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M04007MT <br />3.0 DISCUSSION AND STABILITY ANALYSIS <br />This section of the report presents the results of our stability <br />analysis for the originally proposed gob pile embankment, <br />recommended gob pile embankment and existing gob pile. <br />3.1 Slope Stability <br />The stability of any slope is dependent on many factors. Typi- <br />cally the stability of a slope is analyzed by calculating the <br />anticipated gravitational forces that tend to drive the mass of <br />soil downhill and the anticipated internal strength of the soil <br />along the expected plane of failure that will resist the downhill <br />movements. If the driving forces are equal to or greater than the <br />resisting forces then failure is imminent. A theoretical calculat- <br />ed factor of safety of 1.5 is considered by the geotechnical <br />engineering industry as a minimum factor of safety for a slope to <br />be considered as stable. A calculated factor of safety of 1.0 or <br />less indicates that slope movement is imminent or in process. <br />Failure can occur as slow deformation, creep, or as a somewhat <br />spontaneous failure. <br />Factors that have an adverse influence on slope stability can <br />generally be classified as those that increase the stress (driving <br />force) on the system or decrease the strength (resisting forces) of <br />the soil. <br />Our stability analyses of the site slope soil material was based <br />' on the Bishops method of slices. This method is based on the <br />assumption that the slope soil mass will fail in a rotation mode on <br />a circular arc plane. In this method of analysis the mass of soil <br />' is divided into vertical slices. The forces acting on each slice <br />are evaluated from the equilibrium of the slices; that is, the <br />forces that tend to drive the slice downhill and the forces that <br />' tend to resist the movement of the slice. The equilibrium of the <br />entire mass is determined by summing the driving and summing the <br />resisting forces acting on all slices and comparing these forces. <br />Our slope stability analysis was performed using "An Integrated <br />Slope Stability Analysis" by XSTABL computer software. Our slope <br />stability analysis considered several different cross sections with <br />a total of about 1,000 separate possible failure surface iterations <br />3 <br />~Cam6ert anD ~,~,sociates <br />CONSULTING GEOTECNNICAL ENGINEERS AND <br />IAA TERIAL TESTING <br />