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• predicted maximum room and pillar compressive strain is only 1810.u £ and only <br />880x£ in tension at 1200-ft depth. The application the same infinitely wide <br />panel assumption used in the longwall case reduces the predicted maximum com- <br />pressive strain to 1690 and increases the tensile strain to lOlOa£ at 1200- <br />ft depth. Table 3 and Figures 6,7 and 8 present the "worst-case" room and pillar <br />subsidence predictions. <br />A virgin ground correction was not employed in the case of room and pillar <br />mining because of the limited data available, 13 cases (Abel ~ Lee, 1980, p. 29). <br />Four of these cases were probably for measurements over previously subsided <br />ground. Not making a correction for virgin ground is also conservative, as can <br />be seen by comparing Table 1 with Table 2 for longwall subsidence. Figure 3 pre- <br />• sents the room and pillar vertical subsidence curve used for prediction. <br />1~b ~e prime'semt~su~theapr..ed~ie~ted~maxa~mumwsoum'~andefprill~lraz;~s.~b'sFi~d'e~¢~e~e~eets at <br />~elRer'7e~d~`deep'~°we~n~lY2'00'"~nd``2400='ft:`' The method used follows NCB (1975) pro- <br />cedure once the maximum vertical subsidence prediction is made. <br />"WORST-CASE" TOWER FOUNDATION EFFECTS <br />The footings for the tower foundations will move with respect to each other <br />when subjected to mining induced strains. For example, the 56.7-ft diagonal <br />across the 40 by 40-ft foundation footers will shorten by 0.23 ft if subjected <br />to 4090H ~ in compression, as follows: <br />4090w E = 0.004090 ft/ft <br />0.004090 (56.7) 0.23 ft <br />This example is for the "worst-case" maximum predicted compressive strain for <br />• birgin ground conditions and for the first panel of a series of panels. <br /> <br />