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appear more prevalent along the south wall possibly due to the north facing <br />exposure. <br />10) The small surficial slide located in the exposed highwall face along the west <br />wall, which was noted in previous annual reports, appears unchanged from <br />over multiple years of observation. The slide does not have any impact on <br />the overall stability of the wall, as it is limited to less than a single bench in <br />height, and is considered a localized wedge failure. <br />11) A section of the northeast wall of the main pit originally experienced planar <br />failure along the foliation planes in 1998. Following removal of the next <br />bench in 1999, a larger section that is approximately 350 feet wide by 250 <br />feet high, experienced planar failure. The north wall pit slopes were <br />modified in response to these failures, and based on continued photo <br />documentation and visual monitoring since that time, no additional <br />movement has been detected (Photo 10). As described in previous annual <br />reports, the failure is believed to have occurred when a continuous foliation <br />plane was intersected by two or more existing discontinuities, and <br />daylighted in the exposed highwall. (See the Wedge Stability Analysis <br />section of this report for a complete description of this type of failure). <br />Based on the current topographic map (December, 2003) of the quarry, the <br />overall effective angle of the north pit walls has been modified over the last <br />three benches to an angle of 35° per L&A recommendations in the May <br />2003 report. The failure surfaces (i.e. the surfaces along which movement <br />has occurred) remain at a "residual strength" and therefore are less <br />resistant to additional loading. Although the slope configuration is currently <br />stable, the failure mechanism could potentially be reactivated upon removal <br />of subsequent benches, resulting in movement of additional material. <br />-13- <br />