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~. <br />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 />and second longwall panel are shown on the enclosed map <br />entitled 8519-LS. The monuments have been :surveyed on a <br />quarterly basis since the 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 of the data obtained from the <br />last two surveys are included in this report (second half <br />1986). <br />Results from the June, 1985 showed no detectable subsidence <br />took place. The results from the second half of 1985 <br />surveys showed detectable subsidence as a result of the <br />first longwall panel being advanced 2,750 feet, these <br />results were included in the January, 86 report. The <br />results from the first half of 1986 surveys showed a <br />decrease in subsidence in all rows accept R as a result of <br />the longwall advancing 1,250 ft in the second panel and a <br />•,~'ycantilever effect over the first panel, these results were <br />included in the August, 86 report. <br />The current surveys show that in all rows except S and V, <br />subsidence has increased in the vertical direction when <br />compared to prior data. The maximum subsidence For the <br />affected rows are shown in table 1. <br />The cross-sections show that the ground elevations for the <br />majority of the monuments have decreased, except in rows S <br />and V. This indicates that the beam (or stratagraphic <br />layers), which forced the cantilever to increase ground <br />elevations in March and June (shown in the August 86 <br />report), is now bending and reaching equilibrium over the <br />first longwall panel, except near rows S and V. This is <br />due to increased ground pressure and a breakdown of the <br />entry pillars between the panels. <br />Rows S and V show an incremental increase in ground <br />elevations. This is because the longwall advance at the <br />time of the survey was nearly under these rows. This <br />caused the beam near this area to push up in panel one as <br />panel two subsided (the cantilever effect). As the <br />longwall advances well past row S in panel two, it is <br />predicted that the ground pressure will increase on the <br />beam, forcing it to bent.!. This along with a breakdown of <br />entry pillars between the panels will cause the elevations <br />of the monuments in rows S and V over pine! one to <br />eventually decrease again. <br />