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REP38979
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REP38979
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Entry Properties
Last modified
8/25/2016 12:23:33 AM
Creation date
11/27/2007 8:15:02 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1996083
IBM Index Class Name
Report
Doc Date
5/8/2006
Doc Name
2005 Bi-Annual Subsidence Report
From
J.E. Stover & Associates Inc
To
DMG
Permit Index Doc Type
Subsidence Report
Media Type
D
Archive
No
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r~ <br />~~ <br />\_J <br />monuments to the east were positioned over areas <br />mined previously in the King and U.S. Steel mines <br />and thus results may be influenced by reactivation of <br />movement in these historic mining districts. Selected <br />monuments were surveyed annually using GPS. <br />Monitoring was more frequent at some locations. <br />Deep snows in the winter limited access for survey- <br />ing 3 to 4 months each year. <br />Subsidence engineering parameters include subsi- <br />dence factor, angle of draw, angle of critical defor- <br />mation, and horizontal strain. The subsidence factor <br />is the ratio of maximum measured subsidence to ex- <br />traction height. Because this ratio depends on exca- <br />vationwidth and overburden thickness, it should be <br />measured in supercritical excavations where caving <br />has reached the surface on collapse of the pressure <br />arch. <br />The angle of draw defines the limit of surface move- <br />ments beyond the edge of an excavation. It is <br />measured from a vertical line drawn at the panel <br />edge and a line connecting the panel edge to the <br />point of "no movement" on the surface. In practice, <br />the accuracy ofthe surveying equipment defines the <br />point of no movement. This accuracy is usually <br />about 0.04 m (0.1 to 0.15 ft). Considering the accur- <br />acy of the GPS equipment used at BRL, we have <br />used a value of 0.04 m (0.15 ft) for the limit to sen- <br />siblesubsidence movement. Angle of critical defor- <br />mation is similar to the angle of draw, but is <br />measured to a point of critical deformation with <br />respect to existing structures; it is preferred by many <br />practitioners because it avoids the shortfalls con- <br />nected with accuracy of surveying equipment. <br />Based on subsidence data from 401ongwall panels, <br />Peng [8] found that the angle of critical deformation <br />is ] 0° less than the angle of draw. <br />Horizontal strain is the change in horizontal length <br />of the ground divided by the original length of the <br />ground. Positive strain is used here to show tensile <br />strain indicating an increase in the horizontal length <br />of the ground. Compressive strain (negative nota- <br />tion) occurs when the ground is shortened or com- <br />pressed. Maximum tensile strain is found in super- <br />critical excavations, and maximum compressive <br />strain occurs in subcritical excavations. Horizontal <br />strain increases with an increase in extraction height <br />and decreases at greater depths. Surface topography <br />also influences horizontal strain. <br />Table 1 summarizes estimates for the angle of draw <br />and the subsidence factorbased on regional and site- <br />specific measurements. Regional measurements <br />have identified an angle of draw of 15° to 17°, <br />although a more conservative angle of draw of 25° <br />has also been used in some reports [9]. These meas- <br />urements are in general agreement with USGS <br />measurements in the range of 10° to 21° considering <br />the accuracy of the surveying equipment used in <br />those early days. <br />Table 1. Subsidence parameters for selected North Fork <br /> Valley sites. <br />Seam Subsidence Angleofdraw, Reference <br /> factor degrees <br />B Seam 0.70 I S to 25 Regional <br /> data <br />B Seam, U.S. N/A ]0 to 21 Dunrud <br />Steel 1976 []0] <br />D Seam, Bowie 0.60-0.75 15 to 25* <br />* Higher values used at deep cover for modeling purposes <br />Site-specific measurements show a minimum angle <br />of draw of 15°at monument station SE. Considering <br />all available data from the basin, an average angle of <br />draw of 15° to 17° is typical, although higher values <br />are locally measured at greater depths. <br />Measurements show a subsidence factor of 0.60 to <br />0.75 over the longwall panels. At one monument <br />(22D), the subsidence factor approaches 0.75. The <br />greater subsidence at this location is believed to be <br />influenced by local topography and the orientation <br />of a steep slope into the mined-out longwall panel. <br />3.1. Gate Pillar Behavior <br />Because gate pillar designs influence surface sub- <br />sidence, some recent investigations have focused on <br />evaluating subsidence above gate pillars. The west- <br />ern U.S. measurements show different overburden <br />deformation characteristics influenced by the choice <br />of pillar designs. Based on a comprehensive case <br />study by the USBM in 1991, Dyni [ 11 ]showed that <br />the narrow 9.1-m- (30-ft} wide yield pillars com- <br />monly used in thetwo-entry Utah reserves crushed <br />completely with no influence (or subsidence humps) <br />above the gateroads. This is in general agreement <br />with the measurements over the U.S. Steel mine <br />indicating uniform subsidence over a portion of a <br />40-ft-wide barrier sepazating two room-and-pillar <br />panels [10]. Thus overburden response is charac- <br />A -5 <br />
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