REMEDIATION OF RAILWAY EARTHWORKS

Arup were commissioned by Network Rail to investigate causes of instability of 6 railway earthworks, comprising two cuttings and four embankments located in the Great Western Zone. Once the cause of instability was established, topographic surveys and ground investigations were completed, and remedial solutions designed. The author was part of the geotechnical team responsible for the identification of the causes of failure and subsequent design of remedial measures. The causes of instability included deep seated instability due to failure of the underlying embankment foundation material, and local instability of ballast at the embankment shoulder caused by raising of track level by routine maintenance of the track over a number of years. The stabilisation method adopted for each site was dependent largely on the mode of failure, underlying geology and the need to maintain the operation of the railway during implementation of the proposed works. Solutions included bored concrete soldier piles with regrading of embankment slopes and the use of shear trenches, a novel form of embankment stabilisation involving deep counterfort drains. The paper concentrates on the geotechnical aspects of the projects, and therefore presents details of three of the six earthworks sites considered. This includes the geometry and geology of the sites, the form of the assumed cause of the instability and details of the proposed remedial works. It also provides a commentary on works implementation through an alliance contractor, and identifies the benefits of this method of design and procurement. For the covering abstract see ITRD E123761.