Quantitative landslide hazard and risk assessment: a case study

This paper is concerned with landslide hazard and risk assessment along a railway line south of Sydney in the State of New South Wales, Australia. Attention is focused on a quantitative assessment at a specific site where landslide movements have been triggered by significant rainfall. Although small in magnitude such movements are sufficient to cause train derailment and hence human casualty. Utilizing all available data, the relationship of slope instability to rainfall is first established. Slope stability analyses are carried out to validate the proposed geological-geotechnical model. The concept of landslide triggering critical rainfall magnitude (specific to a given site) is proposed in this paper. Detailed rainfall analysis reported elsewhere (Ko Ko 2001) leads to the conclusion that the most significant period of antecedent cumulative rainfall for this site is 15 days. The historical rainfall data then leads to an estimation of landslide frequency or hazard. The risk to human casualty is then based on an analysis of train operations and their frequency. Different results are obtained for the tourist train service and the freight train service. Some attention is given to tolerable risk criteria proposed elsewhere in the literature.