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conditions than those observed in Britain. As a consequence, the subsidence profile under <br />U.S. conditions should generally be sharper and narrower than that predicted using the <br />SEH methods. However, using profile functions would not necessarily provide a better <br />estimate of the subsidence profile unless site-specific experience in selection of input <br />parameters is available. <br />Using the SEH method to give an estimate of the form of the subsidence profile <br />indicates that, even under British conditions, the subsidence trough would be relatively <br />steep-sided at the limit for an extraction area. In the Mesaverde Formation, the <br />subsidence trough can be expected to be somewhat steeper than that predicted for British <br />conditions. <br />The maximum subsidence over individual panels at low overburden heights will vary <br />depending on the panel width, amount of extraction, and overburden height, but should <br />only approach the maximum possible subsidence. Subsidence over barrier pillars between <br />panels may become quite small at small overburden heights. <br />1.4 DRAW ANGLES <br />The angle of draw, or limit angle, is the inclination (from vertical) of the line <br />connecting the edge of the workings to the surface outside of the mined area as shown on <br />Figure 15-1. Draw angles measured within a specific mining region tend to be of a similar <br />magnitude. Draw angles are influenced largely by the geological conditions. The potential <br />for error in applying an angle of draw measured in one area to another area is considerable <br />(Abel and Lee, 1980). <br />Only limited experience is available for estimating draw angles in the Mesaverde <br />Formation. Dunrud (1976) measured draw angles of 21 degrees 10 20 degrees in weak <br />to moderately strong overburden strata consisting of 650 to 900 feet of Mesaverde <br />Formation. The limit angle steepened to 15 degrees or more in moderately strong <br />overburden 900 to 1,000 feet thick. Gentry and Abel (1978) measured an average angle <br />of draw of 15.5 degrees in the Raton Formation at the York Canyon Mine in flew Mexico. <br />Draw angles of 20 degrees have been reported in Pennsylvania (Brauner, 1973). The <br />subsidence profile done at the Bowie #1 Mine across panels 11 and 12 north in 1986, <br />indicates an angle of draw of 16 degrees. <br />u <br />- 9 - 10/00 <br />PQ-o 4 <br />