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E Slope Stability Analysis <br /> June 29,2018 <br /> Page 4 <br /> 6.0 STABILITY ANALYSIS <br /> A slope stability analysis was performed on Profile A-A', a topographic profile selected from the afore- <br /> mentioned Overlot Grading Plan by AEI. This topographic profile starts 100 feet south of the Vail Valley <br /> Ranch southern property boundary and ends at the southern shoulder of US Highway 6 in the eastern portion <br /> of the site(Figure A.4).According to the grading plan,the site will maintain a consistent 2h:1 v slope in the <br /> southern portion of the site while the northern portion of the site will be relatively flat. Profile A-A' was <br /> intentionally chosen in a location where the topographic relief of the 2h:Iv slope reaches its largest value <br /> of 69 feet near the southern property boundary. <br /> SLIDE, a two-dimensional limit equilibrium modeling software developed by Rocscience, was used to <br /> perform the analysis. It applies a Mohr-Coulomb strength relationship to evaluate slope stability. Bishop's <br /> procedure for analyzing non-circular and circular critical slope failures, which satisfies moment equilib- <br /> rium, was employed. <br /> Based on our test pit investigation and drilling program,WJE defined four main material types to use in the <br /> model including overburden silt/silty sand, sand, clay,and clast-supported gravelly cobbles in a sandy ma- <br /> trix.Three material configurations representing different conditions observed in the field were modeled: 1) <br /> Overburden overlying clast-supported gravelly cobbles, 2) overburden overlying clast-supported gravelly <br /> cobbles with a sand layer, and 3) overburden overlying clast-supported gravelly cobbles with a clay layer. <br /> Although the thickness of sand and clay only reached a maximum of 2 feet and 6 inches, respectively, in <br /> the field, we have conservatively chosen to use thicknesses of 4 feet and 2 feet. The material parameters <br /> were estimated based on our understanding of geological site conditions and experience with similar mate- <br /> rials in the area.Table 1 quantifies the unit weight,friction angle,and cohesion estimated for each material. <br /> We conservatively assumed zero cohesion for all materials, although it is possible that the clay layer and <br /> portions of the clast-supported gravelly cobble material possess cohesion. <br /> TABLE 1 - Slope Stability Material Parameters <br /> Material Type Unit Effective Friction Cohesion,psf <br /> Weight,pcf Angle((D ), <br /> Silty soil 120 32 0 <br /> Sand 130 35 0 <br /> Clay 125 28 0 <br /> Clast-supported <br /> gravelly cobbles 135 38 0 <br /> in a sandy matrix <br /> As previously discussed, D&A encountered gypsum in three out of seven of the boreholes they drilled. In <br /> D&A TH-5,the top of gypsum was logged at an estimated elevation of 6458.5 feet.WJE did not encounter <br /> gypsum during drilling despite reaching estimated terminal depth elevations of 6427 feet, 6423.5 feet, and <br /> 6429.5 feet in TH-1, TH-2, and TH-3, respectively. The elevation of the top of the Eagle Valley Evaporite <br /> is known to be irregular due to its soluble nature. In addition,as a bedrock unit,the Eagle Valley Evaporite <br /> has significantly higher strength parameters compared to the material types listed in Table 1. Conserva- <br /> tively,the Eagle Valley Evaporite was not included in our analyses. <br /> Both non-circular and circular failure surfaces were modeled.For Material Configuration 1,a circular fail- <br /> ure surface was used. Additional circular surfaces were modeled to check the stability of deeper failure <br />