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• ~~ : III IIIIIIIIIIIII III • <br />• sss <br /> <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Depanmeni of Natural Resources <br />131 3 Sherman 51., Room 215 <br />Denver, Colorado BO203 <br />Phnne: 1303) 866-3567 <br />FAX: 1303)832-8106 <br />TO: JAMES STEVENS <br />TOM SCHREINER <br />FROM: James Dillie ~~~ <br />DATE: April 14, 1997 <br />MEMO <br />RE: REVIEW OF SLOPE STABILITY ANALYSIS <br />T.H.E. Quarry -Permit No. M-80-244 <br />~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Roy Rome <br />Governor <br />lames 5. Lochhead <br />Execwrve Dueaor <br />Michael B. Long <br />Division Director <br />Per your request, I reviewed the slope stability analysis submitted to the Division on April 1, 1997 <br />by Ken Klco. <br />A geotechnical investigationof the highwall feature at the referenced quarry was completed by [he <br />operator to determine overall stability of the proposed final highwall configuration. <br />Rock samples were collected from various azeas of the mined face and sent to the Colorado School <br />of Mines Earth Mechanics Institute in Golden, Colorado, for analysis. The samples were properly <br />prepared and analyzed for compressive and tensile strength, bulk density, cohesion and internal <br />friction angles. <br />The density, cohesion and intemal friction angle pazameters were input into a slo~stability software <br />program (Galena, Version 2.0) to analyze the stability of the proposed final highwall configuration <br />using the Bishop, Spencerand Sarma methodologies. Circular failures are analyzed by the Bishop <br />method. Non-circular failures aze analyzed by the Spencer method. The Bishop method satisfies <br />only vertical force and moment equilibrium requirements, whereas [he Spencer m~:thod of slope <br />stability analysisis alimiting equilibrium technique which balances vertical force, horizontal force <br />and moment equilibrium requirements. Either method cannot determine whether or not a slope is <br />safe or whether or not the slope will fail, but only that the probability of a failure is reduced if the <br />factor of safety (FOS) is greater than one (1). <br />Factors of safety aze generallycalculatedfnr two site conditions; static loading and dynamic loading. <br />However, the operator elected to run only a pseudostatic stability analysis, since ttlere is a slight <br />chance this azea could experience a seismic event, Also, the operator felt that if the fz.ctors of safety <br />