The pipelines were laid between Lepe on the Hampshire coast and Gunard on the Isle of Wight,
Led by LMR Drilling and designed by Capita Symonds’ industrial team, the project is part of a scheme by Southern Gas Networks to replace the existing gas supply pipelines to the Isle of Wight which were laid just after the Second World War.
HDD is a no-dig technique used to install pipelines and conduits, especially across large waterways and in areas where traditional open-cut trenching techniques pose a threat to the environment. Typically, a rig is set up on one side of the crossing and a pilot hole is drilled along a predetermined drill path. Having completed the pilot hole, the hole is reamed out to the required diameter, before the fabricated pipeline is towed into position in one piece.
For the Solent Crossings, LMR Drilling drilled full bore pilot holes from both Lepe and Gurnard. This required the pilot holes to pass within a metre of each other, at a depth of up to 90m below the sea surface, before one drill was withdrawn and the borehole intercept made.
Capita Symonds’ industrial team ensured that stresses within the pipeline were maintained at acceptable levels. It is they who claim this to be the world's longest HDD.