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96 South Zuni Street <br />Denver, Colorado 80223-1292 <br />• <br />U <br /> <br />TECHNOLOGIES INC <br />January 7, 1997 <br />Mr. Peter A. Stauch <br />Morrison Knudsen Corporation <br />7100 Fast Belleview Avenue, Suite 300 <br />Englewood, Colorado 80111 <br />Telephone: 1303) 744-7105 <br />Feceim le: 13031 744-0210 <br />Subject: Additional Stability Analyses, Proposed Portal Road Cuts and Topsoil Pile, Bowie <br />No. 2 Mine, Bowie, Delta County, Colorado <br />Job No. 5002-60-2655.05 <br />Dear Mr. Stauch <br />Introduction: On December 5, 1996 we met with representatives from Morrison-Knudsen <br />Corporation, J. E. S[over and Associates and the Division of Minerals and Geology (DMG). <br />During this meeting it was indicated by Mr. Jim Pendleton of the DbfG that additional analysis <br />was necessary to adequately characterize the stability of various elements of the proposed surface <br />facilities at the Bowie No. 2 Mine, located in Bowie, Colorado. The elements in question <br />consisted of proposed cuts along the portal road and the orientation of the proposed topsoil pile. <br />At your request, we have analyzed the stability of various critical cross sections for both the <br />proposed portal road and the topsoil pile. We were provided with grading plans for the <br />proposed portal road and topsoil pile which included cross-sections of the road at about 50 to <br />100-foot intervals. The purpose of this analysis was to estimate the factor of safety of various <br />proposed road cuts and also of the topsoil pile. Recommendations are provided for the <br />mitigation of potential ground water seeps or other instabilities that are either exposed or develop <br />in portal road cut slopes. <br />Subsurface Conditions: The shear strength parameters used in this analysis were determined <br />from the borings and laboratory data obtained during our previous studies. Although the <br />majority of the strength testing was conducted on soil samples from borings located in the area <br />of the upper benches, the borings logs and laboratory testing on samples from borings located <br />along the proposed portal road indicate the soils to be similar. These soils were classified as <br />Lean Clay with Gravel (CL-GC) and were described as a matrix of silty lean clay supporting <br />scattered to numerous gravel to cobble or boulder sized fragments of sandstone- Unconfined <br />compressive strength tests of samples obtained from borings along the portal road varied from <br />900 to over 28,000 psf with an average of about 12,000 psf. Unconsolidated-undrained testing <br />(TJiJ) on undisturbed samples of the clay indicated cohesive values variable from 2,950 to 4,350 <br />psf. <br />Astern • Austin Research Engineers •Chen-Northern • Empire Sails Investigations • Kansas City Testing <br />Maxim Engineers • Nebraska Testing - Patzig Testing • Southwestern Laboratories • Thomas-Hartig • Twin City Testing <br />a 4, <br />H:. <br />