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Figure 6.4: Changes in undrained cohesion for different slope angles .................................... 70
Figure 6.5: Sensitivity plot ....................................................................................................... 71
Figure 6.6: Effect of varying drained angle of shearing resistance (ϕ′) ................................... 72
Figure 6.7: Effect of varying the tangent of angle of shearing resistance ................................ 73
Figure 6.8: Effect of varying bulk unit weight and angle of shearing resistance in drained
conditions ................................................................................................................................. 74
Figure 6.9: Varying bulk unit weight in undrained conditions................................................. 75
Figure 6.10: Varying bulk unit weight in drained conditions................................................... 76
Figure 6.11: Varying bulk unit weight for drained conditions with phreatic surface .............. 77
Figure 6.12: Location of phreatic surfaces ............................................................................... 78
Figure 6.13: Factors of safety when varying angle of phreatic surface.................................... 78
Figure 6.14: Failure surface when phreatic surface angle <10° ............................................... 79
Figure 6.15: Failure surface when phreatic surface angle >10° ............................................... 79
Figure 6.16: Sensitivity plot (GEO-SLOPE, 2014) .................................................................. 80
Figure 7.1: Typical tailings dam cross section ......................................................................... 81
Figure 7.2: Case study embankment in SLOPE/W (2007)....................................................... 81
Figure 7.3: Critical failure surface with sandstone foundation and zero effective cohesion.... 82
Figure 7.4: Critical failure surface of upstream slope with no apparent cohesion and at current
tailings pond level ..................................................................................................................... 84
Figure 8.1: Soil uncertainties flow chart (after Lacasse and Nadim, 1996) ............................. 88
Figure 8.2: Deterministic and statistical descriptions of a soil property .................................. 90
Figure 8.3: Normal and lognormal distribution curves (US ACE, 1997) ................................ 90
Figure 8.4: Normal probability distribution function (US ACE, 2006) ................................... 91
Figure 8.5: Area under the standard normal distribution curve ............................................... 92
Figure 8.6: Comparison of two situations with different means and distributions of factor of
safety (Christian, Ladd, Baecher, 1994) ................................................................................... 93
Figure 8.7: ANCOLD (1994) societal risk guideline (McDonald, 2008) ................................ 95
Figure 8.8: A portion of an event tree ...................................................................................... 98
Figure 8.9: Fault tree analysis vs event tree analysis (Taguchi, 2014). .................................... 98
Figure 8.10: Fault tree for slope failure of a uranium mine tailings dam. ................................ 99
Figure 8.11: Lognormal probability density function of factor of safety .............................. 100
Figure 8.12: Transformed probability density function.......................................................... 101
Figure 8.13: Baseline case 1 in drained conditions ................................................................ 101
Figure 8.14: Baseline case 1 in undrained conditions ............................................................ 104
Figure 8.15: Probability of failure versus number of trials .................................................... 107
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