1987-12-01_PERMIT FILE - C1981017 ‎(193)‎

• Permit No: C1981017
• IBM Index Class Name: PERMIT FILE
• Doc Date: 12/1/1987
• Doc Name: Willard Ownens Comments on Subsidence
• Section_Exhibit Name: Chapter IV Appendix IV-F-3
• Media Type: D
• Archive: No

IUJILLRRO ow Ens
ASSOCIRTEES
4405 W.29th Avenue inc
Denver,Colorado 80212
(3031433.7331
Geotechnical Consultants • Engineering Geology.Geophysics • Ground Water Hydrology
April 29, 1981 Soils&Foundation Engineering
Mr. Douglas W. Bowman
Environmental Coordinator
Mid-Continent Resources, Inc.
P.O. Box 158
Carbondale, CO 81623
• RE: MLRB Adequacy Review -
Subsidence
Project No. 9802-111
Dear Doug:
The followingremarks address
your request of April 22
concerning the adequacy of the Subsidence section of your
MRP application on the Coal Basin mines .
With regard to point 1, it could be emphasized that surface
examination above Mines No. 1 and No. 2 revealed no subsidence.
As stated in our report, an area of 800 feet by 5, 000 feet
had been subjected to the effects created by removal of
16 feet of coal. Therefore, discussion of "worst case"
conditions would become largely theoretical in the absence
of differentiated rock mechanics data, and any calculation
factors to be used must be obtained from references which
contain many empirical assumptions.
The literature on subsidence is sparse regarding measured
ratios of subsidence in Mesa Verde coal mines, an although
it would be preferable to rely upon such available data,
there have been numerous other subsidence studies which
supply statistics of value. Gentry and Abel (1977) report
-maximum subsidence ratios in one Mesa Verde mine (up to 690
feet of cover) as . 71, with determinations as low as . 51.
Dunrud (1976) reports a subsidence ratio of 0.31 measured
at Somerset (probably under less rigid experimental controls) .
Although subsidence ratios in European coal mines 'involve
different geologic environments, subsidence ratios are shown
which vary from 0.10 to 0. 90.