5,675-Foot x 72-Inch HDD Bore for 48-Inch Pipe Sets New Record

By Ben Boere, Project Manager, FlowTex Egypt and Roy Estes, Chief Engineer, Transcontinental Supplies Inc. | March 2011, Vol. 66 No. 3

The Abu Dhabi Tourism Authority is developing a mixed commercial, residential and leisure project on a low-lying island just 500 meters off the coast of Abu Dhabi Island.

The Saadiyat Island development, which will cost US$27 billion, will eventually house about 150,000 residents. With a championship golf course, a New York University campus, a world class performing arts center and a 30,000 square meter Guggenheim Museum, Saadiyat Island is expected to become the cultural capital of Abu Dhabi.

Water infrastructure
Extensive infrastructure development, including storm water drainage, sewer systems, electrical grid stations and a water supply and reservoir system are all part of the development.

It was necessary to install two 48-inch diameter water pipes that cross the Abu Dhabi Channel and connect Saadiyat to the main water network in Al Nakheel Junction.

The original route chosen for the pipeline was rejected by landowners and the project was delayed about a year until an agreement was reached on an alternate corridor for the installation of the two parallel 48-inch steel pipelines and a six-inch conduit for fiber optic cable.

In August 2008, Lindenberg Water and Drainage (a division of Lindenberg Emirates LLC), awarded FlowTex Egypt a contract to drill the HDD bores and install the pipelines connecting Al Nakheel Junction with Saadiyat Island. The first 5,280 foot bore was started Sept. 21, 2009 and the product was pulled May 4, 2010. The second 5,675 foot bore started Oct 19, 2009 and was pulled on July 22, 2010. Drilling was accomplished with Herrenknecht 400 rigs. The bores were drilled concurrently with the same drilling tools used on the second bore after completing a pass on the first bore.

Drilling
Drilling the first 12 ¼-inch pilot hole was difficult due to the rapidly changing soil formations which varied from soft to hard to very hard, often within a few meters. The formation was primarily soft calcareous mudstone, siltstone and sandstone with streaks of crystalline gypsum and sections of hard calcarenite. The design radius of 5,250 feet was not achievable in some areas and radii of less than 3,300 feet had to be accepted. Because of the smaller radii it was decided to make the bores 72-inches rather than the 62-inches as originally planned.

Drilling the pilot hole was so difficult it was decided that the tooling ordered for the original corridor would not be suitable for the harder formation found in the present location.