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~. <br />Catch bench recommendations Page 2 November 8, 2000 <br />See attached figure from Call (1986). Similarly, the wider a catch <br />bench the more effective it will be and the longer it will <br />function. The width of a catch bench is also controlled by the <br />bench height and the maximum size of the rock blocks which may be <br />released over time. In this case the roughly 40foot thickness of <br />the upper sandstone bed, rather than the 15foot thickness of the <br />lower sandstone bed, will control and require an approximately <br />22foot wide catch bench. <br />The access road up to the catch bench can also serve as minor <br />catch benches between the switch backs. They should be sloped <br />slightly inward toward the slope. The inward slope will also serve <br />to channel water toward the sides and off the slope through the <br />down drain riprap channels. The sensitive nature of the clays <br />present in the slope mass necessitates removing rain and snow melt <br />water from the slope as rapidly as possible. The riprap channels <br />should be extended up to the catch bench. Culverts should be <br />placed through the access road where the riprap channels intersect <br />and intercept any water in the access road. It will probably be <br />necessary to clean out the culverts when clearing debris from the <br />catch bench. <br />The safety of the crew excavating the catch bench below <br />the lower sandstone bed should be enhanced by scaling of the <br />obviously loose blocks of rock at the crest of the two sandstone <br />beds and sitting precariously on the angle of repose shale slope <br />between the two sandstone beds. Removing these loose rock blocks <br />now will also extend the time interval between the periodic <br />clearing of debris that will collect on the catch bench. <br />Sincere]y, <br />John F. Abel, Jr. <br />Colorado P.E. 5642 <br />