Laserfiche WebLink
Lined Pit Guide 4 September 2000 <br /> Bentonite Slurry <br /> The initial bentonite slurry must be tested prior to placement in the trench. The slurry may be mixed in <br /> high shear mixers or mixed and hydrated in slurry hydration ponds. In general, a minimum hydration <br /> time of 8 hours will allow the bentonite slurry to meet all criteria. The following is an example <br /> specification for the bentonite slurry prior to placement in the trench. As a rule of thumb, a minimum <br /> bentonite content of 6 percent in the slurry by weight will assure that the requirements will be met. <br /> Viscosity Measured w/Marsh Funnel (API RP 13B-1) less than 40 seconds <br /> Density less than 64 pcf <br /> Filtrate Loss less than 20 cm <br /> pH 6.5 to 10 <br /> The tests listed above should be run 1 or 2 times per shift and at least once per batch of slurry. <br /> The slurry must be further tested after placement in the trench. The tests conducted are for viscosity, <br /> density, sand content, and pH. A typical plan would call for two sets of tests per shift at two locations <br /> in the trench (approximately 2 feet below the slurry surface and 2 feet above the bottom of the trench). <br /> If the density of the slurry in the trench exceeds 85 pcf the excess solids must be removed by depanding <br /> or the slurry replaced with fresh slurry. The slurry level must be maintained at least 3 feet.above the <br /> ground water elevation and no more than 2 feet below the top of the working platform. An example of <br /> a specification for slurry in the trench follows: <br /> Unit Weight 1.03 to 1.40 gm/cm3 <br /> Sand Content ASTM D 4381-84(1993)e1 0 to 20 percent by volume <br /> Soil-Bentonite Backfill <br /> The design should include a slurry trench implementation plan describing the general work sequence <br /> and layout of operations. Borings are taken along the proposed alignment of a slurry wall, preferably <br /> before the development of plans and specifications. These borings are spaced 100-200 feet apart, <br /> depending on the geologic uniformity and nature of the layer the slurry wall will be keyed into. The. <br /> geotechnical information gleaned from the borings is important to the determination of the suitability of <br /> the key layer and-potential-for the material to be excavated from the trench to be used in the S-B <br /> backfill. To obtain a low permeability S-B backfill mixture, plastic soils with an appreciable amount of <br /> fines are needed. Two examples of S-B backfill specifications follow: <br /> Example #1 <br /> 65 to 100 percent passing 3/8" sieve <br /> 40 to 85 percent passing#20 sieve <br /> 25 to 40 percent passing#200 seive <br /> Roll soil to 1/8 inch thread <br />