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)