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Geosyntec (> <br /> C011SUIta ntS Page 2 of 2 <br /> Client: Arcosa LWB Project: Permit Amendment Project No.: DE0374 Task: Exhibit S—Structures Evaluation <br /> Written by: Jonathan Gillen Date: 7/8/2019 Reviewed by: Youngmin Cho Date: 7/9/2019 <br /> Approved by: Poppy Staub Date: 7/15/2019 <br /> 4. Distances are approximate and based on measurements from the closest portion of the Structure to the <br /> nearest top of mine pit slope. <br /> Table 2: Estimated Soil Parameters for Stability Anal ses <br /> Unit Weight,y Friction Angle, Cohesion,c <br /> Material' <br /> (lb/ft3) (degrees) (lb/ftz) <br /> Slocum Alluvium 120 29 0 <br /> Sand)' <br /> Pierre Shale 116 32 1,253 <br /> Sabatini et al.2002)2 <br /> Notes: <br /> 1. Slocum Alluvium strength and unit weight properties are assumed based on <br /> guidance from Das 2006. <br /> 2. Pierre Shale unit weight and strength values obtained from Sabatini et al.,2002 <br /> were used for the static and seismic analysis. <br /> 3. Pierre Shale unit weight values are based on the USDOE(2013)published values <br /> for Pierre Shale at a depth of 153 meters at a site in Oklahoma. <br /> 4. Friction angle and cohesion values for Pierre Shale were varied during the <br /> sensitivity analysis.Refer to the Results section for more details. <br /> Table 3: Stability Analysis Results <br /> Analysis Method Static or Pseudo- Critical Surface Calculated <br /> Static Type FS <br /> Bishop Simplified Static Circular 1.3 <br /> Spencer Static Non-circular 2.9 <br /> Spencer Pseudo-Static Non-circular 2.3 <br /> Notes: <br /> 1. The critical surface for the static circular analysis was located wholly within the <br /> Slocum Alluvium layer and did not extent to the mine slope surface. All other <br /> critical surfaces calculated by the model has safety factors greater than 1.5 for the <br /> static circular condition. <br /> 2. Factors of safety calculated for the sensitivity analysis are presented in <br /> Attachment D and are not included here. <br /> Structures Evaluation <br /> Arcosa LWB Plan—Permit Amendment 2019-07-16 <br />