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3.A Infinite Slope Failure <br />The factor of safety against infinite slope failure of cover materials was calculated under worst case scenario <br />(saturated cover soils). The angle of slope used is based on a closure grade of 6 (Horizontal) to 1 (Vertical) <br />and consistent with designs. The calculated factor of safety against failure of soil cover materials placed over <br />waste is 4.3 under static and saturated conditions. Factor of safety was calculated using the equation given <br />below. <br />Scenario One <br />Scenario Two <br />Factor of Safety = <br />Where: <br />3.B Circular Slope Failure <br />c + h(Ysat - YO cos tamp <br />Ysat h since cow <br />c = Cohesion <br />a = Slope <br />h = Thickness of cover <br />Ysat = Saturated unit weight of soil <br />Yw = Unit weight of water <br />cp = Internal friction angle <br />By inputting slope geometry and soil strength values into the slope stability program Geo- Slope, strength and <br />geometry values can be easily changed in order to help assess the factors of safety of proposed slopes under <br />various conditions. The computer program is a comprehensive slope stability tool that uses a variety of <br />methods for calculating the factor of safety. For this particular analysis, the "Simplified Bishop" and "Mohr - <br />Columb" methods were used to calculate the factor of safety. Slope configurations used were obtained by <br />cutting horizontal cross sections through existing topography at the north end of Cell A, including bedrock <br />outcrops located north of Cell A and above the White River. Two slope stability analyses scenarios were used. <br />The first scenario assumes that a petroleum contaminated soil (PCS) waste fill slope will be constructed atop <br />the natural ground surface located on a nearly flat terrace. Waste fill has been assumed to be constructed to a <br />6(H):1(V) slope. This stability analysis was conducted to determine the internal stability of waste materials <br />placed to a maximum 25 foot height. Based upon analysis results, the minimum theoretical factor of safety <br />regarding internal failure of the waste materials under static conditions is 1.83. Slope stability analysis data <br />and a cross section showing the failure slip surface of this scenario are presented on Figure 1. <br />The second scenario assumes that the cell and waste fill materials will be constructed to grades shown on the <br />design plans. Based upon the plans, the cell will be cut into existing soils and into underlying bedrock to a <br />slope configuration of 3(H):1(V). At cell closure, the waste will have been placed vertically to a maximum of <br />8718 Slope Stability Analyses Page 2 <br />