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Bruce Park Landslide Project No. 25-196 <br />Bowie Mine #2 <br />potential slip planes at depths of 4 to 15 feet. Inclinometer 1-5 showed displacement at a depth <br />of about 2 feet. We believe this is likely due to surface freeze-thaw action. The inclinometer <br />data are presented in Appendix C and are summarized in Table 3. The data indicated the slide <br />is moving at about 0.002 to 0.003 inches per day or about 1 to 1.5 inches per year. These <br />estimates are based on limited readings and the rate of movement will likely vary depending on <br />seasonal conditions. <br />Table 3 - Inclinometer Data <br /> Estimated Ground Estimated Slip Plane feet <br />Inclinometer Surface Elevation (feet) Depth Elevation <br />1-1 8199 ND ND <br />1-3 8250 4 8246 <br />1-5 8257 ND ND <br />1-7 8221 15 8206 <br />ND - Non Defined Slide Plane <br />SLOPE STABILITY ANALYSIS <br />Slope stability was evaluated for the assumed topography prior to slope failure and the <br />existing topography. Slope stability was analyzed at the two profile locations presented on <br />Figure 2. Based on our analysis, we believe the landslide was initially triggered as a result of <br />removal of toe support during construction of the reservoir. Based on back analysis of the <br />existing slope and test results, we used a softened (large strain) strength of 18 degrees for phi <br />and a cohesion of 370 psf for the overburden clays. The assumed strength was based on a <br />back analysis of the existing slope configuration to a factor of safety near 1.0. Our experience <br />indicates that laboratory tests typically overestimate the strength of materials within a landslide. <br />Overestimation of strength is typically due to the difficulty in sampling the failure surface during <br />the subsurface investigation, and also landslide movements (large strains) are generally on the <br />order of several feet. During laboratory testing, sample strains are typically very small at less <br />than 0.5 inches. Therefore, a softened or large strain strength was assumed through back <br />analysis as indicated above. Figures 3 and 4 depict the potential slope failures at the shoreline <br />of the reservoir, which is assumed to be the initial slide movement. The slope stability analysis <br />presented in Figures 3 and 4 indicate further unloading (i.e. loss of confinement) of the toe <br />causing the landslide to advance up slope in a series of smaller coalescing landslides. Figures <br />5 and 6 depict the resulting factors of safety for the upper portions of the slope as a result of <br />unloading of the toe. The resulting factors of safety range between 1.05 and 1.06, indicating a <br />marginally stable slope that is prone to failure with increases in groundwater levels. <br />5