Clay particle interactions control the mechanical macro-behaviour of clayey soils. It is generally accepted that mechanical response of swelling clays is deeply affected by the chemistry of the pore fluid. On the contrary, non-swelling clay dependency on pore fluid chemistry is still under debate, despite the existing evidence in nature (i.e. marine clays) and the numerous academic studies. In general, the electro-chemical factors that influence non-swelling clay mechanical behaviour are: ⅰ) pore fluid electrolyte concentration, ⅱ) pore fluid pH and ⅲ) pore fluid permittivity. A new physicochemical conceptual model is presented, suggesting how both reversible and non-reversible volumetric variations in clayey soils are controlled by electrical factors. The main conclusion states that the entire mechanical behaviour depends on the electric field generated by particle charges. The discussion is based on experimental evidence provided by the laboratory work presented in Sridharan & Venkatappa Rao (1973) on kaolin clay.
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