Artificial islands

ARTIFICIAL ISLANDSARTIFICIAL ISLANDS

SUBMITTED BY:S.MRIDUL NAIDU

2010CET3036

Methods of CreationMethods of Creation1)Expanding existing islets1)Expanding existing islets2)Construction on existing reefs2)Construction on existing reefs3)Amalgamating several natural islets into 3)Amalgamating several natural islets into a bigger island.a bigger island.4)Construction on sea bed.4)Construction on sea bed.5)Land Reclamation5)Land Reclamation6)Oil Platforms 6)Oil Platforms

IntroductionAn artificial or man-made island is an island or archipelago(group of islands) that has been constructed by people rather than formed by natural means.

Reasons for ConstructionReasons for Construction

The following are the major reasons to justify the creation of Artificial Islands:

- urban development (special structures) - industry - waste handling - infrastructure (ports and airports) - extended runways - recreation - mining of natural resources - oil drills and exploration platforms. - tidal or wind energy generation. - recreational structures like hotels or water

parks.

Previous UsagePrevious Usage1) Artificial islands have been used since the seventeenth

century for coastal defence and as extensions of the land

base.

2) Artificial islands are being used as oil exploration and

production platforms.

3) Japan has several artificial islands, with a total area of over

1000 km.

4) Artificial islands are being used to provide a platform for coal

mine ventilation shaft access, positively contributes to the

safety, effective ventilation and reserves of a coal mine.

5) Technology of artificial island construction is available to

construct islands in water depths of 70 m.

6) Artificial islands become a focus for sea life, enhancing the

marine environment.

Under the United Nations Convention on Under the United Nations Convention on the Law of the Sea treaty (UNCLOS), the Law of the Sea treaty (UNCLOS), artificial islands are not considered artificial islands are not considered harbour works and are under the harbour works and are under the jurisdiction of the nearest coastal state if jurisdiction of the nearest coastal state if within 200 nautical miles within 200 nautical miles (370 km) .Artificial islands are not (370 km) .Artificial islands are not considered islands for purposes of having considered islands for purposes of having their own territorial waters or exclusive their own territorial waters or exclusive economic zones, and only the coastal economic zones, and only the coastal state may authorize their construction. state may authorize their construction. However, on the high seas beyond However, on the high seas beyond national jurisdiction, any "state" may national jurisdiction, any "state" may construct artificial islands .construct artificial islands .

Political Status

Design ConsiderationsDesign Considerations water depth wave height range climate ice conditions; tidal range; currents; foundation conditions; earthquake risk; source of materials; shipping lanes; existing pipelines and cables; legal aspects; environmental considerations; and, fisheries considerations.

LOADS IMPOSED IN DESIGN :

Permanent loads

Variable loads

Environmental loads

Permanent loads : a)The weight in air of the structure and superstructures calculated from nominal values of dimensions and mean values of densities.b)Equipment which cannot be removedc)Hydrostatic external pressure and buoyancy in calm sea conditions calculated for mean sea level.d)Ballast including ballast water pressuree)Permanent earth pressure

Variable Loads:a)Weight of equipments , materials and stores which may be removed after the phase considered.b)Variations in internal and external pressure from water,oil,gas,etc. caused by normal operating of the structurec)Loads due to fendering and mooring of vessels, helicopter landing, cranes or drilling operations.

Environmental Loads : a)Wind b)Weather loads due to heating and coolingc)Sea loads like wave loads, tidal loads, currents etc.d)Earthquake and tsunami loads.

The following stages are involved:

1. Temporary tube piles driven into sea bed2. Temporary sheet piles and tie rods driven

into sea bed to support boundary rocks (see figure 1)

3. Permanent boundary rock bunds deposited on either side of sheet piles

4. Hydraulic fill layers deposited between bunds to displace sea water and form island

5. Permanent concrete armour units placed around island to protect it from the waves

6. Piles driven through island and sea bed below to stabilize structure

7. Island interior excavated and temporary sheet pile coffer dam inserted

8. Thick concrete plug slab laid at base of island

9. Reinforced concrete retaining wall built

CONSTRUCTION PROCESS

DREDGING AND SOIL BED PREPERATION

PRECAST PILES CAST IN YARDS, LOADED ONTO BARGES AND PLACED AT SITE.

