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<br />• AUGER MINING <br />The analysis method included determination of the overburden conditions <br />which depend on location and auger penetration distance, analysis of peak and <br />average web stresses, evaluation of allowable coal stresses and consideration of <br />web width to height ratios. The results of the analyses are presented in Appendix <br />A. The web width recommendations are based upon overburden depth assumptions <br />which should be confirmed prior to augering each seam. The assumed bedrock and <br />spoil depths are shown on Table A-1 through A-V. Auger mining is considered <br />feasible for the X, C or D and E-Seams. Auger mining of either the C or D-Seam, but <br />not both, is recommended. It should be emphasized that safe augering is dependent <br />on more than just spacing. The need to monitor bench, roof and drilling conditions <br />and to adjust to these conditions should be constantly considered. Rockfall from the <br />high wall is also a safety consideration and workers should be made aware of the <br />potentially hazardous conditions. <br />• Analysis Methods <br />Auger mining operations were analyzed considering web stresses at the X- <br />Seam and at the C, D and E-Seams, peak stresses for unlined circular openings, and <br />overburden stress versus auger penetration. All analyses are dependent on the <br />strength of the coal seam and overburden stresses. <br />The allowable coal stress was estimated based upon core testing from the <br />original investigation and using a size factor to convert laboratory strengths to field <br />scale strengths. The previous auger analysis2 used a factor of 0.5 to reduce the <br />laboratory coal compressive strength of 2,240 psi to a field scale strength of 1,120 <br />psi. Our review of several referencess,9,T,9 indicates that the factor could range from <br />0.25 to 0.5 with 0.5 being more typical. Consideration of the absolute value of 1,120 <br />psi indicates it is in a normal to low range compared to published coal strengths for <br />a variety of coals. The 0.5 factor and field scale strength of 1,120 psi were <br />~J <br />COLOWYO COAL COMPANY, L. P. <br />CTLR 27,595 4 <br />