Keller is installing about 2,500 piles as part of an £18M slope stabilisation scheme being undertaken by McPhillips (Wellington) on behalf of Telford and Wrekin Council, part-funded by the Department for Communities and Local Government.
Jackfield is a World Heritage site near Telford, in Shropshire, with a long history of slope instability occurring as far back as 1883.
There were a number of severe events in the early 1950s, and in 1952/3 several properties and the road were lost into the River Severn. Since then, development and road construction in the area has been restricted.
The area has played an interesting past in the history of industrial Britain, as the centre for tile making and also a mining area. Indeed one of the major issues, which has probably aggravated the slope stability over the years, is the former mine workings. These have been infilled with cement PFA grout.
Recent monitoring established that the slope was still active and that a further major slip could severely threaten upstream flooding. As a result, Telford and Wrekin Council (TWC) engaged Jacobs to design a stabilisation solution.
TWC and Jacobs’ plan requires the installation of 600mm diameter CFA piles arranged along nine discrete corridors. The piles are about 14m long, bored through the failure zone into the mudstone and reinforced with a 457mm diameter steel tube.
Keller is using a Soilmec R625 and SR80 on the £3.5M contract to drill through the mudstone and, after concreting the piles, the 457mm diameter steel tubes are carefully plunged in to the wet concrete. A further 647, 250mm diameter piles each reinforced with a 139.7mm diameter steel tube, will be installed along the river bank using smaller rigs from the fleet.
“With a horizontal spacing of 0.6-1.75m, this innovative solution will enhance slope stability significantly,” explains Keller piling manager Andrew Davison. “TWC is carrying out pile monitoring at a number of locations, using both precise surveying and vibrating wire inclinometers installed by Keller. It’s clear from early readings, that movement of the slope, which can vary according to rainfall, is now reduced.”