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Progress Report on Tatum House Subsidence issues Page 3 April 12, 1995 The conclusions of the report on the study with respect to the surface were: • There was not enough data to determine the angle of draw or the magnitude of maximum subsidence. (page 5-38) • Vertical displacement of the overburden began when the mining face was 500 ft from the monitoring point. (page 7-3) The coal seam is 600 ft deep at this point, and the bottom of the effected extensometer rod was 194 ft above the mine. • Movements both horizontal and vertical were noted all along the survey lines of surface monuments. (page 7-3) • The overburden appears to subside in a relatively coherent rockmass. (page 7-3) • There is a strong suggestion that the groundwater in the overburden is in direct communication with the surface waters of the Purgatoire River. (page 7-4) Measurements were made on the surface, survey lines 1 and 3 measured the effects of room and pillar mining, survey line 2 measured the effects of longwall mining. The survey lines were 94 surface monuments arranged in lines to measure the changes in elevation and horizontal coordinates as mining progressed underground. A review of the data analysis, demonstrates that the vertical displacements on the surface tended to show a raising of the land surface on the order of a 0.1 ft., more than 500 ft. in front of the mining face, regardless of the type of mining, and then there was a settling as the mining face was developed past the point. Over the longwall the settlement was more than 3 ft., on the other lines over the room and pillar mining, from 0.5 ft to 1.5 ft. The same effect of raising the land surface was noted on each survey line. The surveys were not completed for the full subsidence. Two points were chosen that appear were only effected by the mining under study, the effects of other mining in the area is also noted in the report. An estimate of the depth to mining and the amount of surface displacement on a specific date, indicates that surface movement occurred at angles of 36° 30' and 37° 10' measured from a vertical line at the face to the location of the surface monument. There was substantial horizontal displacement measured also, but the time relationship was not well defined in the report. The measured raising of the land surface has been noted in other studies for other mines, and has been referred to as a "wave effect" by some investigators. Sometimes t'.Zis phenomenon can be attributed to a sliding of the surface soils down hillsides or "piling up" as the result of surface deformations. The important observation is that there was no difference in the initial effects on the surface between ]ongwall or room and pillar mining.