Construction of the Islands


        

Palm Islands is composed of three islands: Palm Jumeirah, Palm Jebel Ali, and Palm Deira, with the last being the most recent works in progress. Palm Jumeirah covers 600 hectares of land and with Palm Jebel Ali add 120 kilometers of beachfront to Dubai. Palm Jumeirah spans approximately four by five kilometers. Palm Jebel Ali covers 6 by 7 kilometers. Palm Deira with an area of 80 square kilometers will be the largest island out of all of them and is equivalent to the area of Paris and London. The World is an archipelago of 300 private islands each with a size ranging from 2-8 hectares, each selling for $7 to $35 million dollars per island. It is 4 kilometers from Dubai’s coast and is a representation of the world’s continents. The Palm Islands and the World extend into relatively deep water of about 10-15 meters.

All three islands have similar palm-shaped structures, although the size of each varies. Nonetheless, they all follow more or less the same state of the art engineering and construction procedures. Therefore, it is sufficient to examine mainly Palm Jumeirah’s design and construction challenges, and then consider special design adjustments to the construction of the consequent islands.        

All three islands share their date palm tree form with a spine, fronds, and a long trunk, a crescent shaped breakwater, sub-sea vehicular tunnel and monorail, sub-sea horizontal directional drilling (HDD) crossings on both eastern and western ends of the site and pies on each side of crescent. Palm Jumeirah, in particular, has 17 fronds and a 1.5 km long trunk. 


Construction of Palm Jumeirah began in August 2001, and is considered one of the world's biggest undertakings. Unlike other previously man-made islands that are built from metal and concrete, Dubai's Palm Islands are made from all natural materials - rock and sand upon Prince Sheikh Mohammed Bin Rashid Al Maktoum's request. Although Palm Islands are artificial islands, the prince desired for a natural appearance that would blend into existing surroundings. Basically, he is asking to build a massive structure without concrete and steel to hold it in place. It is exactly this demanding feature that makes constructing these islands the biggest challenge. Plans for this megastructure project would not have been able to materialize without the collaboration between construction contractors and engineering scientists. 


The first step was to consult with the experts of land reclamation - the Dutch, who increased their land mass by 35%. The biggest problem that needed to be resolved was how an island made out of sand would remain in position. Solutions to that problem are very complex because it is dependent on many factors such as the strength of Dubai's storms, the height of waves and tidal surges, and global warming's impact in raising sea levels. One of the biggest fears was how waves could accumulate over long distances via persistent winds and large currents potentially causing severe destruction to the islands. Luckily, scientists say that the Arabian gulf is the perfect place for such construction because with a depth of 30 m and a width of 160 m, it is too short and shallow for the creation of immensely destructive waves. Nonetheless, even though typical Gulf climate is mild, during the Shamal season, weather conditions are different. During the Shamal season, from November to April, many storms develop over the Northwestern part of the Gulf, where the winds are the strongest, travelling at velocities up to 56 km/hr, and drift toward the Southeast within a few days. Waves ranging from 1 to 2 m high can form from these strong winds, and not to mention, the potential for a catastrophic storm that hits once in a hundred years. As a result, scientists designed the crescent breakwater structure to surround the fronds of the Palm Islands in order to protect the islands for high waves and storms. 

