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1 SUMMARY Project Location: The project is located at the site of the Bear Mine, approximately one-half mile east of Somerset, Colorado, in Gunnison County. Project Description: The project is to consist of the abandonment of the west portal area. The project ~•~i11 consist of the plugging and backfilling of tt-.e existing portal areas above the level of an existing bench fill. Scope of Report: The purpose of this report is to provide the results of an investigation and a computer- assisted limit equilibrium slope stability analysis for several different alternatives available for the abandonment of the west portal area. ' Results of Analyses: Mary different alternatives were considered involving various combinations of procedures, I including backfilling only immediately above the portal areas, backfilling to the top of the existing high wall cut, the use of on-site materials for fill, and the importation of fill materials. Further, the analysis involves several different assumptions with respect to shear strength of existing mate- rials. All of the various combinations or conditions considered are discussed in great detail in the body of this report. How- ever, as a very broad, general summary, it would appear that backfilling to just above the level of the portal area, util- izing on-site fill materials from the existing bench fill, I yields acceptable factors of safety against sliding when the shear strength of the foundation and existing cut slope materials exceeds 91 degrees. All other alternatives, includ- ing backfilling to the top of the existing high wall cut, and I any attempt to fill the entire area of the existing bench fill with imported fill materials, will require a loading berm placed at the toe of the existing bench fill. 1 Additional discussion and more complete recommendations may be ' found in the body of this report. All recommendations are subject to limitations set forth herein. I -1-