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Flow rate measurement errors caused by apparent leakage from the test apparatus during low gradient permeability testing was found to have a significant impact on precision in low gradient hydraulic conductivity test results. A laboratory testing program was conducted on ten similarly configured flexible wall permeameters, using an “impermeable” steel cylindrical block for a test specimen. The fluid pressures used during this test were identical to those used during flexible wall permeability testing. The results of this program showed that all systems had a measurable leakage. This leakage was typically in the range of 5 E-6 ml/sec to 5 E-8 ml/sec. The flow rate measurement error (apparent leakage) was found to have a significant impact on low gradient testing and this impact increased as the hydraulic conductivity measured decreased. Other than lowering the leakage rates through adjustments of the apparatus, increasing the diameter of the test specimen to increase the total flow through the sample was found to be the most effective method of reducing the impact of leakage.
hydraulic gradient, hydraulic conductivity, flexible wall permeability testing, soil liners, volume change, leakage analysis
Professor of Civil Engineering, University of Saskatchewan, Saskatoon, Sask.
Senior Engineer, Golder Associates Inc., Naperville, Il.
Research Engineer, University of Saskatchewan, Saskatoon, Sask.