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1100318 R0T0 0811 JRW1 36 <br />5.3 Analysis of Landslide Cause <br />The analysis of the cause of the Pikeview Landslide included, in part, a slope stability analysis. <br />The purpose of the analysis was to gain insight into the cause of the landslide and the role of <br />various factors affecting the stability of the west wall of Pikeview Quarry. Additional analyses <br />have been performed of other causal mechanisms considered by Exponent and previously <br />advanced by various entities. <br />5.3.1 Slope Stability Analysis <br />A limit equilibrium analysis, based on a two-dimensional geometry, has been performed with <br />Slope/W 2007, a slope stability analysis software available from Geo-Slope International, Ltd. <br />Two principal analyses have been performed: a back calculation analysis and analysis of factors <br />of safety for specified failure surfaces and for critical (i.e., lowest factor of safety) failure <br />surfaces. “Failure surface” is defined as a localized continuous zone within the slope on which <br />the shear strength of the slope material is assumed to have been met or exceeded and on which <br />slope movement is postulated to occur. The search for critical failure surfaces has utilized the <br />Morgenstern-Price and Spencer methods of analysis. These methods are two of the more <br />rigorous limit-equilibrium analyses approaches as they satisfy both force (translation) and <br />moment (rotation) equilibrium. They only differ in the assumption made regarding internal <br />forces within a given set of trial wedges; hence, different minimum factors of safety are <br />obtained using the methods. <br />The inputs into a slope stability analysis include surface geometry, subsurface stratigraphy, <br />groundwater conditions, and subsurface material properties. <br />5.3.1.1 Surface and Subsurface Geometry <br />The ground surface geometry used in the slope stability analysis is based upon topographic <br />survey data for Pikeview Quarry contained in the 2000 Amendment53 and the topographic <br /> <br />53 Permit Application Amendment, Pikeview Quarry, Permit Number M-77-211, Received by Colorado Division <br />of Minerals and Geology on September 22, 2000 (Appendix 14)