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Earth Engineering Consultants.LLC <br /> EEC Project No. 1122096 <br /> Signal Resen•oir Improvements <br /> August 5,2015 <br /> Page 12 <br /> • Sand in drain: shear strength parameters were estimated based on our experience with <br /> similar materials and available literature. <br /> Bedrock: permeability estimated based on our experience with similar materials and <br /> determined in the laboratory to be approximately 1.0 x 10-9 cm/sec, so very <br /> conservative approach herein. <br /> Seismic parameters for the site were determined based on our review of available literature <br /> (International Building Code, 2009), software, and design maps (USGS Earthquake Hazards <br /> Program, 2014, USGS U.S. Seismic Design Maps, 2014). Based on the site location of <br /> 39.99846° N, 104.897420 W and a soil classification of Site Class C, a design peak ground <br /> acceleration (PGA) of 0.086 was selected based on ASCE 7-10 criteria. The selected PGA was <br /> used for the stability analysis. <br /> EEC personnel completed the various slope stability analyses for the Signal Reservoir <br /> modification/improvement project, which includes a toe drain on the downstream toe of slope, <br /> (please refer to the civil drawings for location and specific details), and have appended the <br /> diagrams and the setup information used in the Slope / Seepage W computer design program in <br /> Appendix D of this report. <br /> Based on our stability analyses, the critical slip surfaces were found at high water level (Steady <br /> State Figure), end of construction (EOC Figure), rapid drawdown (RDD Figure), and seismic <br /> (Seismic Figure). The safety factors at the critical slip locations are summarized in the table <br /> below along with the approach method and soil conditions (drained or undrained). Detailed <br /> summaries of the analyses are included on the appended criteria setup sheets included in <br /> Appendix D of this report. The minimum safety factors were found to be greater than required by <br /> the State of Colorado Department of Water Resources, Table 5.5. <br /> Summary-of Safety Factors for Slope Stability-for the Signal Reservoir Dam Improvements <br /> Scenario Soil Condition Minimum Safetv Factor Minimum Safety,Factor <br /> Required <br /> Steady Seepage at High Drained 1933 1 5 <br /> Water Level <br /> End of Construction Undrained 2 353 1 3 <br /> Rapid Drawdown(Duncan. Drained and Undramed 1 530 1.2 <br /> Wright and Wong(1990 <br /> Seismic(Pseudo-static) Undramed 1 784 1 0 <br />