Laserfiche WebLink
page 5 <br />• to perhaps as much as 30° in moderately strong <br />strata beneath steep hillsides which are more <br />than 900 feet (274 meters above the mine work- <br />ings), although tfre precision is reduced on these <br />profiles because they are west of the B-6 bench- <br />mark." <br />NSC has used Fir. Dunrud's work as being representative of the strata ever <br />the E Seam in the Hawk's Nest f4ine, as our E Seam and the highv:ay `ails <br />within the 500-900 foct range above the B Seam. Rather than use the 69° <br />to 70° limit angle as '•1r. Dunrud has done, ':JSC has ci:~osen a 60° limit <br />tingle t0 d1lOV: for d Safety fa•.',LC r. The r~e 5tll ta~lt ;; 1'O,; ected ~UbSldcnC2 <br />effect, considering the 60° limit angle from the pillar extraction in the <br />E Seam is shown on the attached map (note the highvray and shaft are out- <br />• side the surface effects of subsidence). Ir. addition to the barrier <br />pillar and limit angle safety factors, the subsidence measured by Dunrud <br />was over a ccal seam 12 feet thick. ':Jhereas 4JSC's coal seam is between <br />5 and 6 feet thick. This is expected to considerably limit subsidence. <br />As another point, which also limits subsidence, ~JSC's coal seam has an <br />extremely soft floor which squeezes in to partially close the opening, <br />thereby reducing the effective er.traction height and also limitinn sub- <br />sidence. The mechanics of the floor squeeze is that the floor heaves <br />into the opening and tends to alloy the roof to subside rather than to <br />break. <br />(C) Description of '•?easures Taken to Ftitigate the Effects <br />the Effects of Subsidence -The only effects of sub- <br />• sidence other than damage to ±he highway or the intake <br />sfraft which l•JSC has effectively prevented through the <br />use of barrier pillars will be possible damage to the <br />