The atterberg consistency constants: factors affecting their values and a new concept of their significance

The Atterberg consistency constants are affected by the following factors: Size and shape of particles--Disc-shaped, colloidal particles impart plasticity to soils. Plasticity increases with the content of these fine particles. A new theory is advanced to explain the plasticity of soils on the basis of the orientation of the plate-like, colloidal particles. Clay and colloid content--Soils containing a high percentage of clay or colloids possess high plasticities. Chemical composition of the colloid--A low SiO2-sesquioxide ratio of the colloidal material extracted from soils is associated with a low plasticity range on the moisture scale. Nature of exchangeable cations--The divalent cations tend to increase the plasticity of soils by raising both plastic limits. The K ion decreases plasticity and lowers both plastic limits. The Na ion lowers both plastic limits but increases plasticity. Organic matter content.--Organic matter causes plasticity to occur at high moisture contents but does not materially affect the magnitude of the plasticity. The following relationships exist between the Atterberg constants and the dynamic properties of soils: Maximum adhesion occurs at a moisture content fairly close to that of the upper plastic limit. Maximum adhesion is proportional to the plasticity number. The moisture range over which adhesion takes place and the moisture content at which maximum adhesion occurs appear to be functions of the plasticity number. The range of maximum compressibility is approximately the same as the plasticity range on the moisture scale. Maximum compressibility is a logarithmic function of the plasticity number. The maximum resistance offered by a soil to the passage of chisels is a logarithmic function of the plasticity number. A double logarithmic relationship exists between the plasticity number and that moisture content at which the resistance of a soil to the passage of chisels begins to increase rapidly. From these results and preliminary work with cohesion and shear, it appears possible to predict, by means of the Atterberg consistency constants, the values of the dynamic properties of any plastic soil.