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. at Sunland, there are no thick strata of glacial nr glacially derived sediments <br />which are unconsolidated and the bed rock at Sunland consists primarily of <br />shales and thick beds of sandstone. Sunland's overburden characteristics <br />would indicate, if anything, that the subsidence potential here would he <br />toward the low side of the mines studied, as shown in Figure 1, for an 80X <br />extraction rate. The conclusion is supported by the history of mining on the <br />Sunland lease. <br />In fault blocks 1 and 2 where mining is planned in [he Lower Pinnacle <br />seam it is noted from the map that considerable mining of [hie seam has been <br />conducted in the past. In fact, the original Apex Mine No. 1 was operated <br />beginning in 1932 through 1964 when it was abandoned. It is reported that <br />pillar extraction was used in this mine also. The Apex Mine No. 2 was opened <br />in 1965 and is presently on a standby basis. An examination of the caved areas <br />in Apex No. 2 reveals that shortly after the pillars in the room are pulled, the <br />immediate roof caves and swells to the point where the void is almost completely <br />filled. This caving of the immediate rock and its swell, thus filling the void, <br />• probably has some effect on stabilizing the total subsidence of the strata <br />above the mined out areas. It is impossible to say for certain that no sub- <br />sidence has occurred on the surface above the mined out areas. However, <br />there were no apparent signs of subsidence when the property was visited a <br />couple of years ago and an examination of the aerial photographs taken in <br />October ]979 did not indicate any signs of subsidence. Since mining was begun <br />In Apex No. 1 in 1932, almost SO years have passed witliou[ any substantial <br />signs of subsidence in mining the lower I'lnnacle scam. Tl~e remainder of the <br />bower pinnacle to be mined in fault blocks ] and 2, would be expected to act <br />in the same manner as the previous mining. Therefore, it is not known whether <br />subsidence will ever occur, and if so, it may be several decades before signs <br />arc found on the surface. <br />With U~c use of the empirical data, ralculatlons and projections of <br />ultimate subsidence were made. It was calculated that the maximum subsidence <br />over [he Lower 1'innac]e scam in fault blocks 1 and 2 will probably I,~~ between <br />]0 and 39 inches, and that the average over the subsided area would Lc somewhere <br />lJ <br />20 2- <br />ti D. H. EMLING COMPANY <br />