2019-11-12_REVISION - M2004044 (13)

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N TETRA TECH Updated Tucson South Proposed Gravel Mine Slope Stability Analysis November 8 2019 Table 1:Material parameters used in the slope stability models6. Material Parameters Material Moist Saturated Effective Effective Unit Unit Cohesion Friction Weight Weight c' Angle 4)' (pcf) (pcf) (psf) (degrees) Overburden 114 126 50 28 Sand & Gravel 130 137 0 35 Weathered Claystone Bedrock 124 134 0 14 (residual strength) Claystone Bedrock (peak strength) 124 134 100 28 Mud Lens 114 126 50 28 Slurry Wall 110 122 0 0 Reclamation Slope Fill 119 126 25 26 pcf=pounds per cubic foot;psf=pounds per square foot A seismic analysis was also performed for each of the sections described above as required by the DRMS. The seismic analysis accounts for the effects of horizontal acceleration experienced during an earthquake. The horizontal acceleration used was 0.067 g. The value was obtained from a U.S. Seismic Design map of the areas. The U.S. Seismic Design Maps program considers the soil classification and location of the site. For the Tucson South site, Site Class D—Stiff Soil was used. Other applicable DRMS requirements that were used are as follows: • The minimum factor of safety for the static analysis is 1.5. • The minimum factor of safety for the seismic analysis is 1.3. The scenarios were modeled with entry/exit geometry for currently proposed setbacks. The setbacks were adjusted as needed to reach the minimum required factor of safety in each case. 4.3 MODEL RESULTS The model results are given in Table 2. Detailed model results and a comparison with previous slope stability modeling is included in Appendix A. The setbacks listed are the minimum setbacks required. Resulting sections from the model are presented in Figures. It should be noted that the setback requirement for model J is dependent on the reduced phreatic surface in the soils behind the mine cut, care should be given to the dewatering process chosen in the South Pit. 9 U.S. Geological Survey. (2017, July 27). U.S. Seismic Design Maps. U.S. Geological Survey. TETRA TECH r_