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OCT-09-98 02:15P11 FROIA-MIcCULLEYFRI~ILMAN 3034471836 • T-019 P.05/15 F-154 <br />~Tsble 1 <br />Strength and Physical Property Values for Soil, Tailings aad Geomrmbrane lnterface <br />used in the Slope StsbiUty Analysis <br /> Snik Saturated Fliictlon <br />SoU Densfty Density Cohesion Aagle <br />Unlt Material c s d ees <br />1 Tailings 94 100 40 20 <br />2 Embarilarient 130 130 0 35 <br /> (proposed) <br />3 Embankment 123 130 0 30 <br /> (existing) <br />4 Overburden 125 l30 0 32 <br />5 Bedrock 138 138 U 37 <br />6 Tailmg/Geomembrane 100 100 30 17 <br /> Interface <br />7 Soil Buttress above 110 115 0 33 <br /> Tailtn <br />The mitiimiun apparent parameter values, determined Through the reanalysis of the existing condition <br />at the site were then udlizcd in funkier stabihry analyses to assess the factor of safety agaitis[ block failure <br />if the existng exposed tailings were to be removed. This procedure was also used to detetmuie the thickness <br />of surcharge matenal that should be left in place over the existing tailings upstream of the embaiilatient razse <br />to provide a minimum safety factor of 1.2 against failure tinder sonic loading conditions. Figures 2a, 2b, 3a <br />and 3b (static and pseudo static, respectively) present these scenarios graphically and Table 2 summarizes <br />the predicted factors of safety for the respective condtnons. The results show that removal of the tailings <br />would result m instability of the embankment (F.S. = 0.81 for the static condition aad 0 77 for the pseudo <br />static condition). The required surcharge thickness was deteimuied [o be approximately L.5 fr. The smbility <br />of the embankment will be funkier ettltanced as tailings are placed in the new unpoundmrnt. The tailings <br />will be spiggotcd from the new embartlaiirnt so that the itiirial beach will be established iunmcdiately agauis[ <br />the upstream face of the embiuulmirnt raise and the loading from the tailings will act to increase the ballast <br />on The existing underlying wlings upstream of the embankmen[ raise. The impoundment will be inauitaiaed <br />such that the decant pond is toward the back of the impoundment. A revised desibm aoss-section through <br />the impoimdmrnt is shown on Thawing 54G 1-C5. <br />iw6iaeci-xi:vt~veo 3 October 9, 1998 <br />