PILES DRIVEN, SOIL COMPACTED, SURROUNDING BUND CREATED, ARMOUR ROCKS PLACED , PLATFORM SLAB CASTED CONSTRUCTION STARTS.

SOIL BED SOIL BED PREPERATIONPREPERATION

FUNCTIONS OF SAND

THE FUNCTIONS OF SAND IN THE STRUCTURE

ARE AS FOLLOWS:

1)Formation of a protection or isolation layer

2)Providing of ballast weight

3)Providing vertical support or load distribution

4)Providing of horizontal soil pressure

5)Providing of drainage capacity

6)Filling Voids

Process ParametersProcess ParametersSand Characteristics :- Mineral Composition- Grain Size Composition- Fall Velocity Composition

Flow rate and concentration in the discharge pipe : - Mixture flow rate- Concentration of mixture density- Sand Production rate

Geometry of the fill area above water level : - Determined by the following :- minimum dimensions of the sand body and working space on the crest- length along the guide bunds

Density of SandDensity of Sand

-The in-situ density of porosity of the sand fill can be measured using the following techniques :

-Electric Density measurement-Nuclear Density measurement-Density of frozen samples-Dutch cone penetration tests

-The following characteristics are relevant : -Minimum and maximum density-Dry Critical density- Wet Critical density- Critical and steady state density

Processes Involved in sand Processes Involved in sand placementplacement1. Sand winning2. Sand transport3. Formation of sand water jet4. Formation of a crater5. Flowing of sand water mixture on

slope above water6. Flowing of sand water mixture on

submerged slope7. Loss of sand under water8. Sedimentation and formation of

slope

The source of construction materials critical items in the choice of island sites. Ideally, a good quality coarse grained sand must be located within 5 to 10 km of the island site.

The barges are towed to the island site and the sand dumped directly from the trailer.

When the water depth becomes too shallow, the sand is dumped at a borrow pit and pumped by a stationary dredge to the specified site.

The sand is protected by rock revetments and a layer of armour rock.

The top layer of sand can be sprayed with a bitumen emulsion and a layer of soil. Then a suitable grass is planted to reduce erosion.

Soil InvestigationsSoil Investigations

Soil from the borrow pit needs to be investigated for the following:

1)Suitability of the sand as a building material

2)Winning method and the expected production level

3)Determination of the risk of loss of stability of adjacent structures as a result of the sand removal.

Investigation MethodsInvestigation Methods

1) Taking of surface samples2) Borings and Laboratory Tests3) Soil penetration tests4) Cone penetration tests5) Pressiometer or dilatometer6) Density Investigations7) Twin well probe8) Seismic Investigation

The methods of investigation are used to determine the type of deposits, thickness and extent of layers, local variations in soil, level of erosion etc.

PREPERATION OF ISLAND BEDS.NO. PROCESS METHODS

1

SURVEY, INVESTIGATION AND CONTROLS

ELECTRONIC SATELLITE NAVIGATION, SPAR BUOYS, ACOUSTIC TRANSPONDERS, CORING AND SAMPLING, GRAB SAMPLES, SPARKER SURVEY, SIDE-SCAN SONAR,

ACOUSTIC IMAGING, FOUNDATION PENETROMETERS, VIDEO, SUBMERSIBLE AND DIVER INSPECTION

2 PLATFORM DERRIK BARGE, DRILL SHIP, SEMISUBMERSIBLE JACK-UP, GUYED TOWER, HEAVE COMPENSATORS

3SEAFLOOR OBSTRUCTION

REMOVALDRAG-OFF WITH TRAWLERS, SHAPED CHARGES, ROV'S WITH MANIPULATORS,

UNDERWATER BURNING, THERMIC LANCERS

4

DREDGING, REMOVAL OF SEDIMENTS

TRAILER SUCTION HOPPER DREDGE, CUTTERHEAD HYDRAULIC DREDGE, GRAB DREDGE OR CLAMSHELL, CONTINOUS BUCKET LADDER DREDGE, SLACK LINE BUCKET DREDGE, PLOW, JETTING, PIPELINE BURIAL SLED, DEEP-SEA MINING DRAG EXCAVATOR, AIRLIFT, EDUCTORS, REMOTE-CONTROLLED SEAFLOOR

