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Slump cone, gradation, and moisture content test results on the S-13 backfill material were used to <br /> control the backfill material with regard to moisture content, gradation (especially fines content), and <br /> consistency. Sub-par test results in these categories resulted in construction directives which specified <br /> corrective actions that were carried out immediately. Corrective actions included addition/reduction <br /> of slurry added to backfill material, addition of imported fines, and adjustments to the mixing <br /> operations. <br /> Visual inspection of excavated soils and bedrock were continuously conducted during trenching to <br /> determine when adequate bedrock was encountered. The trench met minimum bedrock penetration <br /> requirements of three feet. Frequently, actual depths keyed into bedrock exceeded the minimum <br /> requirements and averaged on the order of three and one half feet to four feet and sometimes as much <br /> jas six feet. Comparing the quality control requirements to the test and field observations indicates that <br /> the project requirements were adequately met. Adjustments were made when required as indicated <br /> by test results and visual observations. <br /> DISCUSSION <br /> General <br /> Slurry wall construction began in early March, 1999 and was completed in June, 1999. Due to <br /> mechanical breakdowns and weather, slurry wall construction was delayed temporarily on occasion. <br /> Test holes were drilled along the proposed slurry wall alignment prior to construction. Observed drill <br /> cuttings, soil types and depth to bedrock measurements were used as reference during construction. <br /> r Depth to bedrock and total trench depths observed during construction are illustrated on the as-built <br /> construction drawing, Platel. <br /> The Hitachi 750 A trackhoe used to excavate the slurry trench was fitted with the appropriate length <br /> "stick" to maintain adequate power and vertical reach along the slurry trench. A modified excavator <br /> bucket equipped with staggered "ripper" teeth was used to remove material from the trench and key to <br /> appropriate depths through bedrock. <br /> A narrow working platform, located near the southwest corner of the proposed alignment, existed prior <br /> to construction. Fill material comprised of overburden stripped from on-site locations was used to <br /> widen the backfill mixing platform, allowing adequate area for the backfill mixing process. The slurry <br /> wall alignment along the south side of the site necessitated a temporary construction easement for a <br /> working platform used during backfill operations. The slurry wall alignment was constructed with an <br /> appropriate offset from the two existing ponds on-site. <br /> -4- <br /> t <br />