Experiments on erosion and fluidization strength of kaolinite clay

The present dissertation is comprised of three manuscripts. In the first part, the self-weight fluidization behavior of kaolinite clay was examined via batch sedimentation tests; two of the experimental cases were also simulated numerically. It was found that mixing conditions and gas entrainment can have significant effects on the reproducibility of batch sedimentation experiments. Further, it was shown that traditional methods of detecting self-weight fluidization via changes in the batch curve or flux curve are not effective for the cases examined. Numerical experiments showed close agreement with the overall conditions observed, further bearing out the assertion that these traditional methods are not sensitive to fluidization. The final sedimented conditions for these tests were used to determine the experimental conditions for the remaining parts. The second part considers the fluvial erosion strength of kaolinite clay, when subjected to water flow in flume experiments. The effects of sediment age, clay content, water content, and microbes are examined. The erosional strength of sediment was shown to increase with sediment age, due to thixotropic hardening. This may occur over a longer time period than previously thought. Erosional strength and water content were shown to vary in an inverse manner, and sand added to a pure clay increased its erosional strength, which agrees with existing literature. An addition of microbes to the kaolinite caused disaggregation of the sediment, which is contrary to some existing literature. It is clear from this study that further work is required to obtain a functional relationship between physical properties and erosional strength, and that cohesive sediments are very sensitive to environmental changes. The final part of this dissertation presents the results of an experimental investigation of the minimum fluidization conditions for kaolinite clay. A bed of pure kaolinite was subjected to varying flowrates of water directed vertically upward through the bed. Few experimental efforts have considered the liquid fluidization of a purely cohesive material, and the definition of a minimum fluidization condition was not clear from a review of literature. Through visual observation, cracking and separation of the bed into layers was evident, and in some cases was followed by water ejection through a hole in the bed. The height of the bed, its volume fraction of solids, and the fluid pressure in the bed were all measured simultaneously as a function of time. Some correlation was evident between the pressure drop through the bed and the flowrate of the water, indicating an asymptotic minimum pressure required to fluidize a clay bed.