2007-10-31_REVISION - M2006080 (2)

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5.06 Slurry Wall Back£dl Type and Placement The slurry wall shall be backfilled with SB backfill mixture consisting of a composite of excavated material from the trench (working platform, overburden, sand and gravel, and bedrock), additional dry bentonite, and bentonite slurry. All oversized material greater than 6- inches in diameter (cobbles, boulders, unbroken pieces of bedrock) shall be discazded and not used in the backfill mixture. The SB backfill shall have the following properties. • Minimum 30 percent fines (passing No. 200 sieve). This criterion will involve placement of a minimum of 2 cubic yards of overburden per lineal foot of trench; • One percent additional dry bentonite by weight; • Slump of 5 to 7 inches; • Wet Density 15 pounds per cubic foot greater than the slurry density; and • Permeability of less than or equal to 1.0 x 10-~ cm/sec. Increased amounts of bentonite (up to 2%) and increases to the overburden component (up to 100%) of the field mix are being considered by Loveland Ready Mix to decrease backfill permeability. These criteria were based on the mix design and other backfill mix designs used for other slurry walls designed by Lyman Henn and/or constructed by Compass Environmental. Section III of this report presents performance results for backfill and slurry planned for use on this project. SB backfill shall be mixed alongside the trench in a contained area and have the consistency of wet concrete when placed. The SB backfill shall be placed from one end of the trench and advance across the trench at aself-seeking slope, typically inclined at 5:1 to 10:1 (horizontal: vertical). The toe of the backfill slope shall extend to the bottom of the excavated trench, such that no more than 5 ft of trench remains open. A clean slurry trench bottom and backfill slope shall be maintained prior to the placement of backfill. The profile of the slurry trench bottom and the backfill slope shall be measured at the end of a backfill placement shift and prior to the next backfill placement shift at intervals of no more than 20 feet. If profiling prior to the next backfill placement shift indicates sedimentation or cave-in has occurred on the Slurry Trench bottom or the backfill slope, the material shall be removed by backhoe, clamshell, airlift pump, or other suitable equipment. This equipment shall be operated in a manner that prevents removal of material from the walls of the Slurry Trench. 5.07 Slurry Wall Working Platform and Construction Limits Slurry wall construction shall occur on a stable and flat working platform from which excavation, backfill mixing, and backfill placement can occur. Sheet 103 shows the working platform configuration that is required for mixing of the SB backfill along the side of the trench. As shown on Sheets 104 and 105, several reaches of the slurry wall alignment will require constmction of a working platform embankment. G:~PROIECI'S\10]021-000 lavelavd Ready Mu SWrty WaI~R. Raorda and Cortepondence\R.I I Rcpons\FirW SWrty Wall Design Report.doc