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" PN; 50363PE <br />December 8, 2005 <br />Page 2 <br />The data developed during the analysis is condensed and used to estimate the forces within a soil <br />mass that tend to drive movement and the forces that tend to resist movement. The ratio of resisting <br />forces to driving forces is often referred to as the "theoretical slope factor of safety" (FOS) which is a <br />somewhat misleading terns to describe this ratio. The ratio is not a true factor o}'safety, but is a <br />useful mathematical characterization of the forces within a soil mass and the associated stability <br />condition of the slope being analyzed. <br />A ratio of less than one (1) indicates that the driving forces within a soil mass are greater than the <br />resisting forces; therefore movement of the slope is occurring. A ratio of one (1 }indicates that the <br />driving forces are equal to the resisting forces, which indicates that movement tivithin the soil can be <br />triggered by only slight increases in the driving forces or slight reductions in the resisting forces. A <br />ratio of greater than one (1) is an indication that the driving forces are less than the resisting forces <br />and the slope is not moving. -Since there are numerous variables and incongruities within most soil <br />masses, a slope is generally not considered as stable until the ratio is 1.5 or greater. <br />We used XSTABL slope stability software to evaluate the stability of computer modeled slope cross <br />sections of select portions of this site. We primarily used the Modified Bishop's Method of slices to <br />analyze the computer modeled slopes. We further evaluated the stability of the slopes on this site <br />using infinite slope stability analysis techniques. The Modified Bishop's Method of Slices evaluates <br />the resisting and driving forces within slices of the sloped soil mass along a theoretical semi-circular <br />failure plane, The semicircular failure plane with the lowest theorefical factor of safety is labeled the <br />critical circle. Our cursory assessment is shown below. <br />TRAUTN <br />A DIVISION OF TRIGONFlg7~3 <br />