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January 15, 2008 <br />5.5 Dragline Cut Face Stability and Monitoring <br />Page 56 <br />The plan for G-Pit is to switch from a T & S operation to a combination of T & S above <br />L-Seam and dragline below L-Seam. The bedding planes in this area are oriented more northerly <br />and has flattened to an 8'-10° dip. The dragline will work itself updip on spoil removing the <br />L-M interburden and downdip removing the M-Q interburden, piling spoils behind to the west. <br />Meanwhile, the T & S fleet is expected to proceed 1-2 cuts ahead and will truck spoil around the <br />dragline to previous K-Pit cuts. The disturbed interburden within the landslide will be handled <br />by the T & S operation; the undisturbed lower interburden will be moved by dragline. <br />The eastward advance of the dragline cuts is expected to be favorable for highwall <br />stability. Bedding will have a slight dip back into the highwall face. This helps stabilize the <br />loose blocks. This operation is similar to that currently being carried out in the F-Dip Pit, except <br />the highwall will not be as high (-120 ft). It is anticipated that normal pre-splitting and cleaning <br />of the 75° highwall face will result in a stable highwall face below the L-Seam. It is <br />recommended that 25-ft-wide by 50-ft-high catch-benches be used on the highwall. The upper <br />T & S cuts will be laid back at 1 H:1 V. <br />The only location were rock mass disturbance might be significant below the L-Seam is <br />near the old G-Dip box cut area. In this location the G-Dip floor buckled upward. This area <br />(cuts G-9 through G-11) is planned for mining in 2015. Additional characterization may be <br />needed at that time to characterize the extent of disturbance below L-Seam. If the rock below <br />L-Seam is disturbed, the highwall should be laid back to 1H:1V or flatter depending on <br />conditions. <br />The likelihood of the landslide reactivating is difficult to quantify. Sudden large-scale <br />movement similar to the 400 ft of movement already experienced might pose a safety hazard to <br />personnel. Such reactivation movement is thought to be unlikely because of the stabilizing <br />effects of the current toe pile plus the following factors. <br />Placing K-Pit spoils at the toe of the landslide in the old G-Strike Pit area provides <br />resistance to additional movement. <br />Mining the updip crest of the landslide early in the sequence reduces loading on the <br />landslide resulting in a more stable condition. <br />If a small portion of the landslide breaks free and slides into the old G-Dip cut, it is not <br />anticipated to move very far (1-10 ft) nor is it likely to move suddenly because there is a rubble <br />pile at its toe which helps stability. Backfilling the G-Dip cut is not anticipated at this time. The <br />dragline will be operated from an engineered spoil pile for which landslide reactivation <br />movement would be away from the equipment and personnel. <br />Monitoring global movement of the landslide block should be continued. It is not <br />anticipated that additional survey benchmarks will be required unless the existing benchmarks <br />are damaged or destroyed. Monitoring frequency should be increased in when the autumn rains <br />are more frequent and in the spring when the winter melt is compounded by spring rains. When <br />displacement rates indicate acceleration, survey frequencies should be increased until rates <br />stabilize. <br />Agapito Associates, Inc.