PERMFILE41761

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

108 • Fourth International Symposium~Salt-Northern Ohio Geological Satiety
the location of the weak bedding planes could be ascer-
tained. Three weak bedding planes located at the depths
of 2l0 feet, 1000 feet, and 1800 feet were assumed. The
locations of these weak planes are shown in Figure 6.
Geometry ojcavity. Because neither the vertical extent
o(the salt producing interval nor the horizontal extent of
solution mining operations was known, the exact location
and geometry of the cavity cannot be determined. From
a rough estimate of total production to the date (August,
1959) when the field measurements were available (5-1/2
million tons), it was estimated that a thickness of IS to IS
feet of salt within the area of producing wells was re-
moved. The area of producing wells teas approximately
2000 feet by 4000 fee[. A number o(cases were analyzed
for the assumed idealized rock profile with a cavity 20 feet
thick and 1000 feet, 2000 feet, and 3000 feet in radius.
These cases are summarized in Table 1.
Obser)rd subsidcrtce profile. The field measurements
obtained indicate [hat subsidence of a magnitude of 2-1/2
[EPTN BElor ,
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TABLE I
Analysis-Case I
Height of Radius of Slip y
Cavity Ift.l Cavity Ift.) Layers Ko pcf
20 1000 Slayers 1.0 144
20 2000 Slayers 1.0 144
20 2000 None 1,0 144
20 3000 Slayers 7.0 144
feet, and horizontal compression of the ground surface in
the immediate plant area of as much as 4 inches per I00
feet, had occurred in a period between 1939 and 1958. I[
teas observed that the subsidence a-as localized within the
mined area. Away from the center of the mined area, the
magnitude of subsidence decreased gradually.
In addition to subsidence observed in the field, caving
in some of the wells was noted. The height of caving above
the sal[ too(ranged from 40 [0 122 feet indicating that the
shale bed separating the ttvo sal[ beds has caved in.
Co)nporlson ojcomputed and observed subsidence pro-
files. The results from the analytical studies conducted for
Case I are presented in Figure 7 and Table ]I. An average
subsidence profile measured in the field is also plotted in
Fieure 7 for comparison. For the cases in which three
weak planes were assumed, the subsidence at the center of
the cavity increases rapidly with increasing radii of the
cavity. The subsidence calculated is 0.62, 4.77, and 16.9
feet for the cases with the radius of the cavity equal to
4000, 2000, and 3000 feet, respectively. For the case with
the radius of the cavity equal to 2000 feet and assuming
no weak bedding plane in the rock mass, the subsidence
was computed to be 1.62 feet. The maximum subsidence
observed in the field was 2.7 feet. It is very interesting to
note by examining the observed and calculated subsidence
profiles presented in Figure7thatthe observed subsidence
could have been predicted if the radius of the cavity were
assumed to be about 1500 feet which is about the size of
the cavity expected in the field and three slip layers were
assumed to exist. (The mined area is approximately 2000
feet by 4000 feet.) The calculated results also indicate [hat
the subsidence profiles computed by assuming the exis-
tence of weak bedding planes are quite similar in shape to
that observed in the field.
~ I Eg • 3stos .sl J . o.)
1
~ DISC S`•nPED p"EH lrlt
nro a~~-~ zo n
Figure 6. Idealized rock pr of,le, Case I.
Case II
Geological conditions. The rock formation at the site is
primarily shale with scattered thin layers of sandstone
found at the depth of 110 to 1140 feet below the surface.
The upper 1000-foot-thick layer is dark gray, green, and
brown, laminated shales o(the Bridget Formation. Below
the Bridget Formation is 240-fool-[hick, grayish-brown
sandy Laney Shale, member of the Green River Forma-
tion.Immediately below the zone are predominantly light
grayish green shale of the Nilkins Peak Member of the
Green River Formation ui[h a thickness o(480 feet. Be-