2015-02-26_REPORT - C1982056 (3)

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e795 oc 6; 6A 6; 0 ee aai e W 6; 6; 6; 67 480 490 500 510 520 90.00 Original 1 Daily Y 80.00 t 75.00 70.00 55.00 A�r X Target With Re- Leveling. Final grades have been revised to incorporate engineered vertical Curves. Predicted Without Re- Leveling $0.00 55.00 50.00 PF Assumes that Final Ballast Adjustments beyond Station 520 are being delayed until subsidence from 8 -Right is substantially complete. Figure S Baseline, Predicted, and Daily Track Elevations after Suggested Daily Ballast Adjustment The lower curve shows the predicted rail profile without re- leveling. The other curves show the daily progress of subsidence, the target profile for re- leveling and the actual, coincident re- leveled track profile. Final differential gradients were maintained within the tolerances specified by the railroad resulting in an increase in the quality of the line. Maximum measured ground and track subsidence was 54 -in which was located north of S- Right's centerline as expected. The predicted 60 -in was not realized primarily due to less than expected subsidence over the rigid -yield pillar pair and increased overburden west of Station 530. The maximum daily rate of subsidence development was approximately 18 -in and corresponded to a daily retreat rate of 140 -ft. Horizontal displacements were of no direct impact to track stability even though up to 14 -in of horizontal movement was observed with up to 6 -in of differential movement between stations. 4.4 Mitigation Mitigation involved periodic re- leveling of the rail to maintain differential gradients within tolerances 530 5Q0 550 560 570 Station required by the rail owner, Union Pacific Railroad. Union Pacific Railroad track maintenance staff made twice -daily inspections and periodic ballast adjustments to maintain the track. Grade tolerances in excess of the originally defined values were permitted due to the low train speeds through the affected section of track. The success of the track re- leveling program was in part due to the availability of a heavy duty Pandrol Jackson tamper rented by Twentymile Coal Company. This machine was able to resist the high horizontal forces associated with trough formation and horizontal displacement during track leveling. Flooding the track with ballast also limited the potential for the rail to buckle. Ballast was brought to the site primarily in bottom dumps so that the ballast could be spread using the regulator. Only minor trackhoe work was required to move side dumped ballast. 4.5 Results Both the coal mining and track re- leveling went according to plan with the face arriving beneath the track within a few days of expectations and complete subsidence being achieved within one week of