2018-12-26_REVISION - M2008078 (31)

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2.3 WATER A. Fresh water, free of excessive amounts of deleterious substances that adversely affect the properties of the slurry shall be used to manufacture bentonite slurry. The Owner shall be responsible for providing the source of the construction water for the project. The water's physical properties shall be in accordance with Table 1. It is the responsibility of the Contractor that the slurry resulting from the water shall always meet the standards of this Specification. 2.4 SB BACKFILL A. The material for trench backfilling shall be composed of fresh slurry,trench slurry, supplemental fines and selected soils obtained from trench spoils. Trench slurry may be disallowed if additives are not acceptable to the Engineer. The backfill mix shall contain a minimum of 1.0%dry-added bentonite by dry unit weight of backfill. The soil shall be friable and free from roots, organic matter, refuse, or other deleterious materials. The backfill shall be thoroughly mixed and reasonably well graded between the following gradation limits: Screen Size Percent Passing (U.S. Standard) By Dry Weight 3" 100% 3/8" 65%-100% No. 20 40%-85% No. 200 >30% B. The permeability of the backfill shall be less than 1 x 10'cm/sec when tested in accordance with ASTM D 5084. The slump of the backfill shall be 4 to 6 inches, and the density of the backfill shall be at least 15 pcf greater than the density of the slurry. C. The fines in the backfill soil shall have sufficient plasticity so that the material can be rolled by hand into a 1/8"thread without crumbling. The water content of the backfill material shall not exceed 20% prior to blending with bentonite and/or slurry. D. Excess sand and gravel excavated from the slurry trench will need to be saved for the slurry wall cap or "wasted" and not included in the final backfill mix. The"wasted" sand and gravel shall be replaced with approved supplemental clayey soils. Supplemental clayey soils may have to be stockpiled along the slurry wall alignment. Samples of the borrow material to be used in the backfill will need to be tested well in advance of slurry wall construction to insure an adequate supply of acceptable material is on hand. The Contractor is responsible for identifying any off-site supplemental fines source and delivering the material to the site. E. Dry bentonite at a minimum rate of 1.0% of the dry weight of backfill material will be added to the backfill prior to mixing. 31 66 17-5 Prowers Aggregate Operators, LLC West Farm Pit Phase 2 Slurry Wall Soil-Bentonite Slurry Walls