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M03107GE <br />3.0 CUT AND FILL SLOPE STABILITY CONSIDERATIONS <br />Our slope stability analysis was based on the assumption that the <br />foundation soil materials which support the excavation cut and <br />fills are the same or stronger than the proposed stockpile fill <br />material. We assumed that formational material would not be <br />encountered in or near the coal processing facility excavation. <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. We understand that the <br />minimum theoretical calculated factor of safety of 1.3 is consid- <br />ered by the Division of Minerals and Geology as a minimum factor of <br />safety for a slope to be considered. Our stability analysis is <br />based on this understanding of a minimum theoretical calculated <br />factor of safety of 1.3. <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 proposed excavation cut and placed <br />fill slopes were based on the Bishops Method of Slices. This <br />method is based on the assumption that the slope soil mass will <br />fail in a rotation mode on a circular arc plane. In this method of <br />analysis the mass of soil is divided into vertical slices. The <br />forces acting on each slice are evaluated from the equilibrium of <br />the slices; that is, the forces that tend to drive the slice <br />downhill and•the forces that tend to resist the movement of the <br />slice. The equilibrium of the entire mass is determined by summing <br />the driving and summing the resisting forces acting on all slices <br />and comparing these forces. <br />Our slope stability analysis was performed using "Slope Stability <br />Analysis" program by Geosoft computer software. Our slope stabil- <br />ity analysis considered two (2) different cross section locations <br />3efined by Mr. Stover with a total of about 2,500 separate possible <br />failure surface iterations for each cross section to help identify. <br />the potential theoretical slope stability. Our discussions and <br />data presentation are based only on the calculated critical circle <br />which presented the lowest factor of safety against ,failure. Our <br />presentation does not include the results of all of the iterations <br />which resulted in a theoretical factor of safety greater than the <br />lowest factor of safety and therefore were not critical. <br />4 <br />• <br />• <br />~J <br />Lambert anD ~,s,oociateo <br />GONSUl i1NG GEO iEGN NICAL ENGINEERS ANO <br />MATERIAL 1E5i1NG <br />