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

4 -
• fracturing and hummocked profiles. This is probably due
to the highly heterogeneous nature of the sediments over
the coal beds, the absence of a strongly-developed fracture
pattern and the great depth of cover.
The horizontal distance away from the edge of a mined-out
area to which subsidence effects are detectable is deter-
mined by the angle of draw. This angle is influenced by
the thickness of the coal removed, rock strength, lithology
and structural features within the rock sequence such as
joints, faults and folds. Topography, and in particular
extensive abrupt slope changes relative to mine depth, also
influences the angle of draw.
In the Somerset area, Dunrud calculated draw angles of from
less than 100 to over 200 the variations apparently depend-
ent on the nature of the overburden strata and depth of
cover. In its original application, MCR adopted 150 as an
average for the worst case situation. CMLRD rejectded this
angle and stipulated that MCR use an angle of 20 .5 for
determining subsidence-affected-area boundaries. MCR
accepted this stipulation. Data acquired since the subsid-
ence monitoring program began in 1981 now allow a more
accurate approximation of this angle.
The equation used in the permit to determine the horizontal
• distance from the edge of a mined-out area to the limit of
subsidence on the surface is :
x = Htanecos20
where x = the horizontal distance to the
limit of subsidence corrected
for topographic slope;
H = the vertical depth of cover at the
edge of the mined-out area;
e = the angle of draw; and
0 = the slope angle from the intersec-
tion of H with the surface to the
limit of subsidence.
In order to determine the angle of draw from subsidence moni-
toring points to mined-out areas, this equation is resolved
for e:
e = tan-1 x
Hcos20
H is determined from mine and surface topographic maps, x is
the distance measured from the edge of the mined-out area to
• the monitoring point, and 0 is calculated using the equation