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Panel 9 -Right <br />_-;G <br />� <br />7/14/97 <br />0G <br />Figure 7 <br />Railroad Subsidence Panel 8 -Right <br />4.1 Subsidence Mitigation Plan <br />Subsidence was predicted using the approach <br />described above with the following additional steps: <br />• Daily subsidence was predicted for points on the <br />rail (Stations) located 100 -ft apart assuming a <br />daily retreat rate of 100-ft/day. Transverse and <br />travelling profile data were used in this <br />prediction. <br />• Daily gradient changes were predicted and <br />required ballast adjustments were calculated to <br />control track gradients within the required <br />tolerances. <br />• Overall ballast requirements were calculated. <br />Culvert extensions required to accommodate the <br />increased ballast footprint were also estimated. <br />• A plan was developed to monitor and mitigate <br />subsidence during undermining. <br />4.2 Monitoring Program <br />The monitoring program included paired <br />measurements on the rail and on the ground adjacent <br />to the track. Where possible, station pairs were <br />established so that the ground station was located <br />�� �► ter, <br />Railroad <br />Panel 7 -Right <br />100 -ft behind the rail station in a line parallel to the <br />direction of face retreat. Thus, the ground station <br />monitored subsidence that the rail would experience <br />the next day. <br />Initial baseline measurements were made when <br />the panel was well outside the zone of influence for <br />the Energy Spur (approximately 2 x depth to mine <br />floor) and continued on a daily basis until the face <br />had retreated beyond a point where it was affecting <br />the track. North, East and elevation survey data <br />were collected daily and uploaded to the prediction <br />software for evaluation. Recommendations were <br />made for ballast adjustments at individual stations on <br />the track to control gradient and strain in the rail. A <br />majority of the daily analysis was conducted at <br />remote sites with recommendations provided to <br />multiple addresses via e-mail. <br />4.3 Subsidence <br />Figure 8 shows the baseline, predicted, and daily <br />track elevations for the Energy Spur track during 8 <br />Right undermining. The upper curve shows the <br />original rail which had differential gradients as high <br />as 0.5% between adjacent 100 -ft segments. <br />