1. The description of the process of the development of the viscoplastic deformations of soils over time is examined on a simple physical basis, which consists in the fact that the strain rate is proportional to the “overstress” with respect to the stabilized-state diagram in the region of both the state that is subcritical with respect to strength, and the region of the translimiting state (unstabilized flow). 2. It is proposed to determine the stabilized-state diagram experimentally, using the relaxation method under kinematic shear. 3. The generalizing expression for determination of the ultimate long-term strength, which varies as viscoplastic shear deformations develop, is given on the basis of examination of the development kinetics of structural defects. 4. Generalizations are cited for the case of the complex stress state using the concepts of instantaneous and stabilized load surfaces.