2006-02-02_GENERAL DOCUMENTS - M1999120

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2.02 BENTONITE Bentonite used in preparing slurry shall be pulverized (powder) premium grade sodium cation montomorillonite and shall meet the most current API Standard 13A, "API Specification for Oil-Well Drilling - Fluid Materials." 2.03 WATER Fresh water, free of excessive amounts of deleterious substances that adversely affect the properties of the slurry shall be used to manufacture bentonite slurry. It is the responsibility of the Contractor that the slurry resulting from the water shall always meet the standards of this specification. 2.04 ADDITIVES Admixtures of the type used in the control of oil-field drilling muds such as softening agents, dispersants, retarders or plugging or bridging agents may be added to the water or the slurry to permit efficient use of bentonite and proper workability of the slurry. However, no additives shall be used except as approved by the Design Professional (see Paragraph B, Standards (c) Additives of the QC Plan). 2.05 BACKFILL The material for trench backfilling shall be composed of slurry and soils obtained from the trench excavation. Supplemental fine-grained soils and dry bentonite will be blended into the backfill as outlined on the construction drawings. The soil shall be free from roots, organic matter, or other deleterious materials. The backfill shall be thoroughly mixed. The fines into the backfill mix shall have sufficient plasticity so that the material can be rolled into a 1/8" thread without crumbling. The backfill shall be reasonably graded between the following gradation limits: Screen Size Percent Passing (U.S. Standard) by Dry Weight 3/8" 65-100 No. 20 40-85 No. 200 ~5 Material excavated from the trench is not expected to meet the above requirements for backfill. Excess sand and gravel excavated from the slurry trench will need to be "wasted" and not included in the fmal backfill mix. The "wasted" sand and gravel shall be replaced with approved supplemental clay soils. Supplemental clay soils may have to be stockpiled along the slurry wall alignment in sufficient quantity to meet the minimum percent passing the No. 200 sieve. Samples of the borrow material to be used in the backfill were tested in advance of slurry wall construction. Laboratory results indicate an addition of dry bentonite at a rate of 1.0% of the dry weight of backfill material will provide an adequate reduction in permeability. The initial moisture content of stockpiled supplemental soils (which includes overburden and wash plant fines) will be periodically monitored for consistency during the slurry wall construction. PART 3 -EXECUTION 3.01 TRENCH EXCAVATION EQUIPMENT Excavation of the slurry trench cutoff wall shall be accomplished by use of any suitable earth-moving equipment or combination thereof such as a backhoe and/or clamshell so that the required width trench can be carried to its fmal depth of cut continuously along the trench line. The width of the excavating tool shall be equal to or greater than the specified minimum width of the cutoff wall. Section 02168 -Page 2 of 5 02/06