PERMFILE134368

• Permit No: C1981022
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: Water Communication Potential from Overlying Workings /Abel, 1992
• Section_Exhibit Name: Exhibit 2.04-E4 Part 6
• Media Type: D
• Archive: No

Sanborn Creek Project Paqe 10 August 21, 1992
• height, at the elevation of the "C" Seam, for a total mining height
of 20 feet. It was further conservatively assumed that the
worst-case 99 percent confidence shale distribution of 96.5
percent, presented in Table 1, between the "E" and "C" Seams was
present, when the actual 99 percent worst-case shale distribution
between the "D" and "C" Seams is only 84.8 percent. The 33 percent
free swell for shale and 67 percent free swell for sandstone, from
Table 2, was used to calculate the weighted average free swell and
then to predict the collapse height of 175 feet, as follows:
Weighted average percent free swell
96.5 x 33$ = 3184.5
3.5 X 67$ = 234.5
100.0 3419.0 / 100 = 34.2$
Conical chimney collapse height (H)
H = 3h(100)/$S h - mining height (20 feet)
H = 3(20)(100)/34.2 $S - percent free swell (34.2$)
H = 175 feet
The 99 percent minimum confidence interburden thickness
between the "C" Seam and the "D" Seam is 180 feet. Therefore, it
is extremely unlikely that chimney collapse will penetrate the
• interburden between the underlying "C" Seam and the overlying "D"
Seam.
Gray, Bruhn and Truka (1977) physically documented the height
of collapse chimney subsidence above the Pittsburgh Seam for 127
cases. Their compilation of the height of collapse chimneys was
doubtless conservative because all their cases breached the ground
surface. Surface weathering no doubt weakened the rock through
which these chimneys developed, more than would be the case for
fresh rock underground. Gray, et al reported chimney subsidence
height without respect to the actual mining height or the
lithology. One of the 127 cases breached the ground surface 200
feet above the Pittsburgh Seam. Table 3 and Figure 3 present the
relative cumulative frequency distribution for their data. Their
Pittsburgh Seam based cumulative probability of an uncontrolled
chimney penetrating through the average approximately 44 feet of
interburden between the "B" and "C" Seams is 34 percent. Gray's
(1977) chimney data from the Pittsburgh Seam also indicates that a
chimney has a minor, approximately 0.8 percent, potential to
penetrate the approximate 190 feet of interburden between the "C"
Seam and the "D" Seam and essentially no probability of penetrating
the approximatelt 340 feet between the "C" and "E" Seams.
The US Bureau of Mines (USBM) provides conservative guidelines
for room and pillar mining beneath bodies of surface water and
• flooded underground mines, information Circular 8741 (1977). The
USBM guidelines were based on prior work by Moore and Nawrocki