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~rvorthwest <br />Geotechnical /Environmental Engineering • Materials Testing <br />October l5, 2001 <br />RAG - Twentymile Coal Company <br />29515 RCR #27 <br />Oak Creek, CO 80467 <br />A[m: Mr. Rick Mills <br />Job Number: 01-5023 <br />Subject: Alternative Gravel Section/Constrnction <br />Recommendations, Batch Weigh Loadout Haul <br />Road, Foidel Creek Mine, Routt County, <br />Colorado. <br />Gentlemen: <br />As requested, NWCC, Inc. (Northwest Colorado Consultants, Inc.) has prepared this report outlining <br />alternative gravel section/construction recommendations for the Batch Weigh Loadout Haul Road to be <br />constructed at the Foidel Creek Mine (RAG-Twentymile Coal Company) in Routt County, Colorado. It <br />should be noted that the previous gravel sections were approved by the DMG in the TR-30 dated 11/24/97. <br />It should also be noted that our firm previously completed a Stability Analysis for the proposed <br />• embankment slopes to be constructed for this haul road in a report prepared under our Job Number 97-3325 <br />and dated November 6, 1997. It should also be noted that the following recommendations, as well as the <br />previously completed stability analysis were conducted using assumed subsurface information and that a <br />formal subsurface investigation has not been conducted in this azea. <br />Alternative Gravel Section Recommendations: It is our understandings that the haul road will generally <br />be subjected to low traffic volumes consisting of fully loaded 100 ton Euclid haul trucks. Therefore, we <br />have assumed an 18-kip equivalent single axle loading (ESAL) of 120,000 for this haul road. Based on our <br />experience with other, similar projects at this mine and our recent observations made at the site, we have <br />assumed a correlated soils resilient modulus of 2000 psi for the roadway subgmde. <br />Based on the assumed subsurface conditions at the site, the assumed traffic loadings and our experience <br />with similar roadway projects at this mine, we recommend that the proposed haul road be constructed with <br />a gravel section consisting of 6 inches of base course gravels overlying a minimum of 18 inches of subbase <br />(pit run) sands and gravels, which in turn are placed on a layer of Tensar SSl Geogrid or an equivalent <br />product. If the geogrid layer is not used then the thickness of subbase gravels should be increased to a total <br />minimum thickness of 36 inches. <br />Subarade/Gravel Section Recommendations: The fill materials placed in the roadway embankments <br />should be uniformly placed and compacted in 6 to 8 inch lifts to at least 95°/a of the maximum modified <br />Proctor density and within 2 percent of the optimum moisture content determined in accordance with <br />• ASTM D1557. <br />(970) 879.7888 • Fax (970) 879.7891 • nwcc@cmn.net <br />2580 Copper Ridge Drive, P.O. Box 775226 • Steamboat Springs, CO 80477 <br />