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West Elk Mine The purpose of this section is to describe, on a site specific basis, and to quantify, to the extent feasible, the various phenomena that are embodied in this definition. This section provides an ~ inventory of sttvctures and renewable resource lands in the current permit azea, which includes / the Box Canyon permit revision area, as well as a subsidence survey analysis, potenfial subsidence consequences, and the subsidence monitoring and control plan. Table 42 of this section provides a list of symbols and definitions for commonly used terms associated with subsidence and used frequently in this section. Table 42 Definition of Subsidence Terms I Symbol Defmitian Dimensions S Vertical Displacement (Subsidence) L Sro Maximum Vertical Displacement (Sro=a4) I- S/Sro Ratio of Vertical Displacement to Maximum Vertical Displacement L/L Sh Horizontal Displacement L t Coal Extraction Thickness L a=(Sro/t) Subsidence Factor L/L Subsidence Factor above Chain Pillars L/L S = •t Maximum Subsidence Above Chain Pillars L d Overburden Depth L Srold Ratio of maximum vertical displacement to overburden depth L/L W~, Critical Extraction Width L!L W/d Mining Width to Overburden Depth Ratio L/L M Tilt (Slope) L/L Mro Maximum Tilt L/L C Curvature, the reciprocal of Radius of Curvature rad/L (i/L,) Cm Maximum Curvature radll. (1/L) E Horizontal Strain (+) is Positive, (-) is Negative L/L Ero Maximum Horizontal Strain L/L ~ Angle of Draw Degrees B Break Angle Degrees (3 Angel of Major Influence Degrees r Radius of Major Influence L It is essential to understand the distinction between the "Apache Rocks permit revision area", the "Apache Rocks mining area" and the "Box Canyon Permit Revision Area" and to be awaze of the terminology regarding the panels in various areas. Consequently, the following defnutions and Map lA (and Map 1 in Exlu'bit 60) have been prepazed. 2.~5-98 RevisedJw.7995PR06;!/96RN03:RevisedMay/999TR89;RevisedJan.1998PR(18;RevirvdJm,.7999PR08