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 sheaz 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/ Mazsh Funnel (API RP 13B-1) less than 40 seconds <br />Density less than 64 pcf <br />Filtrate Loss less than 20 cm3 <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 slung must be further tested after placement in the trench. The tests conducted are for viscosity, <br />density, sand content, and pH. Atypical 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 <br />Sand Content <br />Soil-Bentonite Backfill <br />1.03 to 1.40 gm/cm3 <br />ASTM D 4381-84(1993)el 0 to 20 percent by volume <br />The design should include a slurry trench implementation plan describing the general work sequence <br />and layout of operations. Borings aze taken along the proposed alignment of a slurry wall, preferably <br />before [he development of plans and specifications. These borings aze 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 amounC 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 wive <br />Roll soil to 1/8 inch thread <br />