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Mr. Jim Stover <br />• J.E. Stover & Associates <br />September 9, 1997 <br />page 2 <br />Remedial Measures: We recommend that the slide mass be removed to undisturbed material and <br />the slope either be reconstructed to its original inclination or flattened. It may be necessary to <br />excavate further into the hillside before more competent material can be encountered to begin <br />the portal entrance. This may result in further sloughing. <br />If reconstruction of the slope to its original inclination is selected, it should be accomplished by <br />benching new fill into the slope. Benches should be constructed about every 8 feet in height and <br />should be at least 4 feet wide. Fill should be compacted to at least 90% of the modified Proctor <br />density at a moisture content within 2% of optimum moisture. <br />If the cut slope is flattened, it will probably require an inclination of approximately 1'l0:1 in <br />order to remove the slide mass. The excavated material could then be used as fill above the <br />multi-plate. <br />Portal Benclt Stabilit~Analysis: The original design conducted by Morrison-Knudsen consisted <br />of two benches, a portal bench and a coal stockpile bench, near the coal seam. Bowie Resources <br />• Limited decided to construct a single bench in this area. We have conducted a slope stability <br />analysis of the reconfigured bench fill slope at the request of the Division of Minerals and <br />Geology. The critical section extends from the portal through the hair-pin turn below the fill <br />slope. The subsurface conditions modeled consisted of compacted fill overlying native soil (CL- <br />GC, as described in our previous reports) which was overlying shale and sandstone bedrock. <br />The material strengths presented below were determined by laboratory testing conducted during <br />our previous studies. The strength parameters for the compacted fill were determined from <br />samples compacted at 85 to 90 percent of the maximum density obtained from modified Proctor <br />criteria (ASTM D-1557). Fill placed during construction was compacted to 95 percent of the <br />maximum density as determined by modifed Proctor criteria. Based on this information, we <br />believe the strength parameters of the fill and hence, the results of the stability analysis to be <br />conservative. The following tabulates the parameters modeled in the analysis. <br />Material Compacted Fill Native Soil (CL- <br />GC) Bedrock <br />Total Unit Weight 125 pcf 125 pcf 125 pcf <br />Angle of Internal Friction 0 degrees 0 degrees 0 degrees <br />Cohesion 2,000 psf to 3,000 psf 4,000 psf 5,000 psf <br />• <br />-rR-o ~ <br />