Physical isomorphism in the mechanical behaviour of soils

Abstract

The validity of Buckingham's theorem for a group of soils indicates that the behaviour complies with the condition of physical similitude. Buckingham's dimensionless arguments can be generalized using the conception of dimensionless "criterial" functions, of stress-strain diagram for example; behaviour in harmony with these functions is called physically isomorphous behaviour.By analysing some experimental findings, the author shows that typical for isomorphous behaviour are logarithmic curves (e.g., curve of compression or primary creep) and linear Mohr's envelopes.Two deformation mechanisms are discriminated, that of sliding deformation and that of cataclastic deformation. Only the domination of the first one produces physical isomorphism. Microrheological analysis shows, in a rather qualitative way, that physical isomorphism results from the monotonous strain, stress, and time hardening of the structure of the soils in question. Such structural changes are typical for soft to medium clays and loose sands and for many soils in the range of high pressures. These soils manifest, consequently, physically isomorphous behaviour.The importance of the principle of physical isomorphism is illustrated by its application to creep (Saito–Uezawa relation), to primary consolidation of specimens with varying drainage paths, and to the interpretation of the ratio Ccε/Cαε of compression index to secondary compression index. Key words: model laws, soil structure, compression, creep, shear strength.