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III ~II111~1~11~I III <br />999 <br /> <br />STATE OF COLORA00 <br />Roy Romer, Govei <br />DEPARTMENT OF NATURAL RESOURCES <br />MINED LAND RECLAMATION DIVISION <br />FRED R. BANTA, Dlreetor <br />DATE: July 31 , 1989 <br />T0: Jeff Clayton <br />FROM: Jim Pendleton <br />RE: Cyprus-Or and 4a1 Mine -West Ridge Waste Pile Slope Stability <br />(Permit #C-81-038) <br />I have completed a review of the stability analysis performed far <br />Cyprus-Orchard Valley Coal Mine by CH2M Hill, consulting engineers. This <br />report presents the results of site investigations, sample testing, and <br />stability analysis of the West Ridge Waste Pile. The consultant's report also <br />includes recommendations for remedial modification of the pile. <br />The site investigation, sample collection and testing methods employed by CH2M <br />Hill are in keeping with accepted techniques. The mathematical stability <br />analysis was completed using appropriate material strength values and <br />assumptions determined in the laboratory, the field, or selected from <br />available literature dealing wi1t1 the topic of coal waste disposal. In my <br />opinion, all of the selected material strength values are appropriate for the <br />Cyprus-Orchard Valley situation. <br />The consultant presents several remedial recommendations for treatment of the <br />West Ridge Waste Pile. The over-steepened existing facial slopes should be <br />flattened to 2:1. CH2M Hill observes that fill may be placed as a buttress <br />adjoining the existing toe of the facial slope. They suggest that earthen <br />materials excavated from the west portal bench slump are acceptable for <br />construction of the toe buttress, if placed in lifts no thicker than one foot <br />and compacted to 90% relative compaction, as determined using the standard <br />Proctor test (ASTM D698). The consultant further observes that the fill <br />material available will not be sufficient to affect the 2:1 slope. They <br />suggest excavation of the head of the slope to complete the task. Topsoil <br />cover material will have to be stripped, the waste excavated, and the topsoil <br />cover reapplied. CH2M Hill also recommends the installation of two slot <br />trench toe drains to ensure unsaturated conditions within the waste material. <br />Test pit excavations used to obtain samples were left unbackfilled to <br />accommodate installation of the coarse rock subdrains. Finally, the <br />consultant suggests that "the waste pile reconstruction should be observed and <br />the compaction verified by a qualified registered professional engineer". <br />215 Centennial Building, 1313 Sherman Street Denver, Colorado 80203-2273 Tel. (303) 866.3567 <br />