Clay Mineralogical Aspects of the Atterberg Limits

Data is presented to show that, for artificial soils containing mixtures, in pairs, of kaolinite, illite, and bentonite clay minerals, or these individual clay minerals, the activity will accurately classify the soils with regard to their liquid limit versus clay content relationships, or with regard to their swelling potentials, regardless of the clay mineral composition of the clay friction. Moreover, analysis of these relationships shows that inorganic clays containing these minerals, individually or in pairs, must lie in a relatively small zone of the plasticity chart. For clay mixtures containing more than approximately 5% bentonite, it is shown that mixtures of illite and bentonite are less active than mixtures of kaolinite and bentonite in the same proportions and, correspondingly, they have lower swelling characteristics. It is shown that this fact can be used to advantage in recognizing situations in which the effects of bentonite on the properties of clay soils will be minimized or, alternatively, to effect a minimization of the influence of bentonite or montmorillonite on the properties of a clay.