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Junucn,v 15, 2001' Page 29 <br />4, 2.5 Rounclarti• Conclition,s <br />The vertical boundaries of the model assumed zero-displacement condition simulating <br />symmetry to the west over the hill crest and to the east across the G-Strike spoils. The ground <br />surface was Iree to move as needed and the model base assumed a zero-displacement condition. <br />The initial vertical stresses were gravitational and horizontal stresses assumed lithostatic loading <br />proportional to vertical stresses for Poisson's effect 0''1 -0. <br />4.3 Analysis Sequence and Cases Analyzed <br />Four parameters were varied in assessing the overall spoil stability: slope angle, till <br />height, groundwater level, and the bedding plane strength ofthe Q-Floor mudstone layer. Cases <br />analyzed were based on the combination of these factors. Fill heights and groundwater <br />elevations were relative to the slope toe on the Q-Floor mudstone after mining. The assumed <br />geometry for this case is shown in Figure 17. <br /> <br />au,h%:uri I.,LIr <br />?:onuJ- <br />Po,1. <br />,,, H-4-i Nud.i„nr <br />Figure 17. FLAC Model Cross Section Simulation of G-Pit Spoil Pile with a Slope of <br />37.6" ( I . M:I V) Illustrating; Material Groups and Groundwater Table <br />Hour equilibrium states were computed l6r each spoil slope to determine the stability of <br />the slope for a given groundwater condition. First, the spoil pile was incrementally raised under <br />unsaturated conditions checking stability to obtain the maximum stable spoil height. Next, the <br />model was rerun but with groundwater introduced to examine the effect on stability. Residual <br />strength was then applied to the Q-Floor mudstone bedding plane to simulate long-term <br />conditions and the stability was checked. The final step was to estimate the salch factor of the <br />highest stable slope. <br />The factor ofsatety was estimated by comparing calibrated spoil strength to the strength <br />at the limit ofequilibrium. The limit of equilibrium was determined by gradually reducing the <br />spoil strength until the model did not come to an equilibrium state,. Failure state of the model <br />was assessed using several criteria (including maxinmlm out-of=balance force, maximum <br />velocity, shear strain increment, plastic indicators). The salety factor was computed using <br />Equation 8. <br />Agapito Associates, Inc.