PERMFILE41761

• Permit No: M1999002
• IBM Index Class Name: Permit File
• Doc Date: 6/18/1999
• Doc Name: OBJECTORS EXHIBITS
• Media Type: D
• Archive: No

Analytical Methods • . 113
TABLE IV
Computed and observed surface subsidence-Case II
mined area increases. The tensile strain was calculated to
be maximum,at a short distance outside the mined area
and then decays rapidly with the distance away from the
mined area.
Because of the presence of the weak bedding planes,
relative horizontal movements as much as 0.85 feet were
calculated across those bidding planes. Figurz l2 sltotvs
the horizontal displacement calculated at two vertical sec-
tions 500 and 1200 feet from the tooter of thz mined aria.
Several features should be noted: (I) each drastic chanee
in horizontal displacement is associated with the location
of a bedding plane, (2) larger relativz horizontal displace-
mentsoccur near the surface, and (3) the relativz horizon-
tal displacements occurring within the bidding planes
decrease with increasing distance from the tinter of the
mined area.
Figure ]3 illustrates calculated vertical displacements
along the centerline of the mined area for the cases lvith
none and ll weak bedding planes. It may be noted the[
the vertical displacement increased slightly with increas-
ing depth below the surface. Movements above mined
areas similar to those calculated have been reported by
Mohr (1958). An example of this is shown in Figure 14.
Radius of Height of No. 01 Weak Subsidence
Cavity (ft.l Cavity (ft.l Bedding Planes (ft.l
1080 8 None 0.39
1080 B 2 2.98
1080 8 7 3.29•
1080 8 11 3.40
1080 15 7 2.99
Observed 5.50
'Alter one iteration for no tension analysis
that used in the analysis, the computed subsidence would
be in close agreement with the measured valuzs. The dis-
crepancy between the calculated and observed subsidence
may also be improved if a larger number of the weak
bedding planes is assumed or a larger number of iterations
is performed for the no-tension analysis.
The calculated horizontal strain is illustrated in Figure
11. The horizontal strain distribution is quite similar to
that observed. A larger horizontal compression strain was
calculated at the center o(the mined area. The horizontal
compressive strain decreases rapidly and changes to ten-
sile strain as the distance away from the center of the
0.04
z
0 0.03
N
Z
W
~ 0.02
0.01
0
0,01
v
Z
a
a
J
Q
Z
O
G
O
x
= 0,02
O
u, 0.03
w
a
0 0.04
u
O.DS
0,06

I
I
5 00 100 0 1500 2000 ='500 3000
DISTANCE FROM CENTERLINE (Fi)

i

Figure 11. Percent horizontal strain calcufated for Case II (t = 8 ft., 11 weak bedding planes).