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<br />'• <br />i <br /> <br /> <br /> <br /> <br /> <br />N <br /> <br /> <br /> <br /> <br />1 <br /> <br />1~ <br />Figure 4-1 shows a typical six-entry main road that will be developed in the D and B Seams. The <br />pillar and entry width dimensions vary according to the conditions encountered. <br />4.2.2 Room-and-Pillar Mlnlna Room-and-pillar mining with continuous miners is a standard <br />method of underground coal mining in the United States. This mining system can easily adjust to <br />changes in the geological and physical conditions of the mine. It is possible to exclude undesirable <br />sections of the deposit, negotiate structurally disturbed azeas of the mine, and adapt to variations <br />of the coal seam. The equipment can be easily moved to different locations in the section and the <br />overall system is only minimally affected by a stoppage of any one unit. Although this system is <br />generally more hazardous and more expensive to operate than a longwall system, it is this flexibility <br />that maintains continuous mining machines as a major component of underground coal production <br />in this country. In the Deserado Mine the overall coal reserve recovery from room-and-pillar panel <br />mining is estimated to average about 67 percent because all of the pillars cannot at all times be <br />safely extracted. It is estimated that a continuous miner will produce between 600 to 800 tons per <br />8-hour shift depending upon specific mining conditions. Coal recovery from areas not suited for <br />longwall mining will be accomplished with room-and-pillar mining wherever economically and <br />technically feasible. <br />Atypical room-and-pillar panel will be 1000 feet wide, of varying length and surrounded by 200-foot <br />thick barrier pillars. The panel will be developed by 20-foot wide entries. The pillar size during <br />development will vary from 40'x40' to 50'x50'. The pillars will be partially extracted during retreat. <br />The final pillar size will vary from 32'x32' to 42'x42'. Figure 4-2 shows a typical room-and-pillar <br />panel. <br />4.2.3 LOn~YVall Mlnlna Longwall mining has improved dramatically over the last 15 years. It has <br />gained great acceptance because of its three apparent advantages: <br />1) high recovery of the reserve <br />2) high productivity <br />3) better safety record <br />In longwall mining, coat is extracted from panels that are thousands of feet long and hundreds of <br />feet wide. The shearer cuts coal as it passes back and forth across the longwall face. The coal <br />19 <br /> <br />