PHYSICOCHEMICAL NATURE OF CLAY SOILS DEFORMABILITY 

F. S. Karpenko

Sergeev Institute of Environmental Geoscience, Russian Academy of Science, Ulanskii per., 13, bld. 2, Moscow, 101000 Russia
E-mail: kafs08@bk.ru 

In some cases, the tests on deformation properties of clayey soils have ambiguous, contradictory results that require clarification. Modern scientific concepts allow us to fix these problems, but do not allow us to give them full explanation and understanding. This is due to the fact that the provisions on deformability of soil mechanics are based on the principles of elasticity theory (Hooke’s law). In the case of clay soils, these provisions do not make it possible in all cases to characterize comprehensively the soil response to external load. This is because the theory of elasticity is developed for solid elastic bodies and does not take into account the internal structure of clays. In the present paper, the problems in determining the strength of clay soils are considered from the standpoint of the physicochemical theory of effective stresses. This theory is based on the ideas of the internal structure of clays. The main idea implies that the structure of clays depends on the contacts formed between mineral particles, where the external stresses transmitted to soil are concentrating. The prevailing type of structural contacts in clays determines the properties of the latter. Deformability is a special property of clay soils controlled by its composition and internal structure independent of the conditions of load application to it and characterized by the actual effective deformability value. This is the maximal stress transferred to the soil contacts that does not exceed the value of the potential minimum at which the attracting forces between the particles continue to prevail at the contacts. Under these conditions, clay soils exhibit elastic deformation properties. The actual effective deformability in soils with the same predominant type of contacts depends on the number of contacts. The numerical deformability characteristics of contact types are determined for different clay soil varieties to characterize the actual effective deformability. The parameters of relationship between the actual effective deformability in clays and their deformability characteristics are obtained from the soil testing by standard methods.

Key words: deformability, structural contacts, contact type, number of contacts, potential minimum, actual effective stresses, actual effective deformability 

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