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2010-05-12_PERMIT FILE - C1981010
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Last modified
8/24/2016 4:11:49 PM
Creation date
6/16/2010 1:47:05 PM
Metadata
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Template:
DRMS Permit Index
Permit No
C1981010
IBM Index Class Name
Permit File
Doc Date
5/12/2010
Doc Name
Revised K-Pit Butttress Fill Stability Analysis, Feb 2010
Section_Exhibit Name
Appendix T
Media Type
D
Archive
No
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February 1, 2010 <br />EXECUTIVE SUMMARY <br />Page 1 <br />Over the past 2 years, Agapito Associates, Inc. (AAI) has worked with Trapper Mining, <br />Inc. (TMI) to develop a suitable plan for the mining of K -Pit from a geotechnical point of view. <br />As this project has progressed, new information has been obtained, and the focus of attention has <br />changed to the point that AAI felt it was necessary to re- evaluate the K -Pit buttress and the <br />mining of K -Pit with this latest information. TMI agreed, and commissioned this report. <br />The results from this latest modeling indicate that there are some natural, potentially <br />unstable areas within the mining area in existence prior to K -Pit mining. Rerunning the previous <br />slope models in FLAC /Slope without the "filtering" of near- surface failure planes confirmed <br />these results. AAI has identified areas of concern within the K -Pit mining footprint that should <br />be approached with the understanding that gradient of the slopes in this area should be reduced to <br />decrease the potential of movement. These areas are generally small., and any movement would <br />be away from mining activities. These localized areas do not represent a global instability, but <br />rather, areas of concern. Haul roads would be the one exception to slide exposure; therefore, haul <br />road cut slopes should be reduced to less than a 3:1 horizontal: vertical ratio (3H:1V). As always, <br />proper drainage of surface runoff in these areas is critical. <br />As previous modeling indicated and current modeling confirmed, the K -Pit buttress is not <br />required for long -term stability of the reclaimed K -Pit. Earlier modeling also suggested the <br />buttress would enhance the stability of K -Pit mining; however, the current modeling indicates <br />that the buttress does not stabilize the slopes for the mining below the KIL -10 cut. The stability <br />of this area can be obtained by reducing the slope by pre- stripping cuts KIL -1.3 and KIL -14 to <br />the I -Seam. Once the back slope has been reduced to a slope less than 3H:1 V, the factor of <br />safety (FOS) increases to 1.183 from 0.725. After the I -Seam is removed from cut KIL -15, the <br />.FOS increases to 1.855. <br />When the initial modeling was focusing on deep- seated failure plains, the loading of the <br />K -Pit buttress needed to be concentrated over the reclaimed G- Strike -Pit. However, when the <br />potential movement of near- surface failure plains is included, the sub -grade below the buttress <br />fails with the surcharge loads of the proposed buttress configuration. A design incorporating a <br />maximum thickness of 50 ft and maximum slopes of 3H:1 V will meet the long -term stability <br />requirements. <br />1.0 INTRODUCTION AND BACKGROUND <br />During October, 2006, there was a landslide event in what was then called the G -Pit. <br />This area is now defined as K -Pit and L -Pit. The general path of the slide block was to the north- <br />northeast, which is the general dip of the structure in the area. The slide area was bounded by G- <br />Dip -Pit on the east, and G- Strike -Pit on the north. Based on extensive computer modeling, <br />Agapito Associates, Inc. (AAI) believes that the failure surface was relatively deeply rooted <br />along L -Seam mudstones (Agapito Associates, Inc. 2007). <br />With substantial surface minable reserves in the K -Pit area, Trapper Mining, Inc (TMI) <br />has developed a mine plan to exploit the reserves. The initial spoils from the K -Pit stripping will. <br />Agapito Associates, Inc. <br />
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