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.._ REGES'UE~ OCT 2G 1983 Pnc~ ~/7 W,,,., ~~ APPENDIX B MINED LAND RECLAMATION DIVISION Stability of Fill Slopes at Mine Site Colo. Dept. of Natural Resources An analysis of the fill slopes on the project was made on the basis of criteria set forth in the University of Kentucky publication "Stability of Spoil Banks and Hollow Fills Created by Surface Mining" by Yang H. Huang, Basic assumptions after revievr of the University's findings and an analysis of conditions existing at the site are as follows: 1, Seepage within the fill bench should not be a problem, a, Formations dip arovay from the slope, b, Adjacent mines will relieve or drain seepage from the potential aquifer b elow the coal seam, c. Site drainage will proclude accumulation of water, d, Area is very dry ( 12 in. rainfall/year) 2, Values for cohesion and the internal angle of friction were assumed from testing set forth in the publication, that is: c = 200 psf ~ = 30° a, Compaction and construction control will improve these factors on slopes constructed for the mine, b, Existing spoil is quite hetrogeneous; thus, taking a representative sample becomes a question of judgement, c, It was stated that these factors are conservative for design purposes. d, An analysis of mine spoil should be made after the mine is in operation and the waste disposal fill re-analyzed accordingly (% co a1, % rock, % shale, etc,), 3. Soils on the gulch are very thin, with numerous sandstone outcrops protruding, It was therefore assumed that potential failure will occur in the fill, 4. An underdrain system has been shovm under the waste disposal area to prevent buildup of water behind the toe dike. A sketch of the system is enclosed, Essentially the mine site has been designed to leave existing marginal fill slopes in their present condition. The spoil has