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Memo to Tom Schreiner <br />Slope Stability Analysis <br />November 21, 2003 <br />Permit No. M-1978-056 <br />• The pertinent geotechnical properties of the strata are as follows: <br />Friction <br />Overburden 115 pcf 50 psf 24 degrees <br />Sand and Gravel 126 pcf 0 35 degrees <br />Fully Softened Shale 125 pcf 0 26 degrees <br />Residual Strength Shale 125 pcf 0 14 degrees <br />Shale Bedrock 125 pcf 700 psf 26 degrees <br />The safety factors against failure when the likely location of the phreatic surface is analyzed aze <br />between 1.08 and 1.14. Given the temporary nature of the excavated pit slopes and the conservative <br />nature of the analyses, these low safety factors aze considered mazginal. <br />Conclusions: <br />1. In addition to providing the required information described in this memo, the Operator should <br />consider establishing lazger setbacks from the manmade structures than the 10 feet currently <br />proposed and should reconsider the efficacy of making an enforceable permit commitment to <br />maintain the excavation slope at no steeper than 1.25H:1 V. <br />2. The Operator should backfill the excavated pit slopes in the vicinity of manmade structures to <br />the final reclamation grade as soon as possible following mining in a particulaz area. With the <br />responses to the other issues discussed in this memo, have the Operator provide a backfilling <br />and grading plan, which can be flexible, but that does ensure that the mazginally stable <br />excavated slopes will not persist for an undue period of time. <br />enclosure(s) <br />cc: Carl Mount, DMG (via email and w/o enclosures) <br />c:~acs~L.OANER MP.CHINE~My Documents~D~sham stability memo.doc <br />