Scientific basis of physical, mechanical and mathematical nature of soil internal friction angle

The results of retrospective studies of the physical nature of soil internal friction angle are given in the paper. The triune nature of the soil internal friction angle is determined: physical, mechanical and mathematical. With the help of the analysis of the initial data of normative strength characteristics of different types of soils and their theoretical study, the factors representing the physical nature of the soil internal friction angle φ are identified; new types of classification of silty-clayed soils are discovered: loamy clayed sand and loamy dusty sand; the values of the degree of tangent function of the soil internal friction angle, determining the values of resistance power of adhesive bond in the shear of loamy clayed sand, loamy sand, loamy dusty sand and sand are discovered for the first time. Using the models of inclined plane mechanisms, the factors of mechanical nature of the soil internal friction angle are defined. Mathematical nature of the soil internal friction angle is represented by the fact that it is determined by the reverse tangent power function with the ratio argument of critical shear stress of soil to a constant normal stress of its compression in shear. The conclusions on the study results are made.