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TABLE A - II X -SEAM AUGER SPACING AND EXTRACTION RATIOS TYPE AND SIZE OF AUGER Analysis Seam Factor of Safe , PeneVation and Overburden Conditions Circular 6 -Foot Diameter Circular 7 -Foot Diameter Rectan ular 13 -Foot Width Location Thickness Type Auger Bedrock Depth Spoil Depth W W/D Extraction W W/D Extraction W W/D Extraction tt Penetration tt max tt max tt in % in °h in North Wall West Pit Variable 1, 2 10 2+ l0 1.5 0 to 300 BS 160 42 0.56 29.6 4B 0.57 35.0 114 1.00 54.9 10 1.5 500 170 170 64 0.89 24.9 72 0.66 29.26 138 1.21 50.4 Eas[ Wall West Pit Variable 3 10 2+ to 1.5 0 to 500 222 to 250 0 55 0.76 26.7 64 0.76 31.2 119 1.04 53.9 3A 10 2 to 1.5+ 0 to 500 273 to 350 0 82 1.14 22.0 96 1.14 25.7 176 1.56 44.4 3B 10 2 l0 1.5+ 0 to 500 273 l0 350 0 82 1 .14 22.0 96 1.14 25.7 176 1 .56 44.4 North Wall Streeter Pit 4 10 Uniform 0 to 500 200 0 46 0.64 28.7 54 0.64 33.5 114 1.00 54.9 FS=2 West Wall Streeter Pit 5 10 Uniform 0 to 500 250 0 68 0.94 24.2 80 0.95 28.2 140 1 .30 46.8 FS=2 NOTES: 1. Analysis Location, refer to Fig. A-1 2. Factor of Safety conditions (average web stress). Variable -Indicates overburden depth increases with depth of auger penetration (Fig. A-3). - Factor of Safety is a minimum of 2.0 at face, and 1.5 at maximum auger penetration. Uniform -Indicates uniform, maximum overburden depths were used, FS minimum of 2. 3. W -minimum web width recommended (in.). Minimum 42 in. for 6 tt. dia.; 48 in. for 7 tt. dia.; and W/D > 1 .0 for rectangular. 4. W/D indicates approximate width to height ration of web. Minimum of 0.57 for circular and 1.0 for rectangular. 5. Circular extraction ratios were calculated based upon full seam thickness and exact auger diameter. 6. Rectangular extraction ratios were based upon an auger height equal to seam thickness minus 6 inches. 7. Between 300 and 500 foot au er enetretion inter lation can be used to determine web width