PERMFILE60488

• Permit No: C1981018A
• IBM Index Class Name: Permit File
• Doc Date: 10/10/2003
• Section_Exhibit Name: Section III. Mine Description
• Media Type: D
• Archive: Yes

• should be produced. This amount of tensile strain probably caused some surface cracks to open up.
Since the mining and subsequent subsidence occurred more than ten years ago, normal weathering of
the surface would have erased any surface cracking or other visible evidence of subsidence. This has
in fact been found to be true; a visual inspection of the surface over the caved areas showed no
surface cracks, tilted trees or other indications that subsidence had even occurred.
III.A.7.c Subsidence Prediction. Predictions of the maximum surface subsidence and horizontal
tensile strain for the Deserado Mine D Seam and B Seam longwall panels are presented in Table III-1.
Map No. 119 and 120 show the locations of these panels within the mine. These predictions are
based on results of subsidence studies made by the U.S. Bureau of Mines and on the model produced
by the British National Coal Board.
The USBM studies were conducted in underground coal mines having similar geologic conditions as
that found in the Deserado Mine. The NCB model is based on 187 subsidence profiles measured
across 165 longwall panels. The Deserado Mine subsidence predictions were derived primarily from
the British National Coal Board model with input from a model developed by the U.S. Bureau of Mines
at the York Canyon Mine. The predictions rely more heavily on the NCB model which is based on 187
subsidence profiles measured across 165 longwall panels. The York Canyon model is based on
information collected from only 11 profiles. It is recognized that the British model is for their
• Carboniferous strata, whereas the Deserado Mine strata is late Cretaceous and Tertiary. The
Cretaceous formations found in the U.S. are generally stronger than the British Argillaceous strata.
(The Deserado Mine Mesa Verde formation above the coal seam is discussed in the geology section
of this application.)
The NCB subsidence prediction model is recognized as the most accurate and conservative reference
available. Although the NCB subsidence prediction model was based on different coal bearing
lithology than that found in the U.S., it was used to predict the Deserado Mine subsidence because it is
conservative, accurate and widely accepted in the mining industry.
The inputs to the longwall subsidence prediction model are depth, mining height (seam thickness) and
panel width. Maps 122 and 133 present the overburden and seam thickness isopachs for the D Seam.
These inputs plus the panel geometries permitted the calculation of the predictions in Table III-1.
Monitoring of the surface above room and pillar mining operations is rarely undertaken; however, data
are available from the few surface subsidence-monitoring programs over failed pillars (Table III-2). The
subsidence reported is much less than that predicted by the widely used NCB model for longwall
mining -the uniform extraction of a thickness of coal across a wide and long area. Maximum
• Midterm Review (8/2002) III-il