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<br />~~ <br />The soil-bentonite (S-B) backfill was composed of four components: 1) soil excavated from the <br />trench, 2) high clay content soil material borrowed on-site, 3) slurry removed from the trench <br />heading during excavation and mixing operations, and 4) dry bentonite applied at a rate of 0.5 to 1.0 <br />percent of the dry weight of the backfill soils. <br />QUALITY CONTROL TESTING <br />Resident engineering services were provided by D&A during the slurry wall construction. These <br />services included continuous on-site construction observation, sampling, field-testing of soils for <br />various parameters, collecting backfill samples for laboratory permeability testing, and the <br />assimilation of as-built information. A daily log of construction progress was kept. A summary of <br />the quality control test results is presented in Appendix A. <br />A specified material quality control program was followed throughout the slurry wall construction. <br />Test types, frequency, and specified values are summarized on Table 1. In order to provide the <br />quickest possible testing result turn-around time, a testing laboratory was set up on-site. Testing <br />equipment included a mud balance, Marsh funnel, microwave oven for drying samples, triple-beam <br />balance, portable sieve shaker, various sieves, wet washing apparatus, ambient temperature filter <br />press, pH paper, sand content kit, and slump cone apparatus. <br />A rapid turn-around time of the test results allowed for near real-time adjustments to the various <br />slurry trench parameters throughout the project. Testing conformed to industry standards, including <br />the American Petroleum Institute -Specification 13A, the American Petroleum Institute <br />Recommended Practice -Specification 13-B-2, and ASTM C-143. Specific test results are shown <br />in Appendix A. <br />Slurry viscosity, as measured using a Marsh funnel apparatus, and unit weight values, as measured <br />using a mud balance, were maintained within the acceptable range (V >_40 seconds-Marsh, S.G. _ <br />1.03 to 1.40) except as noted. Only once did the viscosity dropped below the 40 seconds-Marsh due <br />to an excess of water in the slurry mix. The low viscosity was corrected and the slurry viscosity in <br />the trench was maintained above the minimum acceptable level. <br />Filter cake formation of the slurry, and filtration loss were analyzed using an ambient temperature <br />filter press assembly. Filtration loss testing results were generally within the acceptable range. A <br />sand content kit was used to measure the percent sand by volume suspended in the slurry. Sand <br />content was found to generally range from 5 to 22 percent. In a few instances the sand content of <br />the in-trench slurry sample was found to be above the desired maximum value of 20 percent. In <br />these cases, the problem was corrected by adding more slurry from the mixing pond at the point of <br />trenching and a stoppage of backfilling. Trench depth measurements taken in front of the leading <br />edge of the backfill indicated that athree-foot key way depth was maintained in all of the areas <br />where the sand content was found to be above 20 percent. <br />Slump cone, gradation, and moisture content test results on the S-B backfill material were used to <br />control the backfill material properties. Test results in each of these areas were consistently within <br />the acceptable range, except as noted in the "Backfill Quality" section. In a couple of instances, the <br />slump test and/or visual inspection resulted in construction directives, which specified corrective <br />_ 3 _ September 2007 <br />Heit ConstruMion Report <br />L• <br />