Murphy in box-jack pilot drives

J Murphy & Sons recently completed two pilot tunnels for a sub-highway box-jack project in Kent, England, using a precast concrete lining segments from new supplier F P McCann at its Cadeby works. The work was part of Phase Two of Kent County Council’s A-road improvement scheme that caters for over 20,000 vehicles a day near Kent Airport, and due for completion in 2012.

The scheme includes the need for a 125m-long underpass beneath Foads Hill and a railway at Cliffsend. In an innovative design this required two parallel pilot tunnels within which the necessary rails for underpass box-jacking would be laid. Murphy used its TBM, named ‘Doris’ to make the drives through chalk either side of the drive line for the concrete box underpass to be jacked into and through the hill.

McCann supplied 268 concrete segment lining rings, each of 3.05m i.d. and 1.0m wide. These were delivered from Cadeby over a period of six weeks.

Murphy’s tunnel construction manager, Lee Aspden said, “We were extremely pleased with both the service F P McCann provided and the finished quality of the segments. Operating in some extreme weather conditions towards the end of the second drive was challenging for us the contractor, and our suppliers.”