REP10860

• Permit No: C1981014
• IBM Index Class Name: Report
• Doc Date: 11/28/1983
• Doc Name: ROCK MECHANICS SUBSIDENCE STUDY DORCHESTER 1 COAL MINE
• From: MLRD
• To: BOB LIDDLE
• Permit Index Doc Type: SUBSIDENCE REPORT
• Media Type: D
• Archive: No

Richard D. Lamm
Governor
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DEPARTMENT OF NATURAL RESOURCES
David H. Gelches, Executive Director
MINED LAND RECLAMATION DIVISION
DAVID C. SHELTO N, Director
DATE: November 28, 1983 ~„~
T0: Bob Liddle
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FROt4: Jim Pendleton _ ~ c.',
RE: Rock toe nits/5 idence Study--Dorchester No. 1 Coal Mine
Pursuant to your request, I have reviewed the Rock Mechanics report
submitted by Dorchester Coal Company. This report, prepared oy
John F. Abel, Jr., PE 5642, presents an analyses of pillar stability for
the proposed underground workings at the Dorchester tJo. 1 underground
coal mine in Fremont County, Colorado.
This sort of analytical exercise is a valuable component of any
underground mine's design process. In the particular case of the
Dorchester No. 1 Mine questions have arisen during the permit review
process relating to the potential effects of subsidence of the
underground workings upon overlying or adjacent property, structures,
public facilities, park lands, etc. Subsidence of the overlying ground
surface is directly influenced by underground pillar stability.
Subsidence can occur due to elastic deformation or failure of the roof,
as well as failure of the supporting pillars. However, in the event that
pillars are designed to prevent failure, the likelihood of surface
subsidence of significant magnitude is greatly reduced. In combination
with an appropriate analytical demonstration of roof stability, it could
be assumed that subsidence would be limited to the minor effects of
elastic deformation of the beaming roof and elastic deformation of the
pillars, both of which should be minor and unlikely to cause material
surface damage.
At this point in the process Dorchester Coal Company has informally
submitted this pillar stability analysis for my consideration. It is my
understanding that they believe it would be a component of a future
barrier pillar width requirements determination. Lacking a definition of
the report's specific purpose, I have reviewed it merely to determine its
prudence in relation to the current state-of-the-art of pillar stability
design. I offer the following observations for your consideration.
(1) The report analyzes the possible implications of utilizing a pillar
slabbing approach in developing portions of the Dorchester No. 1
t+{ine, in comparison to the more conventional technique now being
utilized. This technique has been used at the Roadside Mine, with
which Mr. Abel has also been involved in a consulting capacity, with
success. This analytical technique is in keeping with the prudent
state-of-the-art.
423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. [phone]