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PERMFILE123352
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PERMFILE123352
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Last modified
8/24/2016 10:21:08 PM
Creation date
11/25/2007 11:25:42 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1980007
IBM Index Class Name
Permit File
Doc Date
12/11/2001
Section_Exhibit Name
Exhibit 60 Subsidence Evaluation for Apache Rocks Mining Area & Box Canyon Lease Tract
Media Type
D
Archive
No
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Subsidence Evaluation For <br />Exhibit 60 The Apache Rocks And The Box Canyon Mining Areas Page 14 <br />• 4.5 Break Angle <br />The break angle, the angle (B, from a vertical reference) of a straight line projected from the zone <br />of maximum horizontal tensile strain at the ground surface to the boundary of the mine workings, <br />is more important than the draw angle for hydrologic analyses (Figure 2). The break angle <br />provides a means of determining zones, in relation to underground mine workings where surface <br />water most likely may be impacted. The break angle reportedly averages 10 degrees less than the <br />corresponding draw angle (Peng and Geng 1982). <br />The break angle ranges from -9 to 3 degrees in the current West Elk Mine subsidence monitoring <br />network. Topography appeazs to control the location of the zone of maximum tensile strain and <br />consequently the break angle. For example, the break angle is 3 degrees where tilt direction <br />(caused by subsidence) is opposite to the direction to the slope of the ground surface (42 percent <br />slope), but is -9 degrees where the tilt direction is in the same direction as the slope of the ground <br />surface (32 percent slope) (Table l). <br />Tensile strain caused by subsidence commonly reaches a maximum value in lineaz zones above <br />mining panels. The location of these zones can be determined by the break angle (the angle of <br />the break line from panel boundaries to the zone of high tensile strain. At panel boundaries with <br />solid coal, subsidence data from the West Elk Mine monitoring network shows that the break <br />• angle for subcritical mining panels ranges from -9 to 3 degrees with an average expected value of <br />about 0 degrees. <br />Information from the West Elk Mine subsidence monitoring network also indicates that the zone <br />of increased horizontal tensile strain ranges from 100 to 150 feet wide above mine boundazies <br />and from 100 to 250 feet wide above the chain pillazs. This zone is located approximately above <br />the edges of the panels or slightly outside the panel boundaries and above the center of the chain <br />pillars, unless adown-slope component of movement occurs on steep slopes in addition to the <br />differential tilt component. Cracks tend to be more common and more permanent in zones above <br />mine boundaries, barrier pillars, and unyielding chain pillars (Figure 5). Any surface or neaz- <br />surface water that might be present in this zone has a higher probability of being impacted than <br />that occurring in the centers of the panels. <br />4.6 Angle of Major Influence <br />The angle of major influence, R, (also called angle of influence) is defined by Peng (1992, p. 1 I) <br />... as the angle between the horizontal and the line connecting the inflection point and the edge <br />of the radius of major influence." The radius of major influence (r) is therefore the horizontal <br />distance from the vertical projection of the inflection point to the point of maximum subsidence <br />and the limit of subsidence (Figure 2). The angle of major influence is used for computer <br />C~ <br />831-032.181 Wright Water Engineers, Inc. <br />
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