Rock slope stability: a case study at Coles Quarry, Backwell, North Somerset

Coles Quarry, which produced both roadstone and concreting aggregates from the Carboniferous Limestone, was one of six extractive operations operated by RMC Aggregates (South West) Limited. Production ceased on 31 March 1999. Owing to the inherent environmental problems at Coles quarry, the company had been planning since the late 1980s to transfer its local limestone production operations to a new site, Freemans Quarry. However, a final limited-life extension to Coles Quarry was required because the company needed to maintain production whilst Freemans Quarry was undergoing development. An original application for a southeastward extension of Coles Quarry was submitted in November 1991. However, in January 1992 these development proposals were called into question by a substantial planar failure. This paper summarizes work undertaken over a period of approximately ten years, which comprised the characterisation, analysis and resolution of problems associated with the potential for planar failure at Coles Quarry, to enable both the stabilization and safe development of the southeastern quarry extension.