2008-03-21_PERMIT FILE - C1980007A ‎(8)‎

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 3/21/2008
• Section_Exhibit Name: Exhibit 60E Subsidence Evaluation for the South of Divide & Dry Fork Mining Areas
• Media Type: D
• Archive: Yes

1. Maximum vertical displacement above the chain pillars (Scp) is expected to range from 0.8 to
2.4 feet (0.1 to 0.3t) where the extraction thickness is 8 feet, 1.2 to 3.6 feet (0.1 to 0.3t),
where the extraction thickness is 12 feet, and from 1.4 to 4.2 feet (0.1 to 0.3t), where the
extraction thickness is 14 feet.
2. Maximum vertical displacement (subsidence, Sm= a • t) is projected to range from 4.8 to 6.4
feet (0.6 to 0.8t) where the extraction thickness is 8 feet, from 7.2 to 9.6 feet, where the
extraction thickness is 12 feet, and from 8.4 to 11.2 feet (0.6 to 0.8t), where the extraction
thickness is 14 feet.
• Panel E9: This panel trends about N10°E and is of supercritical width.
1. Maximum vertical displacement above the chain pillars in this shallow overburden is
expected to range from 1.2 feet (0.1t), where the extraction thickness is 12 feet and from
1.4 feet (0.1t), where the extraction thickness is 14 feet.
2. Maximum subsidence is projected to range from 8.4 to 9.6 feet (0.7 to 0.8t), where
extraction thickness is 12 feet, and 9.8 to 11.2 feet (0.7 to 0.8t), where the extraction
thickness is 14 feet.
Dry Fork Mining Area: Overburden depth above the projected E Seam longwall centers ranges
from 800 to 1,400 feet. With a projected longwall panel width of 1,080 feet, and assuming that the
chain pillars (gate road pillars) are similar to those in longwall panel 17 of the Apache Rocks mining
area, maximum subsidence (vertical displacement Sm= a • t) is predicted as follows (Table 3) for the
Dry Fork area of panels E2 through E6:
• Panels E2 to E6: These panels, which will trend roughly N801W, are generally subcritical (width-to
depth ratio (W/d) ranges from 0.77 to 1.35).
1. Maximum vertical displacement above the chain pillars (Scp) is expected to range from 0.9 to
2.7 feet (0.1 to 0.3t) where the extraction thickness is 9 feet and 1.0 to 3.0 feet (0.1 to 0.3t),
where the extraction thickness is 10 feet.
2. Maximum vertical displacement (subsidence, Sm= a • t) is projected to range from 5.9 to
6.1 feet (0.6 to 0.8t) where the extraction thickness is 9 feet and from 6.2 to 7.0 feet, where
the extraction thickness is 10 feet.
5.3.1.2 Maximum Tilt
Maximum tilt (Mm) was calculated from differential vertical displacements at the West Elk Mine
monitoring network in terms of the ratio of maximum vertical displacement to overburden depth
(Sm/d in dimensionless units UL) (Table 1 and Figure 5). Tilt values at West Elk Mine range from
1.4 to 2.1 percent. Maximum calculated tilt ranges from about two to three times Sm/d (2 to 3 (Sm/d))
at West Elk Mine. Maximum tilt in the South of Divide and Dry Fork mining areas is projected to
range from 2.2 to 2.3 Sm/d. Maximum tilt in four different mining areas studied by Dunrud (2006,
p. 9) in the Western United States ranges from 2.5 to 5 (Sm/d).
South of Divide Mining Area: As stated earlier in this report tilt above the eight longwall panels
(panels E1 to E8) and the single panel (E9) is projected to range between 2.2 and 2.3 Sm/d for coal
extraction thickness ranging between 8 and 14 feet. These values are based on subsidence
measurements at West Elk Mine (Table 1, Figure 5). The overburden depth above the longwall
panel centers ranges from 400 to 1,425 feet (Table 2).
• Panels E1 to E8: Maximum tilt in these panels is projected to range from 0.007 to 0.037 (0.7 to
3.7 percent) where 8 feet of coal is extracted, from 0.013 to 0.044 (1.3 to 4.4 percent) where 12
feet of coal is mined, and from 0.013 to 0.064 (1.3 to 6.4 percent) where a 14-foot thickness of
coal is mined (Table 2).
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