2014-10-10_PERMIT FILE - C1996083 ‎(8)‎

• Permit No: C1996083
• IBM Index Class Name: Permit File
• Doc Date: 10/10/2014
• Section_Exhibit Name: Volume IIIA Exhibit 15 Subsidence Prediction
• Media Type: D
• Archive: No

Using the SEH method to give an estimate of the form of the subsidence profile
indicates that, even under British conditions, the subsidence trough would be relatively
steep -sided at the limit for an extraction area. In the Mesaverde Formation, the
subsidence trough can be expected to be somewhat steeper than that predicted for British
conditions.
The maximum subsidence over individual panels at low overburden heights will vary
depending on the panel width, amount of extraction, and overburden height, but should
only approach the maximum possible subsidence. Subsidence over barrier pillars between
panels may become quite small at small overburden heights.
1.4 DRAW ANGLES
The angle of draw, or limit angle, is the inclination (from vertical) of the line
connecting the edge of the workings to the surface outside of the mined area as shown on
Figure 15 -1. Draw angles measured within a specific mining region tend to be of a similar
magnitude. Draw angles are influenced largely by the geological conditions. The potential
for error in applying an angle of draw measured in one area to another area is considerable
(Abel and Lee, 1980).
Only limited experience is available for estimating draw angles in the Mesaverde
Formation. Dunrud (1976) measured draw angles of 21 degrees to 20 degrees in weak to
moderately strong overburden strata consisting of 650 to 900 feet of Mesaverde Formation.
The limit angle steepened to 15 degrees or more in moderately strong overburden 900 to
1,000 feet thick. Gentry and Abel (1978) measured an average angle of draw of 15.5
degrees in the Raton Formation at the York Canyon Mine in New Mexico. Draw angles of
20 degrees have been reported in Pennsylvania (Brauner, 1973). The subsidence profile
done at the Bowie #1 Mine across panels 11 and 12 north in 1986, indicates an angle of
draw of 16 degrees.
We have assumed an angle of draw of 25 degrees for this study. This corresponds
to the draw angle widely accepted as a conservative number in the North Fork Valley.
PR -14 - 11 - 03/14