Map of Dubai

Dubai, the second largest of the seven emirates that constitute the United Arab Emirates (UAE), is the hub of commerce and tourism in the Middle East today. Among the landmark projects currently under development in Dubai, none has been more eye-catching and newsworthy than the Palm Islands, widely stated to be the eighth wonder of the world.

The Palm Jumeirah is a man-made island about 5 km in diameter. It covers an area of 600 hectares and was reclaimed from the sea. Once complete, the development will increase the Dubai shoreline by 75 km. The added coastline will not just create leisure opportunities for residents and visitors; it will also provide extensive habitat to marine life. Parsons is supervising construction services for a 1.4-km-long subsea vehicular tunnel that will connect the spine of the island to the outer crescent. The tunnel has been procured as a design-build contract.

The tunnel is being constructed using the cut-and-cover method. The tunnel comprises three cells with the outer cells carrying three lanes of traffic and two pedestrian walkways in each direction. The central cell is for services and emergency evacuation.

Sheet Pile Cofferdam with Discharging Pumps in Center

To build the project under dry conditions, the project required the construction of a 2.4-km-long sheet-piled cofferdam up to 400 m wide with a total covering area of 300,000 m². The construction sequence was to dredge, form the dike, install sheet piles, and drain the cofferdam. A total of 920,000 m³ of earthwork was used to form the dikes. Sheet piles measuring 30 m were installed to cut off seepage into the cofferdam. More than 4.3 million m³ of seawater was discharged from the cofferdam in 45 days using nine high-capacity pumps. During this process, Parsons made sure that special care was taken to protect marine life. To ensure the safety and proper maintenance of the cofferdam, an advanced early warning monitoring system was installed, and instrumentation was installed at strategic locations to provide information on the deflection of sheet piles, settlement of dikes, and water level inside the dikes.

Tunnel Diagrams

Under Parsons’ direction construction of the permanent works commenced after the cofferdam area was drained and dry. A 125-m-wide navigation channel is being provided with a minimum draft of 10 m above the armor protection to the roof slab of the structure.

Tunnel characteristics:

• Length: 1,398 m
• Maximum grade: 6% with a 60-kph design speed
• East portal approach: 241 m
• Reinforced concrete box section: 969 m
• West portal approach: 188 m
• Structural width: 38 m
• Internal clearance height: 5.52 m

Close View of Tunnel Construction at Spine Side

Foundation leveling concrete (blinding) was placed after the ground surface was leveled and compacted. The deepest point of the underwater tunnel is about 25 m below the high water level. Parsons ensured that special care was taken for dewatering so that neither the foundation bed nor the working formation was disturbed. A ground stabilization operation was also performed to minimize excess settlement.

Protective armor stone will be placed on the tunnel roof slab after the sides of the tunnel have been backfilled and the material has settled. The armor stones will be transported to the site by bucket-equipped rock barges. Surface water runoff, including washdown and spillage within the tunnel and approaches, will be collected via a continuous positive drainage system that will gravitate to three sumps: the crescent portal, spine portal, and low point sumps.

Construction of Tunnel Structure in Completion Phase

The tunnel also includes mechanical and electrical services such as a ventilation system that comprises 28 jet fans. These axial flow fans will be directly driven by internally mounted single-speed reversible motors that can deliver the air and thrust in either forward or reverse. The tunnel also has an advanced firefighting system that complies with the requirements of NFPA (National Fire Protection Association) 14, 20, and 24. The fire detection and alarm system will include two fire alarm control panels installed in each portal.

Heat/smoke detectors will consist of linear heat detectors for the service tunnel, an automatic smoke detection system, and manual call points. The main features of the traffic management system include traffic lights at tunnel portals, vehicle counting, vehicle speed monitoring, and an automatic incident detection system using CCTV. The security and surveillance system will also be monitored by the CCTV system with fixed-focus and pan/tilt/zoom cameras. The CCTV surveillance system, fire detection ventilation fans, drainage pumps, and lighting system will be monitored and controlled by a supervisory control and data acquisition (SCADA) system.

Project Highlights:

• Undersea tunnel being constructed using cut-and-cover techniques
• More than 4.3 million m³ of seawater pumped out
• Project has won numerous safety and quality awards
• 2,500 + laborers working daily on site at peak
• 185,000 m³ of concrete poured
• 30,000 tons of reinforcing steel used
• Tunnel fully equipped with electromechanical services

Parsons has been working in the Middle East for more than 50 years and in the UAE for nearly 30 years: our first UAE office was established in Abu Dhabi in 1978. Parsons currently has more than 1,000 employees working at offices in UAE, Qatar, Bahrain, and Oman. Our portfolio of ongoing projects in the Middle East includes major highways, bridges, rail and transit, airports, and infrastructure for major private developments.

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