Scientists calculated that for breakwater crescent to be functional along the 5 km radius of Palm Jumeirah, it had to be at least 3 m above waves, 11.5 km long and 200 m wide in cross section. The company that constructed the breakwater crescent was Archirodon Overseas. This project required 9 barges, 15 tugboats, 7 dredgers, 30 heavy land-based machines, and 10 floating cranes. The islands themselves would be made out of an obscene amount of sand dredged from three massive barren sea beds nearby (from the gulf), while the breakwater crescent out of rock and sand, though mostly rock. The bottom sand layer of the crescent breakwater is 7.4 m thick. The challenge of dumping this sand layer was that it had to be done when the sea was the calmest to ensure stability. This was exceptionally difficult during the Shamal season. During this time, construction contractors fell behind the already tight schedule. Then, barge-loads of rubble were dumped on top of the sand layer to raise the breakwater crescent from 4 m below to approximately 4 m above the sea. Sloping layers take out force of waves as it comes into contact with the walls. Since, sand and rubble are the base of the breakwater crescent, how does the breakwater actually protect the islands? The real protection comes from the outer armor, which is made out of huge boulders of rocks with each rock weighing up to 6 tons! 5.5 million cubic meters were obtained from 16 quarries around the Emirates - enough to build 2 Egyptian pyramids! The rocks were piled on barges and instantly shipped to the construction site in less than 24 hours. Then, a floating conveyor belt operating all day and night, discharged the 40,000 tons of rock per day to the breakwater crescent. The other miracle is how this stone wall is expected to stay in place without concrete to secure it. Scientists claim that rocks were selected by size and weight and specially positioned by cranes. As easy way to think of this is how a key fits in a keyhole. The rocks work the same way - each rock must "interlock" with the adjacent one to tackle forces of the sea. However for safety precautions, scientists perform frequent checks to make sure the rocks in the breakwater are not drifting away. For this reason, scientists send divers undersea to survey the ocean floor, every 27 m, looking for cracks and splinters in rocks or "rock fatigue" caused by strong waves. The last thing they want is for the breakwater to disintegrate because that could be fatal to the existence of the islands. 


BREAKWATER


Breakwater Crescent Palm Island Jumeirah

The breakwater crescent of Palm Jumeirah is about 11 km long and 200 m wide in cross section. It stands over 13 feet above low tide sea level and sits in 34 feet of water at the deepest point. The crest of the breakwater is 3-4m above mean sea level. The seaward slope is one in two. The composition of the breakwater consists of coarse sand, quarry run, and 5-6 tonnes of sand. The seaside breakwater is protected by rubble mound armor. The lowest layer of the breakwater is filled with sand. Rocks weighing one ton were placed on top of the sand followed by two more layers of rocks. In addition, there are two 328-foot openings on each side of the breakwater to enhance water circulation. According to the Case Study No.1 Design of Palm Island, water renewal time is approximately 13 days, slightly different than the estimated average renewal times in another article, which stated 10.1 days. The fact that the latter estimate was derived during the construction period can explain the different results. Water circulation around the fronds and open sea is critical for marine life, supply of oxygen and the removal of pollution. Furthermore, there is a retaining wall between the Crescent and fronds. Another layer of rock is placed in front of the wall to reduce overtopping quantity. (Stive)




Breakwater Crescent Palm Jebel Ali

The breakwater crescent of Jebel Ali is 15 km long and 200 m wide in cross section. The crest height, 4.25m above sea level, is higher than Jumeirah’s because of the greater water depth. The seaward slope, however, is the still one in two. There are a retaining wall between the crescent and the palm islands, and three openings, more than Jumeirah because of its greater crescent length. (Stive)




                                                                       





Breakwater Crescent Palm Deira

The breakwater crescent of Palm Deira will be 21 km long, the largest breakwater in the world. The crescent will be divided into 12 districts, and will have 6 openings for water circulation. The special feature to Palm Deira is that each of the districts will have land sticking out to create more beach land for investors. These are referred to as "fingers," and will be 250 m long. It is located in the internal part of the crescent 350 m from the fronds. (AMEinfo)






SUB-SEA DRILLED DIRECTIONAL CROSSINGS 

The sub-sea vehicular tunnel and monorail connect the spine tip to the crescent and help facilitate utility services to hotel and leisure developments on the crescent. Six sub-sea HDD crossings are built at the eastern and western ends of the sites. The eastern crossing from Frond D to the crescent is 580m in length at water line, with an average boring length of 680m, while the western crossing is 700m long at the water line with an average boring length of 800m. In order to gain experience, Al Naboodah Engineering Services, the company in charge of installing 12 HDD crossings and 2 micro tunnels for electricity cable installation decided to first build the shorter eastern crossing. The pipes, located at a depth of 13m to 16m below the seabed in water depth ranging from 7m to 14m, provide for drinking water, telecommunications, wastewater and the discharge of treated sewage. (Gahir, et.al)

