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ponald A. Crane Page 2 <br />The Contractor's report has summarized the actual construction of the ColoWyo _ <br />fill (page 2 of the Contractor`s report) from the 6,590 to the 7,000 foot <br />levels. The Contractor has performed an analysis of fill based on the <br />"as built" Co date plus the projected design of the fill to its ultimate <br />elevation of approximately 7,100 feet. Certain pre-construction and <br />post-construction characteristics of the fill. and fill area were identifie•? <br />either from the data supplied by the operator or were assumptions based on <br />accepted engineering experience. The contractor employed a modified <br />"Spencer's Method" for stability analyses. The method is accepted by this <br />office as applicable for the "slope stability .analysls where variations in <br />water table, strength, anis[ropy, slope configuration, surface pressure and <br />pore pressure can be used" (page 6). <br />OSM has identified ten variables utilized by the Contractor to make the <br />analyses. These are listed in Table I as are the sources of infocmation for <br />the variables. All data necessary far the stability analysis were obtained <br />from the mining and reclamation plan except for water table conditions at the <br />fill site. Strength parameters of the weathered bedrock were estimated from <br />strength tests performed up slope of Streeter Canyon (11/75 Wahler report). <br />An internal angle of Friction was also estimated for the colluvium based on <br />penetration tests and was determined foc the spoil using the angle of <br />repose--usually a conservative estimate of the internal angle of friction. <br />Three values of spoil pile Friction angle and three values of spoil density <br />were used to calculate factors of safety. Four water table locations were <br />analyzed. Other variables were held constant. The parameters are summarized • <br />below: <br />VARIABLES AL7D CONSTANTS FOR STABILITY luYALYSES <br />CONFIGDR9TIGN: COLOWYO lv:3h to 7,000', lv:6h to 7,100' <br />OSM lv:3h to 7,100' <br />SPOIL: 0 Angle: <br />Cohesion: <br />Density: <br />COLLUVIUM: 0 Angle: <br />Cohesion: <br />Density: <br />35, 37, 39 degrees <br />0 psf (pounds per square foot) <br />105, 110, 125 pcf (pounds per cubic foot) <br />26, 40 degrees <br />0 psf <br />120 pcf <br />WEATHERED BEDROCK: 0 Angle: 10 degrees <br />Cohesion: 2,500 psf <br />Density: 135 pcf <br />WATER TABLE: Intersect toe of slope at 10, 50, 100, and 150' <br />The Contractor concludes, and OS~1 concurs, that there is little difference in <br />the factors of safety obtained for each case except when the colluvium 0 of 4G <br />degrees is used. For the 40 degree case, a somewhat higher (up to 20 percent) <br />factor of safety is attained for the ColoWyo configurations. The lower factor • <br />of safety for the OSM configuration results from the assumption that the face <br />of the fill would extend upward higher than does the projected configuration <br />of Cololdyo's fill. In all cases where reasonable assumptions were made <br />