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APPENDIX 2.05.4-1 (continued) <br />• Factor of Safety For Dry Slope <br />2:5T3tati cT eai ng <br />p (degrees) FS <br />`~- T:TS <br />33 1.62 <br />31 1.50 <br />29 1.39 <br />27 1.27 <br />As indicated above, factors of safety generally exceed 1.3. The lowest <br />values of friction angle in the above tabulation represent the more clayey <br />materials present in the backfill. Since these soils are likely to have at <br />least a nominal cohesion component of strength, the actual factor of safety <br />would be expected to be somewhat higher than reflected in the above calculations <br />which neglect cohesion. <br />Previous studies have also estimated a pseudo-static seismic coefficient of <br />0.05. Under the same assumptions discussed above, the seismic stability of the <br />• proposed 2.5:1 slope sections is tabulated below: <br />Factor of Safety For Dry Slo e <br />2. Seismic Loa _ing <br />Pseudo~tatic oef~icient = 0.05 <br />H (degrees) FS <br />~- T:T~'f <br />33 1.41 <br />31 1.30 <br />29 1.20 <br />27 1.10 <br />Factors of safety for seismic loading range from 1.5 to 1.1, which exceed <br />the value of 1.0 ordinarily required for earth dams.(2) <br />From the foregoing analysis, it can be concluded that locally-steepened <br />portions of the mine backfill slopes can be graded to 2.5:1 without significant <br />risk of overall instability. <br />• 2 U.S. Army Corps of Engineers, 1914, "Proposed Guidelines for Safety Inspec- <br />tion of Dams" <br />- 346 - (Rev. 5/86) <br />