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• J.E. Storer & Associates, Inc. Slope Stability Analysis, Road Fill and Portal Fill Roadside Mine, Cameo, CO January 26, 2007 Page 2 benching (4 feet horizonffiI into the native slopes for every 15 feet vertical fill height) be accomplished. We have further assumed that the designed drains, both surface and subsurface, performed with moderate efficiency. The proposed fill materials were subjected to laboratory testing for classification purposes. The two "extreme" samples (No's. 1 and 3) are presented. The samples were subjected to Modified Proctor Testing (ASTM D-1557) as the lower optimum moisture will be a distinct advanffige when silt or clayey fines are encountered. The additional sheaz strength will also be an advantage. SLOPE STABILITY ANALYSIS Slope stability calculations were performed on the proposed embankrrrents. The sffibility analysis addressed the individual slope and the "global" condition of the entire embankment. The analysis was performed using the PC software SLOPFJW module within GeoStudio 2004, Version 6.20, Geo-Slope International LTD, Calgary, Alberta, Canada. The analysis utilized the Limit Equilibrium Theory for the factor of safety, incorporating four methods. Fellenius or Ordinary Method Bishop Simplified Method Janbu Simplified Method Morgenstern-Price Method = Moment Equilibrium = Moment Equilibrium = Foree Equilibrium = Moment and Force Equilibrium The Morgenstern-Price Method, incorporating both Moment and Force Equilibrium Theory, is generally considered to be the more "accurate" of the four methods, but all methods must be compared due to different modeling assumptions. The Fellenius or Ordinary, Bishop Simplified, and the Janbu Simplified Methods are commonly utilized in older slope stability softwaze. No seismic coefficient was assumed in these calculations. Several models were assumed for the existing and proposed embankments. Our final model assumed that the stonnwater retention pond conffiins 6 feet of water, part of a temporary free water surface in the lower sandy gravels and cobbles of the Ancient Colorado River Terrace, ht addition, the soils in the embankment are assumed to be very moist. A free water surface was assumed to develop along the "French Drain" alignment at and west of the Old Portal beneath the new fill. Our analysis modeling utilized soil strength considerations suggested in Mesri & Shahien,'Residual Strength Mobilized in First-Time Slope Failures," January 2003, in the Journal of Geotechnical and GeoEnvironnrenffiI Engineering, ASCE, USA. The Mesa Verde Formation (soft rocks) were originally modeled as "softened" for our initial compuffi- . tions of the "native" slope conditions prior to the placement of fills. The factor of safety (FS) for these original rock slopes was greater than 1.7 for a global type condition. Sloughing and near surface type failures were encountered, which become restrained when covered with the older fill. As a sufficient factor of safety for the Mesa Verde Formation was determined, our final computations designated the PR-3 A14-8-2 (New 01107)