The main challenges of the installation of sub-sea horizontal directional drillings on Palm Jumeirah specifically, was that there were close spacing between the bores (holes), changing soil conditions along the drilling alignment (fill/rock) and brackish (slightly salty) groundwater. To resolve the second problem, vibrocompaction technologies were used just like in the case with sand in the palm's fronds themselves. (Gahir, et.al)







Besides the scientific challenges to this construction project, another challenge was the pressure to finish the islands in such a limited amount of time - 3 years. In order to keep ahead of schedule, the company constructing the islands, decided to start laying the sand foundation under the sea. Yes, time constraints forced both companies - the one constructing the breakwater crescent, and the one constructing the islands to complete both structures simultaneously. However, eight months into the project, it wanted to bring them above sea level. In April 2002, after 550 m of the breakwater crescent was completed, the company finally brought out the fronds. This decision was based on a study conducted that sought to minimize constructions risks, to be elaborated below. It explains the different sediment transport processes that occurred during construction time. 

The islands themselves, the fronds were made out of an obscene amount of sand - 94 million cubic meters of it! That is enough to cover the whole of Manhattan 1 m deep! One would assume that acquiring even that huge amount of sand would not be difficult for a country with sand as their biggest resource (deserts). However, sand from the desert is not the most suitable type for construction of the Palm Islands because it is too fine and "flaky". Instead, sand was obtained from 60 nautical miles out of sea, from the bottom of the Persian Gulf. This is sand was superior because it was coarse, dense and resistant to wave impact. The sand was dredged by the Belgian company Jan De Nul and the Dutch company Van Oord, and was sprayed using dredging ships. Sand placement was guided by Differential Global Positioning Systems (DGPS) allowing for an error of less than 0.39 of an inch beyond imagined boundaries (since there are no rigid mold to hold it in place). The way this works is that five men walk around the entire island daily in the hot temperature and high humidity levels, carrying these cumbersome gadgets behind their backs, and receive signals from the Prince's own satellite system, located 676 km up in space. (This technology rivals those of the Russian and US military!) The height and position of the deposited sand is recorded and reveals the coordinates (like on a graph) where precisely, the dredges should make additional deposits. The sand was dredged at very high speeds at 10m/s. It took less than 1 hour to fill an 8 ton tank with sand! This process,  known as the rainbowing process, is when a dredging ship propels sand from the ocean floor and forms a high arc in the air, as shown in the picture. After the rainbowing process, the sand rises 4 m above water. 

After a year, two-thirds of the breakwater crescent had been completed, but then scientists encountered another problem, which was the lack of adequate water circulation around the fronds with the open sea. Thus, scientists had to make alterations to the blueprint of the breakwater crescent, and so they made two openings in the breakwater. The breaks were to be connected by bridges. These openings would prevent water stagnation and permit marine traffic. A tide would rush in two times a day, replenishing the water supply every 14 days. 

Another challenge was that since the sand was rainbowed or sprayed, the sand is loose and uncompacted even though sea bed fine material is already cleansed, since it is from great ocean depths. Usually sand compaction would happen naturally over time, but there is no time as the Prince rushes the completion of this project due to declining oil banks, Dubai's main source of revenue. Also, road rolling is not an option in this project because the sand is too deep - 12 m deep. Another potential challenge is the fact that Dubai lie on the edge of an earthquake zone. If sand has low cohesiveness, and there is an earthquake, a process known as liquefaction can develop. This process entails that as the earthquake shakes the Earth's surface, sand particles will move. The sand particles will compact, pushing the water between the particles up, as a result, liquifying the ground. This will ultimately cause the island to sink in the sea, which is not supposed to happen considering all the people and money invested in this project. To resolve the problem, constructors used vibro compaction technologies which made loose sand denser by saturating it with high-pressured water an air, and vibrating it with probes). In January 2004, two thousand holes were drilled into the ground as a result. These efforts helped secure sand in place. Then, additional sand was dumped to fill the remaining space. The process of stabilizing the fronds took approximately 8 months. Although a time-consuming process, it is absolutely critical that a firm sand foundation is established because the city is supposed to support an urban population of 120,000 people. 


