Engineering geological and geophysical investigations of a slope failure at Edinburgh Castle, Scotland

Edinburgh Castle is one of Scotland's most important heritage sites. It was built on a classic 'crag and tail' structure where the crag consists of columnar jointed basalt and the tail of sediments protected from glacial erosion by the 'crag'. In 1997 apparent instability was observed on the southern side of the 'tail'. A shallow slope failure was proved to have taken place within saturated, layered, cohesive to noncohesive, loose to dense heterogeneous fill on a slope of 44 degrees. The date of the initial failure is not known, but is likely to have taken place over a period of many years, since at least the 1950s. Remediation works were subsequently undertaken to stabilise the slope, consisting mainly of the installation of soil nails, a bi-axial geo-grid and minor filling to mitigate the effects of the ground movements and to facilitate repair of the retaining wall.