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r- <br />~. <br />. <br />3.0 BACKGROUND INFORMATION <br /> <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 />_ <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 /> *_ the T.~<~~ dry density of the in situ <br />testing. They also found tr= <br /> _ <br />n the order of ~:: _~ ~~~acf,. Morrison-Knudsen further <br />waste is o <br /> _ <br />performed triaxial tests to" evaiuaL~B 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 ~ = 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 propcsed refuse <br /> pile indicated acceptable factors of safe*_y, higher than 1.5 for <br /> both the existing refuse pile configurations with slopes 38 de- <br /> gtees and for the proposed pi 1 e, with a slope equa 1 to 27 degrees <br />• (approximately 2(H) 1(V)), for a slope height of 300 feet. <br />' As the current MLRD regulations require tie maximum slope of <br /> the waste disposal facility not to exceed 2(H) 1(V), the future <br /> extensions of the waste diposal and the new waste disposal <br />r 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 ?2 inches in thickness. <br />~: <br />3.2 ROCK TUNNEL DISPOSAL FACILITY <br />j'~ The character and physical properties of the rock tunnel <br />~ <br />`~ waste were studied in detail by Lincoln DeVore in 1979. Lincoln <br /> DeVore also performed the required stability analyses znd re- <br />l <br />L <br />1 =, _ <br />