Meanwhile another challenge arose, and that is erosion. All beaches face erosion, but unlike natural beaches, man-made ones when faced with erosion do not naturally replenish itself. Gradually, sand will wash way, piling up further along the structure. Below different kinds of sediment transport processes are discussed for clarification of how erosion works. If sand is not replaced or frequently monitored, the shoreline will no longer be straight. In extreme cases, the beach may disappear altogether. So constant monitoring is a must. Constructors need to prepare sand for erosion events. 

Previously, it was mentioned that sand that erodes, leaves one area, and accumulates in another area along the structure. So a good question is Could success of megastructure cause the mainland's downfall? Usually currents push sand along the coastline equally, resulting in a straight beach line. However, by building Palm Islands near the shoreline, the wave movement in the area changes. In some cases, sand will be deposited to the mainland's beaches, extending the beach, but in others, shorelines may erode from 5 to 10 m per year. This can potentially destroy much properties and businesses in the mainland. Again, this calls for constant maintenance to ensure that shorelines of the mainland and Palm islands remain relatively the same over time. 



To understand better the effects of strong waves/currents on erosion, we will examine a study that examines the sediment transport processes from these sand-filled islands. Information obtained from this study was used to plan the optimal construction schedule. 

Sediment Transport Processes 

Waves attack the island, making sand drift away from the outlined fronds and trunk. The greatest loss is at the ends of the fronds because there they encounter a combination of littoral (long-shore) and perpendicular (cross-shore) sand transports, not to mention, how the frond ends are the least protected part of the island at the beginning stages of construction. 

Wash-over transport

Wash-over transport occurs when the crest level is lower than the wave run-up level. The waves wash over and reshape the constructed berm. The sand is moved by tidal currents parallel to the shore, down-slope directed density currents, and breaking wave-induced currents. During the winter, when there are severe storms and higher waves, more breaking of waves occur, resulting in greater transport rates and more sand loss. However, since the first winter (2001-2002) had relatively mild climate, there were low transport rates and less sand loss.

Long-Shore Transport

Long-shore Transport occurs when the crest level is higher than the run-up level of waves. Essentially this means that waves are blocked. Transport is parallel to the berm. Three types of formulas were used to measure long-shore transport: CERC, Bijker (1971), and Van Rijn (1993). 


Long-shore transport rates for a 45°wave approach angle

According to the table, transports calculated by Van Rijn were 100 fold of those calculated by Bijker and CERC. Bijker and CERC had the “same magnitude” of long-shore transport rates. There are discrepancies between the transports because each formula measures certain variables that may have been neglected or not weighed as much in other formulas. For instance, Van Rijn takes beach slope into account. (Less steep slopes result in lower transport rates.) Bijker and CERC suggest that slope does not really affect long-shore transport. (de Jong, et. al)

Cross-Shore Transport

Cross-shore transport is perpendicular to the coastline. Sand will be moved more down the slope and less upwards, resulting in a less steep slope over time. The crest line will shift toward the shore and sand will deposit outside the boundaries.Cross-shore transports were measured using three formulas: Swart’s model, Durosta, and Unibest-TC. Swart’s model states that sand transport is dependent on wave height, wave period and grain size. Durosta is used more for computing offshore-directed sediment transport of dune profiles during storm conditions – good for computing the erosion process along steep initial slopes of Palm Island. Unibest-TC is good for computing cross-shore sediment transports and the change in profiles along a coastal profile of any shape due to waves, long-shore tidal currents and winds.

Data revealed that small waves did not substantially alter the beach profile. The profile was only affected by higher waves – those greater than 0.5m tall. 


                   
                Calculated Crest Line Regression for Significant Wave Height of 1m                                         Calculated Crest Line Regression for Significant Wave Height of 3m


                                                                        

Illustration of Wash-over, Long-shore, Cross-shore Sediment Transports

Below is a cross-profile before and after exposure to waves. The active zone is directly influenced by wave action. The upper boundary (hm) is where the wave run-up is above still water level. There is a lot of sand in suspension in the breaker zone. As seasonal wave climate changes, the breaker zone may move seawards.


