2016-10-27_REVISION - C1981041

• Permit No: C1981041
• IBM Index Class Name: Revision
• Doc Date: 10/27/2016
• From: James A. Beckwith Attorney & Councelor at Law
• To: DRMS
• Type & Sequence: TR69
• Email Name: BFB
• Email Name: DIH
• Media Type: D
• Archive: No

14
both the third. and fourth -west panels had been retreated.
The average mining height in this arca was 7 ft; the
maximum subsidence was approximately 16 pct of the
mining height. This tack of subsidence indicates that the
support pillars that were left under Cottonwood Creek had
prevented any major effects on the drainage pattern of the
creek. The subsidence profiles for lune 1991 show that no
further subsidence had occurred in the creek arca. The
survey in June 1991 included only Ll-IA1 and Al -A26
because to survey the other monuments in this area
required a trilatcration survey as opposed to a facile level
survey. No surface cracking, changes in drainage, or
surface damage were noted either during the survey in
1986, or during the 1991 survey. The subsidence profile
for the C -line is shown on figure 14. The maximum value
for subsidence on this line as of April 22, 1983 was ap-
proximately 2.4 ft and occurred at station C27 prior to
mining of the fourth -west pant. The maximum subsid-
cncc in this area was approximately 32 pct of the mining
height, some innucncc from the adjacent panel develop-
ment was also prevalent in this profile toward the end of
the C -line (C41 -C49), which showed a subsidence value of
0.4 ft. Calculations regarding the angle of draw between
the third- and fourth -west panels (using the C•lin and
A-line transverse profiles across th • barrier pillar) yielded
an average 8' to 11' angle of draw for this section. The
fourth -west panel was mined during the later part of 1995.
The subsidence profde for the Wine is shown in fig-
urc 14. The maximum value for subsidence on this line
was approximately 2.7 ft and occurred at station LA7. The
maximum subsidence for this line was 37 pct of the mining
hcrght. The lack of subsidence is the area around Cotton-
wood Creek (L.31-135) iadicates that the support pillars
had not failed. Directly below the stream, mining aver-
aged approximately 50 pct extraction. The pillars west of
L37 were retreat mined. The ability of the barrier pillars
to protect the creek was apparent, since the subsidence
prafdes show link or no subsidence in the immediate area
around Cottonwood Creek.
The purpose of the residual subsidence survey per-
formed in June 1991 in the third -west section was to evalu-
a1c the long-term effectiveness of the barrier piNars below
Cottonwood Creek. The level survey included Al -A26 and
Li -L39. The resuks from the residual subsidence sun-ey
performed in 1991 are shown in figure 14. The elevations
of the survey monuments had not changed substantiaNy
from the survey performed April 1986. The data from the
survey performed in 1991 illustrate that the barrier pNlars
below Cottonwood Creek had not failed.
SUMMARY
The Bureau performed subsidence monitoring at the
Roadside Mine from 1981 to 1985. A survey to evaluate
residual subsidence at this site was performed in June
1991, and the results from this survey showed that no
measurable residual subsidence had occurred in any of the
three monitored sections (within the standard error of the
instruments). Several structures (pipelines and utility
lines), roads, and streams were above the mine. No phys-
ical damage to these structures or the stream was observed
by Bureau personnel, nor was any type of utility service
interrupted because of subsidence. Barrier pillars were
used to reduce subsidence hencath these structures and
minimize damage.
The maximum subsidence measured over the three sec-
tions was 3.0 ft, or 40 pct of the extraction height, and was
located in the northwest section on the C- and B-lines of
the monitoring networks. A shortage of surveys precluded
evaluation of the timing between the immcdiatc roof col-
lapse, pillar crushing, pillar punching, ovcthurden failure,
and subsequent surface subsidence.
Surface cracks were observed in one arca and were
deemed to be tension cracks resuking from subsidence.
Visual observation of the area affected by subsidence dur-
ing the survey of June 1991 showed a crack approximately
I to 2 ft wide aad up to 9 ft deep. The length of the crack
was approximately 200 ft, with the deepest section in the
middle of the length. The tension crack appeared in an
arca of high tension on the surface, immediately above a
panel edge. Erosion of this crack could have served to
broaden and deepen it during the time frame between the
last two surveys. The subsidence profiles showed no meas-
urable change in elevations from 1994 to 1991. No other
cracks were detected in other sections of the study area.
The piNars below Cottonwood Creek wcrc first-mincd
only, wish no observable changes to the local drainage
patterns. Overall, the physical effects on the surface were
negligible except for the surface crack in the northwest
section.