PERMFILE42013

• Permit No: C1980007
• IBM Index Class Name: Revision
• Doc Date: 6/13/2005
• Doc Name: Exhibit 60B Subsidence Evaluation For the South of Divide Mining Area
• Type & Sequence: PR10
• Media Type: D
• Archive: No

Subsidence Evaluation For
Exhibit 608 South of Divide Mining Area Page 8
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present in azeas of positive curvature, which become zero downwazd at the neutral surface, then
reverse to compressive stresses below the neutral surface.
In flat or gently sloping terrain, verticai displacement typically increases inwazd from the limit of
the subsidence depression, is half the maximum value at the point of inflection, and is maximum
in the middle of the depression (also called subsidence basin or subsidence trough). Horizontal
displacement and tilt increase inwazd from the margin of the depression to a maximum at the
point of inflection and become zero again at the point of maximum vertical displacement
(Figure 3). Maximum values of tilt, curvature, and strain, discussed herein, apply only to slopes
less than about 30 percent; values maybe greater on slopes steeper than 30 percent.
Positive curvature (convex upward) and horizontal tensile strain increase inwazd from the mazgin
of the depression to a maximum about midway between the depression mazgin and the point of
inflection and decrease to zero again at the point of inflection. Negative curvature (concave
upwazd) and compressive horizontal strain increase inwazd from the point of inflection to a
maximum about midway between the point of inflection and the point of maximum vertical
displacement and decrease to zero again at the point of maximum vertical displacement.
5.3.1.1 Maximum Vertical Displacement (Subsidence)
The following range of vertical displacements (subsidence values) are projected for the South of
. Divide mining azea, based on the baseline data obtained from subsidence measurements above
the 1NW, 2NW, and 3NW longwall panels at West Elk Mine (Figure 4, Table 1). The projected
range of maximum vertical displacements, for the South of Divide mining area is shown in
Table 2.
South of Divide Mining_Area: Overburden depth above the projected E Seam longwall centers
ranges from 400 to 1,425 feet. With a projected longwall panel width of 1,080 feet, and
assuming that the chain pillazs (gate road pillazs) aze similaz to those in longwall panel 17 of the
Apache Rocks mining azea, maximum subsidence (vertical displacement Sm a • t) is predicted
as follows (Table 2):
Panels EI to E8: These panels, which will trend roughly N80°W, will range in width
from subcritical to supercritical (width-to depth ratio (W/d) ranges from 0.76 to 2.7).
1. Maximum vertical displacement above the chain pillars (S~) 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 O.St) 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
O.8t), where the extraction thickness is 14 feet.
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831-032.620 Wright Water Engineers, Inc.