2014-12-24_REVISION - M2004051 (4)

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bentonite and proper workability of the slurry. However, no additives shall be used except as approved by the Engineer. 2.05 BACKFILL The material for trench backfilling shall be composed of slurry, dry bentonite, and selected soils obtained from the designated borrow area. The soil shall be friable and free from roots, organic matter, 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 3/8" 65 -100 No. 20 40 -85 No. 200 ? 25 The fines in the backfill soil shall have sufficient plasticity so that the material can be rolled into a 1/8 -inch thread without crumbling (a measurable plasticity index). The water content of the backfill material shall not exceed 20% prior to blending with bentonite and/or slurry. 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 final backfill mix. The wasted sand and gravel shall be replaced with approved supplemental on -site clay soils. Supplemental clay soils may have to be stockpiled along the slurry wall alignment as directed by the Engineer. 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. Initial laboratory results indicate an addition of dry bentonite to the soil/bentonite backfill is required at a rate of 1.0 percent of the dry weight of backfill material to provide an adequate reduction in permeability. PART 3 - EXECUTION 3.01 TRENCH EXCAVATION EQUIPMENT Excavation of the slurry trench cut -off 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 final depth of cut continuously along the trench line. Excavation equipment used shall have the capability to excavate at least two (2) feet deeper than the maximum depth shown on the drawings. Special chopping, chiseling or other suitable equipment may be used as necessary to satisfactorily accomplish the required excavation. The width of the excavating tool shall be equal to or greater than the specified minimum width of the cut -off wall. Additional equipment such as air lift pumps, slurry desanders or other approved methods shall be used to clean the trench bottom and/or slurry in accordance with the requirements of the Specifications. 3.02 SLURRY BATCHING PLANT The slurry hatching plant shall include the necessary equipment including a mixer capable of producing a colloidal suspension of bentonite in water, pumps, valves, hoses, supply lines, and all other equipment as required to adequately supply slurry to the trench. Storage ponds shall be provided to store initially mixed slurry to allow hydration and to serve as a reserve in cases where substantial slurry loss from the trench through underlying pervious zones or other reasons may occur. The slurry shall be agitated or recirculated in the storage ponds as required to maintain a homogeneous mix. All slurry for use in the trench shall be prepared using a suitable mixer. No slurry is to be made in the trench. Mixing of water and bentonite shall continue until bentonite particles are fully hydrated and the resulting slurry appears homogeneous. Wattenberg Resource Pond 3 Slurry Wall Section 02168 — Slurry Wall Construction Page 2