Cross-Profile Before Exposure to Waves


Cross-Profile After Exposure to Waves


The results of the study revealed the following: 1) Building the sand island above the waterline in unsheltered water would allow for cross and long-shore transport to take its course and result in immense sand loss. 2) Unprotected fronds can break through during severe winters. 3) When the crest level is adequately below water level, crest deformations will only result when there are extreme storm conditions. 4)Deformations in general are far less than if the crest were above water. (de Jong, et. al)

The proposal for the best construction procedure was that during the first winter (first Shamal season) in 2001, since the development of the breakwater is still limited, (the profile is still below 4m), there are lower transport rates (because most of the structure is still undersea), the width of the fronds will be under-filled to allow for possible deformation. In addition, in between sand bars, there will be walkways to permit space for dredgers and the safety of construction workers. Sand can be dumped without being rainbowed. After the first winter, construction workers will work on one frond at a time starting with the top end of the palm so that each completed frond can serve as shelter for the next one to be constructed. Filling sand will be done in an anticlockwise manner (west to east) so there is minimum interference with the construction of the eastern crescent breakwater and maximum protection of the dredger. There are greater deformations if the crest level is raised to just below the wave run up level. Therefore, if going to raise above water, final crest level should be reached or almost reached. Reshaping is due to wash-over transport with crest of 4m only happens during severe circumstances. There is less reshaping than in case of the crest level above water level. (de Jong, et. al)

By conducting this study, Van Oord Acz, the sand-dredging contractor and islands constructor, made the right decision to stay underwater for the first winter, only raising the fronds above water when there was adequate protection from breakwater crescent. (de Jong, et.al)





Constructors were also concerned about the ecological effects of the Palm Islands, so a few times a month, divers surveyed the fish and corals in the water. To their pleasing, they discovered that the breakwater crescent because it is made of rock and provides shelter, attracted more fish, not to mention, new species. From this discovery, Palm developers were inspired to build the biggest artificial reef in the world, eventually to compete with Australia's Great Barrier Reef. Two jet fighter planes were dropped to the sea floor to provide a diving platform for people. The reef facing the Northwest has a berm 32m wide at 2.5m below mean sea level. The shallow and long nature of it helps to break severe waves during storms. The core of the reef is made up of sand to reduce the amount of rock required for the project. For the reef in general, there are granular filter layers in between the sand and rock to help reduce sand loss. To protect the outer reef while still attracting marine life and maintaining aesthetics, Royal Haskoning designed 1m-wide, 25km long, low crested reef breakwaters (2m above mean sea level). The breakwaters like those of the islands also contain openings for water circulation. The physical appearance of the artificial breakwater reef was to resemble that of tropical islands like the Maldives, and as a result, a chain of waterways, canals, and lakes were constructed. 




                                    Artificial Breakwater Reef

As if the project was not ambitious enough, Dubai decided to dream on. After Palm Jumeirah, Palm Developers immediately proceeded with plans for Palm Jebel Ali, which is supposed to be twice the size of Palm Jumeirah. This island is intended to be a tranquilizing spot and therefore does not contain as much islands - 29 luxury islands and water homes along the breakwater crescent that spell out an Arabic poem scribed by Prince Sheikh Mohammed Bin Rashid Al Maktoum. Furthermore, Palm Developers wants to construct Palm Deira, which is expected to the be the biggest island out of all three, with an area 15 times as much as the first. Undergoing this project would require 1,500 million cubic meters of sand! In addition, to all these Palm Islands, Palm Developers want to build "The World." The World’s islands are 5-10 km away from the coast, and travel to and from the destination will require air/marine transportation. So far there has been great demand for the World's islands - a third of the World is already sold out. Two of the palm islands have been sold. But Dubai will not stop there! The next project is the Waterfront, a cloud-shaped land adding 75 km of water, long enough to connect to its deserts. Dubai is taking on not just one mega-project, but many as it strives to become the most popular world destination.


