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The AAPG/Datapages Combined Publications Database

Utah Geological Association

Abstract


Environmental and Engineering Geology of the Wasatch Front Region, 1995
Pages 157-160

Rockfall Hazard Probabilistic Risk Analysis: A Case Study, Ogden Canyon, Utah

Craig V Nelson

Abstract

A large, industrial corporation maintains a VIP residence at the base of a steep talus slope in upper Ogden Canyon. A rockfall hazard risk assessment was requested following a near-miss of the cottage by a large (estimated at 4,500 pounds) dolomitic boulder sometime during the evening of May 16 or 17, 1994. The path of the boulder was traced by connecting the damaged vegetation and the bounce impact impressions on the ground back to a near-vertical bedrock outcrop. The Colorado Rockfall Simulation Program (CRSP) was used to model rockfall down the slope for rocks of various sizes and shapes. A statistical model was developed using a probability tree with nodes for different rockfall-event scenarios. Joint probabilities for impact were summed to provide a marginal probability of the structure being impacted by any given rockfall event as less than eight-in-one thousand. The probabilities of more than zero impacts in a year were calculated (assuming a poisson distribution) for a range of annual events. Preliminary recommendations for rockfall-hazard reduction at the site were also provided. Given the statistical risk data, the corporation was able to compare the probabilistic risk-assessment data to corporate risk preferences to determine an acceptable response to the rockfall hazard.


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