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- o n <br />Data in the studies was used to analyze the relative factors of <br />• safety of the road upgrading. Geophysical studies defined horizons <br />which would be uncovered by the road cuts. Soil analysis defined <br />soil characteristics in the road cuts. Soil samples were gathered <br />iii the winter when access was limited. These samples give us an <br />idea of the parameters inherent to this area but may not be precise. <br />The data were entered into a computer program which uses the method <br />of slices to determine f3ct.,['s of safety. Cases analyzed were: <br />I. Original Topography <br />2. Existing Road <br />3. Design Road Cut <br />4. Reclamation <br />Although analysis was completed for original topography, it should <br />be emphasized that the present landform includes the cuts made to <br />construct the existing haul road. <br />Relative safety factors were generated by the program and could be <br />higher or lower than the values given. Geophysical studies <br />indicated boundary lines but could not determine exactly what the <br />boundaries were (i. e., soil-rock interface or soil-soil interface). <br />Geological investigations indicate that these boundary lines are <br />soil-rock interfaces and rock-rock interfaces, as evidenced by the <br />sandstone outcrops directly beneath the existing haul road. <br />• fiach cut was analyzed using conservative assumptions based on the <br />data in hand. Although precise formulas exist for calculation of a <br />safety factor, the data inserted into these formulas must be <br />infinitely accurate to give precise factors of safety. This data <br />must then be analyzed and scrutinized before calculations can <br />/ proceed. With these constraints in mind, it was decided that <br />stability analysis could proceed but would be limited to relative <br />factors of safety. The goal would be to produce an increase in <br />stability over what has existed, without failure since 1977. <br />Line 1 is the road cut closest to the mine site at Station 103+00. <br />The original ground had a safety factor of approximately 1.094. Tlie <br />existing road cut increased the safety factor to 1.146. Only slices <br />over five feet deep were analyzed; therefore, minor crest sloughing <br />was not represented. The design of August 1981 was then analyzed. <br />Although submitted to DMG, our on going analysis had raised <br />questions about this design's stability. A factor of safety of <br />1.055 provided the incentive to rethink our approach. This reduced <br />factor of safety apparently resulted from the reduction in mass at <br />the toe of the slope allowing the soil to slip along the stiff <br />boundary which would be uncovered at the toe of the cut. In all <br />cases, this boundary was assumed to be a smooth line. This worst <br />case assumption is contradictory to the stair step effect that is <br />exhibited in the surrounding landform. <br />• <br />'~ <br />`~i'; 1;'' 0 .' J 3 <br />