Preferential flow paths through soil and rock and their association with landslides

This article discusses preferential flow paths through soil and rock and how these contribute to the style and timing of landslides. The importance of geological compartmentalization because of the presence of aquicludes such as weathered dykes and faults is emphasized as is channel flow through fracture networks and through natural pipes in soil‐like material. Although piping is a contributing factor to some landslides, as generally recognized, it can also be a sign of inherent distress in a developing landslide where water flow exploits cracks in the dilating rock mass. It is suggested that the association might be targeted in ground investigation. Inactive or low activity pipe systems can be identified by the anomalous presence of alluvial sediments at depth in the geological profile, whereas active pipe systems may simply comprise voids that could be misinterpreted as core loss during ground investigation. Examples of pipe systems encountered during ground investigations are given for various landslides and several case studies are illustrated in this article. Mitigation measures for preventing landslides triggered by rainfall are discussed together with the difficulties associated with preferential flow paths.