TABLE B6: GEOTECHNICAL STABILITY SUMMARY SECTION 1 – WEST SLOPE Stability Analyses Strength Parameters Figure Slide Surface Result Comment Static max operation – peak drained strength conditions Stockpile and foundation Drained strength parameters applied using effective stresses based on excess porewater pressures due to fill placement. B11a Foundation – Circular FOS = 1.92 Above FOS = 1.5. Criteria met. B11b Foundation – Base Slide FOS = 2.25 Static max operation – peak undrained strength conditions Stockpile and foundation Combination of drained and undrained parameters applied using effective stresses based on excess porewater pressures due to fill placement. B12a Foundation – Circular FOS = 1.63 Above FOS = 1.5. Criteria met. B12b Foundation – Base Slide FOS = 1.53 Post-earthquake max operation – Undrained conditions Stockpile and foundation Combination of drained and post-earthquake softened undrained parameters applied using effective stresses based on excess porewater pressures due to fill placement. B13a Stockpile – Circular FOS = 1.65 Above FOS = 1.2. Criteria met. B13b Foundation – Base Slide FOS = 1.28 B13c Stockpile – Base Slide FOS = 1.21 EQ max operation 1 in 150 year embankment response Stockpile and foundation Combination of drained and post-earthquake softened undrained parameters applied using effective stresses based on excess porewater pressures due to fill placement. Post-earthquake strength applied from for assessment of yield acceleration B14 Full stockpile embankment ky = 0.04g 0.8 to 4 cm See Table B11 for seismic parameters used for determining co-seismic deformations. Displacements estimates indicate acceptable performance with minor displacement in the 150 year return period case. For the 2500 return period case the displacements of 11 to 47cm for the maximum operation profile would result in minor damage to liners and drains however the risk is limited as the displacement reduce to minor for the depleted closure profile. EQ max operation 1 in 2500 year embankment response B14 Full stockpile embankment ky = 0.04g 11 to 47 cm EQ max closure 1 in 150 year embankment response B15 Full stockpile embankment ky = 0.18g < 0.5 cm EQ max closure 1 in 2500 year embankment response B15 Full stockpile embankment ky = 0.18g 0.6 to 5 cm
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