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Mr. Chris Oestreich <br /> June 29,2023 <br /> Page 4 <br /> MATERIAL PROPERTIES <br /> The material index and engineering strengths utilized in this slope stability report are discussed below. <br /> Aggregate Unit <br /> The strength properties for the in-situ Aggregate Unit were based geotechnical laboratory testing,standard penetration <br /> tests(SPT),our experience at similar sites and engineering judgment;the following parameters have been used to <br /> model the Aggregate Unit. <br /> Unit Weight Cohesion C'psf Friction Angle 0'° <br /> (PO <br /> 130 175 35 <br /> Finer Grained Alluvium <br /> The strength properties for the in-situ Finer Grained Alluvial Unit were based geotechnical laboratory testing,standard <br /> penetration tests(SPT),our experience at similar sites and engineering judgment;the following parameters have been <br /> used to model the Aggregate Unit. <br /> Unit Weight Cohesion C'psf Friction Angle O'° <br /> (PSI <br /> 125 200 30 <br /> Bedrock <br /> Bedrock at the base of the mine is daystone. For the claystone bedrock,two potential strength conditions were <br /> considered. These strength conditions are referred to as: 1)peak strength,and 2)residual strength. <br /> Peak strength is the maximum shear strength the claystone bedrock exhibits. The shear strength is made up of both <br /> cohesion(diagenetic bonding)and internal friction. Under short-term conditions for unsheared claystone,peak strength <br /> governs behavior. If a sheared surface or sheared zone is present within daystone because of faulting,slippage <br /> between beds due to folding,past shrink-swell behavior,stress relief,weathering,or from a landslide,the cohesion along <br /> the sheared surface is reduced to zero,and the angle of internal friction is decreased,due to alignment of day minerals <br /> parallel to the shear plane. Under these conditions a claystone exhibits its lowest strength known as residual strength. <br /> Residual strength bedrock occurs in discrete zones,parallel with the sheared surface or zone,whereas fully softened <br /> strength occurs over a broader area(not used in this modeling). Based on data from site investigations,the residual <br /> strength claystone was modeled in a 2-foot thick,weathered layer overlying the peak strength bedrock as follows: <br /> Unit Weight Friction Angle�'° <br /> (pcf) Cohesion C'psf g <br /> Peak= 124 Peak=100 Peak=26 <br /> Residual= 110 Residual=0 Residual= 14 <br /> STABILITY ANALYSES RESULTS <br /> The stability analyses assumed the mining will be per the mine plan. The plan indudes dry mining in the mine cell as the <br /> water level in the cell is controlled by dewatering. Exterior mine slopes in the slurry wall lined cells will not exceed 1 h:1 v. <br /> Setbacks listed in Table 1 (below)indicate the setback from the structure to the mining limits. <br /> The factor of safety shown below is the minimum factor of safety of the conditions listed above. <br />