DREDGE

5

DREDGING, REMOVAL OF HARD SEDIMENTS AND ROCKS

HYDRAULIC BACKHOES, DIPPER DREDGES, POWER ACTIVATED CLAMSHELL BUCKETS, PLOWS, SHAPED CHARGES, BLASTING IN DRILLED HOLES, CHISELS, HYDRAULIC AND PNEUMATIC ROCK BREAKERS, DRIVEN SPUDS, CUTTERHEAD

DREDGES, HIGH PRESSURE JETS

6PLACEMENT OF UNDERWATER

FILLS

DIKES OF ROCKS OR CLAY BUNDS TO CONTAIN SAND, CONTROLLED UNDERWATER DEPOSITION, DUMP ENMASSE FROM HOPPER BARGES, TREMIE,

BUCKET, SKIP, CHUTE OR LADDER

7

DENSIFICATION, CONSOLIDATION AND

STRENGTHENING OF FILLS

DEEP VIBRATION, SURFACE VIBRATION, DYNAMIC COMPACTION WITH DROPPED WEIGHTS, EXPLOSIVES OR AIRGUN, DEPOSITION IN MASS,

PRESATURATION, SELECTION OF OPTIMUM GRADING

8

CONSOLIDATION AND STRENGTHENING OF WEAK SOILS

SAND PILES, VIBRATION, FREEZING, PRESURCHARGING, SURCHARGING WITH MEMBRANE AND DRAINAGE, SURCHARGING

WITH STRUCTURE AND BALLAST, WICK AND SAND DRAINS, DRAINAGE WELLS, PERIPHERAL SURCHARGING, CEMENT

INJECTION, CHEMICAL GROUTING, LIME INJECTION, DEEP CEMENT MIXING, ELECTRO-OSMOSIS

9 PREVENTION OF LIQUEFACTION DENSIFICATION, DRAINAGE WELLS, PERIPHERAL APRON OF GRADED ROCK

10

LEVELING OF SEAFLOOR OR EMBANKMENT

HYDRAULIC DUSTPAN DREDGE WITH HEAVE COMPENSATOR SUSPENSION OF DREDGE HEAD, DRAGS, BOTTOM-SUPPORTED

SCREED FRAME, SCREED FRAME FROM TLP OR HEAVE COMPENSATED PLATFORM, HORIZONTAL SCREW AUGUR

11

PROVISION OF UNIFORM SUPPORT UNDER BASE OF

STRUCTURE

UNDERBASE GROUTING, UNDERBASE SAND INJECTION OR SAND FLOW, TREMIE CONCRETE, GROUT INTRUDED AGGREGATE, MUD

JACKING

12EXCAVATION BENEATH

STRUCTUREARTICULATED DREDGE ARMS, AIRLIFT, JETS, EDUCTORS, DRILLS

13

SCOUR AND EROSION PROTECTION

SACRIFICIAL FILL, ROCK, FILTER ROCK, FILTER FABRIC, ARTICULATED MATTRESSES, SANDBAGS, GROUT FILLED POROUS BAGS, SKIRTS ON STRUCTURES, APRONS AND FLOW CONTROLLED DEVICES AT

BASE OF STRUCTURES, ARTIFICIAL SEAWEED, SAND ASPHALT AND ROCK ASPHALT BLANKETS, UNDERWATER CONCRETE SLABS

14 TURBIDITY SUPPRESSION BENTONITE-CEMENT SLURRIES, DISCHARGE OF FINE SAND BLANKET

DREDGINGDREDGING

Dredging Basics

Dredging is the maritime transportation of

natural materials from one part of the water

environment to another by specialised dredging

vessels. In a usual dredging cycle, self-

propelled ,trailing suction ,hopper dredgers,

barges and other ships spend the majority of

their time sailing back and forth between

excavation sites and placement sites,

transporting materials between the port and the

borrow site; sailing between borrow sites; and

sailing from sites where material has been

extracted to unloading or placement sites.

