Investigation of infiltration and drainage flow processes in unsaturated soil using a centrifuge permeameter

This thesis provides an improved understanding of water flow in unsaturated soils, which is needed for the analysis and design of geotechnical structures in the vadose zone, including slopes, landfill or mine tailing covers, pavements, embankments, and retaining walls. The vadose zone undergoes cyclic infiltration and drainage cycles that can be investigated to gain insight into the hydraulic properties. The appropriate hydraulic properties including the soil water retention curve (SWRC) and hydraulic conductivity function (HCF) should be used in the analysis. Key concepts evaluated in this thesis include the impact of different boundary conditions on the measured volumetric water content and matric suction profiles during infitlraiton and drainage, definition of the transient hysteretic behavior of the SWRC, and the role of pore air pressure during infiltration into unsaturated soils.;A large-diameter, heavily-instrumented centrifuge permeameter was developed to study infiltration and drainage in an unsaturated soils. The permeameter can control infiltration and measure outflow from the specimen during centrifugation. Five tensiometers and dielectric sensors were installed in pairs along the length of the soil specimen to measure changes in matric suction and volumetric water content, respectively.;The permeameter was used to evaluate the flow processes in an unsaturated, fine sand. The centrifuge was spun at a constant g-level (50 times that of earth gravity), and a constant infiltration rate was applied to the top boundary of the specimen until the soil specimen reached steady state conditions. Then the infiltration was stopped and the soil specimen was allowed to drain until approaching equilibrium (no-flow condition). This series of infiltration and drainage tests were conducted for three different bottom boundary conditions to characterize the performance and capabilities of the permeameter.;The measured matric suction and volumetric water content profiles for free-draining conditions correspond well with analytical solutions to Richards' equation in the centrifuge. These profiles, along with those for the other boundary conditions, were used with the instantaneous profile method to define the SWRC and HCF. With the proper interpretation, the three methods resulted in similar hydraulic properties. However, the free drainage boundary is the most appropriate for hydraulic characterization of unsaturated soils.