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f <br /> BRIERLEY <br /> ASSOCIATES v x <br /> Creating Space Underground <br /> MEMORANDUM <br /> DATE: 12/30/16 <br /> TO: Transit Mix Concrete (Attu. Brandon Heser) <br /> FROM: Brierley Associates (Steve Kuehr, Sarah Myers) <br /> SUBJECT: Addendum to Geotechnical Design Report for Daniel Sands Wash Fines Pit <br /> Brierley provided drawings, specifications and a basis of design report for the new wash fines pit <br /> in September 2016. In December 2016, DRMS (Colorado Division of Reclamation, Mining, & <br /> Safety) pointed out some areas of concern that are to be addressed before approval can be <br /> granted. This addendum addresses those issues. <br /> Volume Comparison <br /> The new embankment will be constructed below the existing ground surface and is not <br /> considered a jurisdictional dam by the State Engineer's Office. As outlined in the original design <br /> report and further outlined below, the dam has been designed and engineered not to fail. <br /> Nevertheless, we have considered the inundation that would occur if indeed it were to fail. <br /> Assuming that the maximum volume of 452 acre-ft(water/fines at embankment crest)was <br /> spread across the portion of the pit east of Academy Blvd, the resulting water/fines surface <br /> would be at an elevation of 5796 to 5798 feet. The elevation of S Academy Blvd which borders <br /> the west edge of this area is approximately 5812 feet. This inundation area is entirely on Transit <br /> Mix property and would not affect S Academy Blvd. There is a mining operations underpass <br /> beneath Academy Blvd. The invert elevation of the underpass is 5782. Although, the <br /> water/fines do not overtop Academy Blvd, a portion of the fines/water would likely flow through <br /> the tunnel and then southerly to the portion of the site that borders Bradley Rd.We believe that, <br /> given the low likelihood of an embankment failure combined with a post-failure water/fines <br /> surface that is lower than Academy Blvd, off-site impacts, if any, would be insignificant. <br /> Slope Stability Analysis of New Embankment <br /> Brierley conducted a slope stability analysis on the Daniels Sand wash fines engineered <br /> embankment. Slope stability was analyzed using the computer program SLOPE/W, developed <br /> by GEO-SLOPE International (Geostudio 2012). SLOPEM utilizes limit equilibrium principles to <br /> analyze potential failure surfaces within a user defined two-dimensional geometry. Slip surface <br /> ranges can be defined using a variety of methods. Scenarios analyzed in this report defined <br /> failure surface locations over a range of entry and exit points. The Morgenstern-Price Method <br /> was used to calculate critical slip surfaces and associated safety factors. Using this <br /> methodology the factor of safety for a given geometry is determined by calculating the ratio of <br /> resisting forces to driving forces on a particular trial failure surface. The slip surface with the <br /> lowest factor of safety against sliding is described as the minimum factor of safety for the <br /> defined conditions. <br /> 990 S.Broadway,Ste.222, Denver,CO 80209 1303.703.14051 www.BrierleyAssociates.com <br />