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- 11 - LJ Gated in most unfavorable topographic and geotechnical con- . ditions and it should be eliminated if the number of mine entries is reduced. Entries 2, 3, and 4 are located in a more favorable topography assuming that the portal cuts remain at approximately the same locations as indicated. Future changes '; in the bench elevation and the cut locations could of course it change these conclusions. Entries 1, 3, and 5 were selected for slope stability analy- ses; the method of analyses is decribed in the Appendix A. Plate No. 7 shows a back analysis (a back analysis is the stability analysis which assumes the natural slope without any excavation; it either assumes the safety factor equal to one or it calcu- lates the safety factor for known strength properties) of the slope at mine entry 5 prior to any excavation. The back analysis ~: shows that if we assume the soil strength parameters as they were obtained by the soil testing and "saturated" conditions with ,. ground water coinciding with the topographical surface, the minimum factor of safety is on the order of 1.0 (0.985 exactly). This confirms the earlier discussed condition of marginally stable slopes under saturated conditions. It also means that no unsupported excavations should be performed an such a steea slope. Results of further analyses of the same portal are shown on Plate 8. A first analysis was run assuming that a cut was ex- i cavated (saturated conditions, Case 5-2). As it could be ex- pected,the minimum factor of safety is slightly lower than in the back analysis (0.932); it is evident again that the exca- ', vation is not feasible. Two further cases (5-3, 5-4) assume the ground water lowered to 10 and 20 feet below the surface. Mini- ; mum factors of safety increase to F.S. ~ 1.321 and 1.535. For fully drained conditions, the factor of safety increases to 1.758. t•7e feel that for the permanent solution, safety factors • higher than 1.5 should be obtained. oo+~ro.ocauunq..c