PERMFILE41761

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

AnalyricalAlethodr • • 109
DISTANCE FROM CENTERLINE (FT)
2
3
4
!. 5
r
~. fi
~ 7
z
w
~ 8
u
a
~ 9
a
u,
o !0
J 11
Q
^ ]2
~ I3
14
15
16
17t
is
0 1000 2000 }000 4000 5000
0
i.-___
1

-fir

NOTES
- - - - OBSERVED SUBSIDENCE PROFILES
CALCULATED SUBSIDENCE PROFILES

_ o--4 RADIUS OF CAVITY R = 1000 FT
(WITH 3 SLIP LAYERS)
0- O. RADIUS OF CAVITY R = 2000 FT
(WITH 3 SLIP LAYERS)
'V RADIUS OF CAVITY R = 2000 FT
(WITHOUT SLIP LAYERS)
Q---4 RAD)U$ OF CAVITY R = 3000 FT
(WITH 3 SLIP LAYERS)
I

Figure 7. Subsidence profiles far various rad,i o! a tliso-shaped cavity, Case I.
TA6LE II
Observed and computed surface subsidence-Case I
Radius of No. of Weak Subsidence
Cavity lft.l Bedding Planes If t.l
[000 3 0.62
2000 None 1.62
2000 3 4.77
3000 3 16.9
Observed 2.7
low the Wilkins Peak Member is the Tipton Member of
the Green River Formation composed of interbedded
sandstones and brown shales. Scattered layers of trona
were found to be located within the Wilkins Peak Mem-
ber. The main seam mined is situated at the depth of 1557
to 1567 feet. The idealized rock profile with approximate
values of the rock properties obtained from 3-D velocity
logs is shown in Figures 8 and 9. In Figures 8, and 9, 7
and 11 possible weak bedding planes were assumed, re-
spectively, within the rock mass. The locations of these
weak planes were selected wherever there is a drastic
change in the dynamic modulus obtained from 3-D
velocity logs. It should be noted that because of [he nature
and type of rock present at the site, it is possible that a
larger number of weak planes may be expected in the field.
Geometry of cavity. As shown in Figures 8 and 9, an
average height of the cavity was 3 feet. An equivalent area
of the cavity was assumed to be 90% of the total area
mined. Because the shape of the actual cavity is a square,
for the purpose of analysis, the cavity was assumed to be
a circular disk with the same area as the equivalent cavity.
The radius o(the cavity was calculated to be 1080 feet.
Four problems as summarized in Table III were analyzed.
Problems 1, 2, and 4 were examined with the cavity 8 feet
thick, and with none, 7 and I 1 weak planes, respectively,
present in the rock profile. Problem 3 was analyzed assum-
ing the cavity is I S feet thick and with seven weak planes
in the rock mass to study effects of cavity thickness on the
calculated subsidence.
Observed subsidence profile. As much as 5.5 feet of
subsidence was measured near the centerline of the cavity.