ARTIFICIAL ISLANDS

SUBMITTED BY: B.A.W 2012

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. Methods of Creation 1)Expanding existing islets 2)Construction on existing reefs 3)Amalgamating several natural islets into a bigger island. 4)Construction on sea bed. 5)Land Reclamation 6)Oil Platforms

Reasons 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 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 over1000 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

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

Design 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 loadsVariable 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 removed c) Hydrostatic external pressure and buoyancy in calm sea conditions calculated for mean sea level.

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 structure c) 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 cooling c) Sea loads like wave loads, tidal loads, currents

The following stages are involved:

1. Temporary tube piles driven into sea bed 2. 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 PREPERATION

FUNCTIONS OF SANDTHE 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 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 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 placement1. 2. 3.

4.5.

6.7. 8.

Sand winning Sand transport Formation of sand water jet Formation of a crater Flowing of sand water mixture on slope above water Flowing of sand water mixture on submerged slope Loss of sand under water Sedimentation and formation of

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 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 Methods1) 2) 3) 4) 5) 6) 7) 8)

Taking of surface samples Borings and Laboratory Tests Soil penetration tests Cone penetration tests Pressiometer or dilatometer Density Investigations Twin well probe 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 2 3

ELECTRONIC SATELLITE NAVIGATION, SPAR BUOYS, ACOUSTIC TRANSPONDERS, SURVEY, INVESTIGATION AND CORING AND SAMPLING, GRAB SAMPLES, SPARKER SURVEY, SIDE-SCAN SONAR, ACOUSTIC IMAGING, FOUNDATION PENETROMETERS, VIDEO, SUBMERSIBLE CONTROLS AND DIVER INSPECTION

PLATFORM SEAFLOOR OBSTRUCTION REMOVAL DREDGING, REMOVAL OF SEDIMENTS

DERRIK BARGE, DRILL SHIP, SEMISUBMERSIBLE JACK-UP, GUYED TOWER, HEAVE COMPENSATORS DRAG-OFF WITH TRAWLERS, SHAPED CHARGES, ROV'S WITH MANIPULATORS, UNDERWATER BURNING, THERMIC LANCERS 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

4

HYDRAULIC BACKHOES, DIPPER DREDGES, POWER ACTIVATED CLAMSHELL DREDGING, REMOVAL OF BUCKETS, PLOWS, SHAPED CHARGES, BLASTING IN DRILLED HOLES, CHISELS, HARD SEDIMENTS AND ROCKS HYDRAULIC AND PNEUMATIC ROCK BREAKERS, DRIVEN SPUDS, CUTTERHEAD DREDGES, HIGH PRESSURE JETS 5 DIKES OF ROCKS OR CLAY BUNDS TO CONTAIN SAND, CONTROLLED PLACEMENT OF UNDERWATER UNDERWATER DEPOSITION, DUMP ENMASSE FROM HOPPER BARGES, TREMIE, FILLS BUCKET, SKIP, CHUTE OR LADDER

6 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

SAND PILES, VIBRATION, FREEZING, PRESURCHARGING, SURCHARGING WITH MEMBRANE AND DRAINAGE, SURCHARGING CONSOLIDATION AND WITH STRUCTURE AND BALLAST, WICK AND SAND DRAINS, DRAINAGE WELLS, PERIPHERAL SURCHARGING, CEMENT STRENGTHENING OF WEAK SOILS INJECTION, CHEMICAL GROUTING, LIME INJECTION, DEEP CEMENT MIXING, ELECTRO-OSMOSIS DENSIFICATION, DRAINAGE WELLS, PERIPHERAL APRON OF GRADED ROCK 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 UNDERBASE GROUTING, UNDERBASE SAND INJECTION OR SAND FLOW, TREMIE CONCRETE, GROUT INTRUDED AGGREGATE, MUD JACKING ARTICULATED DREDGE ARMS, AIRLIFT, JETS, EDUCTORS, DRILLS 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 BENTONITE-CEMENT SLURRIES, DISCHARGE OF FINE SAND BLANKET

9 PREVENTION OF LIQUEFACTIONLEVELING OF SEAFLOOR OR EMBANKMENT

10 11 12PROVISION OF UNIFORM SUPPORT UNDER BASE OF STRUCTURE EXCAVATION BENEATH STRUCTURE SCOUR AND EROSION PROTECTION

1314TURBIDITY SUPPRESSION

DREDGING

Dredging BasicsDredging is the maritime transportation of natural materials from one part of the water environment to

another by specialised dredging vessels. In a usualdredging 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 betweenborrow 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

storageof contaminated materials Annual Turnover of the dredging industry: 6.3 Billion $ (2008)

EXTERNAL CONDITIONS DURING CONSTRUCTIONGROUP A : THOSE WHICH DETERMINE THE USE AND EFFICIENCY OF EQUIPMENT, BREIFLY SUMMARIZED UNDER THE HEADING OF WORKABILITY GROUP 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.

S U C T I O N D R E D G E

C U T T E R S U C T I O N D R E D G E

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 asand 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

T R A I L I N GS U C T I O N

D R E D G E

E D U C T O R D R E D G E

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

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 ConsiderationsEnvironmental conditions consist of two major aspects: - Weather climate -Wave climate Temperatures 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 dredgers overall capacity. Violent storms can lead to autonomy requirements when means of escape are required.

Local FacilitiesA 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 consumables - Availability of shore pipelines and/or barges - Availability of shelter area -Water depth for spud tilting and ladder tilting

other

* Restrictions in water depth can determine the way of

Geometrical PropertiesGeometrical 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 distribution Soil 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 capacity The 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 dredgers hull itself. Both may constitute an obstacle in case of vertical quaysides.

Spud carriage The application of a spud carriage is common practise for large CSDs. 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. Automation Large 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 Owners 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) 2) 3) 4) 5)

BOTTOM SLIDING DOOR STONE DUMPING VESSEL DUMPING BARGE RAINBOWING DUMPING BARGE WITH RECESSED DOORS 6) PIPE UNDER WATER 7) CONE VALVES 8) PIPE UNDER WATER + DIFFUSER 9) SPLIT BARGE 10)PIPT ABOVE WATER 11)GRAB CRANE 12)GRAB CRANE + PIPE

SAND AND ROCK PLACEMENT MECHANISMS.

CONCRETING

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 location

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 metre 2) 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%

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) TREMIE 2) SHIP MOUNTED BOOM 3) HOISTS, CRANES, ETC.

SHETCH SHOWING TREMIE CONCRETING

SHIP MOUNTED CONCRETE PLACEMENT BOOM

HOISTS ETC, ON GROUND OR BARGE/SHIP MOUNTED.

OTHER PROCESSES

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 rockrather 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

SKETCH SHOWING THE VIBROCOMPACTION PROCESS

Soil Compaction Techniques

FAMOUS ARTIFICIAL ISLANDS

KANSAI AIRPORT, JAPAN

THE WORLD- DUBAI

PALM JUMERIAH - DUBAI

BURJ AL ARAB HOTEL, DUBAI

PROBLEMS AND CHALLANGES1) 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,