Dredging vessels support:Port infrastructure development

Land reclamation for commerce, residences

and recreation

Energy enterprises including oil and gas

exploration and

delivery and offshore wind farms

Environmental remediation of brownfields and

safe storage

of contaminated materials

Annual Turnover of the dredging industry: 6.3

Billion $ (2008)

EXTERNAL CONDITIONS DURING CONSTRUCTION GROUP A : THOSE WHICH DETERMINE THE USE AND EFFICIENCY OF EQUIPMENT, BREIFLY SUMMARIZED UNDER THE HEADING OF WORKABILITYGROUP B: THOSE ARISING FROM A CHANGE IN THE HYDRAULICS AND MORPHOLOGY OF THE AREA, OCCURING AS A RESULT OF THE WORKS, THIS INFLUENCE CAN BE OF A TEMPORARY OR PERMANENT NATURE.GROUP C: THOSE ARISING FROM ENVIRONMENTAL CONSIDERATIONS, ALSO THIS EFFECT CAN BE OF A TEMPORARY OR PERMANENT NATURE.

Common dredging methods :

Suction Dredging : Sand will be dredged by putting the suction tube deep ( > 10 m) into the sand layer. Under the influence of gravity forces the sand departs from the slope and flows downward in the direction of the suction mouth. Cutter Suction Dredging : With cutter suction dredging the suction tube is provided with a rotating cutter head. The swing movement is initiated by the means of a forward-side-winch wires directly behind the cutter head. A spud pole positioned on the ships aft functions as centre of the swing movement.

Trailing suction dredging : A draghead

attached to a suction pipe is trailed over the

bottom of the seafloor. Due to erosive forces at

the narrow opening between the draghead and

the bottom and the application of blades in

the draghead results in the formation of a sand

water mixture, this mixture in pumped in the

hopper and the sand settles whereas the water

overflows.

Cutter Dredging : For less permeable sand the

face formation will deliver a small contribution

to the production. In this case the soil has to

be retrieved with the cutter head. In less

permeable sand, large cutting forces cause

significant wear and tear to the teeth of the

cutting head.

CRITERIA FOR DREDGER SIZE:

1.  Volume of material to be dredged.2.  Time allowed to complete the project.  Days, weeks and months.3.  Hours that you will work.  1 shift, 2 shifts or 3 shifts? 4. Type of material to be dredged.  Fine sand, medium sand, large sand, small gravel, large gravel, silt, clay, cobbles 3 to 10, boulders +10 inches [254mm].  5. Dredging sediments or undisturbed material.  Undisturbed material is much more difficult to dredge. 6. Horizontal pumping distance. 7. Vertical pumping distance called static head.  vertical distance from the water surface to the discharge point.9. Maximum digging depth. Distance from the water surface to the lowest point of dredging. DREDGES ARE AVAILABLE IN SIZES VARYING FROM A FEW METRE LONG BARGES TO FEW HUNDRED METRE LONG VESSLES

Factors in selection of Cutter Suction Dredger

• Kind of soils and operation area• Dredging depth, capacities• Degree of self-sufficiency, self-propelled or

stationary.• If self-propelled: which cutter ladder position

(bow or stern oriented)• Seagoing dredging capability.• Type and stroke of spud carriage (flexibility

required)• Spud handling and hoisting system(s).• Cutter type, diameter, speed, power.• Pump characteristics.• Requirements related to noise and vibrations

(incl. construction fatigue)• Degree of automation.

Environmental Considerations

Environmental conditions consist of two major aspects:- Weather climate-Wave climateTemperatures of air and water as well as humidity define the weather climate.The chance of violent storms blowing up is a major aspect to be considered.Wave climate is characterized by wave height, period and its distribution (spectrum). Statistics in respect of wave appearance in time is useful.Both climates affect workability. Workability is part of the dredger’s overall capacity.Violent storms can lead to autonomy requirements when means of escape are required.

Local Facilities

A wide range of local facilities can be stated. If only few facilities are expected to be available then a high rate of autonomy of the dredger is required.

Examples of local facilities are:- Repair area ashore- Workboats or other supporting vessels- Supply of spares- Supply of bunkers, drinking water and other consumables- Availability of shore pipelines and/or barges- Availability of shelter area-Water depth for spud tilting and ladder tilting

* Restrictions in water depth can determine the way of tilting.

Geometrical Properties

Geometrical properties are related to the dredging work itself.- Water depth at start- Water depth to be realized-Canal width, slope.

Soil PropertiesSoil properties of the material to be dredged strongly influence the production of the dredger. Examples are:- Density- Hardness, strength- Grain size distributionSoil properties can also influence the workability of the dredger. Hard soil means small allowance of wave induced ships movements.

