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Slurry Wall Design Report Loloff Pit 5/24/2016 Page 11 of 16 6 SLURRY WALL DESIGN The project drawing set is included in Appendix C. 6.1 Slurry Wall Alignment The proposed slurry wall alignment is shown on Sheet SH-2. The alignment was determined by Brierley Associates in conjunction with Hall-Irwin. The alignment length is approximately 5,574 linear feet. The work is to be completed in accordance with technical specification section 31 56 00 Soil-Bentonite Slurry Walls provided in Appendix D. 6.2 Slurry Wall Working Platform Slurry wall construction shall occur on a stable and flat working platform from which excavation, backfill mixing, and backfill placement can occur. Sheet SH-19 shows the working platform configuration that is required for mixing of the backfill along the side of the trench. Along the northeast corner of the proposed alignment, the ground surface increases in elevation while the bedrock gets deeper, resulting in a maximum height between the existing ground surface and the top of bedrock of approximately 102 feet. To get through the weathered bedrock and install the key, the slurry wall construction would need to be approximately 110 feet in this location. Through conversations with Hall-Irwin, in order to accommodate available equipment, the reservoir will be designed with a maximum slurry wall height of 75 ft. In order to accommodate the maximum slurry wall height, the work pad in the northeast corner of the pit will need to be constructed at el. 4622 ft. Temporary cuts up to 35 ft in height will be required to construct the temporary work pad. In order to accommodate a 60 ft wide work pad, temporary fill slopes are also required along parts of the proposed alignment. Temporary fills are to be placed at a maximum slope of 2H:1V. The maximum height of the temporary fills required to construct the work pad is approximately 30 feet, located in the southwest corner of the proposed alignment. Large fills are required here because the alignment has been shifted towards the existing pit to provide sufficient clearance from the XCEL right-of-way. The total volume of earthwork required for work pad construction is estimated below. Cut 118,000 CY Fill 35,000 CY Along the alignment, the working platform shall be constructed with a maximum 1.0 percent grade along the alignment. Portions of the alignment which require cuts or fills are indicated on sheets SH-4 to SH-7. The target elevation for the top of the reservoir is el. 4634 ft. Where the work pad elevation is lower than this, a low permeability berm will be constructed on top of the slurry wall. Because the slurry wall can only be constructed at a maximum 1% grade, the working pad elevation will grade between elevation 4634 ft along the south west end of the pit and 4622 ft along the north BRIERLEY ASSOCIATES Creating Space Underground