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• <br />April 1989 <br />The MINAP analysis was used to determine the offset boundary <br />barriers ti~at need to be established to avoid stability problems <br />as mining approaches the boundary of excavations in the <br />previously mined out seams. Figure 3.4.A.9 is a plan view of <br />Area III which was used in making a comparative evaluatioir of <br />offset barriers and extraction ratios. Figure 3.4.A.10 and <br />3.4.A.11 illustrate boundary offset barriers and pillars needed <br />between panels along Section A-A" of Figure 3.4.A.9 for longwall <br />and room-and-pillar mining for Area III. Offsets, including <br />barrier pillars, for longwall are much narrower than those needed <br />for room-and-pillar mining. Differences in extraction are also <br />expected in the other areas of the property. This result shows <br />ate advantage for longwall over room-and-pillar when mining three <br />seams at West F.lk. <br />TABLE 3.4.A.15.1 <br />PILLAR SIZE AND FACTOR OF SAFETY-AREA I, B SEAM <br />- LONGWALL MINING <br /> <br /> Factor Recommended <br />Pillar Analyzed Pillar of Pillar <br /> Width x Length Safety Width x Length <br /> (ft x ft) (ft x ft) <br />Mains 60 x 120 1.5 60 x 120 <br />Barrier 200 x 700 2.2 180 x 700 <br />Gate 30+ x 100 .9 35+ x 100 <br />Bleeder 90 x 100 1.5-.9+ 90 x 100 <br />Starting <br />room barrier 110 x 700 N/A-1.Ox 120 x 700 <br />+ = 9 ft Mining freight <br />x = lagging cave <br />• <br />