Quantitative risk assessment of rock slope instabilities that threaten a highway near Canmore, Alberta, Canada: managing risk calculation uncertainty in practice

摘要

We present a quantitative risk assessment (QRA) to guide decision-making for selection of rock fall protection strategies. The analysis corresponds to a section of highway near Canmore, Alberta, Canada; where rock falls are common. Environmental concerns, tourism, and economic activities overlap the project area, which increased the complexity of the decision-making process. QRA was adopted to improve highway user safety and minimize effects on natural, social, and economic environments. Uncertainty was associated with hazard and consequence quantification, and the study elicited plausible ranges of input variables for risk calculation. Expected and range in risk were calculated for current conditions and after mitigation. Individual risk to highway users was found to be low, following the limited exposure of any particular individual. Current total risk was calculated at 2.9 x 10(-4) probability of fatality and a plausible range between 2.0 x 10(-5) and 5.5 x 10(-3). The slope protection configuration selected had a residual total risk between 9.0 x 10(-4) and 2.9 x 10(-6), and a best estimate of 4.5 x 10(-3). The risk levels were evaluated against criteria previously used in Canada and were considered an appropriate balance between project costs, public safety, environmental concerns, tourism, and economic activities after mitigation.