2006-02-02_GENERAL DOCUMENTS - M1999120

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3.02 SLURRY BATCHING PLANT The slurry batching 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. 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 and fully hydrated and the resulting slurry appears homogeneous. 3.03 BACKFILL MIXING AND PLACING EQUIPMENT Equipment for mixing and placing backfill may consist of a suitable type of earthmoving or grading equipment, such as bulldozers, or blade graders, or blenders such as a pug mill, that are capable of thoroughly mixing the backfill materials into a homogeneous paste having the required gradation and properties and placing the material in the trench as hereinafter specified. 3.04 SLURRY TRENCHING Excavation shall be carried to final depth at the point where excavation is started and then the fmal depth of cut shall be carried along the line of the trench. Excavation shall proceed continuously from the starting point to the fmishing point. Slurry shall be introduced into the trench at the same time trenching is begun 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 bentonite slurry shall always remain at least 2' above groundwater level and shall not be permitted to drop more than 3' below the surface of the slurry trench working platform except as approved by the Design Professional. The Contractor shall have personnel, equipment, and materials ready to raise the slurry level at any rime. To this end, the Contractor shall have personnel on call to raise the slurry level, weekends and/or holidays included. 3.05 KEY Unless otherwise directed by the Design Professional, the bottom of the slurry trench will be keyed 4' into the underlying suitable bedrock beneath the site as indicated by soil borings or trench cuttings. The depth to bedrock and the final depth and penetration of the trench shall be measured and checked by the Slurry Trench Specialist and Quality Control Representative immediately following excavation at a minimum frequency of once per every l O lineal feet of trench. Lignite was encountered during the geotechnical investigation. Where lignite is encountered, key trench excavation shall extend through the lignite and be keyed a minimum of 1' into underlying suitable bedrock. During construction, if additional areas of lignite are encountered, the Design Professional shall be notified so that the key trench depth can be re-evaluated, if appropriate. 3.06 EXCAVATION REFUSAL Typical bedrock key excavation using the Komatsu PC750 (or equivalent excavator) is estimated at a minimum rate of 2' of depth per 1/2 hour fora 30' to 40' long "set" or "cut". In some cases, it maybe necessary to continue to excavate difficult bedrock to achieve a key into suitable, relatively impermeable strata. When these conditions are encountered, the Contractor and Design Professional shall document the length of trench affected and the time expended in achieving a suitable key. Bedrock excavation refusal shall be determined by mutual agreement of the Contractor and Design Professional. In no case shall the Design Professional unreasonably withhold determination of bedrock excavation refusal. 3.07 CLEANING TRENCH BOTTOM Upon completion of excavation, any loose material or cuttings shall be removed from the bottom of the trench with the excavation tools or other suitable means such as air lift pumps. The Slurry Trench Specialist and Quality Control Representative shall verify that the trench bottom has been cleaned of all granular material prior to allowing backfill placement. The depth to bedrock and total trench depth shall be measured and recorded every 10' as the trench excavation advances. Backfill slope profile soundings and trench backfill bottom soundings will be measured at the start and the end of each shift, and in events where trench backfill operations are suspended for more than 2 hours. If the soundings indicate a difference of more than 6" to those 02/06 Section 02168 -Page 3 of 5