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West Elk Mine and from 100 to 250 feet wide above the chain pillars. This zone, is located approximately above the edges of the panels or slightly outside the panel boundaries and above the center of the chain pillazs, unless adown-slope component of movement occurs on steep slopes in addition to the differential tilt component. Cracks tend to be more common and more permanent in zones above mine boundaries, barrier pillazs, and unyielding chain pillars. Any surface or neaz-surface water that might be present in this zone has a higher probability of being impacted than that occumng in the centers of the panels. Angle of Major Influence The angle of major influence, (3, (also called angle of influence of the point of evaluation) is defined by Peng (1992, p. 11) "... as the angle between the horizontal and the line connecting the inflection point and the edge of the radius of major influence." The radius of major influence (r) is therefore the horizontal distance from the vertical projection of the inflection point to the point of maximum subsidence and the limit of subsidence (See Exhibit 60B, Figure 3). The angle of major influence is used for computer modeling by the influence function method. In the B Seam mining at West Elk Mine, the angle of major influence ranges (from a horizontal reference) from about 70 to 80 degrees. For E Seam mining in the South of Divide mining area, the angle of major influence is also expected to range from 70 to 80 degrees, which was used for the computer modeling described below. The angle of major influence may also be referenced to the vertical, as has been done for the break angle and angle of draw. The angle of major influence (from a vertical reference) is roughly equal to the angle of draw, and is therefore predicted to range from 10 to 20 degrees. Relation Between Dynamic and Final Subsidence Deformations Maximum dynamic tilt (change of slope) and horizontal tensile and compressive strain are reportedly less above longwall mining panels than are the final tilt and strain values at panel boundaries. Dynamic tilt and strain decrease, relative to final tilt and strain, as the rate of face advance increases. Dynamic tilt and strain reportedly decrease with increasing speed of longwall coal extraction (Peng 1992, p. 20-21). Based on observations in a West Virginia coal mine: 1. Maximum dynamic tilt decreased by an average of 42 percent (from 0.0024 to 0.0014) as the mining face rate of movement increased from 10 ft/day to 40 ft/day; dynamic tilt, therefore, decreased by 14 percent as the face rate of movement increased by 30 ft/day. 2. Maximum dynamic tensile strain decreased by an average of 22.5 percent (from 0.0031 to 0.0024) as the mining face velocity increased from 10 ft/day to 40 ft/ day; dynamic horizontal tensile strain decreased by 7.S percent as the face increased by 30 ft/day. C~ 2.05-121 Revised November 1004 PR70