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3.3 CLEANING TRENCH BOTTOM <br /> A. Upon completion of excavation, any loose material or cuttings shall be removed from the bottom of the <br /> trench with the excavation tools or other suitable means such as air lift pumps. If the unit weight of the <br /> slurry in the trench exceeds the specified limits, or becomes unworkable,the heavy slurry shall be <br /> removed from the trench by airlift pump, clamshell, or other methods approved by the Engineer or the <br /> excess solids shall be removed from the slurry by settling ponds, screening, or desanding. The trench <br /> bottom shall be cleaned of debris and excess sand sediment prior to backfilling. The trench shall be <br /> sounded immediately before placing backfill, and soundings shall be compared to the trench excavation <br /> soundings to verify the bottom. At a minimum, soundings shall be taken each morning and each <br /> evening and as given in Section 3.9.H and compared to monitor for cave-ins or excessive settlement. <br /> The spacing of the each sounding shall be a maximum of 10 feet along centerline. <br /> 3.4 BACKFILL MIXING <br /> A. The backfill shall be mixed on site. If the backfill is mixed beside the trench,the contractor shall <br /> control and provide sufficient equipment and work platform space to support slurry spills, trench <br /> stability, and mixing equipment operation. Unmixed materials shall not be allowed to fall into the <br /> trench. If the backfill is mixed in a remote location,the contractor shall build and maintain adequate <br /> haul roads and the mixing pit or pad. The mixing pit or pad shall be lined with compatible soils or other <br /> materials to prevent contamination from unsuitable materials. In either case,the contractor shall be <br /> responsible for the quality of the backfill. <br /> B. Backfill materials and bentonite may be pre-mixed by blending in mechanical blenders or by <br /> windrowing, disk harrowing, bulldozing, blading or by other approved methods. Mixing and blending <br /> shall be performed in such a manner as to produce the required gradation of backfill. The backfill <br /> material shall be thoroughly mixed into a homogeneous mass, free of large soil clods, lumps or pockets <br /> of fines, sand, or gravel. <br /> C. Slurry, dry-added bentonite, trench-excavated soil and supplemental fines shall be mixed until <br /> homogeneous,tested for acceptability, and then immediately placed in the trench. <br /> D. The backfill shall be sluiced with bentonite slurry from the trench or fresh bentonite slurry during <br /> blending operations. Sluicing with water will not be permitted. Occasional particles of up to 3 inches <br /> in their largest dimensions will be permitted. Just prior to placing, the backfill material shall have a <br /> slump of 4 to 6 inches. To this end,the materials shall be shall be sampled and tested for permeability, <br /> density, and slump after preparation. <br /> 3.5 BACKFILL PLACEMENT <br /> A. The backfill shall be placed continuously from the beginning of the trench, in the direction of the <br /> excavation,to the end of the trench.The advancing toe of backfill shall be within reach of the trench <br /> excavator at all times such that the trench bottom can be cleaned in accordance with Section 3.4.A <br /> above. Excavation must permit inspection and measurement immediately after completion and prior to <br /> backfilling. Placing operations shall proceed in such fashion that the surface of the backfill below the <br /> slurry shall follow a reasonably smooth grade and shall not have hollows, which may trap pockets of <br /> slurry during subsequent backfilling. Free dropping of backfill material through the slurry will not be <br /> permitted. Initial backfill shall be placed by lowering it to the bottom with clamshell bucket or backhoe <br /> until the surface of the backfill rises above the surface of the slurry or by lead-in slope. Additional <br /> backfill may then be placed in such manner that the backfill enters the trench by sliding down the <br /> forward face of the previously placed backfill. To accomplish this, sufficient backfill shall be piled <br /> behind the crest of the existing backfill slope to cause a mudwave action at the face of the backfill. The <br /> backfill shall not be dropped or deposited in any manner that will cause segregation. <br /> 31 66 17-8 <br /> Prowers Aggregate Operators, LLC <br /> West Farm Pit Phase 2 Slurry Wall Soil-Bentonite Slurry Walls <br />