2018-12-26_REVISION - M2008078 (31)

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1. Equipment for mixing and placing backfill may consist of any suitable earthmoving or grading equipment, such as bulldozers, or blade graders or backhoes, or blenders such as a pug mill,that are capable of thoroughly mixing the backfill materials into a homogeneous blend having the required gradation and properties and placing the material in the trench as specified. Soil clods shall be broken to 3 inch maximum size by the backfill preparation equipment and methods employed. Deleterious materials, debris and oversize particles, shall be removed from the backfill before approval for placement. PART 3 - EXECUTION 3.1 SLURRY TRENCHING A. Excavation shall proceed continuously from the starting point to the finishing point. Slurry shall be introduced into the trench at the time trenching begins and shall be maintained in the trench during excavation and until backfilled. The Contractor shall maintain the stability of the excavated trench at all times for its full depth. The level of the bentonite slurry shall always be maintained at least 3 ft above groundwater level and shall not be permitted to drop more than 2 ft below the surface of the working platform. The Contractor shall have personnel, equipment, and prepared slurry ready to raise the slurry level at any time. To this end,the Contractor shall have personnel on call as necessary to check the trench levels and to raise the slurry level on weekends and/or holidays. B. When crossing an existing slurry wall, carefully expose existing slurry wall as shown and clean surface until existing soil-bentonite backfill is neatly exposed. 3.2 KEY DEPTH A. Unless otherwise directed,the bottom of the slurry trench will be keyed the minimum specified penetration into the specified stratum indicated. If the backhoe or a clamshell is unable to achieve the minimum specified penetration into the less-weathered rock stratum the assistance of ripping teeth, or drop chisels may be necessary. Excavation refusal is defined as the inability to excavate more than 9 inches of depth over a bottom trench length of 20 feet in a period of 60 minutes with the approved excavator in proper and effective operating condition. If a minimum key depth of 12 inches is not achieved after excavation refusal, excavation shall continue until a second refusal period, or a 12 inch minimum key depth is reached, whichever is sooner. The depth to the top of the stratum shall be measured after these soils are identified in the excavation spoils. The final depth and key penetration of the trench shall be measured and checked by the Contractor and approved by the Engineer immediately following excavation. Weathered bedrock will be encountered and will not be considered as the less-weathered rock stratum. The onsite approving engineer will determine when the excavation has encountered the weathered and less-weathered rock stratums. Key depth shall be carefully compared to boring logs to assure that the key is excavated into the less-weathered bedrock stratum. 31 66 17-7 Prowers Aggregate Operators, LLC West Farm Pit Phase 2 Slurry Wall Soil-Bentonite Slurry Walls