Laserfiche WebLink
Slurry Wall Design Report <br /> Loloff Pit <br /> 5/24/2016 <br /> Page 9 of 16 <br /> 5.3 Backfill Mix Preparation <br /> To represent the conditions anticipated along the proposed alignment, we prepared a <br /> conservative calculated blend of the select backfill components. The laboratory backfill mix <br /> design consisted of a blend of approximately 70 percent sand and gravel and 30 percent clay <br /> borrow to achieve an overall backfill mix containing approximately 25 percent fines (material <br /> passing the#200 sieve). Bedrock was not included in the laboratory mix designs because it is <br /> not expected to break down during field mixing. <br /> The slurry was thoroughly blended using a hand-held electric mixer. Clay borrow and coarse <br /> alluvium components were mixed with bentonite slurry until a 5 inch slump was achieved. In <br /> addition, to develop a conservative laboratory backfill mix design, dry bentonite powder was not <br /> added to the mix. The sample was placed into a cylinder container(4 inch by 8 inch) for testing. <br /> The permeability test (ASTM D 5084), performed by Advanced Terra Testing (Lakewood, CO) <br /> consisted of subjecting a sample to a 10 psi confining pressure in a triaxial permeameter and <br /> using the constant rate of flow method (flow pump), with a maximum gradient of 10, to <br /> determine permeability. The tap water at the Advanced Terra Testing laboratory was used as <br /> the permeant. <br /> Due to the variability of the soil properties, fines content, and mixing, the field mix design will <br /> include 1.0 percent dry bentonite powder by dry weight which will reduce the permeability of the <br /> field backfill mix. <br /> 5.4 Backfill Mix Results <br /> Under field conditions and with the addition of 1.0 percent dry bentonite, the backfill mixtures <br /> are expected to meet the requirements specified in herein. Laboratory test results are provided <br /> in Table V. <br /> The backfill mixes were also designed for grain-size compatibility. A filter criteria approach was <br /> used to evaluate the potential for squeezing or piping of the backfill mix into the sand and gravel <br /> formation. This design process resulted in the graded backfill specification presented herein. We <br /> have determined that if the backfill is proportioned as discussed below it should meet the <br /> graded backfill requirement. <br /> To achieve a minimum of 25% fines in the backfill mix, two supplemental fines borrow sources, <br /> Davis Farm Fines and Derr Import, have been identified. The Davis Farm Fines is the preferred <br /> source of supplemental fines for the slurry wall due to its relatively higher fines content. If <br /> sufficient quantities of this material are not available, the Derr Import may be used. Due to its <br /> lower fines content, larger quantities of Derr Import will be required to achieve an overall mix <br /> design containing a minimum of 25% fines. <br /> Import requirements were calculated on a dry unit weight basis in order to yield the required <br /> 25% fines. If Davis Farm Fines are used, approximately 10,000 cubic years of supplemental <br /> fines will be required. If the Derr Import is used, approximately 17,000 cubic yards of <br /> supplemental fines will be required. The percentage of in-situ sand and gravel and supplemental <br /> fines on a dry unit weight and volumetric basis are summarized below. Mix quantities by <br /> stationing are provided in Table VI. <br /> BRIERLEY <br /> ASSOCIATES <br /> Creating Space underground <br />