AN OVERVIEW OF LANDSLIDES IN THE UNITED KINGDOM AND THE INVESTIGATION AND REMEDIATION OF THE CHIPPING CAMPDEN LANDSLIDE

British landslides have a long history of being documented and investigated. As such, there is a wealth of information, including digital data. Classic landslides areas include the east and south coast of England, the South Wales Coalfield, the Pennines and the Scottish Highlands. The Chipping Campden Landslide occurred on a high speed railway cutting, constructed by Brunel in the 1850s. In March 2013, a translational landslide occurred on the north-east railway cutting. The landslide was marked by a distinct back scarp approximately 5m high. The slipped mass was about 50m wide, 30m high and 200m long. At the landslide toe horizontal ground movements were observed to reach up to 2m, and the general direction of slope movement was towards the railway line, which presented an unacceptable level of risk to the railway, if left unremediated. A desk study and visual inspections showed the slope to comprise glacial deposits overlying sedimentary sequences of Lower and Middle Lias. Rotary cored boreholes were logged to identify zones of the potential slip surface. Inclinometers were used to identify slope movement, together with time domain reflectometry (TDR) arrays, both installed within the boreholes to help identify the depth of the shear plane. Surface movements were also monitored to assess the rate of movement. Following the acquisition of data and monitoring information, a series of landslide models were generated using traditional slope stability analyses (non-circular slips modelled using Oasys SLOPE software) and time dependent finite element analysis (using LS-Dyna). This confirmed the geometry of the translational failure mechanism and indicated the generation of a strain-softened layer over some 150 years, resulting from the stress relief of the original cutting excavation, as a potential cause of the failure. The landslide was remediated without disrupting the operation of the railway itself. This included the excavation of about 45,000m³ of debris and approximately 1,700m of drainage. Furthermore, all of the excavated materials was reused, resulting in no waste being generated. The project was acknowledged by Network Rail’s Star award for health, safety and environmental performance, and became a finalist for the UK Ground Engineering Award in 2015.