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~~ • • illlllllllllllllllll ,.4~J~ STATE O~ CC~~vl9~~~ Roy Romer. Governor ~.. DEPARTMENT OF NATURAL RESOURCES \\,,.~ ,' MINED LAND RECLAMATION DIVISION ~: ; ~ -' i-~, FRED R. BANTA, Director DATE: October 25, 1989 T0: Randy Price \ ~~ FROM: Jim Pendleton ~- ,.-v.t- `~^~ RE: Fruita Mt' Recla, ion Revision - Fruita "1 Bench Stability Pursuant to your request, I have Fruita #1 Rock Fill" included as Reclamation Permit of the Fruita prepared by Grep Lewicki, Colo. P Computer slope stability routine of Kentucky, named "REAME". This widely known and accepted within reviewed the "Slope Stability analysis of the Appendix A within the "Application for 11ine Complex..." This stability analysis was .E. X22804. Mr. Lewicki's analvsis uses a developed by Dr. Yana Huano of the University computer simulation modeling routine is the Civil Enaineerinp discipline. Material samples were collected from the fill by Mr. Lewicki and subjected to laboratory analysis. The actual observed field material density values were used to prepare samples for laboratory shear strength testino. A shear strength value of 0 cohesion and an angle of internal friction of 37 decrees were determined at the field density of 116 lbs. /cu.ft. Dr. HUa n0's conversion technique was utilized to compensate for oversized durable material within the fill, resulting in an effective shear strength of 41 deorees. While this is an empirical correction technique, Fir. Lewicki compensated for its use by performing sensitivity-t we ca]culations usino a range of shear strength values. The slope stability analysis determined that at a reduced facial anole of 2.Dh:1.Ov, the minimum projected slope stability factor of safety encountered fora failure slice of more than 5 feet in thickness was 1.77. When usino the observed lab value of 37 deorees, the minimum safety factor is 1,54. Placing the modeled plane of failure deeper in the fill results in progressively increasing factors of safety. In my opinion, Mr. Lewicki has done a commendable job of analyzing the Fruita #,1 Rock Fill's slope stability. His technique is empirically based, but his approach is reasonable and conservative in his choice of material strength values. I recommend that we accept his analysis as submitted. Further, 1 recommend that we approve the proposed reduction in facial slope angle of the Fruita 1 Rock Fill to 2.Oh:1.Ov. The analysis projects that an acceptable slope safety factor in excess of the required 1.5 will be achieved with the proposed configuration.