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February, 2005 <br />value for the FS of the failure circle greater than or equal to 1.0. In some cases cell <br />depth and soil types were similar enough to allow setbacks to be determined from that <br />of another cell. For example, the excavation depth and soil types of cell 2 and cell 3 in <br />phase 10 were very similar and therefore, setback recommendations for cell 3 are <br />based on analysis for cell 2. <br />Overall, recommended setbacks are consistent with values used for other pits in the <br />area previously analyzed by Weiland, Inc. with similar soils and depth to groundwater. <br />The results are sufficiently conservative to satisfy the requirements of the Colorado <br />Division of Minerals and Geology agency. Recommended setback distances from <br />streams could be tightened with better phreatic surface data, however additional soil <br />analysis would be required to meet this end. Existing soil boring information was <br />utilized for this study to conserve costs. The boring information provided adequate input <br />information for the scope of this study. <br />1.4.1 LIMITATIONS OF STUDY <br />In some cases, only one or two boreholes were utilized to determine the underlying <br />stratigraphy in the area for a given cell. The actual stratigraphy could vary due to the <br />uncertainty of the soil thickness data. For this reason, rational but conservative input <br />data was utilized to offset soil thickness uncertainty. <br />Distributed loads due to soil stockpiling at or near the edge of the excavation were not a <br />consideration for the scope of this study. <br />Dead and live loading due to equipment operation at or near the edge of the excavation <br />was not included in the scope of this study. <br />Earthquake and tension crack coefficients were not utilized with this slope stability <br />application. Analysis of the slopes during earthquake was considered beyond the <br />scope of this report. Although this area of Colorado is relatively stable geologically, that <br />does not mean that liquefaction of soils due to earthquake could not occur at or near <br />this site and affect the stability of excavated slopes. The likelihood of slope failure due <br />to liquefaction of soil precludes the need to investigate this type of failure. <br />The slope stability program utilized for this analysis returns output that indicates a 0.5:1 <br />slope will fail even though field observation of similar pit excavations indicate 0.5:1 <br />slopes can, in fact stand. This offers proof of the conservative nature of the input data <br />utilized for this study. <br />Fort Lupton Pit Slope Sfabifity Study, Page 5 of 5 <br />