Settling of Kaolinite in Different Aqueous Environment ABIDIN KAYA Department of Transportation, Materials Research Laboratory, Honolulu, Hawaii, USA ALI HAKAN O ¨ REN AND YELIZ YU ¨ KSELEN Civil Engineering Department, Dokuz Eylul University, Buca, Turkey Settling characteristics of soils carry great importance for geotechnical engineers since sediments properties are formed during the settling of soil particles in an aqueous environment. In this study, settling characteristics of kaolinite are investigated. Differ- ent ionic strengths of NaCl, CaCl 2 and AlCl 3 were considered as a function of pH in aqueous environment of varying solid concentrations. Factors affecting the settling characteristics and fabric of kaolinitic sediments have been identified. The results of the study reveal that kaolinite settles in either flocculated or dispersed forms depending on pH and ion concentration. Flocculated settling occurs in acidic pH due to formation of flocs in edge-to-face structure with increasing positive charges at the particle edges. Dispersed settling occurs in alkaline pHs when ionic strength is low. When ionic strength is increased in alkaline pHs, kaolinite particles settle in flocculated form. Furthermore, the results show that pH has a significant role on the final sediment thick- ness or void ratio of kaolinite. Densely packed structures in alkaline and loosely packed structures in acidic aqueous environments are formed depending on pH level. Results also show that as the solid concentration increases, the settling rate decreases due to buoyancy effect. Finally, the zeta potential of kaolinite is correlated with the final sedi- ment thickness or void ratio of kaolinite as a function of pH. This correlation proves that there is a good agreement between zeta potential and the final sediment thickness or void ratio, especially when the soil is settled in a dispersed form. Keywords dispersed, edge-to-face, flocculated, kaolinite, pH, sediment thickness, settling, solid concentration, void ratio, zeta potential Introduction In general, clay mineral type, ionic strength, pH and solid to water ratio control the settling process of soils in aqueous environment. Although intermediate settling characteristics can be observed, flocculated and dispersed settlings are the two extreme characteristics that soil particles undergo depending on the above men- tioned factors. The structure and fabric of the settled soils are the functions of a complex interaction between soil particles and the aqueous environment because surface charges of particles are influenced by the ionic strength of the medium. Received 23 August 2005; accepted 16 March 2006. Address correspondence to Abidin Kaya, URS Corporation, 615 Piikoi Street, 9th Floor, Honolulu, HI 9681. E-mail: Abidin_Kaya@urscorp.com Marine Georesources and Geotechnology, 24:203–218, 2006 Copyright # Taylor & Francis Group, LLC ISSN: 1064-119X print/1521-0618 online DOI: 10.1080/10641190600788429 203