Laserfiche WebLink
0 <br />• considered appropriate for this analysis. The estimated load on the web will depend <br />on the overburden depth of rock and spoil. These conditions vary. Bedrock was <br />assumed to have an average unit weight of 157 pounds per cubic foot (pcf) and spoil <br />130 pcf. <br />The auger mining was broken down into general analysis areas for each <br />seam, with each area having similar overburden conditions. The location of analysis <br />areas (1 through 5) for the X-Seam are shown on Fig. A-1. Analysis areas for C, D <br />or E-Seam (6 through 8) are shown on Fig. A-2. <br />A typical auger face view and a definition of terms and equations used are <br />shown on Fig. A-3. We used average web stresses to calculate web spacings. We <br />also checked peak stresses at the edge of auger openings using closed form elastic <br />formulas for circular unlined openings". These elastic peak stress calculations <br />suggest factors of safety ranging from 2.2 for the X-Seam to 1.2 for the E-Seam and <br />• appear satisfactory. <br />The results of our calculations for various auger locations, seams and <br />penetrations of 300 or 500 feet are shown on Tables A-I to A-V. For penetrations <br />between 300 and 500 feet linear interpolation can be used. Fig. A-4 shows typical <br />cross-sections illustrating the overburden depth assumptions and factor of safety <br />variations. If the overburden depths (bedrock and spoil) conditions shown on the <br />tables is exceeded, then the web width equation shown on Fig. A-3 can be used to <br />calculate revised widths. Web width versus bedrock overburden depth charts are <br />provided on Fib. A-5; where combinations of spoil and bedrock are present the <br />equation on Fig. A-3 should be used. <br />The analysis was performed to provide a minimum factor of safety of 2.0 near <br />the slope face, reducing to a minimum of 1.5 at maximum auger penetration. This <br />was for average web stress conditions. Typical sections are shown on Fig. A-4. <br />Width to height ratios (W/D as shown on Fig. A-4) were also checked. Confinement <br />pressures decrease as the width to height ratio decreases. The width to height ratio <br />COLOWYO COAL COMPANY, L. P. <br />GTL? 29,585 S <br />