Reinforced Earth® Retaining Walls and Bridge Bearings
URS, Atkins, Donaldson
The Scottish Borders had been without a railway since Lord Beeching’s cuts in the 1960s, and after closure in 1969, some of the track alignment was built on. Consequently, the new Borders Railway incorporates a number of structures to get across new roads or as part of a revised track alignment. The £294M project required 31 miles of track and seven stations, 42 new bridges and 95 refurbished bridges. It is the longest new UK domestic railway for over 100 years and runs from Newcraighall, five miles SE of Edinburgh to Tweedbank near Galashiels.
The longest new bridge was the Hardengreen Bridge, a 72m long, two-span structure which crosses a roundabout on the A7. Here, the approach embankments have been built using Reinforced Earth with precast panel walls. The walls on this structure reached 10.5m high. In total, 26 structures benefitted from Reinforced Earth walls with approximately 11,000 square metres being supplied.
The system used was the Terraquad square panel facing (nominally 1.5 m sq panels) with either high adherence galvanised steel reinforcing strap in the rail structures or Geostrap polymeric reinforcement in the highway structures. The steel straps produce a stiffer reinforced fill which resists the high dynamic loads from the trains better. Backfill was 6i/6j granular material with a minimum phi of 36 degrees. This system was designed and supplied by Reinforced Earth Company (RECo), a subsidiary of Freyssinet.
Freyssinet supplied bridge bearings to seven of the Border Railways structures. Of the 107 bearings supplied, 52 were elastomerics, 46 were mechanical pot bearings and 9 were guide, pin or rocker bearings.
Main construction started in April 2013 and was completed in summer 2015.