AN EMBANKMENT failure in southwest Scotland last October not only severed rail links with Stranraer but also with ferry services to Ireland.
The collapse, near Glenluce on the Ayr to Stranraer railway line, left 25m of unsupported track on the 20m high sand fill embankment, either side of a newly formed steep-sided gorge. The gorge was formerly the course of a stream running in a culvert beneath the structure, which follows the contours of a steep slope.
The stream flows from high ground in the west to an alluvial plane to the east. It became swollen after heavy rainfall but because ebris had blocked the culvert, high water pressures built up behind the embankment before washing part of it away.
Consultant Donaldson Associates and First Engineering carried out the design and construction of a replacement section, built using crushed rock fill and armour rock from local quarries.
All the failed material was removed and benches excavated into the underlying natural soil and adjacent embankment fill. Rock armour was placed at the toe of the slope with crushed rock fill forming the core and upper parts of the embankment.
Some 4000t of material was excavated from the embankment and replaced with 6000t of imported rock fill over four days.
A new culvert was also incorporated in the design, as well as a 15m high gabion cascade to train the water down from near the crest of the embankment to the flood plain.