WORKS CITED

e Jong RE, Lindo MH, Saeed SA, Vrijhof J. 2003. Execution Methodology for Reclamation Works Palm Island 1. Terra et Aqua [Internet]. [cited 2009 4 Dec]; 92. Available from: http://www.terra-et-aqua.com/dmdocuments/Terra-et-aqua_nr92_03.pdf

Gahir J, Radwanski R, Tamer AH. 2006. Design and Construction Challenges of Sub-Sea Directional Drilled Crossings on the Palm Jumeirah, Dubai. Tunneling and Underground Space Technology [Internet]. [cited 2009 December 4]; 21:3-4. Available from: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V58-4J9MSV7-3&_user=18704&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1126410491&_rerunOrigin=google&_acct=C000002018&_version=1&_urlVersion=0&_userid=18704&md5=7abb10dd3874c3721f61ff6a3fe76407

Hellebrand S, Fernandez J, Stive R. 2004. Case Study: Design of Palm Island No. 1 Dubai. Terra et Aqua [Internet]. [cited 2009 4 Dec]; 96. Available from: http://www.terra-et-aqua.com/dmdocuments/terra-et-aqua_nr96_05.pdf

Stive RKH. Low Crest Breakwater Design For Dubai Islands Projects. Netherlands: Royal Haskoning, Maritime Division. Available from: http://library.coastweb.info/808/1/Microsoft_Word_-_Stive_paper.pdf

Unknown. "The Palm Deira will showcase unparalleled engineering, says Nakheel." AMEinfo. 25 Nov. 2009<http://www.ameinfo.com/49340.html>.

IMAGES CITED

RAINBOWING PROCESS PIC

Nakheel-Palm Deira, Rainbowing. 11 October 2007. Eikongraphia. Web. 5 Dec. 2009. <http://www.eikongraphia.com/images/ThePalmDeiraJul07CopyrightNakheel2S.jpg>.

BREAKWATER PALM JUMEIRAH PIC

Stive RKH. Low Crest Breakwater Design For Dubai Islands Projects. Netherlands: Royal Haskoning, Maritime Division. Available from: http://library.coastweb.info/808/1/Microsoft_Word_-_Stive_paper.pdf

BREAKWATER PALM JEBEL ALI PIC

Palm Jebel Ali. Unknown. CBA Asset Management. Web. 5 Dec. 2009. <http://www.cbaonsite.ch/dubai-immobilier/projets-immobilier-dubai/palm-jebel-ali/photos/palm_jebel_ali_06.jpg>.

BREAKWATER PALM DEIRA PIC

Palm Deira. Unknown. Dubai Property Group. Web. 5 Dec. 2009. <http://www.dubaipropertygroup.com/resources/images/locationImages/palm-deira.jpg>.

SUBSEA DRILLED CROSSING AND FIRST OVERVIEW OF PALM ISLANDS STRUCTURE PICS

Gahir J, Radwanski R, Tamer AH. 2006. Design and Construction Challenges of Sub-Sea Directional Drilled Crossings on the Palm Jumeirah, Dubai. Tunneling and Underground Space Technology [Internet]. [cited 2009 December 4]; 21:3-4. Available from: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V58-4J9MSV7-3&_user=18704&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1126410491&_rerunOrigin=google&_acct=C000002018&_version=1&_urlVersion=0&_userid=18704&md5=7abb10dd3874c3721f61ff6a3fe76407

CROSS PROFILE EXPOSURE TO WAVES AND SEDIMENT TRANSPORT PICS

de Jong RE, Lindo MH, Saeed SA, Vrijhof J. 2003. Execution Methodology for Reclamation Works Palm Island 1. Terra et Aqua [Internet]. [cited 2009 4 Dec]; 92. Available from: http://www.terra-et-aqua.com/dmdocuments/Terra-et-aqua_nr92_03.pdf

ARTIFICIAL REEF PIC

Fish repopulate the coral reef after it was shifted to a new location off the Dubai coastline. 7 June 2009. The National. Web. 3 Dec.    2009.<http://www.thenational.ae/apps/pbcsi.dll/bilde?Site=AD&Date=20090607&Category=NATIONAL&ArtNo=706069945&Ref=AR>.


 

 

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Tida Choomchaiyo,
Dec 5, 2009, 7:22 PM
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