Compacted kaolinite-chemical interactions: Microfabric and hydraulic conductivity studies

The extensive use of compacted clayey soils as barriers to contaminant transport requires better understanding of the relations between clay microfabric and hydraulic behavior. This research is aimed to address two problems: (1) to better understand the hydraulic behavior exhibited by clay compacted at different water contents; (2) to study the effects of chemical permeation on microfabric and hydraulic conductivity of compacted clay. Ultrathin section transmission electron microscopy (TEM), mercury intrusion porosimetry (MIP), computer aided image processing, and hydraulic conductivity measurement were used to investigate the microscopic and macroscopic features of compacted kaolinite.; Kaolinite compacted dry of optimum is composed of aggregates of randomly arranged domains. Pore size distribution has revealed the existence of large interaggregate pores leading to relatively high values of hydraulic conductivity. More ordered fabric has been observed in kaolinite compacted at optimum water content. The matrix is composed of densely stacked face-to-face domains while aggregates are constructed by stair-stepped face-to-face arrangement of domains. The dispersed matrix is responsible for the maximum dry density obtained at optimum water content while the flocculated aggregates may explain why hydraulic conductivity of compacted clay does not reach a minimum value simultaneously. Dispersed fabric characterized by preferentially oriented domains has been observed in kaolinite compacted wet of optimum. The minimum value of hydraulic conductivity of clay compacted slightly wet of optimum is probably due to the removal of large interaggregate pores resulting from the destruction of aggregates, as indicated by the the uni-modal distribution of pore size measured by MIP.; The permeation of inorganic chemicals caused no significant change in microfabric, pore size distribution, and intrinsic permeability of kaolinite compacted slightly wet of optimum. Local flocculation of clay particles was observed by TEM as a result of permeation of organic chemicals due to clay-chemical interactions. The permeation, however, all led to significant reduction in hydraulic conductivity of compacted kaolinite. Other factors relating to physical properties of organic chemicals and testing procedures are postulated to have dominated the macroscopic results over clay microfabric.