Pipe installation using the Horizontal Directional Drilling method

Intrafor has completed the installation of three pipelines in Middle Island, Hong Kong, using Horizontal Directional Drilling (HDD). The pipelines will be used by the main contractor, Hong Kong Electric, to install 22kV cables between the south of Hong Kong Island and a nearby island for the Royal Hong Kong Yacht Club.

The project has been carried out from November 2015 to May 2016 adopting a three-stage pilot, ream and pull programme.

The first phase of the project, involving the drilling of three 5.5” pilot holes of 175m in length, was closely monitored to meet the requirements in terms of accuracy and collect a full suite of drilling parameters. The drilling was carried out under the seabed, encountering soft marine clays and sands capped at the start and ends of each crossing by hard rock – sometimes only moderately or slightly decomposed.

HDD is a preferred method when facing such challenging and varied ground conditions. The technique can be used in all geologies from hard rock to soft soil achieving high degrees of accuracy while seldom requiring any pre-treatment. Another of its main features is its steerability, which allows HDD holes to avoid both man-made and natural obstacles. This steerability was vital to the successful completion of the project which provided only a small receiving pit already congested with existing services.

After the pilot-stage, the holes were reamed using a 13” hole-opener to allow the installation of 225mm-diameter HDPE pipes.