PERMFILE47760

• Permit No: C1981010
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: BLASTING
• Section_Exhibit Name: APPENDIX L
• Media Type: D
• Archive: No

STATE OF COLORADO
I
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Roy Romer, Gove
DEPARTMENT OF NATURAL RESOURCES
MINED LAND RECLAMATION DIVISION
DAVID C. SHELTON, Director
DATE: March 31, 1987
T0: Grego Squire
FROM: Jim Pendleton - ~C"~'-'-"-
RE: TRAPPER MINE ER P.EVISION N0. 1 APPLICATION
(Permit FI C- -010)
I have reviewed Trapper Mining, Int.'s request to extend its permit area, in
order to surface mine coal overlying Empire Energy's proposed underground mine
workings. Trapper correctly observes that, if the surface mining is not
completed first, the surface coal resources may be rendered unrecoverable.
Trapper must blast the overburden and coal prior to excavation. Trapper
correctly anticipates a Division concern regarding the safety of the
underground workings within the Eagle Mines. Trapper states that it will
perform blasting during shift breaks, in order to minimize the risk. While
this is undoubtedly a desirable component of a safe blasting plan, it is
inadequate to demonstrate the adequacy of their plan to protect the
underground mine workings.
I have several specific concerns related to the effects of blasting of the
sup?rimposed operations upon the underlying Eagle i•tine workings. The
propagation of shock waves from the surface blasting could increase the
overburden load and reduce the strength of the supporting pillars leading to
failure of those pillars. Empire has included analyses of underground mine
pillar safety in its previous permit documents. These analytical calculations
should be revised by Trapper Alining, in order to include the incremental
loading proposed by acceleration of the overburden, resulting from the blast
wave passing through the mined horizon. In order to amend the pillar strength
calculations appropriately, Trapper 14ining will need to project the peak
partial velocity and acceleration caused by their proposed blasting. Their
past blasting studies could provide applicable data. Utilizing the resultant
acceleration factor, the pillar strength calculations could then be amended to
reflect the dynamic overburden loading instantaneously applied to the pillars
as the blast shock wave passes.
There will also be a concern for long-term effects upon the safety of the
underground mine workings. !Jill the repeated exposure to hlasting vibration
degrade the roof and ribs, leading to small roof falls or rib blowouts?
X23 Centennial Building, 1373 Sherman Street Denver, Colorado 802032273 Tel. [phone]