Stabilisation of the Jackfield slope at Ironbridge Gorge, Shropshire

Abstract

The Ironbridge Gorge in Shropshire, UK, is young in geological terms and is generally prone to slope instability. Jackfield is an area on the banks of the River Severn that has a record of known slippages; these are put into geological and historical context. A scheme was proposed to stabilise the slope, adopting a hybrid method of analysis and design. The evolution of this scheme is outlined with particular emphasis on the design of the piles that were a fundamental part of the solution. Piles were used to stabilise the landslide by mobilising available passive resistance in the underlying stable ground mass and transmitting that resistance into the overlying slide mass, adopting the Viggiani method. The difference between the approaches of the geotechnical and structural aspects of the design is discussed in some detail as the design team was careful to avoid compounding factors of safety; this is illustrated by a numerical example. The determination of pile strength is outlined and a worked example for ascertaining pile spacing is included along with installation details.