs or drains over water or soft top layer
Part Part 33Suggested large scale land Suggested large scale land reclamation procedurereclamation procedure
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An innovative LandAn innovative Land Reclamation Method using the Enhanced Vacuum ground improvement scheme
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Floating PVD Installation machine
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Courtesy of Prof Yan
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Use of waste for land Part 4
reclamation
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Alternative fill materials
• Excavated clay/soilC l (400 000 t 200 000 3 / )• Copper slag (400,000 t or 200,000 m3 /yr)
• Sewage sludge (240,000 t /yr or 240,000 m3 /yr)• Rubber tyres, plastics etc.
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Copper slag Marine clay
240,000 t /yr
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Bedok WasteWater Reclamation Plant
Sewage sludge
Using Sludge for Land Reclamation• There is a shortage of land reclamation
materials in Singapore So it would be highlymaterials in Singapore. So it would be highlydesirable if sludge can be treated and used forland reclamation.
• For this purpose, the stabilized sludge and otherwastes have to meet the following threerequirements:
Ad t t h i l ti
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– Adequate geotechnical properties,– Minimum environmental impact,– Cost-effective.
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Physical Properties of Sewage Sludge
PropertyProperty ValueValueWater Content % 514 Solids Content % 16.3 Bulk Density (Mg/m3) 1.02Specific Gravity 1.634Liquid Limit (LL) % 397Plastic Limit (PL) % 63Plasticity Index (PI) % 334
Consolidated under 80 kPaWater Content % 180 Undrained Shear Strength kPa 14Compression Index 1.2Permeability m/s 10–10
Methods of Treatment
• Chemical treatment, e.g., use cement or otherbindersbinders.
• Mechanical treatment, e.g., consolidation.• Thermal treatment, e.g., firing.• A combination of the above.
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Combined Method
• A method combining both the chemical andA method combining both the chemical andmechanical approaches can be used to treatsludge.
• To adopt this combined method, sludge is mixedwith binders first. The mixture can then be
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with binders first. The mixture can then beconsolidated under a surcharge.
A48C Sample 1 - 40 days
138.80
40
60
80
100
120
140
160
Axi
al S
tress
(kPa
)
Sludge 50% Cement 8.5% Lime 4% Copper slag 37.5%
0
20
40
0 5 10 15 20Axial Strain (%)
A58C Sample 1 - 40 days
244 92
250
300
Sludge 50% Cement 8.5%
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244.92
0
50
100
150
200
0 5 10 15 20 25Axial Strain (%)
Axi
al S
tress
(kPa
)
Lime 4% Marine clay 37.5%
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Method 1: On-site Consolidation
• Mix dewatered sludge with cement and other waste materials, e.g., l d i l i difi d t i icopper slag and marine clay, using a modified concrete mixer or mix
on-site.• Dispose the mixed sludge into a reclaimed site.• Install horizontal/vertical drains and consolidate the sludge using
vacuum preloading.
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Sludge Mixer
Sludge + binders +
Sludge Mixer 5m3
Sludge + binders + waste + etc.
With an inner filter drum for dewatering
Sludge output:
20,000 t /mth:
= 666 t/day
~ 650 m3/day
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dewateringy
Need 130 trips per day.
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Horizontal Drainage for Vacuum Preloading
Vacuum pump
Sludge
Sludge
Vacuum pump
Dike
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Horizontal drain
Vertical + Horizontal Drains + Vacuum Preloading
Vacuum pumpVacuum pump
Dike
Sand
Sludge
Membranes
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Horizontal + vertical drain
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Method 2: Geotextile Bags
• Mix dewatered sludge with binders and other waste materials and put the mixture into geotextile bags of 60x40 cm.
• The bags can be piled up before dumping for the mixture to consolidate.
• The bags are then dumped to the seabed. • The bags will be capped by a sand layer.
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BargeBarge
Bags
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Seabed marine clay
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Sand fill
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Conclusions
• This presentation shows that ultra-soft, highwater content soil or sludge can be used aswater content soil or sludge can be used asfill materials for land reclamation.
• The key in treating slurry type of soil is theformation of a working platform. The methodsto create a working platform include: 1) sundrying; 2) capping with sand or competenty g; ) pp g psoil; 3) use of geotextile; 4) cement mixing;and 5) dewatering. The use of some of thesemethods are illustrated using case histories.
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Conclusions (Cont’d)
• To convert sewage sludge into fill materialf l d l ti bi d h i lfor land reclamation, a combined chemicaland mechanical treatment method isrequired.
• Two methods of using sewage sludge forland reclamation are suggested. In bothmethods the sludge will be mixed with 10
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methods, the sludge will be mixed with 10-12% of cement and waste materials (marineclay or copper slag) before disposal anddisposed sludge mixture will be consolidatedon site.
Acknowledgements
• I would like to THANK– YOU for your participation and discussion!
Prof Victor Choa for gi ing me the opport nit to ork on land– Prof Victor Choa for giving me the opportunity to work on land reclamation projects and his mentoring
– Prof Bengt Broms for his inspirations– Prof Yan Shuwang of Tianjin University for 14 yrs’ collaborations– JTC, in particular Mr Lam Kok Pang, for providing opportunities
to carry out some R&D studies on new land reclamation methods– HDB, in particular Mr Lim Soo Kim, for involving me in the
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training and discussions of some of their land reclamation projects– My researchers and students, Liu Haojie, Guo Wei and He Jia.