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possible. Additionally, the deeper cover in the Apache Rocks and the Box Canyon mining areas <br />~ may require design alterations to gate roads, pillaz sizes and barrier pillars as well. <br />Geologic Properties Influencing Subsidence - 2.05.6 (6)(e)(i)(B) <br />Subsidence is influenced by the local geology in the following ways: <br />Geologic structure -Attitude of the bedrock, faulting, and jointing may control mine layout and <br />mining method. In steeply dipping, faulted coal beds, for example, a certain mine layout and <br />method, such asroom-and-pillaz or limited panel-pillar may be required. Joints often control the <br />way in which the roof rocks break, cave, and fracture, both underground and at the surface during <br />mining and subsidence. In relatively flat-lying, unfaulted coal seams like the Apache Rocks and the <br />Box Canyon mining azeas, there is latitude to develop the most, efficient layout and method to <br />recover a maximum amount of the coal resource with a minimum of impact. <br />Streneth and behavioral properties of the rocks -These properties may control the amount and rate <br />of subsidence. Strong, brittle sandstones and siltstones tend to break and cave in lazge blocks on the <br />mine floor. The bulking factor is greater for strong rocks than it is for soft, weak rocks. The greater <br />bulking factor of strong, caved material commonly reduces the height of caving and the subsidence <br />factor over soft, weak rocks. Conversely, the height of fracturing often is greater for strong, brittle <br />rocks than it is for soft, weak rocks. <br />• Stratig~raphic sequence -The stratigraphic distribution of rock units (stratigraphic sequence) <br />influences the effects of mining and subsidence. For example, strong and brittle sandstones in the <br />mine roof, as discussed above, can reduce the height of caving compared to shales, whereas <br />sandstones in the fractured zone above the caved zone may increase the height of fracturing <br />compared to shales. <br />hi addition, the subsidence factor may be less where the overburden contains a greater proportion of <br />thick, strong sandstones compazed to thin, weak shales. A unit that may reduce the subsidence <br />factor is the locally thick Lower and Upper Marine Sandstones that underlie the D and E-Seams. <br />These sandstones are about 100 feet thick in the eastem panel area and the eastem part of the <br />western panels of the Apache Rocks mining azea; they aze approxunately 100 to 125 feet thick in <br />the Box Canyon mining area and the northwestern part of the current West Elk Mine azea. <br />Moisture content -Wet or saturated conditions in the mine roof and overburden tend to reduce the <br />bulking factor of the caved roof rocks. Therefore, the subsidence factor commonly is greater under <br />wet conditions than it is in dry conditions. In general, the greater the saturation of the mine roof and <br />overburden rocks, the greater the subsidence factor. <br />Subsidence Prediction Based on Local Mining Experience - 2.05.6 (6)(e)(i)(C) <br />Much information has been gathered regarding subsidence at the West Elk Mine due to local <br />mining of the F-Seam (room-and-pillaz method) and B-Seam (longwall method). Subsidence <br />~, monitoring of a grid network has been conducted from 1985 to 1998, and has provided <br />considerable data regazding the effects of varying overburden thicknesses, mining heights, and <br />2.05-III March 2005PR11 <br />1~~ ~ <br />"'~ <br />