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page two <br /> 28 November 2012 • <br /> M12058MT <br /> - unsaturated, as constructed, <br /> - full reservoir water level, saturated embankment steady state <br /> from the phreatic surface within the embankment, and <br /> - rapid draw down, saturated embankment, reservoir drained. <br /> Rapid draw down is the most critical embankment condition. <br /> This occurs when the reservoir is full from the impounded water <br /> and the reservoir is drained rapidly so that the embankment soil <br /> materials remain saturated and there is no upstream water within <br /> the reservoir. Because rapid draw down is the most critical <br /> embankment condition and the most likely instability this is the <br /> scenario that we assessed. The other embankment conditions will <br /> be more stable than the rapid draw down scenario. <br /> The stability of any slope is dependent on many factors. Typi- <br /> cally the theoretical stability of a slope is analyzed by <br /> calculating the anticipated gravitational forces that tend to <br /> drive the mass of soil downhill and the anticipated internal <br /> strength of the soil along the expected plane of failure that <br /> will resist the downhill movements. If the driving forces are <br /> equal to or greater than the resisting forces then failure is <br /> imminent. A theoretical calculated factor of safety of 1. 5 is <br /> considered by the geotechnical engineering industry as a minimum <br /> factor of safety for a slope to be considered as stable. A <br /> calculated factor of safety of 1.0 or less indicates that slope <br /> movement is imminent or in process. Failure can occur as slow <br /> deformation, creep, or as a somewhat spontaneous failure. <br /> Factors that have an adverse influence on slope stability can <br /> generally be classified as those that increase the stress <br /> (driving force) on the system or those that decrease the strength <br /> (resisting forces) of the soil . <br /> Our stability analyses of the embankment slope was based on the <br /> Bishops Method of Slices. This method is based on the assumption <br /> that the slope soil mass will fail in a rotation mode on a <br /> 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 /> lanndmimbAssuadez <br /> CONSULTING GEOTECHNICAL ENGINEERS <br /> AND MATERIAL TESTING <br /> Appendix 2.05.3(4)-6 Page 3 December 2018(TR-19) <br />