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tan <br />Geotechnical /Environmental EnQlneerinQ • Materials <br />Subject: Stability Analysis, Batch Weigh <br />Loadout Haul Road, Foidel Creek Mine. <br />Routt Cotmty, Colorado. <br />Gentlemen: <br /> <br />November 6, 1997 <br />Twentymile Coal Company <br />29515 County Road 27 <br />Oak Creek, CO St0467 <br />Atm: Mr. Tavis Rogers, P.E. <br />Job No. 97-3325 <br />As requested, Northwest Colorado Consultants, Inc. has prepared this report to present a stability <br />analysis for the proposed haul road to be constructed between the batch weigh and loadout facility and <br />existing Haul Road C at the Foidel Creek Mine in Routt County, Colorado. We understand that a <br />minimum static factor of safety of 1.30 must be demonstrated for the haul road under a fully loaded <br />condition. <br />Proposed Construction: Based on the plans provided and our discussions with your office, we <br />understand that the project will consist of construction of approximately 875 feet of haul road between <br />existing Haul Road C and the Batch Weigh/Loadout Facility. The haul road will consist of a 30-foot, <br />gravel surfaced roadway designed for use by fully loaded 150-ton Euclid haul trucks. The roadway <br />crosses the Foidel Creek drainage between Stations 0+50 and 2+50 and installation of a 42-inch CMP is <br />planned to carry the discharge in this area. To carry the traffic loads over expected soft subgrade <br />conditions in this area, the roadway section will be built up with imported base course materials. The till <br />materials will also be underlain by a layer of Tenser geogrid reinforcement. In addition, safety berms <br />will be constructed along both sides of the roadway and we have assumed that the berms will be finished <br />to a minimum of 3 feet above the finished roadway surface. <br />Stability Analvsis: To determine the factor of safety for the roadway embankment, a mathematical model <br />was established. A microcomputer program, SB-Slope, was used to establish and model the proposed <br />embankment geometry, loading conditions and soil strength values. This program uses Bishop's <br />Simplified Method of Slices to calculate factors of safety against failure. <br />No subsurface investigation was conducted for this study and the soil strength values ttsed in the analyses <br />are based on assumptions of the subsurface conditions to be encountered in the vicinity of the Foidel <br />Creek drainage and our experience with past projects N this area. [t is assumed that natural clays will be <br />encountered beneath the topsoil and that these clays are medium plastic, medium stiff and very moist. <br />(s~o) a~s•~aaa • Fax (970) 679.7891 APPROVED NOY 2 4 1994 <br />29585 U.S. 40 West, Box 775226 • Steamboat Springs, CO 80477 <br />