PERMFILE121286

• Permit No: C1981025
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: Subsidence at North Thompson Creek Mine
• Section_Exhibit Name: 4.0 Appendix 4-H
• Media Type: D
• Archive: No

Borst Possible Subsidence Effects
Full Extraction Mining. The angles of draw and maximum subsidence
values presented in the preceding section represent the subsidence phe-
nomena that may occur as a result of full extraction mining. As a con-
sequence. these maximum subsidence values represent the worst case
values for full extraction mining 1f the engineering prediction techni-
que used is valid. In simplest terms, in areas of full extraction min-
ing, the maximum amount of subsidence that can possibly occur will
occur.
Development Mining. In those areas where mining will consist only of
widely spaced development entries. the worst possible subsidence effects
' • would result from a collapse of the entry.
The possibility of an entry failure has a very low probability factor.
The ratio of the entry opening volume to the volume of the surrounding,
unmined coat is low enough to preclude any maJor failure.
Should the low probability failure event occur, the small ratio of entry
opening width to overburden depth will preclude any surface manifesta-
tion of the failure. The overburden has sufficient height to allow for
the development of astable arch above the failed entry.
Based on these factors, there are no worst possible subsidence effects
from the development mining. Subsidence will not occur.
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