Analysis of rockfall hazards at Los Alamos National Laboratory
In the early years at Los Alamos National Laboratory, rockfall hazards were intuitively recognized and avoided. Hence mesa tops were selected over canyon floors for construction sites, although some canyon bottoms were still used. The Omega West reactor site was located in a narrow portion of Los Al...
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2008
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| Online Access: | http://www.osti.gov/servlets/purl/10185281 https://www.osti.gov/biblio/10185281 |
| Summary: | In the early years at Los Alamos National Laboratory, rockfall hazards were intuitively recognized and avoided. Hence mesa tops were selected over canyon floors for construction sites, although some canyon bottoms were still used. The Omega West reactor site was located in a narrow portion of Los Alamos Canyon adjacent to 400 foot high vertical cliffs. In 1944, a quarter-mile long rock catcher was installed above the reactor to protect the facility from occasional rockfalls. In addition, an annual rock catcher inspection was initiated. Between 1944 and 1993, 24 separate rockfall events were documented; individual rocks trapped in the catcher ranged in size from 300 to 21,000 pounds. These rockfall inspection data were arranged into an annual exceedance series, and a frequency analysis was performed. This type of analysis is routinely employed in flood studies when stream gaging records are available. Prior to this study, however, such techniques had never been used with rockfall data. This analysis indicates that the annual rockfall series is approximately log-normally distributed, and that the 500-year rockfall event will probably exceed 187 tons. In addition, a Markov generation scheme, which preserves the statistics of observed logarithms from the historical data, was used to generate a synthetic rockfall series. These synthetic data suggest that the cliff face will retreat at an average rate approximating 2 to 3 centimeters per 1000 years. This rate is comparable to independently computed rates that range from 4 to 14 centimeters per 1000 years. These cliff-face erosion processes are important because they affect mesa-top trench burial operations of low-level radioactive wastes. |
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