Laserfiche WebLink
1 <br />searching method, using a random technique for generating circular surfaces was used. Factors of safety <br />were calculated by the Bishop (critical failure) method. <br />3.2.3.2 material Properties <br />' Specific input parameters for the program include cross-section geometry, material properties <br />(effective cohesion, effective friction angle, bulk density, and saturated density), phreatic surface profile and <br />' earthquake accelerations. The soil parameters used are based, in-part, on laboratory information presented <br />in Appendix D. In the absence of specific laboratory data for any given parameter, consen~ative values were <br />assigned based on engineering judgement and previous experience with materials of similar type. Values <br />' that had to be estimated for this project include unit weights and strengths for the existing embankment <br />material and for the underlying bedrock. The values for the respective parameters used in the analyses are <br />summarized in Table 3.1. <br />TABLE 3.1 <br />SLOPE STABILITY ANALYSIS- MATERIAL PROPERTY SUI1111fARY <br /> <br />1 <br /> <br /> <br />1 <br /> Saturated <br /> Bulk Density Density Cohesion Friction Angle <br />Soil Unit Material c r^ c L- s ~ de <br />1 Tailings 94 100 0 20 <br />2 Embankment 130 130 0 35 <br /> (proposed) <br />3 Embankment 123 130 0 30 <br /> (existing) <br />4 Overburden 125 130 0 32 <br />5 Bedrock 138 138 0 37 <br />' 3.2.3.3 Stability Analysis Results <br />Computer mode] analyses were performed to evaluate the stability of various components of the <br />proposed tailings impoundment facility under static and pseudostatic conditions. Results of the analyses <br />are presented graphically on figures included in Appendix E. The numerical results of the analyses are <br />' summarized in Table 3.2 below. <br />In each case analyzed, the static and pseudostatic factors of safety were greater than 1.2 and l.l, <br />respectively. These values are generally considered to be minimum acceptable values for suitable assurance <br />against slope failure. The results Tor Case 5 indicate factors of safety that are equal to or only slightly above <br />' these standards. However, Case 5 represents conditions that will not persist for any significant period of <br />time. These are the conditions that will exist immediately following completion of the embankment raise, <br />before any tailings are deposited in the impoundment. As soon as any tailings are placed, however, a <br />t <br />10 <br />