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Geotechnical: Trip back in time

Keller is installing 2,500 piles as part of an £18M scheme to stabilise a World Heritage Site.

Keller piling

Precious: The work is being carried out in a World Heritage site

Jackfield is a World Heritage site near Telford, in Shropshire, with a long history of slope instability dating back to 1883.

There were a number of severe events in the early 1950s, and in 1952/3 several properties and a road were lost into the River Severn. Since then, development and road construction in the area has been restricted.

The area, which sits in the Iron Bridge Gorge, has played an interesting part in the history of industrial Britain, as a centre for tile making and mining area.

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.

“This innovative solution will enhance slope stability significantly”

Andrew Davison, Keller

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 continuous flight augur 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 Soilmec R625 and SR80 rigs on the £3.5M contract to drill through the mudstone and, after concreting the piles, the 457mm diameter steel tubes are carefully plunged into 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.

“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 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,” says Davison.

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