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• CTL/THOMPSON, INC. CONSULTING GEOTECHNICAL AND MATERIALS ENGINEERS July 14, 1980 Kerr Coal Company Box G Steamboat Springs, Colorado 80477 Attention: Mr. John Gates Subject: Haul Road Construction Kerr Coal Company Walden, Colorado Job No. 6396 Gentlemen: As requested, we have reviewed laboratory testing conducted on spoil ma- terial from the Kerr P1ine located near Walden, Colorado and performed • slope stability analyses to determine the suitability of mine spoil for the construction of haulage roads. We understand that it is desired to construct future haul roads at the Kerr mine using mine spoil developed from present mine locations. We also understand a maximum haul road em- bankment height of 40 feet is presently being considered. The purpose of this investigation was to determine the suitability of using mine spoil for the construction of haul roads as required under 30 CFR 816.152(d). Haul roads constructed using material containing less than 85 percent, by volume, of rock larger than 12 inches in the greatest dimension, shall have embankment slopes not steeper than 2:1 (horizontal to vertical). The above section also requires a minimum factor of safety of 1.25 for all embankments. We understand that overburden material will be used to construct haul roads. For the purpose of this analyses we have considered that overburden used to construct future haul roads at the Kerr Mine will have strength prop- perties similar to those determined in previous studies by our firm on overburden materials from the Kerr Mine. Our previous investigations in- dicate that compacted overburden generally consists of gray and brown clay- stone, shales and sandstone. Samples obtained from field density tests were subjected to Proctor compaction tests. The results of Proctor compaction tests are shown on Figs. 1 through 3. Remolded samples of overburden were prepared and subjected to unconsolidated-undrained direct shear tests. The results of direct shear tests indicated that compacted overburden has co- hesion values on the order of 2,000 psf and an angle of internal friction on the order of 20 degrees. • 1701 SOUTH FEDERAL 6LVD. SUITED DENVER, COLORADO 60219 (303) 9345473