PERMFILE103730

• Permit No: C1980007
• IBM Index Class Name: Revision
• Doc Date: 12/2/2004
• Doc Name: 2.05.5 Post-Mining Land Uses
• Type & Sequence: PR10
• Media Type: D
• Archive: No

West Elk Mine
Differential vertical lowering of the continuous deformation and near surface zones causes
vertical displacement (S), horizontal displacement (Sh), tilt (M), and horizontal strain (E). Each of
these parameters is graphically illustrated in Figure 2, Exhibit 60B. In flat or gently sloping terrain
(slopes less than about 30 percent), surface profiles of subsidence depressions aze similaz to flexure
of fixed-end, laterally constrained beams. Tensile stresses aze present in azeas of positive curvature
decreasing to zero at the neutral surface before which they reverse to become compressive stresses
(see Figure 1, Exhibit 60B).
In flat or gently sloping terrain, vertical displacement typically increases inward from the
limit of the subsidence depression, is half the maximum value at the point of inflection, and
is at its maximum in the middle of the depression (also called subsidence basin or
subsidence trough). Horizontal displacement and tilt increase inward 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 (Exhibit 60B, Figure 3). Maximum values of tilt,
curvature, and strain, discussed herein, apply only to slopes less than about 30 percent;
values may be greater on slopes steeper than 30 percent.
Positive curvature (convex upward) and horizontal tensile strain increase inward from the
margin of the depression to a maximum about midway between the depression margin and
the point of inflection and decrease to zero again at the point of inflection. Negative
curvature (concave upward) and compressive horizontal strain increase inward 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.
Maximum Vertical Displacement (Subsidence)
Longwall mining panels are defined by their panel width to overburden depth ratio as subcritical,
critical, or supercritical. The subsidence literature indicates that a panel width to overburden
depth ratio between 1.0 and 1.4 (average of 1.2) generally defines the critical longwall panels.
Those panels with panel width to overburden depth ratios exceeding this value aze defined as
supercritical, and those which are less are defined as subcritical.
cache Rocks Minin Area -Overburden depth above projected eastern longwall panel centers (B
Seam mining only) of the Apache Rocks mining azea ranges from about 950 feet neaz the head of
Sylvester Gulch to about 2,250 feet near the south end of West Flatiron {see Map 14 for details).
Overburden depth above the western panel centers ranges from about 500 feet to about 1,050 feet
for the E Seam and 700 feet to 1,250 feet for the B Seam.
With a projected longwall panel width of 950 feet, and assuming that the chain pillaz dimensions
will be similaz to the current West Elk mining azea, maximum subsidence (Sm at) is predicted as
follows:
• Eastern Panels -The eastern panels, which trend about N80°W, will range from about critical
to subcritical in width in the west ends of panels El, E2, E3, and E4 SE (numbered from north
2.05-113 Revised Navember2004PR10