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s <br />Y <br />Slope Stabiliht Analysis <br />Varra Gravel Operation - Duftm Pit <br />Greeley, Colorado <br />Page 4 <br />100 year flood events were simulated. The soil characteristics as presented earlier were <br />used in the analysis. Computer generated data sheets are presented in Attachment C. <br />A review of Attachment C shows existing bank profiles are stable with calculated safety <br />factors between 1.25 and 1.38 for mine and pit side flood conditions. Static condition <br />simulations indicated a safety factor of 1.6. <br />Discussion <br />The field investigation indicates that the embankment separating the Varra Durham <br />gravel operations and the Cache la Poudre River is primarily composed of sand and <br />gravel. These deposits have a high internal friction angle. The slope of the embankment <br />varies between less than 18 and 42 degrees, with the majority of the bank much less <br />than 30 degrees. The high friction angle and moderate bank slopes creates an <br />inherently stable condition. The high permeability of the bank material reduces the <br />potential for excessive pore pressures within the bank during rapid drawdown events. <br />The bank slopes with out modifications are stable - even during flood event <br />simulations. Data suggest that proposed bank modifications will not adversely affect <br />bank stability. As the bank material is primarily dense to very dense sand and gravel it <br />is our opinion that subsidence after a flood event will not occur to any significant <br />degree. The fact that the bank has been in place on the order of decades without any <br />history of failure supports the analysis presented herein. If any significant modifications <br />to proposed or existing bank slopes occur this analysis should be considered invalid.