1987-12-01_PERMIT FILE - C1981017 ‎(185)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 12/1/1987
• Doc Name: Air Pollution Control Plan
• Section_Exhibit Name: Chaper IV Section A
• Media Type: D
• Archive: No

Chapter IV
A study accomplished by Dr. Bruce A. Collins for Mid - Continent in 1985 based on four
years of subsidence monitoring data concludes that the maximum vertical displacement
under worst case conditions would not exceed 7.2 feet. See Collins' study at Appendix
IV -F -4.
The surface expression of the amount of vertical subsidence, even under worst case
conditions, should appear in a relatively uniform pattern. This would be due to the
predominantly weak, highly - stratified rock (alternating strong brittle sandstones and
plastic shales) throughout the stratigraphic column (and particularly those at and near
the surface) and the magnitude of the depth to the coal bed over which subsidence
stresses are distributed.
These conditons are conducive to "plastic" deformation of the surface as opposed to
development of widespread random fractures and hummocked profiles.
The resultant horizontal dimension of subsidence is determined by the angle of draw.
The angle of draw is influenced by rock strength and structural features within the rock
sequence, such as joints and faults. Topographic features such as extensive
(compared to mine depth) abrupt slope changes also affect angle of draw.
The angle of draw has been measured in rocks similar to those in Coal Basin as 12
degrees to 20 degrees. It is believed that an average of 15 degrees would include the
worst case situation. Therefore, the horizontal distance from the rib line of the mine
panel to the edge of disturbance would be:
x = h tan 15 cos G
x' = horizontal projection fo the limit of draw corrected
for topographic slope
h = vertical depth from coal to the surface
0 = the angle of slope taken from the horizontal.
Depth from the surface to the B Bed ranges from 2200 feet to 2800 feet throughout
most of the planned mining area during the five year permit period. Therefore,
subsidence could occur on the surface from 600 to 750 feet from the vertical extension
of the edge of the coal to be mined.
The Dr. Collins study at Appendix IV -F -4, based on four years monitoring data,
determines that the worst case angle of draw would not exceed 18 degrees and that
subsidence could occur on the surface from 400 to 815 feet from the vertical extension
of the edge of mined out areas.
In summary, this analysis of worst case surface subsidence concludes that the
maximum vertical disturbance above the Coal Basin underground workings would be
30