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J(HIUM'Y 15, 2008 Pgge 23 <br />4.0 St"ll. S1'AI3lLrrN' ANALYSIS <br />The mining plan in the K-Pit area calls for spoils to be placed in three areas: ( 1) downdip <br />of the landslide, (2) in Horse Gulch, and (3) in previously mined K-Pit cuts. In K-Pit area. the <br />spoils will he set on relatively steep inclined bedding of the weak Q-Floor mudstone where spoil <br />stability is a concern. A stability analysis of the spoil pile was performed to assess the maximum <br />height of the spoil pile heture spoils become unstable on the bedding. <br />The analysis was performed using the two dimensional (2D) numerical modeling <br />program, FLAC." The analysis used calibrated rock mass properties obtained from the G-Pit <br />landslide FLAC31) stability analysis.`' The strength properties of the spoils were calibrated <br />from recent minor spoil failure events in the l.-Dip Cut #2. 'T'he spoil stability analysis was <br />pertormed to determine the maximum stable height of spoils for expected spoils and Q-Floor <br />mudstone bedding conditions. Various spoil slope angles, fill heights, and groundwater levels <br />were simulated for assessing overall spoil stability. <br />4.1 Calibration of Spoil Strengths <br />A simple 3D model was developed of L-Dip Pit Cut #2. The purpose ofthe model was to <br />calibrate the strength ofthe spoils to observe spoil slump behavior. While mining 7.D-02 on the <br />Q-Seam cut, a large volume of spoils began to creep front the spoil pile to the west into the open <br />seam area. Although the dragline was sitting on the spoils at the time, the spoil movement was <br />downdip. <br />Figure 14 shows the surveyed cross section ofthe ID-02 pit spoil failure showing pre- <br />slide profile (green line) and post-slide profile (magenta) of the spoil slide that started on <br />August 18, 2007. The east-west cross section is shown at N 404,700. The extent ofthe cracking <br />to the north on August 19, 2007, had also been mapped. The slide extended further to the north, <br />but no one was allowed in the area after August 20, 2007. The spoil pile was about 120 11 high <br />and had a slope lace angle of about 42°. <br />This inturmation was used to calibrate the strength properties of the spoil since it is <br />known that 12041-high spoil pile placed on the 8° northward sloping Q-Floor nutdstones with a <br />42° slope face is known to exceed its limit ofeyuilibrium and fail. <br />A 3D analysis was performed using FI.AC3D numerical modeling program. Figure 15 <br />illustrates the 31) conceptual model ofthe ID-03 spoil pile with the open Cut #2 to the east anti <br />the 120 ft of spoils to the west. The bedding was assumed to dip 8° to north. The spoil face was <br />assumed to dip 42° to the N83.7°E to allow for thickening downdip. The thickness of the <br />Q-Floor mudstone was assumed 14 ft thick to include carbonaceous mudstone, thin sandstone, <br />" FLAC (2005), "Fast Lagrangian Analysis of Continua - User's Guide," Itasca Consulting Group, Inc. <br />Minneapolis, MN, Version 5.0. <br />is FLAC'31) (2005), Fast Lagrangian Analysis of Continua in 3 Dimensions - User's Guide," Itasca Consulting <br />Group, Inc., Minneapolis, MN, Version 3,0. <br />1o Agapito Associates, Inc. (2007), "G-Pit Lant1slide Stahilir?' Remi-I Task Z" prepared for Trapper Mining, Inc., <br />March 19. <br />Agapito Associates, Inc.