Keeping the tide at bay

Terraforce concrete blocks used on Palm Jumeirah to protect foundation and provide access to beach

At the start of the millennium, Dubai had become the fastest growing tourist destination in the world. This placed huge demands on its beaches and the idea was proposed to build a circular island offshore. HH Sheikh Mohammed Bin Rashid Al Maktoum then had the vision that an island in the shape of a palm leaf would maximise the beach area.

To realise the vision took exceptional planning. Nothing on this scale of land reclamation had ever been attempted before and experts were brought in to look at every aspect, from offshore wave conditions to disposal of waste water.

A crescent was added to the design, a breakwater that would protect against the worst imaginable sea storms, yet still offer uninterrupted views of the sea.

These three 12-square-mile man-made islands – The Palm Jumeirah, Palm Jebel Ali and Palm Deira – are dubbed the “Eighth Wonder of the World” and billed as the largest land-reclamation project in the world; the islands will create a large number of residential, leisure and entertainment areas.

Today, people live along the 16 fronds of Palm Jumeirah and the 11 kilometre crescent that surrounds the palm itself is filling with hotels and entertainment venues. Built entirely on natural rock and sand, and surrounded by coral reef, Palm Jumeirah is proving the ideal place to live, invest or enjoy the holiday of a lifetime.

The project was uniquely demanding. The crescent was built in multiple layers using sand, a water permeable sheet, small rocks and two further layers of armour rocks weighing up to six tonnes.

Underwater excavators, guided by divers, then laid the inside ‘toe’ of the crescent. An astonishing 92,234,000 cubic metres of sand was then transferred to build up the landmass.

Advanced Global Positioning technology ensured that the land was reclaimed to within one centimetre of the proposed design. Ikonos, the world’s first privately owned satellite, orbits the earth 14 times a day, supplying high resolution photography of the project.

Connecting the crescent to the mainland required a subsea tunnel. During its construction an area of the sea was drained using a coffer dam and the seabed excavated to build the tunnel itself. The sea was then allowed back inside the dam area.

Made possible by the wide continental shelf off the Dubai coast, and the relatively shallow depth of the Persian Gulf, Palm Jumeirah was constructed from about 94 000000 m² of sand dredged from the bottom of the Persian Gulf. The sand fill was placed directly onto the (typically) 10.5m deep seabed using bottom dump dredgers. Above sea level, the top 3m of the reclamation was achieved using a dredging technique known as “rainbowing” in which the sand fill was sprayed – using dredging ships guided by GPS – over the surface of the emerging island.

The reclamation was made of calcareous sand, which was locally cemented into a soft sandstone. Although Dubai is a low risk earthquake zone, Nakheel’s design consultant mitigated the risk of liquefaction by specifying vibro compaction ground improvement – this will also help to control differential settlements across the reclamation.

Access to beach and sea
One of the assurances made by the developers was that all residents would have access to beach and sea. After completion of the fronds of the palm however, it was found that at low tide insufficient water was reaching the ‘armpit’ area – where each frond joined the main stem of the ‘trunk’ – thus necessitating deepening of the sea bottom levels in these areas. This in turn called for a retaining wall system to be put in place, protecting the foundations of the buildings and also allowing for the creation of a suitable beach.
Terraforce concrete blocks used on Palm Jumeirah to protect foundation and provide access to beach
In October 2005, a phone call came through to Simon Knutton of Knutton Consulting – a well established engineering company involved in authoring the original design guidelines for CRB walls in South Africa – from Project Manager John Lund, with whom Simon had worked some 15 years previously. “We need to design a system of barrier blocks leading down to the beach and sea….can you assist?”

At this stage Simon Knutton, after having sourced and sent to Dubai photographs of every available block in South Africa – liaised closely with Holger Rust, Director of Terraforce, this particular South African company having had long experience and success in the field of concrete blocks. After Terraforce supplied the necessary information on the proposed block system, drawings and prototypes were produced, and in November Knutton flew to Dubai with a proposal and sample block. Despite an alternative system being proposed by the dredging company, Knutton left after a short meeting with a confirmed design appointment.

As part of their ongoing co-operation, Knutton and Rust also decided on a strategy to chose a suitable manufacturer for the blocks and within two weeks, after proposing the idea to the company earmarked by Knutton, Rust negotiated an agreement with Alan Sakr, Director of Consent LLC, a Dubai based precast company, appointing them as exclusive producers of Terraforce blocks in the Persian Gulf Region.

Consent LLC wasted no time in springing to action and immediately spent 50 000 € on ordering a new mould box in Germany for their machine. The L16 blocks, adapted to local conditions, can be produced 8 blocks per pallet, 16 blocks per m². Under the oversight of Knutton Consulting, 50 000 blocks were produced in Dubai and in March 2006 Rust travelled to Dubai to assist Johannesburg based Jan Rabie of Telegenix with a test section of walling constructed on the island. Following final sign-off by the client, production then began in earnest, with Rabie being retained as consultant on the construction side.

From the sourcing and selection of the original product, followed by arranging for the dimensional alteration of moulds to suit the Dubai manufacturer through to design of the highly-flexible layout of the walling, Simon Knutton was closely involved at each step, in close co-operation with the other companies concerned. Knutton Consulting were scheduled to keep a watching brief over the ongoing construction of the walling. Either Simon Knutton himself or, alternatively, the laying team trainers were required to be on-site for six days each month to ensure that the design concept was adhered to and that the quality of laying was maintained.

Terraforce concrete blocks used on Palm Jumeirah to protect foundation and provide access to beachTo Holger Rust the project shows once again how co-operation of South African know-how can successfully penetrate lucrative markets in far away places. “Credit has to go to all those who are helping this impressive project proceed smoothly, the more overseas exposure for us as South African service providers, the more benefit to the local economy. We really need to work together and showcase our competence to the rest of the world.”

Did you know?
Dutch scientists were called in to study the area and perfect the plans to make sure the island would remain intact over time and through storms, and function correctly. However, the owners refused to wait until they had completed their investigation, and ordered construction to commence immediately. After the island had been constructed, the Dutch scientists discovered that the tide could not reach all around the palm and if left, the water would stagnate at the top of the palm, and it would become a haven for algae and mosquitoes. The owners saw this as unacceptable and ordered action to be taken immediately. The scientists then came up with the current design, which has two channels through the outer ring, each about a quarter of the way around from the nearest end. These channels allow the tide to come in through the sides as well, and this means that all of the water in the palm is replaced every two weeks.

Interesting link:
More about the Palm Jumeirah

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