A quantitative assessment of the risks associated with landslides from the Alpine Way was carried out. The assessment was undertaken to provide a basis for understanding the Thredbo Landslide in comparison with risks accepted or understood in society. The assessment used information which would have been available prior to the Landslide. The assessment entailed classification of the geometry, geomorphology, groundwater conditions and stability of the main fills along the Alpine Way from the Park Boundary to Dead Horse Gap. This data was supplemented by surveys of known historic and recent landslides. The annual probability of failure of a given fill along the Alpine Way is assessed to be approximately 1 percent. It is also estimated the annual probability of the Alpine Way fill above Carinya becoming mobile is about 1 percent. The consequences of a mobile failure depend upon the travel distance. This distance, and vulnerability of persons within it, was assessed. The travel distance for mobile failures was estimated from the measurements of the historic failures and more recent identified slumps along the Alpine Way. This data shows the distance of travel for a mobile failure at the Carinya site lies between stopping behind Carinya to continuing well beyond Bimbadeen and reaching the Thredbo River. These travel distances are in accord with worldwide experience and more importantly in accord with extensive experience with failures in Hong Kong which has similar geology and geotechnical conditions. Estimates of the expected deaths from mobile landslides above Carinya show a range from 1 to 2 fatalities for a small landslide during the daytime in the low season to more than 45 deaths for a large mobile landslide during the night in the peak season. The analyses show that, prior to the remedial work which is now completed along the Alpine Way above the Carinya site, the individual risk of death for a mobile failure at the Carinya - Bimbadeen site was over 2000 times the level suggested by the NSW Department of Planning for tourist developments. A lower bound estimate has also been assessed and this was over 200 times the limit suggested.
展开▼
