ABSTRACT
The intensity of interaction between the three constituent phases of unsaturated soils represents the main factor conditioning their behaviour. Due to this interaction the pressure of held water is always less than that of atmosphere and this pressure deficiency is refereed to as the moisture suction of the material. The paper presents the explanation of the principal properties of unsaturated soil like water retention capacity, permeability, compressibility, shear resistance, compactibility and others technological properties. Since the main factor of soil behaviour are their nature and the moisture and density state in the second part of the paper are represented a method to characterization of these factor by prints and nature diagram (log d90, Ar) and state diagram (w, V=100/ρd). The use of this method of systematization of geotechnical data allows to establish analogies between various kind of soil and, on this base, the forecast of design parameters. This method offers a opportunity to a better understanding of soil behaviour and to give full value of past experience. The didactic experience for many years shown that about mentioned approach is useful for a better understanding of soil behaviour.
