PERMFILE52001

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 6/2/2006
• Section_Exhibit Name: Exhibit 60B Subsidence Evaluation for the South of Divide Mining Area
• Media Type: D
• Archive: No

Subsidence Evaluatron For
Exhibit 60B South of Divide Mining Area Page 10
• above bamer pillars or lease boundary barrier pillars than chain pillars because of their greater
rigidity (for example, the large tension crack on the north side of Lone Pine Gulch).
The tensile strains obtained from the curves in Figure 5 are believed to be conservative for the
South of Divide mining area- Maximum horizontal tensile strains, measured by the author in
bedrock during annual observations in the Apache Rocks area (in hard brittle sandstone, where
the only strain is revealed by cracks), were 0.0031 to 0.0062 (0.31 to 0.62 percent). These
values are about 35 to 45 percent less than those shown in Table 1. The tensile strain is
considered to be close to a maximum value for those observed by the author in the Apache rocks
area because 1) the features are located above the area if influence of a large solid coal pillaz,
and 2) no greater strain was observed in the Apache Rocks mining area.
South of Divide Wining Area: Maximum tensile and compressive horizontal strains are
calculated, using the values obtained from the West Elk Mine area, and as projected in Figure 5
(Table 2). These values are believed to be conservative, based on the author's annual
observations over the last seven years in the Apache Rocks mining area.
• Panels EI to E8: For these eight panels, projected horizontal tensile strain ranges
from 0.004 to 0.022 (0.4 to 2.2 percent) where the planned coal extraction thickness
is 8 feet; from 0.007 to 0.027 (0.7 to 2.7 percent) where the extraction thickness
equals 12 feet; and from 0.007 to 0.039 (0.7 to 3.9 percent) where the extraction
thickmess equals 14 feet
• Horizontal compressive strain ranges from -0.004 to -0.024 (-0.4 to -2.4 percent)
where the extraction thickness equals 8 feet; -0.007 to -0.029 (-0.7 to -2.9 percent)
where the thickness equals 12 feet; and -0.007 to -0.042 (-0.7 to -4.2 percent) where it
equals 14 feet (fable 2).
• Panel E9: Predicted horizontal tensile strain in this single panel ranges from 0.018 to
0.027 (1.8 to 2.7 percent) where the coal extraction thiclmess equals 12 feet and 0.021
to 0.031 (2.1 to 3.1 percent) where the extraction thickness equals 14 feet
Compressive strain this panel is predicted to range [irom -0.018 to -0.029 (-1.8 to -2.9
percent) where the extraction thickness equals 12 feet and -0.021 to-0.034 (-2.1 to
-3.4 percent) where it equals 14 feet ("f"able 2).
5.3.2 Maximum Projected Depths of Surface Cracks
Curvature, or differential tilt (curvature is the second demative of vertical displacement with
respect to horizontal distance) of subsided rock layers causes horizontal strain. Comparison of
calculated curvature values and horizontal tensile strain derived from horizontal displacement
measurements, therefore, provides a means of calculating the depth of the neutral surface, and
hence the maximum depth of tension cracks from the surface. The neutral surface is the
boundary between tensile and compressive strain

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