1987-12-01_PERMIT FILE - C1981017 ‎(284)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 12/1/1987
• Doc Name: Subsidence Study By Dr. Bruce Collins
• Section_Exhibit Name: Chapter IV Appendix IV-F-4
• Media Type: D
• Archive: No

5 -
0 = tan-1 x
•
where 0 and x are defined as above and y is the difference
between the original elevation of the subsidence monitoring
point and the surface intersection of H (see Figures 1 to
19 below for illustrations) .
Two sets of points and associated areas of mine workings
were used to approximate the angle of draw (A) ; diagrams
and calculations are included below. The first set in-
volves monitoring points MC-13 and MC-14 and the face of
longwall 102 , Dutch Creek No. 1 mine. MC-13 is the last
monitoring point in the MC-10-16 series on the approximate
centerline of longwall 102 (B bed) that had moved as of
August 9 , 1985 , the date of the last survey, while MC-14 ,
178 feet northwest of MC-13 , was the first point showing
no movement as of that date. The location of the face on
August 9 was approximated by taking the mid-point of measured
face advance as surveyed on August 1 and August 20, 1985 .
H was determined by drawing structure contours on the top
of the coal bed from the nearest available survey control
points in the mine and defining the coal bed elevation by
projecting a straight line from MC-14 back through MC-13
to the face; determining the surface elevation over this
intersection by projection of the slope between MC-14 and
MC-13 , whose original elevations are precisely known (the
• surface in this area slopes quite evenly, and this method-
was thought to be more accurate than picking the elevation
of the H intersection of the surface off a topographic map) ;
and subtraction. H was thus determined to be 2 ,866 feet,
x, the distance from the longwall face to MC-13 , was 743
feet, and the slope angle 0 was calculated as- 7 . 90 . Using
the second equation given above, the angle of draw A was
calculated as 14 . 80 . Similarly, for point MC-14 H remains
the same (2 ,866 feet) , as does slope angle 0 (7 . 90°) , with
x measured at 921 feet, giving an apparent angle o°f draw
(remembering that MC-14 had not subsided) of 18 .14 . Clearly,
the actual limit of subsidence is between MC-13 and MC-14 ,
which are 178 feet apart; assuming that this limit is actually
half-way between these two points, H and 0 remain the same,
with x equal to 832 feet, giving an approximation of the
actual angle of 16 . 48°
This average, rounded to 16.50 is obviously significantly
less than the 20. 50 stipulated by CMLRD. However, it must
be recognized that in this case the limit of coal extraction,
i.e . the longwall face, is moving, at a rate of approximately
4 . 5 feet per day during the time period of interest, and that
point MC-13 (as well as MC-10, 11 and 12) has in all likeli-
hood not stabilized. Thus a second set of points, in which
the point which had subsided was stable or nearly so, was also
used to approximate the angle of draw. This set includes con-
trol points TP-2 and TP-4 , monitoring point MC-8 and longwall