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Memo to Steve Renner <br />Fruita Highwall Stability <br />page 9 <br />The primary analysis repeated the analysis performed by Mr. Lewicki <br />with these more conservative material properties. The <br />configuration represents that of the maximum 60 foot height of <br />backfilled highwall with a lh:ly (45°) facial slope. This <br />represents the situation encountered near the front of the original <br />portal bench fill where the dipping subcrop attains its maximum <br />elevation above the reclaimed surface in each of the adjacent <br />bedrock spines. Using SBSLOPB to complete the analysis results in <br />a Static Slope Factor of Safety of 0.62 for shallow-seated failure <br />and 0.75 for deep-seated failure. <br />I then performed a aeries of partial backfilling scenarios at <br />incremental lower facial angles, in order to determine the <br />sensitivity in regard to the facial angle, as tabulated below. The <br />maximum slope angle sustainable at a Static Slope Factor of Safety <br />above 1.3 was determined to be 2h:ly (26.6°). <br />Fruita Portal Highwall Stability Analysis <br />Sensitivity to Slope Gradient <br />Slope Gradient Failure Depth Static FS Pseudo FS <br /> <br />lh:ly (45°) shallow 0.62 <br /> deep 0.75 <br />1.Sh:ly (33.7°) shallow 0.89 0.720 <br /> deep 1.26 1.049 <br />2h:ly (26.6°) shallow 1.33 1.052 <br /> deep 2.05 1.655 <br />3h:ly (18.4°) shallow 2.55 1.797 <br /> deep 3.00 2.126 <br />Conclusion <br />American Shield Coal Company has been directed to completely <br />backfill the highwall at the Fruits mine portal bench, which <br />reaches a maximum height of 60 feet. M_y analysis concludes that <br />this task can not be accomplished. As an.alternative I chose to <br />investigate what facial angle could be sustained in a stable <br />configuration. The analysis determined the maximum sustainable <br />reclaimed backfilled slope gradient to be 2h:ly (26.6°). Based <br />upon the 53 foot stable original bedrock bench cut width determined <br />