APPCOR12443

• Permit No: C1996083
• IBM Index Class Name: Application Correspondence
• Doc Date: 5/31/1996
• Doc Name: BOWIE RESOURCES LIMITED BOWIE 2 MINE FN C-96-083 NEW PERMIT APPLICATION
• From: DMG
• To: J E STOVER & ASSOCIATES
• Media Type: D
• Archive: No

J.E. Stover & Associates -31- May 31, 1996
Bowie No. 2 Mine
1.2 MINING SCHEDULE AND RATE OF SUBSIDENCE
The preparer states; "It is reasonable to assume that the initial
subsidence is negligible compared to the final, maximum
subsidence." The report further states; "While subsidence of
small magnitude will occur during mining of entries and rooms,
the majority of the subsidence will occur during and after pillar
recovery." These statements are generally true, but not
necessarily certain; particularly if discontinuities in the rock
mass, such as faults, are encountered during development. These
discontinuities can become the locus of dramatic short-term
ground mass response. Instances of this phenomena occurred
within the East workings of the Bowie No. 1 mine (previously the
Orchard Valley mine). For this reason it is important to
anticipate the possible subsidence implications of faults within
the mine plan area.
The preparer relates a general conceptual characterization of
subsidence response above retreating longwall workings, as
developed by Gentry and Abel above the York Canyon Mine's
longwall workings. The application of longwall subsidence
experience to room and pillar extraction assumes that efficient
and relatively complete pillar recovery will be accomplished. In
instances where pillar recovery, due to bad ground conditions,
equipment problems, or water problems is less efficient than
projected, the distribution of strain, the magnitude of ultimate
subsidence, and the timing of subsidence will be effected.
Therefore, it will be important to establish the effectiveness of
pillar recovery in retreat early in the operation of the Bowie
No. 2 mine. Further, if recovery proves to be less than
projected, it may be necessary to place high resolution monuments
above early panels to determine the actual character of ground
subsidence manifested.
1.3 SUBSIDENCE MAGNITUDE AND PROFILE
The preparer references an NCB method for projecting the maximum
subsidence above a panel of sub-critical width. Figure 15-3, a
reproduction of Figure 3 of the Subsidence Engineer's Handbook
(SEH), is used to determine the projected maximum subsidence
above a partially extracted super-critical panel. Exhibit 15
determines a subsidence factor (Smax} of 0.472 for this
situation, which results in a maximum projected vertical
subsidence of for the 12.0 feet extracted height of 0.472 x 12.0
feet = 5.7 feet. The preparer next applies figure 4 of the SEH,
which corrects maximum projected subsidence for the effects of
sub-critical panel width. Exhibit 15 determines an s/S
(subsidence correction factor} of 0.23. In accordance with SEH
methodology the super-critical panel maximum subsidence is