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~~ <br />MainCressonSlopeEvaluation AdrianBrown <br />,~ <br />7.2.2 Kink Band Analysis <br />As noted above, it is possible that a shear zone or kink band could form in the Main Cresson Mine walls, <br />in particular the east wall (the highest wall). In order to include this possibility in the analysis, the <br />parameters have been re-computed with kink-band formation in mind, using the theory of Ladanyi and <br />Archambault (1970). The parameters are as follows: <br />Dry slope <br />Effective stress cohesion {c) = 0.3 MPa (41 psi) <br />Effective stress friction (~) = 46° <br />Maximum slope height (H) = 700 feet <br />Material density (y) = 1431b/cult <br />The dimensionless Hoek and Brown chart parameter is computed as follows (adjusting for unit <br />conversions): <br />c / ['y H tan ~] _ (41 lb/in2 * 144 in2/ftZ) / [ 1431b/ft3 * 700 ft * tan(46°)J = 0.057 <br />The analysis process is also illustrated in Figure 21. The chart parameter value is used to draw a radial on <br />the Circular Failure Chart No. 1 (for dry slopes) from Hoek and Bray (1971), p. 234. The points where <br />this radial intercept the slope angle curves produce values of the variable tan ~ / F (where F =Factor of <br />• Safety). The Factor of Safety can be found from: <br />F = tan ~ / [tan ~ / F (from chart)] <br />The result of the analysis are indicated on the figure, and the computation of the factor of safety is <br />performed as follows: <br />Slope angle tan ~ / F ~ tan ~ Factor of safety <br />80° 1.24 46° 1.036 0.84 <br />70° 0.97 46° 1.036 1.07 <br />60° 0.78 46° 1.036 1.33 <br />50° 0.63 46° 1.036 1.64 <br />Based on these values, the factor of safety against overall collapse of the slope along a shear zone or kink <br />band would appear to be reasonably high, and indicate that the factor of safety against this style of failure <br />exceeds 1.3 fora 60° slope, the steepest slope which can be excavated. <br />• <br />1385D.980612 57 <br />