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Mr. Phillip Courtney <br /> February 15, 2023 <br /> Page 4 <br /> MATERIAL PROPERTIES <br /> The material index and engineering strengths assumed in this slope stability report are discussed below. <br /> Overburden <br /> The strength properties for the in-situ overburden were based on our experience at similar sites and engineering <br /> judgment; the following parameters have been used to model the overburden. <br /> Unit Weight Cohesion C'psf Friction Angle V <br /> c <br /> 114 50 27 <br /> Alluvial Sand and Gravel <br /> The sand and gravel is generally a fine to medium-grained sand overlying a fine to coarse grained sand that is typically <br /> medium dense and locally gravelly. The alluvial sand and gravel unit was modeled as follows: <br /> Unit Weight Cohesion C'psf Friction Angle(P' <br /> c <br /> 129 0 35 <br /> Bedrock <br /> Bedrock below the alluvium is claystone. Claystone is generally a weak bedrock. For the claystone bedrock, two <br /> potential strength conditions were considered. These strength conditions are referred to as: 1) peak strength, and 2) <br /> 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 claystone 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 clay 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 1-foot thick, weathered layer overlying the peak strength bedrock as follows: <br /> Unit Weight <br /> (pc fJ Cohesion C'psf Friction Angle (P' <br /> Peak = 126 Peak = 100 Peak =25 <br /> Residual = 110 Residual =0 Residual = 16 <br /> Soil-Bentonite Slurry Wall <br /> The proposed slurry wall will consist of a mix of the overburden, alluvial sand, and imported bentonite. The resulting mix <br /> will produce a non-Newtonian fluid with some shear strength characteristics based on a reduced friction angle of the <br /> overlying overburden. Based on engineering judgment, we modeled the slurry wall as follows: <br /> Unit Weight Friction Angle (P' <br /> (pcfl Cohesion C psf <br /> 115 0 0 <br />