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- 12 - <br />t <br />1 <br />1 <br /> <br /> <br />lJ <br />Similar analyses were run for the portal of mine entry 1. <br />If the same strength parameters are used for the unexcavated <br />slope under saturated conditions (Plate 9), the minimum factor <br />of safety is F.S. = 1.486. After the excavation, the factor of <br />safety decreases to 1.284. If the ground water is lowered 10 <br />or 20 feet below the surface, factors of safety increase to <br />1.706 and 1.973 respectively. It can be seen that factors of <br />safety at entry 1 are generally more favorable than at entry 5. <br />More favorable topography (flatter slope above the portal) is <br />the reason for the increased stability. <br />The inner three entries (2, 3, and 4) are located in more <br />favorable conditions; the slope above them is much flatter than <br />above the entries 1 and 5. The middle entry 3 was selected to <br />analyze the stability conditions of this slope configuration; an <br />alternative assuming a cut instead of a retaining wall was in- <br />vestigated at this entry as well. <br />Plate 11 shows the back analysis of the existing slope using <br />two sets of strength parameters: one identical to that obtained <br />by testing and one set of lower, arbitrarily selected, strength <br />parameters. The analyses show favorable factors of safety gen- <br />erally higher than 1.5 indicating no stability problems of <br />natural slopes even under saturated conditions. <br />Plate 12 shows the stability analyses for a retaining wall <br />and for a cut which is excavated at a slope of 2 (H) 1 (V). <br />Two important conclusions can be drawn from the analytical <br />results: a cut slope 2 1 provides slightly higher factors of <br />safety than a retaining wall; factors of safety are not con- <br />sidered to be sufficient under saturated conditions for a perma- <br />nent solution. It is evident that the retaining wall can be <br />o`o-xroeo consw.+a.c <br />