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<br />~II ~I~II~~I~~~~~II~ <br />STATE Or ~,vi99vi~D0 <br /> <br />MINED LAND RECLAMATION DIVISION <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, CO 80203 <br />303 866-3567 <br />Fn%:303 832-8106 <br />RoY Romer, <br />Gavenar <br />DATE: September 10, 1992 <br />T0: Janet Binns <br />FROM: Jim Pendleton ~,~ <br />RE: Stability gf~the Frui a #1/#2 Mine Highwall & Bench <br />C ermit #C-81-O15) <br />pF' COQ <br />~`~///;;;~~~~8 <br />>•1~4 <br />~ ~H 76 ~ <br />Michael B. Long, <br />Onisian Director <br />I have reviewed the brief summary report submitted by Mr. Greg Lewicki, P.E., <br />on behalf of the American Shield Coal Company. This brief letter report <br />addresses the stability of the highwall above the reclaimed mine bench at the <br />Fruita #1/#2 mines. The report relies entirely upon empirical performance <br />evidence to support its conclusion. <br />Mr. Lewicki presents empirical evidence in the form of photography of the <br />highwall dating from 1974, 1984 and 1989. The evidence demonstrates that the <br />highwall has remained stable and intact over the past 18 years. Only a few <br />very limited blocks of debris have fallen from the highwall onto the reclaimed <br />portions of the slope. This agrees with my personal observations of the mine <br />bench. During the relatively long permitting history of the Fruita #1/#2 <br />mine, the operators have been required to complete several stability analyses <br />of the mine bench and the highwall. As a result, the mine bench was <br />reconstructed. <br />The stability of rock highwalls is extremely difficult to analyze. Contrary <br />to an earthen fill, the ultimate stability of a rock highwall is normally <br />predominantly controlled by the pre-existing planes of weakness, such as <br />faults, joints and bedding. The highwall at the Fruita mine, which blends <br />with the naturally erosion resistant sandstone at the site, is impressive to <br />view. Only the lowest, approximately fifty feet constitutes the excavated <br />highwall. The remainder of the impressive highwall actually pre-existed the <br />excavation. However, very few planes of weakness are evident on the highwall. <br />Ultimately, after all the analyses have been completed and approved, it is the <br />performance of the highwall which demonstrates whether or not the <br />configuration excavated highwall is stable. In the case of the Fruita #1/#2 <br />highwall, time has demonstrated it to be abnormally stable. In my opinion, <br />the empirical evidence presented by Mr. Lewicki documents the performance of <br />the highwall. <br />Ignoring opinions concerning esthetic quality, I am pursuaded that the <br />empirical performance of this particularly highwall has demonstrated that it <br />is stable in its present configuration. Redisturbance of the highwall or the <br />adjacent fill or slopes could reduce their stability through vibration. In <br />addition, this 18 year old highwall has survived several periods of severe <br />frost and abnormal precipitation. <br />