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Pinning down a troublesome embankment

AMEC PILING recently carried out a major railway embankment stabilisation which included installing nearly 150 soil nails.

The £260,000 contract for Birse Rail was the latest attempt to stabilise a failed 50m long section of the Railtrack embankment near Armitage in Staffordshire, following a number of unsuccessful repairs.

The 10.5m high embankment on the mainline track between Crewe and London slopes at about 38degrees and toes directly into the fast-flowing River Trent. It comprises fill and ballast, overlying clay and Sherwood Sandstone.

Site access was limited so a 2.5km haul road and a 40m long Bailey bridge across the river had to be built before work could start.

First stage was to install and carry out pullout tests on five nails. Then 148 nails, between 9m and 15.5m long, were installed in five rows at 1.75m centres from a complex four-level scaffold platform.

Between 16mm and 36mm in diameter, the nails are made up of coupled lengths of galvanised Gewi bar supplied by Dywidag Systems (International).

Space restrictions meant that installation had to be done by a small TechnoDrill 1.5t Twintech TD308 drilling rig. The duplex system was used with air flush, with a down-the-hole hammer used to penetrate obstructions and the sandstone.

After installation, face meshing was tied to the soil nail plates and gabion walls built (materials for both supplied by Maccaferri). Reno mattresses were also placed before final landscaping.

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