Stability analysis of a human-influenced landslide in eastern Belgium

The area of the Pays de Herve in eastern Belgium is strongly affected by recent landslide activity. Dormant landslides are widespread in the region and some of these dormant landslides have been reactivated by human activity such as highway construction, suburban development, or building of industrial sewage pipes. The investigated landslide was reactivated by heavy rainfall events in the late 1990s. During this reactivation an existing industrial sewage pipe was damaged and the chemically loaded waste water drained into the landslide mass. The current landslide movement is assumed to be heavily influenced by the additional water supply as well as by the chemical activity of univalent ions in the clay fraction leading to a decreased shear resistance. Consequently, the movement-triggering rainfall thresholds are reduced and result in a decreased overall slope stability. This study describes a general methodology of field investigation, data collection and laboratory testing for an exploratory study. Influences of chemical properties of soil and soil water and their effects on landslide stability are analysed, discussed and related to findings of other studies. Although no clear empirical evidence for a dependency between slope stability and ionic loaded soil water was found in this study, we suggest the existence for such a relationship. We conclude that this particular landslide would not have moved based on current environmental conditions. The leaking waste water might favour current landslide movement.