PERMFILE41947

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 4/8/2005
• Section_Exhibit Name: 2.05 Operation and Reclamation Part 2
• Media Type: D
• Archive: Yes

Maximum Vertical and Horizontal Displacement, Curvature, .Tilt, Horizontal
• Strain, and Depth of Surface (Tensile) Cracks
Differential vertical lowering causes vertical displacement (S), horizontal displacement (Sh), tilt
(M), curvature (C), and horizontal strain (E). Each of these parameters aze graphically illustrated in
Figure 2, Exhibit 60, hi flat or gently sloping terrain (slopes less than about 20 percent), surface
profiles of subsidence depressions are similar to flexure of fixed-end, laterally constrained beams.
Tensile stresses are present in areas of positive curvature decreasing to zero at the neutral surface
before which they reverse to become compressive stresses (see Figure 1, Exhibit 60).
The following paragraphs project these subsidence pazameters for the Apache Rocks and Box
Canyon mining areas. The subsidence projections aze based on data obtained from subsidence
measurements in the current mining azea and geology, topography and proposed mining
configurations (Map 51 and Map 52).
Projected Vertical and Horizontal Displacement
In flat or gently sloping terrain, vertical displacement typically increases inward from the mazgin of
the subsidence depression, is one-half the maximum value at the point of inflection, and is
maximum in the middle of the subsidence depression (also calledi 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.
• Positive curvature (convex upwazd) and horizontal tensile strain increase inward from the mazgin 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
upwazd) and compressive horizontal strain increase inward from the point of inflection to a
maximum about midway between the point of inflection and fhe point of maximum vertical
displacement and decrease to zero again at the point of maximum vertical displacement,
Longwall mining panels aze 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 aze defined as subcritical.
cache Rocks Mining Area -Overburden depth above projected eastern Longwall panel centers (B-
Seam mining only) of the Apache Rocks mining azea ranges from about 950 feet near 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 pillar dimensions
will be similar to the current West Elk mining azea, maximum subsidence (Sm at) is predicted as
• follows:
2.05-115 March IOOSPRII
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