The geometry of slip surfaces beneath landslides: predictions from surface measurements

A knowledge of the slip surface profile beneath a landslip is essential for stability analysis and for the design of remedial works. This note sets out to demonstrate the accuracy of a technique that utilizes the measurement of surface displacements to predict the position and shape of the slip surface. The proposed technique is tested in model studies of all major classes of landslip and is used on three large landslips for which corroboratory evidence of the position of the slip surface, located by traditional site investigation methods, is available. The results indicate that, from a knowledge of ground surface displacements alone, the depth of the slip surface can be confidently predicted to within 2% of the distance between ground stations. The usefulness of this technique for planning and costing-feasibility studies, site investigation programmes, and prospective remedial measures is also discussed.