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<br />It was assumed, however, that future expansion of thc~ waste piles <br />• will be built using slightly flatter slope angles. As mentioned earlier, <br />the present slopes are on the order of 32° - 35°. It is recommended <br />that future expansion of the waste piles should be built with flatter <br />slopes. Slopes on the order of 35° will not be acceptable as final <br />reclaimed slopes, and from a practical point of standpoint it is prefer- <br />able to build the piles at a flatter angle rather than to modify the <br />constructed slopes later, just for reclamation purposes. Slopes on the <br />order of 2 (H) 1 (V), or about 26°, generally are acceptable for re- <br />clamation purposes. Such slopes frequently have been used at other mines <br />and they generally are stable if materials of sufficient strength are <br />present below and within the pile. These flatter slopes also enable <br />easier placement of soil cover and vegetation for reclamation purposes. <br />This approach was used as a basis for the stability analysis for <br />future expansions. Based on information from representatives of Cotter <br />Corporation, no further waste piles will be placed on steep slopes above <br />the bottom of the valley. Accordingly, the only stability problem <br />• that theoretically could occur is on a pile with the height considerably <br />increased during the future expansion. Such a typical section is presented <br />together with the results of the stability analyses on Plate 13, Results <br />of Stability Analysis - Final Waste Piles, Figure 4. <br />The stability analyses for future waste pile expansions indicate <br />a relatively high factor of safety of 1.51 against surficial failures <br />for the assumed slope configuration. For deep-seated failure involving <br />shear failure through the underlying colluvial soils, facters of safety <br />of 1.42 (dry conditions) and 1.30 (wet conditions) are calculated. Po- <br />tential failure through the waste pile material, just above +;he colluvial <br />soils, shows higher factors of safety (1.90 and 1.76 for dry and wet <br />cases, respectively). In view of the conservative assumptions employed <br />for the shear strength and the extent of the colluvial soils, these <br />factors of safety are considered to constitute acceptable v~ilues for the <br />long-term stability of the future and reclaimed piles. <br />`J <br />- 25 - <br />