2015-02-26_REPORT - C1982056 (3)

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� 3 G 4. > i Figure 7 Railroad Subsidence Panel 8 -Right 4.1 Subsidence Mitigation Plan Subsidence was predicted using the approach described above with the following additional steps: • Daily subsidence was predicted for points on the rail (Stations) located 100 -ft apart assuming a daily retreat rate of 100- ft/day. Transverse and travelling profile data were used in this prediction. • Daily gradient changes were predicted and required ballast adjustments were calculated to control track gradients within the required tolerances. • OveralI ballast requirements were calculated. Culvert extensions required to accommodate the increased ballast footprint were also estimated. • A plan was developed to monitor and mitigate subsidence during undermining. 4.2 Monitoring Program The monitoring program included paired measurements on the rail and on the ground adjacent to the track. Where possible, station pairs were established so that the ground station was located �� i V i . 100 -ft behind the rail station in a line parallel to the direction of face retreat. Thus, the ground station monitored subsidence that the rail would experience the next day. Initial baseline measurements were made when the panel was well outside the zone of influence for the Energy Spur (approximately 2 x depth to mine floor) and continued on a daily basis until the face had retreated beyond a point where it was affecting the track. North, East and elevation survey data were collected daily and uploaded to the prediction software for evaluation. Recommendations were made for ballast adjustments at individual stations on the track to control gradient and strain in the rail. A majority of the daily analysis was conducted at remote sites with recommendations provided to multiple addresses via e -mail. 4.3 Subsidence Figure 8 shows the baseline, predicted, and daily track elevations for the Energy Spur track during 8 Right undermining. The upper curve shows the original rail which had differential gradients as high as 0.5% between adjacent 100 -ft segments.