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laboratory mix design. In addition, to develop a conservative laboratory backfill mix <br />design, dry bentonite powder was not added to the mix. <br />It is anticipated that the field mix design will consist of a blend of approximately 50% <br />sand and gravel and 50% overburden and bedrock which should increase the percentage <br />of fines in the field backfill mix. Due to the variability of the soil properties, fines <br />content, and mixing, the field mix design will include 1 % dry bentonite powder by <br />volume which will reduce the permeability of the field backfill mix. Increased amounts <br />of bentonite (up to 2%) and increases to the overburden component (up to 100%) of the <br />field mix are being considered by Loveland Ready Mix to decrease backfill <br />permeability. <br />B. Beutonite Slurry <br />Bentonite slurry used in the backfill mixture was created with dry bentonite powder and <br />site water. Dry bentonite powder was Wyoming bentonite distributed by Wyo-ben in <br />Billings, Montana. A measured amount of dry powder bentonite was used to create a <br />slurry with a minimum Marsh Funnel viscosity of 40 seconds. A summary of <br />laboratory test results performed on the slurry is presented in Table V and are included <br />in Appendix B. <br />4.03 Backfill Mix Preparation <br />Lyman Henn prepared a calculated blend of the select backfill components to represent the most <br />conservative conditions anticipated along the proposed alignment. Table V shows the <br />proportions percentages of components in the mix. The slurry was thoroughly blended using a <br />hand-held electric mixer. Soil and bedrock components were mixed with bentonite slurry until <br />a 3 to 6 inch slump was achieved. No additional dry bentonite was added to the mixture. A <br />sample from the mix was cast into a cylinder container (4 inch by 4 inch) for testing. The <br />permeability test (ASTM D 5084) consisted of subjeciing a sample to a 20 psi coning <br />pressure in a triaxial permeameter and using the constant rate of flow method (flow pump), with <br />a gradient of 10. <br />4.04 Backidl Mix Results <br />The test results from the backfill mix design met the engineering criteria. The measured <br />permeability of the mix was 3.9 x 10-$ cm/sec. Laboratory test reports are provided in <br />Appendix B. <br />G:NROlECTS\10'!021-000 laveland Ready Mu Slwry Wa11~R Records and Cortespvvdevice~R.l l Repoets\F~vai Shury Wall Dea,gv Report.doe <br />