PERMFILE46063

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 5/21/2004
• Section_Exhibit Name: Exhibit 07e-8 PR6 Railroad Evaluation Final Report
• Media Type: D
• Archive: No

SubTerra, Inc. Twentymile Coal Company 6/19/2003
PR6 Rail Line Evaluation
1.2 Aaoroach
This phase of remedial planning followed the process used to estimate pre-ballasting
requirements for prior undermining of the Energy Spur. The overall approach included:
1. Extending track survey data input to the spreadsheet for the incremental length of track that
would be affected (to Station 370).
2. Comparing prior estimated subsidence with actual subsidence over Panels 12 and 13 Right.
3. Estimating the subsidence along each section of track for each panel extraction and the
associated re-leveling requirements. These are presented in both tabular and graphical form.
4. Evaluating whether re-elevation would require fill or ballast placement in Fish Creek or its
AVF.
Our approach utilized one large, integrated spreadsheet ko model maximum and transient
subsidence displacements at predetermined locations (or Stations) along the railroad alignment
for each of the planned longwall panels. Preliminary assessments were also made of the
increase in ballast height required during partial re-leveling of the Energy Spur as each panel
passes beneath it.
The starting track elevations for Stations down track to Station 370 were determined from prior
baseline surveys and survey data obtained during 12-Right and 13-Right undermining of the
Energy Spur supplemented by an April, 2002 survey by Twentymile Coal Company.
• 2. Subsidence Prediction
A substantial quantity of subsidence data has been collected by Twentymile Coal Company over
more than a decade during the extraction of longwall panels ranging from 625-ft to 1,000-ft wide
at depths from 600-ft to over 1,000-ft. These data were used to create Figure 2, which shows the
relationship between maximum subsidence and the panel width/panel depth ratio.
Cover in the Northern Mining District is typically thicker than elsewhere in the mine and ranges
from 1,100 to 1,200-ft providing for panel width/panel depth ratios of from 0.7 to 0.8 in the vicinity
of the Energy Spur. Figure 3 shows transverse subsidence profile predictions for the first and
subsequent panels. Subsequent extraction of the third and subsequent panels is predicted to
result in profiles having the same shape as the second profile in Figure 3 centered about the
center of the third panel (see Figure 5) or subsequent panels. These are the predicted final
profiles that would be realized after a panel has passed at least full depth past the point of the
section.
As noted above, two panels have previously undermined the Energy Spur in the Northern Mining
District. Subsidence data, obtained from surveys of ground stations conducted during these two
periods of undermining, were used to check the initial predictions. The results of the comparison
are shown in Figure 4. Figure 4 shows the initial effects of 12 Right and then the cumulative
effects of 12 and 13 Right. Initial subsidence over the rigid-yield pillar pair is slightly less than
predicted and a broader hump results from the subsequent extraction of the adjacent panel. This
tendency has been checked for in the current prediction.
Table 1 and Figure 6 shows the predicted subsidence profile along the Energy Spur due to 14-
• Right undermining. The "predicted subsidence" curve was calculated by subtracting the original
cumulative prediction for 13 Right from the original cumulative prediction for 14 Right. This