Osmotic softening of overconsolidated clays

This paper analyses the results of laboratory compression and swelling tests on two strongly overconsolidated clays of marine origin. The tests were carried out on undisturbed specimens taken at various depths from ground surface. During the tests, some specimens were exposed to distilled water and others to a concentrated salt solution similar to seawater. The results show that exposure to distilled water causes much higher swelling. The chemical part of swelling is therefore noticeable; it strongly depends on the stress level and it prevails on the mechanical part under very low values of confining stress. Moreover, it is extremely slow. On the basis of such results, it is possible to interpret the field trend of void ratio against depth from the ground floor. The large difference between the consistency of the superficial softened layers and that of the underlying hard materials can be interpreted as a physicochemical effect of exposure to rainwater.