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3. 0 BACKGROUND INFORMATION <br /> 3. 1 COAL REFUSE DISPOSAL FACILITY <br /> The existing coal refuse disposal facility was studied in <br /> detail by Morrison-Knudsen Company in 1977. In their studies, the <br /> character of the coal refuse and its physical properties were <br /> evaluated and a series of stability analyses was performed to <br /> verify the stability of the existing piles and to estimate the <br /> stability of the future facility extensions or the stability of a <br /> new facility. <br /> The results of their testing confirmed that the coal refuse <br /> material can be classified as well-graded, silty gravel (GM) in <br /> accordance with the Unified Soil Classification System. <br /> Compaction tests performed on this material indicated maximum dry <br /> densities between 88.2 to 93.4 pcf. Compaction tests performed by <br /> Morrison-Knudsen were modified to yield non-standard compactive <br /> energies and cannot be used for direct comparison with recent <br /> testing. They also found that the mean dry density of the in situ <br /> waste is on the order of 80 to 82 pcf. Morrison-Knudsen further <br /> performed triaxial tests to evaluate the shearing resistance of <br /> the waste. The tests were performed on samples which were com- <br /> pacted to 80 pcf. An angle of friction 0 = 26 degrees and <br /> cohesion C = 1, 100 psf was evaluated from triaxial testing. A <br /> drained triaxial shear test indicated an effective stress <br /> friction angle of 39.6 degrees, with' zero cohesion. <br /> Stability analyses of both the existing and proposed refuse <br /> pile indicated acceptable factors of safety, higher than 1.5 for <br /> both the existing refuse pile configurations with slopes 38 de- <br /> grees and for the proposed pile, with a slope equal to 27 degrees <br /> (approximately 2 (H) : 1 (V) ) , for a slope height of 300 feet. <br /> As the current MLRD regulations require the maximum slope of <br /> the waste disposal facility not to exceed 2 (H) : l(V) , the future <br /> extensions of the waste diposal and the new waste disposal <br /> facilities have been designed in slopes not exceeding 2 (H) . <br /> 1 (V) . <br /> In their Permit Application, Mid-Continent proposed to <br /> transport the coal refuse from the wash plant to the disposal <br /> site by a conveyor belt. A dozer spreads and compacts the refuse <br /> in layers not exceeding 12 inches in thickness . <br /> 3. 2 ROCK TUNNEL DISPOSAL FACILITY <br /> The character and physical properties of the rock tunnel <br /> waste were studied in detail by Lincoln DeVore in 1979. Lincoln <br /> DeVore also performed the required stability analyses and re- <br /> 2 <br /> GEO•MYDRO CONSULTING,INC. <br />