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1100318 R0T0 0811 JRW1 17 <br />extending southward from where the motion was first observed, and the <br />movement was observed over the entire mass below this rift.46 <br />The third motion of the Pikeview Landslide and “rift” described above is consistent with the <br />ground crack traversing undisturbed ground above the headscarp located in the highwall. The <br />ground crack is identified in Photograph 10. This ground cracking is consistent with a larger <br />instability extending further upslope and establishes the upslope boundary of the Pikeview <br />Landslide. As discussed below, the portion of the slope enveloped by this landslide boundary <br />experienced episodic movement after December 2, 2008. All these movements shared two <br />common characteristics. First, they occurred as translational rock slides on a common failure <br />surface. Second, the post-December 2, 2008 slope movements are nested within the boundary <br />of the Pikeview Landslide created on December 2, 2008. <br />The Pikeview Landslide is consistent with a translational rock slide where the predominant <br />movement occurs along a more or less planar surface. During displacement, the rock mass <br />rubblized and behaved similar to a soil-type failure with spreading along the toe. Notable <br />characteristics of the rock slide are the pressure ridge that formed at the north toe and the <br />displacement through and over the backfill placed at the south end of Area H. The <br />manifestation of the pressure ridge is consistent with buttressing support provided by the middle <br />bench in Area H; the condition of the pressure ridge on the day of the failure is shown in <br />Photograph 13. The displacement of landslide debris through and across backfill placed in the <br />southern portion of Area H and into Area H on the day of the failure is shown in Photograph 14. <br />Following the slope failure, a remote slope monitoring system was installed, consisting of an <br />array of prisms on the slope whose positions are regularly monitored from a stationary total <br />station located outside the failure area. The system became operational on September 3, 2009. <br />Because of landslide movement, several prisms have become unreadable. Photograph 15 shows <br />the locations of the prisms. Figure 16 provides an example of the monitoring data. <br /> <br />46 United States Department of Labor, Mine Safety and Health Administration, Pittsburgh Safety and Health <br />Technology Center, Mine Waste and Geotechnical Engineering Division, Report No. MW09-008, February 23, <br />2009, page 5 (Appendix 36)