Primary aspects for the capacities of the dredgers are:- cutter capacity- dredge pump capacity- swing length and speed- spud carriage availability and stroke- Automation

Cutter capacityThe cutter capacity mainly depends on:- cutting torque- cutter reaction force- cutter speed- swing winch pull- spud reaction- soil properties- angle of the cutter(ladder)

Dredge pump capacity

-required flow rate and head

-discharge pipeline length(differ for pumping

ashore and barge loading)

-density of the mixture

-soil characteristics

-suction mouth performance.

Therefore a lot of scenarios have to be calculated

to find an optimum design point of each pump.

Swing length and speed

A great distance between cutter and work spud enables a cutter dredger to execute a wide cut per swing. This results in a high dredging efficiency. On the other hand it increases the minimum workable canal width, making small works difficult.

The rudders and propellers of a self-propelled CSD constitute an obstacle and require protection or retractable propellers may be provided. Retraction challenging because available space in the ladder pontoons is very limited and loss of displacement (moon pools) in the same area is not favourable.Appendages above the waterline are anchor boom pivots or the dredger’s hull itself. Both may constitute an obstacle in case of vertical quaysides.

Spud carriageThe application of a spud carriage is common practise for large CSD’s. This increases the efficiency of the dredger significantly. The larger the stroke of the carriage the more swings can be made without spud repositioning and consequently the higher the efficiency of the dredger.

AutomationLarge cutter dredgers are complex dredgers with complex operations. Therefore process automation and monitoring instrumentation are relevant because they will increase the efficiency of the dredger. Automation can be executed to a lot of levels, which depends on the Owner’s philosophy and the cost and skills of personnel.

Increased main dimensions of the dredger result in significant lower movements of the vessel in waves.

AutonomyThe rate of autonomy is a result of the availability of facilities at the dredging work location. Examples of facilities to increase the autonomy of a cutter dredger are:

- Deck crane and cutter changing equipment

- Cutter repair platform

- Spud tilting system

- Anchor booms

- Barge loading

- Deadweight, tanks and store spaces

- Tools and other repair/maintenance equipment

- Accommodation

- Means of escape

POSITIONING SYSTEMS AND ACCURACIES :

-MEDIUM AND LONG RANGE SYSTEMS LIKE GPS

ETC.

-MICRO WAVE SYSTEMS

-RANGE BEARING SYSTEMS

-VISUAL SYSTEM

PUMPING THE DREDGED MATERIAL :

The material dredged from the seafloor is placed either by the dredger itself by pumps on deck, or by pipelines or barges.

COMPARISION BETWEEN SAND PLACEMENT MECHANISMS.

1) BOTTOM SLIDING DOOR2) STONE DUMPING VESSEL3) DUMPING BARGE4) RAINBOWING5) DUMPING BARGE WITH

RECESSED DOORS6) PIPE UNDER WATER7) CONE VALVES8) PIPE UNDER WATER +

DIFFUSER9) SPLIT BARGE10)PIPT ABOVE WATER11)GRAB CRANE12)GRAB CRANE + PIPE

SAND AND ROCK PLACEMENT MECHANISMS.

CONCRETINGCONCRETING

Design Phases Concrete Sea Structures :

1)Construction including construction ashore and in-situ wherever possible.2)Transportation including transportation of the structure or a part of the structure from shore to sea, or from shore to barge, open-sea transporting and mooring operations.3)Installation : Installation of the structure at its final location , ie. Period of start of submerging from transport position or launching from barge, including piling, grouting or anchoring, until the platform is ready for normal operation. 4)Operation : The period from completed installation till decommissioning or removal from location5)Retrieval : Includes retrieval or removal of the structure.

MATERIALS FOR UNDERWATER CONCRETE :1)CEMENT : OPC or Rapid hardening cement, moderate to low C3A content, water cement ratio less than 0.45, pozzolanic materials like silica fume, blast furnace slag, etc of high quality may be added for strength / workability, high alumina cement should not be used. Minimum content of 400 kg / cubic metre2)AGGREGATES : Natural sand or gravel, crushed rock. Rough cubic or spherical shape, consistent quality and grading, marine aggregates and those with shell content should not be used.3)WATER : Clean and free from harmful matter, sea water must not be used in reinforced, pre- stressed, or structural underwater concrete, subjected to wetting and drying.4)ADMIXTURES : Air-entraining agents to counter expansion contraction, workability aids and retarding admixtures. Admixtures containing more than 0.1% chloride content should not be used.

