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2.5 SLURRY TRENCH CUTOFF <br /> A. A slurry trench cutoff wall shall be constructed to the lines, grades, and cross sections indicated on the <br /> drawings. The trench shall have essentially vertical walls, a minimum width of 36 inches, and shall key <br /> a minimum additional depth of 12 inches into the designated stratum as shown on the drawings. A <br /> generalized description of the soil profile through which the slurry trench cutoff is to be constructed is <br /> shown. <br /> 2.6 TOLERANCES <br /> A. The following tolerances shall apply to the slurry trench dimensions and construction. <br /> 1. The slurry wall alignment as shown has been chosen to allow a sufficient separation between the <br /> slurry wall and the crest of the gravel pit slope. It is critical that the slurry wall be constructed on the <br /> shown alignment and not deviate from centerline by more than 1 ft left or right. <br /> 2. The slurry trench shall be plumb within 3 degrees of vertical. <br /> 3. The depth of the slurry trench shall be measured or surveyed to within 3 inches of the desired <br /> elevation. <br /> 4. The excavating tool shall be at least as wide as the design width of the slurry trench. <br /> 5. Overlaps and changes in direction of the slurry trench shall require a full depth over excavation at <br /> least 5 ft beyond the centerline of the trench. In cases where the trench must be re-excavated(for <br /> example, due to an extended shutdown, cave-in,rework,etc.)the overlap into acceptable backfill <br /> shall be at least 10 ft. <br /> 2.7 EQUIPMENT <br /> A. Trench Excavation <br /> 1. Excavation of the slurry trench cutoff wall shall be accomplished by use of any suitable earth- <br /> moving equipment, or combination thereof, such as a backhoe, clamshell, chisels, and ripper teeth <br /> so the trench can be carried to its final depth of cut continuously along the trench alignment. The <br /> excavator shall have the capability to excavate at least 5 ft deeper than the maximum depth shown <br /> on the plans. Special chopping, chiseling or other suitable equipment may be used as necessary to <br /> satisfactorily accomplish the required excavation. The width of the excavating tool shall be equal to <br /> or greater than the specified minimum width of the slurry trench. Additional equipment such as <br /> airlift pumps and slurry desanders shall be used to clean the trench bottom slurry in accordance with <br /> the requirements of the specification. The trench excavation equipment shall be capable of <br /> excavating the required key into the designated stratum. <br /> B. Slurry Batching Plant(s) <br /> 1. The slurry batching plant shall include the necessary equipment including a high shear mixer <br /> capable of producing a colloidal suspension of bentonite in water, pumps,valves, hose, supply lines, <br /> and all other equipment as required to adequately supply slurry to the trench and/or the backfill <br /> mixing operation. Storage ponds shall be provided to store initially mixed slurry to allow hydration, <br /> and to retain a reserve in case substantial slurry loss through underlying pervious zones occurs. All <br /> slurry held in storage shall be agitated or recirculated to maintain a homogeneous mix. All slurry <br /> for use in the trench or backfill shall be prepared using a suitable mixer. No slurry is to be made in <br /> the trench. Mixing of water and bentonite shall continue until all particles are fully hydrated and the <br /> resulting slurry is homogeneous. <br /> C. Backfill Mixing and Placing <br /> 31 66 17-6 <br /> Prowers Aggregate Operators, LLC <br /> West Farm Pit Phase 2 Slurry Wall Soil-Bentonite Slurry Walls <br />