EMPIRICAL CONDITIONS OF PLASTICITY IN CALCULATIONS OF THE SUBGRADE BY SHIFT

Given the tendency to increase the service life of road pavement, as well as the need to design structures for heavy traffic of heavy and very heavy vehicles, it is nec-essary to replace the Mohr – Coulomb plasticity condition with another criterion with higher tangential stresses. In addition, an analysis of the modern normative cal-culation for shear resistance showed that the tangential stresses from the temporary load and from the own weight of the layers of pavement located above the layer un-der consideration are calculated for areas rotated to the main axes at different angles. The paper analyzes the plasticity conditions of Mohr – Coulomb, Drucker – Prager, Matsuoka – Nakai, Lade – Dun-can, and the empirical criterion G.K. Arnold. It is shown that for points belonging to the axis of symmetry of the load, in which there is a stress state which characterized by the main stresses 1>(2=3), the results of cal-culating the tangential stresses by the analytical plasticity criteria and the Mohr – Coulomb condition are identical. Therefore, G. K. Arnold empir-ical criterion is con-sidered as a variant of replacing the Mohr–Coulomb condition. It is established that the tangential stresses, calculated by this criterion, have higher values than the stresses determined by the generally accepted plasticity criterion. The difference be-tween the results of thecalculation of tangential stresses increases with increasing angle of inter-nal friction. A new calculation scheme is proposed, consisting in the fact that the pressure transmitted by the layers of pavement to the surface of the soil checked by resistance to shear is calculated first, and then the tangential stresses in the tested subgrade are calculated. It is shown that, in this case, the most dangerous point at which the greatest tangential stress occurs is located at some distance from the surface of the tested half-space. The scope of the empirical criterion is established.