5) REINFORCING STEEL: Plain Bars, deformed bars, welded fabrics may be used provided details of size, mechanical properties and bond properties supplied by manufacturer.

6) SHEATHING: Rigid or semi-rigid water-tight metal sheathing should be used. Should be spliced with tightly fitting sleeves and the joints bound with waterproof tape.

7) GROUT : Usually OPC cement, aggregates if used in large ducts should consist of siliceous granules, finely ground limestone, trass, pozzolan or fine sand ; admixtures to be used after testing, sea water should not be used.

CONCRETE PLACEMENT UNDERWATER:1)TREMIE2)SHIP MOUNTED BOOM3)HOISTS, CRANES, ETC.

SHETCH SHOWING TREMIE CONCRETING

SHIP MOUNTED CONCRETE PLACEMENT BOOM

HOISTS ETC, ON GROUND OR BARGE/SHIP MOUNTED.

OTHER OTHER PROCESSESPROCESSES

BREAKWATER CONSTRUCTION:

Breakwater: A structure which breaks the

force of the waves, it is constructed close to the

island and acts as a protection against strong

currents and winds.

The breakwater is constructed using multiple

layers of sand, a water permeable sheet, small

rocks, and layers of armour rocks

The breakwater should be constructed out of

rock rather than concrete to encourage the

creation of an artificial reef.

Two openings in the breakwater were created in

order to prevent the water inside from

stagnating.

BREAKWATER

IMAGE : PALM JUMERIAH , DUBAI

VIBRO COMPACTION:

During an earthquake, water-saturated soils can lose their strength and transform into a liquid-like state. This process of liquefaction could cause the reclaimed islands to settle or sink.

Thus special provisions need to be made to prepare the sand base under the structure so that it does not compact. This is done using vibro-compaction.

Vibro Compaction is a process by which sand particles are caused to float, and then they are rearranged into a denser state. A vibration probe penetrates the soil and moves down via a combination of vibration, and jets of water and/or air.

The vibrations of the probe reorganizes the soil particles, compacting them. More infill (sand) is added until there is a column of compacted material.

SKETCH SHOWING THE VIBRO-COMPACTION PROCESS

Soil Compaction Soil Compaction TechniquesTechniques

FAMOUS ARTIFICIAL ISLANDS

THE WORLD- DUBAI PALM JUMERIAH - DUBAI

KANSAI AIRPORT, JAPAN

BURJ AL ARAB HOTEL, DUBAI

PROBLEMS AND CHALLANGES

1)EXCESSIVE COST INVOLVED IN CONSTRUCTION

2)SLOW CONSTRUCTION PROCESS DUE TO LIMITED AVAILABILITY OF DREDGERS.

3)ENVIRONMENTAL IMPACT DUE TO REMOVAL AND PLACEMENT OF SAND. CAN BE PREVENTED THROUGH SHALLOW CUTS.

4)SETTLEMENT OF THE ISLAND IN DEEP WATERS, AS IN THE CASE OF KANSAI AIRPORT, JAPAN

5)EXCESSIVE EXPOSURE TO WINDS, TIDAL FORCES AND EARTHQUAKE AND TSUNAMI LOADS HENCE SPECIAL PROVISIONS REQUIRED.

ADVANTAGE : ANY SHAPE, ANY SIZE, ANYWHERE.

REFERENCES1)Construction of offshore structures – Ben C. Gerwick – John Wiley and sons2)ARTIFICIAL SAND FILLS IN WATER – Centre for civil engineering research and codes - A.A.BALKEMA/ROTTERDAM/BROOKEFIELD.3)FIP Recommendations for the design and construction of Concrete sea structures– THOMAS TELFORD LIMITED.4)Conceptual design of large Cutter Suction Dredgers; Jaap L. van Overhagen, Marcel Boor, André Kik and Caspar H.M.Kramers5)Brochure : European Dredging Industry6)Case Study : Burj Al Arab, Dubai7)Man Made Land Features : The Palm Jumeriah and Dubai’s Artificial Islands : Terry Austin.8)Artificial Offshore islands : Patric J.F. Hannon, J.Wayne LeBlanc.