The role of flooding in the activation of landslides in rail infrastructure

The effects of flood-induced embankment failures include infrastructure downtime, but, in more serious events, derailments and fatalities occur. From a review of global railway embankment failures, a new classification of four types of flood which cause slope failure was produced and key driving processes hypothesised. Internal erosion, driven by differential flood head, has the potential to cause material alteration following flooding by redistributing fine particles and altering material structure. Bender elements were used to measure material changes caused by internal erosion. Relationships between particle loss, shear wave velocity, permeability and sample strength were considered. Increases in the mass of material removed from samples caused reductions in sample strength. Following particle removal, multiple strain hardening-softening cycles developed during loading. High temporal resolution permeability and shear wave velocity measurement during seepage showed a relationship between the two properties; particle deposition is thought to have caused permeability reductions and shear wave velocity increases. Decimetre-scale physical slope models were used to identify where changes in material behaviour due to seepage-induced particle migration are likely to occur in slopes. Fines deposition caused mean grain size reductions of 4.5%, and 9% increases in coefficient of curvature, across the slope toe region. Increases in grainsize, due to fine particle removal, occurred near water inflow. Coupled with evidence from triaxial testing, these data suggest that permeability barriers may form in embankments, increasing pore water pressures and decreasing slope stability. Numerical modelling predicted the effects of these material changes on displacement caused by live rail loading at an embankment scale. Areas of particle loss caused displacement increases. Zones of deposition showed less consistent increases in displacement. An improved understanding of flood types which cause destabilisation, failure recording practice alteration and non-intrusive monitoring of changes in slope properties following flooding will allow for enhanced predictions of failure behaviour and stability assessment.