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AXOM <br />Henderson 3 Dam Buttress Design <br />January 26, 2018 <br />Page 3 <br />A subsequent laboratory program followed the field program and included a suite of strength and <br />index tests on disturbed and undisturbed samples to supplement the existing material <br />characterization understanding. <br />Materia! Characterization <br />Laboratory testing included index testing and engineering properties testing on disturbed and <br />undisturbed samples collected from the test hole investigation to characterize the materials within the <br />tailings impoundments. The testing focused on characterizing two different tailings layers, the <br />coarser tailings seen in the majority of the tailings impoundment shell and a layer of fine tailings <br />encountered mostly near the foundation. The laboratory program also included characterizing the <br />foundation soils. The material characterization for the Henderson tailings storage facility was updated <br />using the data gathered during the field investigations and laboratory -testing program. <br />Figures 2 and 3 reflect the updated internal geometry for Study Section 2 and 4a based on CPT and <br />borehole information included on the figures. The location of Study Section 2 and 4a are shown on <br />Figure 1. Table 1 below shows the summary of material properties for all material types in 3 Dam. <br />Table 1: Dam Material Properties Summary <br />Geotechnical Review <br />The updated information from the material characterization and field investigation was then used to <br />review the overall 3 Dam stability performance under undrained and post -earthquake loading <br />conditions. Initial evaluations focused on undrained loading stability. Regrading of the original 3 <br />Dam embankment approved under TR -27 (approved by DRMS on April 10, 2017) was performed in <br />Y.IDCM-ROJECTSW fROM1494-HUC R" 5O6t- 3 GAA &1rMM DESIGN LETTER RM" -REV 6_ FMMLDOCX <br />Drained Strength <br />Undralned <br />Strength <br />Post -Earthquake <br />Material <br />Unit <br />Weight <br />CohesionCohesion <br />f <br />} <br />Cohesion , <br />Type <br />(lid <br />c' <br />c' <br />c' <br />(ice) <br />(degrees) <br />(psfl <br />(degrees) <br />(psfl (degrees) <br />Unsaturated <br />117 <br />38 <br />0 <br />38 <br />0 38 <br />Tailings <br />0 <br />Anisotropic <br />Coarse <br />119 <br />0 <br />38 <br />Inclined (CIU') Su/p'=0.50 <br />Sjp' = 0.24 <br />Tailings <br />Horizontal (DSS) <br />Sul '=0.30 <br />Anisotropic <br />Fine Tailings <br />119 <br />0 <br />37 <br />Inclined (CIU') Su/p'=0.35 <br />S�Ip' = 0.10 <br />Horizontal (DSS) <br />Sulp'=0.27 <br />Upper <br />Foundation <br />135 <br />0 <br />28 <br />Sjp' = 0.28 <br />Su/p' = 0.27 <br />Lower <br />135 <br />500 <br />35 <br />500 <br />35 <br />500 <br />35 <br />Foundation <br />Containment <br />135 <br />500 <br />35 <br />500 <br />35 <br />500 <br />35 <br />Berm <br />Geotechnical Review <br />The updated information from the material characterization and field investigation was then used to <br />review the overall 3 Dam stability performance under undrained and post -earthquake loading <br />conditions. Initial evaluations focused on undrained loading stability. Regrading of the original 3 <br />Dam embankment approved under TR -27 (approved by DRMS on April 10, 2017) was performed in <br />Y.IDCM-ROJECTSW fROM1494-HUC R" 5O6t- 3 GAA &1rMM DESIGN LETTER RM" -REV 6_ FMMLDOCX <br />