Fourth IGS-Ferroco Terzaghi Oration: 2014 Soil Clay Mineralogy and Physico-Chemical Mechanisms Governing the Fine-Grained Soil Behaviour

Engineering behavior of fine-grained soils depends upon the clay mineralogical composition of the soils and the pore medium chemistry as well. A greater part of the soil-pore liquid interaction is both physical and physico-chemical in nature. This can be attributed to the charge deficiency on the surfaces and edges of the clay platelets and the associated electrical attractive and repulsive forces. Clay minerals that are present in the fine-grained soils can be broadly grouped into kaolinitic and montmorillonitic types. This paper discusses in detail the physical and engineering behavior of fine-grained soils as influenced by the dominant clay minerals composing them and by the pore medium chemistry. It has been brought that the liquid limit, sediment volume, undrained shear strength and compressibility behavior of kaolinitic and montmorillonitic clayey soils are quite opposite to changes in the pore medium chemistry. The drained strength and secondary compression coefficient of both kaolinitic and montmorillonitic fine-grained soils are primarily controlled by the modified effective stress (i.e., net contact stress at the particle level), which takes into consideration both attractive and repulsive forces in addition to the conventional effective stress. The hydraulic conductivity of fine-grained soils is significantly influenced by the nature of the fluid, especially so in montmorillonitic soils.