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• more realistic model. Wkh a coal waste strength of ~ = 35 <br />degrees a factor of safety of 1.6 was calculated. For the lower <br />bound coal waste strength of ~ = 30 degrees a factor of safety <br />of 1.3 was calculated. <br />The results of the analysis showed little sensitivity to variations in unit weight. <br />The computed factor of safety varies with the strength parameters selected. For all <br />conditions modelled (except earthquake) the factors of safety were over 1.5. For <br />~ earthquake conditions the calculated factors of safety are 1.3 or greater. The high <br />water condition is not considered likely. The pile configuration and slope were <br />conservatively designed and the analysis confirms the high relative degree of <br />~ stability. <br />To summarize, the stabilty analysis indicated adequate factors of safety <br />• utilizing conservative strength values and considering earthquake effects. The <br />`I\~ stability is sensitive to water level which was expected for a cohesionless fill <br />U 5 material. Drains have been designed to control groundwater conditions well below <br />~J ~~ <br />~ ~\_ conditions which will seriously affect pile stability. The pile slope, location and <br />/~1 configuration were selected to provide a high degree of stability which was <br />confirmed by the analysis. <br /> <br />Effects of Underground Mining <br />We were provided information on ground motions which are being monitored <br />~ at the site by Mr. Peter Swanson of the V.S. Bureau of Mines. The monitoring <br />program is very preliminary but has detected ground motions which appear to be <br />related to the underground mining. The actual cause or mechanism has not been <br /> <br />• determined. The ground motions attenuate rapidly with distance and the potential <br />16 <br /> <br />