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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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Use of lumpy clay dredged from seabed in Tuas

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Use of ultra soft soil at Changi East

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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

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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.