My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
GENERAL39115
DRMS
>
Back File Migration
>
General Documents
>
GENERAL39115
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
8/24/2016 7:58:39 PM
Creation date
11/23/2007 10:00:28 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1980007
IBM Index Class Name
General Documents
Doc Date
4/13/1990
Doc Name
APPROVAL TO RETREAT MINE NW SUBMAIN AND PANELS OF MT GUNNISON 1 MINE PER SPECIAL CONDITION 5 OF MINE
From
WEST ELK COAL CO INC
To
BLM
Permit Index Doc Type
WILDLIFE
Media Type
D
Archive
No
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
3
PDF
Print
Pages to print
Enter page numbers and/or page ranges separated by commas. For example, 1,3,5-12.
After downloading, print the document using a PDF reader (e.g. Adobe Reader).
View images
View plain text
<br />': <br />Mr. Jim Ferguson <br />April 9, 1990 <br />Page 2 <br />surveys completed previous to mining the panels and seven <br />post-mining surveys were utilized to determine the magnitude <br />and extent of subsidence which has occurred and can be <br />expected by retreat mining the F seam (see Exhibit 3.4.A.6, <br />"Subsidence Evaluation for Mt. Gunnison No. 1 Mine", in Volume <br />2A of WECC's Mine Plan and Reclamation Permit). Based on <br />these data and utilizing the Modified National Coal Board <br />Methodology for predicting subsidence, a subsidence profile <br />for the NW1S panel in the area of the nests has been prepared <br />(see attached drawings). Note that the profile is exaggerated <br />to be able to show the small vertical change over the larger <br />horizontal distances. <br />Projected subsidence in the center of the panel cross-section <br />with 500 feet of cover would be approximately 2.73 feet and <br />with 250 feet to cover would be approximately 3.92 feet. The <br />angle-of-draw of subsidence affect beyond the vertical extent <br />of the mined out panel is predicted to be 14.4 degrees or 130 <br />feet (with 500 feet of cover). The actual affect of <br />subsidence to a nest tree would be dependent on the depth of <br />cover and location of the tree in relation to the mined out <br />panel. <br />Trees located over the center area of the mined out panel (in <br />the center of the subsidence profile) would be generally <br />lowered by subsidence. Based on the subsidence profile, the <br />greatest change in surface slope over a 100 foot distance with <br />250 feet of cover would be approximately 2.5 feet (or 2.5$ <br />change) and with 500 feet of cover would be approximately 1.2 <br />feet (or 1.2~ change). These changes are so small that no <br />affect to trees located either in the 14.4 degree angle of <br />draw margin or directly above the mined out panel is <br />anticipated. Tension cracking in the 14.4 degree margin areas <br />generally is not significant when overburden is greater than <br />30 times seam height (or 210 feet in this case), though some <br />tension cracks may occur at the surface. Subsidence is not <br />instantaneous, but occurs over several months. Should a tree <br />be affected by tension cracks even though no subsidence <br />induced tension cracks have been found above any other mined <br />out areas of the mine, it is not expected to suddenly cause <br />the tree to topple. <br />Mining shown on the attached plan of the Northwest Submains <br />and panels is projected based on the seam height and coal <br />quality found in drill holes in that area. These plans are <br />subject to change, depending on the actual conditions <br />encountered during mining. We may not be able to mine the <br />panels out to the extent shown, for instance, or some pillars, <br />
The URL can be used to link to this page
Your browser does not support the video tag.