The paper deals with the formation of limiting bulk densities of sandy soils of different origin against different values of humidity and varying structural features. The authors have identified that the optimum moisture content is typical for sands and clays exposed to mechanical compaction. The nature of this dependence is different from the one between the density and humidity of clay soils. These differences are driven by the peculiarities of formation of bound water shells in the event of low humidity. A linear dependence between the optimal humidity of sands and maximal molecular moisture capacity has been identified. The authors make a statement based on the proven de pendence between the maximal molecular moisture capacity and the morphology of sands. Their statement is that the formation of bound water shells in the low humidity environment is dependent not only on the fineness of particles, but, to a higher extent, on the peculiarities of the shape and the nature of the surface of sand grains. Another important factor of impact on the density of sandy soils in the natural environment consists in their humidity. Multiple researchers believe that the correlation between density and humidity of sands is to be the subject of research. It is noteworthy that limit densities of air-dried sands are to be assessed. Therefore, any sands have some particular bound water content, and the lower the intensity of treatment of sand particles, the higher the water content. The findings demonstrate that in most cases typical coagulatory and transitory contacts of non-saturated sands are to be considered in line with the ideas expressed by V.I. Osipov, as the above contacts determine the formation of effective stresses from the prospective of the physicochemical theory.