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.

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.

Source: parsons.com