The importance of exact estimation of plastic deformations in the soils and building materials is noted. The defining relations for stresses and endochronic type deformations generalizing the theory of Sanders-Klyushnikov were proposed. Quasi-statistical equations of the new theory are based on the Novozhilov’s idea about the independence of motion of piecewise-linear plane yield surfaces and the technology of conversion from flow theory to endochronic theory. The practical formulas for calculating the uniaxial active and reversible loading of the material are presented. The similarity and difference between the new theory and the Sanders-Klyushnikov’s version are demonstrated on the several examples.