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Longwall subsidence and slope monitoring points were <br />installed and surveyed in the fourth quarter of 1984. The <br />location of these points and the advancement of the first, <br />second and third longwall panel are shown on the enclosed <br />map entitled 8519-LS. The monuments have been surveyed on <br />a quarterly basis since longwall production began in May, <br />1985. The results from the first three surveys were <br />submitted and reviewed in January, 1986. The results from <br />the fourth and fifth surveys were submitted and reviewed in <br />August, 1986. The results from the sixth and seventh <br />surveys were submitted and reviewed in February, 1987. The <br />results from the eighth and ninth surveys were submitted <br />and reviewed in July, 1987. The results of the data <br />obtained from the tenth and eleventh surveys are included <br />in this report (second half 1987). <br />Results from the these reports are as follows: <br />1. June, 1985 showed no detectable subsidence took place. <br />2. Dec, 1985 surveys showed detectable subsidence as a <br />result of the first longwall panel being advanced 2,750 <br />feet. <br />3. June, 1986 surveys showed a decrease in subsidence in <br />all rows except R as a result of the longwall advancing <br />1,250 ft in the second panel and a cantilever effect <br />over the first panel. <br />4. Dec, 1986 surveys showed that in all rows, except S and <br />V, ground elevations had decreased in the vertical <br />direction when compared to prior data. This was due to <br />the longwall being mined 2,900 ft in the second panel <br />causing the strata to bend down as the entry pillars <br />between the panels failed, thus, overridinc~ the <br />cantilever effect. <br />5. During the June 87 surveys, the longwall wzis mining in <br />the fourth panel. The results showed minimal change <br />over the first and second panel. This shoors that <br />subsidence has reached its maximum. Further evidence <br />of this was indicated by a test run by the BLM using <br />pressure cells located under the gob. This; test shows <br />that pressure from the gobbed areas is staying constant <br />and has reached its maximum. <br />-1- <br />