2011-02-14_PERMIT FILE - C1980007A ‎(3)‎

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 2/14/2011
• Doc Name: SUBSIDENCE EVALUATION
• Section_Exhibit Name: Exhibit 60E Subsidence Evaluation for the South of Divide and Dry Fork Mining Areas
• Media Type: D
• Archive: Yes

Subsidence Evaluation for the
Exhibit 60E South of Divide and Dry Fork Mining Areas Page 12
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.
Dly Fork Mining Area Overburden depth above the projected E -seam longwall centers ranges
from 800 to 1,800 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 trend roughly N80 1 W, and are generally subcritical (width -to-
depth ratio (W /d) ranges from 0.60 to 1.35).
1. Maximum vertical displacement above the chain pillars (S .,) 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, % = 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 6.0 to 8.0 feet,
where the extraction thickness is 10 feet.
5.3.1.2 Maximum Tilt
Maximum tilt (M 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
(S in dimensionless units L /L) (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 S (2 to
3•(S,,,/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 S,,,/d. Maximum tilt in four different mining areas studied by
Dunrud in the Western United States ranges from 2.5 to 5•(S,,,/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 S,,,/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 El 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 -1oot thickness of coal is mined (Table 2).
I*
831 - 032.810 Wright Water Engineers, Inc.