REP47670 - Laserfiche WebLink

Home Browse Search

..`. under pressure and ground elevation decreased again in the first panel. The weight of the stratagraphic layers over the second and third panel is basically the same, therefore no ground cantilever occurred. It is predicted that the fourth panel will cause no increases in elevation in the third panel for the same reason. The results showed minimal subsidence over the first and second panel. This indicates that subsidence is reaching or has reached its maximum. Further evidence of this was indicated by a test run by the BLM using pressure cells located under the gob. This test show that pressure from the gobbed areas is staying constant and has reached its maximum. If strictly determining an angle of draw from the first monument showing change, the cross-sections show an angle of draw of -1.19 degrees in row K and 8.53 degrees in row S on the updip side of the gob. This variance along this edge of the gob is the result of monuments in row S being located on reclaimed spoil from strip mining. If the angle of draw in row S were determined using the definitions of surface settlement as areas where the change in ground elevation is uniform ko a side of a subsidence basin the end point would be point 5-22 and angle of draw -1.16. This angle of draw is more consistent with row K and the subsidence Dasin along that edge and therefore used. The monuments over the reclaimed spoils have settled, not subsided, as is common with all spoils from strip mining. The end points for the angle of draw were determined incorporating the definition for surface settlement written above. The angle of draw and end point locations are as follows: END ANGLE OF ROW POINT DRAW !DEGREES) COMMENT K K-20 -1.19 [IFDIP SIDE OF GOB NPR P-4 19.78 BEHIND GOB S S-3 19.10 DOWNDIP SIDE OF GOB S 5-21 -1.16 UPDIP SIDE OF GOH The angle of draw and the maximum subsidence shown above are all within the predicted ranges submitted in Empires' permit. The permit predicted the maximum subsidence to be 8-feet and the maximum angle of draw to be 20 degrees. The monitoring points will be surveyed again in December. Results from these surveys will be submitted in the next semiannual report.