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3.2 KEY DEPTH <br /> A. Unless otherwise directed,the bottom of the slurry trench will be keyed the minimum specified <br /> penetration into the specified stratum indicated. If the backhoe or a clamshell is unable to achieve the <br /> minimum specified penetration into the less-weathered rock stratum the assistance of ripping teeth,or <br /> drop chisels may be necessary and no extra payment will be made.The depth to the top of the stratum <br /> shall be measured after these soils are identified in the excavation spoils.The final depth and key <br /> penetration of the trench shall be measured and checked by the Contractor and approved by the <br /> Engineer immediately following excavation.Weathered bedrock and sandstone bedrock will be <br /> encountered and will not be considered as the less-weathered rock stratum.The onsite approving <br /> engineer will determine when the excavation has encountered the weathered and less-weathered rock <br /> stratums. <br /> 3.3 CLEANING TRENCH BOTTOM <br /> A. Upon completion of excavation,any loose material or cuttings be removed from the bottom of the <br /> trench with the excavation tools or other suitable means su 'ft pumps. If the unit weight of the <br /> slurry in the trench exceeds the specified limits,or beco s nwor the heavy slurry shall be <br /> removed from the trench by airlift pump,clamshell,o er methods ved by the Engineer or the <br /> excess solids shall be removed from the slurry by s g po ,screenin r desanding.The trench <br /> bottom shall be cleaned of debris and excess san 'me for to backfilling.The trench shall be <br /> sounded immediately before placing backfill,and so shall be compared to the trench excavation <br /> soundings to verify the bottom.At a mini • soundin II be taken each morning and each evening <br /> and as given in Section 3.9.1 and compare. for c ins or excessive settlement.The spacing <br /> of the each sounding shall be 20 feet along . <br /> 3.4 BACKFILL MIXING <br /> A. The backfill shall be mixed • - te. If t backfil mixed beside the trench,the contractor shall control <br /> and provide sufficient equ -nt .• - i.rm space to support slurry spills,trench stability,and <br /> mixing equipment operation. ed maters. s shall not be allowed to fall into the trench. If the <br /> backfill is mixed in oc.. • the contractor shall build and maintain adequate haul roads and <br /> the mixing pit • :d.The ,: pi sad shall be lined with compatible soils or other materials to <br /> prevent cont. .tion from itab e materials. In either case,the contractor shall be responsible for <br /> the quality of th- kfill. <br /> B. Backfill materials an. • • e may be pre-mixed by blending in mechanical blenders or by <br /> windrowing,disk harro , :,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 6 inches in <br /> their largest dimensions will be permitted.Just prior to placing,the backfill material shall have a slump <br /> of 3 to 6 inches.To this end,the materials shall be sampled and tested for permeability,density,and <br /> slump after preparation <br /> Loloff Slurry Wall 3156 00-7 <br />