Particle Interaction and Soil Swelling

Abstract

Particle interaction discussed in this paper may be limited, in which contiguous interacting plate shaped particles are within 10 Å of each other, or extensive, in which surface separations exceed 40 Å. Extensive swelling is caused by the interaction of Gouy‐Chapman diffuse double layers and the conditions under which diffuse double layer theory can be used to describe extensive swelling are re‐viewed. The essential feature of extensive swelling is its dependence on electrolyte concentration.X‐ray studies of the variation of d(001) spacings for montmorillonite and vermiculite when saturated with divalent and large monovalent ions have been discussed as examples of limited swelling. This behaviour is contrasted with sodium montmorillonite which exhibits extensive crystalline swelling for concentrations less than 0.3 M NaCl.The similarity of the swelling behaviour of a montmorillonite crystal and of a parallel assemblage of crystals constituting a domain has been noted and presented as an argument for domains being regarded as particulate entities in calcium saturated clay materials.The limited crystalline swelling of calcium montmorillonite and domain swelling of calcium saturated clays is little affected by electrolyte concentrations less than molar. The inter‐crystalline swelling which occurs in soils and clay materials is triggered off by the adsorption of two layers of water; the adsorption of the two layers of water at areas of crystal overlap release mechanical energy stored as a result of crystal bending and packing on the drying cycle. This release of mechanical energy creates pores in which liquid is held by surface tension forces as distinct from water held at the clay solution interface by hydration and osmotic forces.The use of chloride exclusion measurements to provide information on the nature of particle interaction is discussed. The information presented on domain structure and ion distribution at interfaces, as deduced from chloride exclusion measurements, reveals that diffuse double theory is completely inadequate for describing swelling of calcium clay systems and for predicting the pore solution composition.