Laserfiche WebLink
• <br />Doc Date:12/11/2001 <br />III IIIIIIIIIIIII III <br />sss <br />APPENDIX 3.5-8 <br />PROCEDURE FOR CALCULATING FACTOR OF SAFETY <br />FOR ROADWAY CUT AND FILL SLOPES <br />• <br />~_ <br />• <br />The first step in performing a slope stability analysis is to determine the <br />geometry of the slope and a probable failure surface. The geometry of the slopes were <br />determined by surveying cross sections of rood cuts and fills aT the mine site. From <br />these cross sections, representative "worst case" examples of a road fill and road cut <br />were selected to do a slope stability analysis. The profiles were reproduced os <br />accurately as possible on drawings at a scale of I" = 20'. A circular failure surface <br />was constructed for each case to provide the greatest amount of weight with the least <br />amount of resisting forces. This included a loaded haul truck in the case of a road fill. <br />The sliding mass, was then divided into five slices as shown.in Tables I and 2. The <br />parameters which were defined for each slice are the angle a of the base of each <br />slice, the vertical stress on the base of the slice (given by the product of the vertical <br />height h and the unit weight y of the rock and soil), the uplift water pressure <br />(which was considered negligible) and the additional weight exerted by the haul truck <br />(T). Constant values such as cohesion and density of the material were estimated using <br />Table 3. After the slice parameters were defined, the values of X, Y and Z were <br />calculated for each slice using the formulas shown in Table 4. The water force (O) and <br />haul truck weight (T) were added to The sum of Z (the sum of the components of the <br />weight of each slice acting parallel to the failure surface). An initial estimate off = <br />I.0 was assumed for the factor of safety and used in the factor of safety equation. If <br />the difference between calculated (F) and the assumed (f) factor of safety is greater <br />than 0.001, the calculated factor of safety is used as a second estimate of f for a ne w <br />factor of safety calculation. This process is repeated until the difference between <br />successive factors of safety is less than 0.001. After the final factor of safety has <br />been calculated it is used to satisfy two conditions in The Bishop analysis. Condition I <br />_ ensures that the effective normal stress on the base of each slice is always positive. <br />Condition 2 ensures that the analysis is not invalidated by conditions which can <br />' sometimes occur near the toe of a slope in which a deep failure surface has been <br />assumed. <br />Revised 3/82 3.5B-1 <br />