Effective stress development in kaolin and bentonite clays during the hydro-mechanical loading

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The knowledge of hydro-mechanical response of the two extreme clays namely, kaolin and bentonite are important due to their presence in many parts of the world and these clays are subjected to wetting cycles under external loads during the monsoon. Bentonite clays are further subjected to combined hydraulic and mechanical loading from the surrounding saturated rock mass or ground water during the placement in nuclear waste repositories and landfills, respectively. In this work, it will be shown that kaolin is a collapsible soil similar to the loess soil. The collapse mechanism in kaolin is, however, due to changes in particle association (fabric) with the interaction with different porefluids. Collapsible soils are known to withstand high normal stresses without undergoing a significant volume change in air-dry state. The soil is, however, susceptible to a large volume change upon wetting. Several physicochemical parameters strongly influenced the particle association in kaolin by altering the charges on the particle surfaces and edges due to interaction with different pore-fluids. The collapse nature of the kaolin is investigated with great detail in this work. Wetting induced collapse behavior of kaolin was studied under the influence of pore-fluid chemistry using a multi-scale approach. The influence of pH, salt concentration, and dielectric pore-fluid environment on the clay behavior was analyzed using sedimentation and collapse tests. The collapse test results were well corroborated with the sedimentation test data, SEM images of lyophilized specimens, and edge isoelectric point (IEPedge). The influence of inundation fluid and inundation pressure on the fabric changes and collapse potential was elucidated.
Supervisor: T.V Bharat