PERMFILE139235

• Permit No: C1981033
• IBM Index Class Name: Permit File
• Doc Date: 4/6/1986
• Section_Exhibit Name: INTERACTION OF SUBSIDENCE & LANDSLIDING
• Media Type: D
• Archive: No

• 7.2.2 Zone Area Method
The zone area method is also an influence function technique.
The influence of the extracted area on any given point on the
surface is determined by the construction of a series of circular
zones or concentric rings around the point, with the outer radius
of the circle being a function of the angle of draw and the
overburden thickness. The subsidence is obtained from summation
of the portions of each zone or ring extracted multiplied by its
particular zone or subsidence factor. This particular method
utilizes seven zones of influence for extracted areas. The
effects of coal pillars are determined by the use of a
compensating influence function based on a circle divided into
• five concentric zones. The technique is readily computerized and
requires the following minimum information:
1. A defined area in which values of subsidence are
required;
2. A description by rectangular coordinates of the area
extracted and the areas where pillars wi 11 be left in
place;
3. The gradient and dip direction of the coal seam;
4. Surface elevation at each grid point;
5. The coal seam elevation at the extreme southwest corner
of the grid;
6. The seam thickness.
Subsidence values are calculated for each grid interval position
• within the defined surface grid area. Magnitude of subsidence as
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