The 1.4km sub-sea tunnel project on The Palm Jumeirah is approaching completion with the waters of the Arabian Gulf now entirely submerging the tunnel.
The 38m-wide tunnel connects the tip of the island’s trunk to the crescent and will ultimately provide transport access for those wishing to visit more than 20 five star hotels that will be located on the island’s breakwater. The entire project is expected to be completed in May 2007.
The tunnel comprises three cells: two outer vehicular cells with pedestrian sidewalks, which will carry three lanes of traffic each way; and the middle cell used for emergency evacuation and services. From the top of the tunnel to the surface of the sea there is a 10m deep navigation channel which is 125m wide, while from the sea level to the bottom of the tunnel’s foundations is a distance of 25m at the deepest point.
Around 200,000 m? of reinforced concrete, 30,000 tons of reinforcing steel, 260,000 m? of sand dry backfilling, 450,000 m? of wet backfilling around the tunnel, 53,000 tons of dry rock armor placement, and 57,000 tons of wet rock armor placement have been used in the creation of the tunnel.
Dr. Tamer Al Hafez, Nakheel Senior Geotechnical & Tunneling Engineer, said: “The Palm Jumeirah is a marvel of engineering, admired around the world, but located within the island are also a number of projects which are significant engineering achievements in their own right.
“The construction of a sub-sea tunnel is a complex and skilled undertaking and requires a range of innovative construction techniques and a dedicated team that can cope with a challenging and demanding working environment. The sub-sea tunnel has required the skills, expertise and vision of some of the world’s leading engineers and it’s an incredible sense of achievement to see the vehicular tunnel disappear under the waters of the Arabian Gulf - an achievement that everybody involved in the project can be extremely proud of.”
To build the tunnel under dry conditions, the project required the construction of two 1.2km long dykes, 2m below sea level, using approximately 1 million m? of dredged backfill material. A 2.4 km-long sheet-piled cofferdam (a type of dam that is constructed to exclude water from an area that is normally submerged) up to 400m wide with a total covering area of 300,000 m? was then constructed on top of the dykes using 30m deep sheet piles driven into rock. These dykes were later prepared and used as temporary roads to provide construction traffic access for the crescent developers.
Construction started on the dam in October 2004 and was completed in August 2005. Once the dam was built, more than 5.5 million m? of seawater was pumped from the cofferdam in just 45 days and when the dam was entirely drained of water, construction of the tunnel could commence.
Running parallel to this work was a marine life rescue operation led by the Nakheel Environment Department to prevent fish and other marine creatures from becoming trapped inside the dam after it was closed. This included catching the fish alive and relocating them in the waters on both sides of the cofferdam. Approximately two thousand fish from 35 species were safely relocated.
Construction of the tunnel structure was completed at the start of 2007 and the back discharging of sea water began in February. In took an average combined daily rate of 40,000 m? of water to fill the 3.5 m? dam volume. Before flooding, water level inside the coffer dam was maintained on -25 DMD, but as of this week the water level inside the dam area is now equal to the level outside at about + 1.8 DMD.
The main contractor of the project is Taisei Corporation with Parsons De Leuw Cather as supervising consultants and Parsons Brinkerhoff as project managers. Al Naboodah is the civils subcontractor, Halcrow is the design subcontractor and MEP subcontractor is Kinden.