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'iiATl. OI CfJI QIIAII/r 4rt nnrrl~U i/.'d M, r:••vm.,. <br />DEPARTMENT OF NATURAL RESOURCES <br />D. Monte Pascoe, EKecu live Dir eelor <br />I~11NEU LAND RF.I:LAI~IA'I'ION <br />423 Centennial Building, 1313 Sherman Street <br />Denver, Colorado 80203 Tel (303) 839-3567 <br />T0: <br />FRnT1: <br />SIIAJECT <br />October 27, 1980 <br />Marion Dodson/Paul <br />Jim Pendleton <br />Slope Stabili Ren egarding <br />Slone Carbon est Mine. <br />III IIIIIIIIIIIII III <br />999 <br />David C. Shelton <br />Director <br />Parking Lot Embankment at Western <br />'.•iy review of the Slone stability reoort has dete mined that something is <br />in error. The consLl7tants safety factor calculations are much to ]Tigh for the <br />existing situation. I do not have access to the reference sited by Dan Rine!Tart, <br />who prepared the analysis. !1o1~'ever, I sunnect that an error exists in two parameters; <br />the shear strength testin,^_, and its utilization within the safety factor calculations. <br />Normally, the laboratory prepares a range of shear tests at different confining <br />pressures. graphical analysis of the testing data is then prenared,plotti.ng normal <br />stress ( 6 ) versus shear strength ( T ) allows the determination of <br />the cohesion intercept (c) and the angle o.f internal friction ( ~ ). <br />~~~ <br />L ~ ~ <br />~ c <br /> <br />Dan F.inchartnotcs that the labor.1to1y testing was flawed, but he sumes a value for <br />cohesion of twenty-eight hLUldred pounds per square foot. iwty experience suggests <br />that a proper value for the cohesion intercept of from one hlmdred Hounds per square <br />foot: to five hLlndred Hounds per square [DO[, and twenty to thirty degrees for <br />the angle of internal friction (~ would have heen more appropriate. Use of more <br />appropriate values will undoubte lyTCduce calculated safety factors to within ex- <br />pected normals. i expect in this case values slightly in excess of unity. Under <br />the existing regulations, Sec. 4.03.1(3)(d)(ix) such a parking lot (haul road) <br />embankment must obtain a safety factor of L 25 or greater. <br />I suggest that you request the consultant submit completed materials testing <br />and a graphical representation of the testing data, as well as a thorough report <br />including a description of••11is analytical technique. It would be helpful if he <br />would send a Xexrox copy of the appropriate reference. <br />mab <br />