Slope stability evolution of a deep-seated landslide considering a constantly deforming topography

Slow-moving deep-seated landslides are characterised by continuous deformation, constantly changing topography and sliding-mass geometry. Deformation rates are predominantly controlled by temporal dynamics of pore pressure. Progressing movements typically cause an over-steepening of a landslide's foot, making these areas more susceptible to secondary slope failures and piggyback slides that, once they occur, change the geometric boundary conditions of a slope. This study presents an integrated topographic monitoring and geomechanical modelling approach, which is suitable for both model-based replication of the landslide's hydro-meteorological drivers and assessment of the long-term effect of topographic changes on the stability behaviour of a large deep-seated landslide. Parametrised at the Vogelsberg landslide (Tyrol, Austria) the integrated approach quantified considerable mass relocations between 2007 and 2020 at the landslide's foot and assessed respective effects on slope stability. Additionally, scenarios of past and future topographies were reconstructed and projected. Mass relocations of the order of 25 000 m(3) were assessed between multiple airborne laser scanning acquisitions covering a period of 13 years. Based on annual uncrewed aerial vehicle laser scanning campaigns, area-wide 3D displacements were analysed, exceeding a magnitude of 200 cm a(-1) at small parts (2.500 m(2)) on the steeper foot of the active landslide. The main landslide body (0.28 km(2)) moves considerably slower with movements of 2-10 cm a(-1). Besides spatio-temporally varying hydrological drivers, topographic changes can have a severe impact on slope stability and therefore modify the spatiotemporal activity of the landslide. It is shown that, besides the hydrometeorological drivers, the varying elevation of the landslide's toe is a key parameter determining the long-term trend of slope stability. With the presented approach the formation and evolution of the Vogelsberg landslide can be understood and explained.

Automated summary

This study presents an integrated approach for monitoring the topography and modeling the geomechanics of slow-moving deep-seated landslides. The study quantified mass relocations and assessed their effects on slope stability, showing that the elevation changes at the landslide toe are a key parameter determining the long-term trend of stability. The approach provides a better understanding of the formation and evolution of landslides.