The aim of the article is the development of the theory of strength and deformation of clay soils under conditions of triaxial compression under combined alternating long-term static and cyclic loading. As a result of the research, new experimental data were obtained on the peculiarities of the stress-strain state of clay soils under triaxial compression under combined alternating long-term static and cyclic loading, as well as the development of base sediments of foundation models in laboratory conditions. The significance of the results obtained for the construction industry lies in the fact that experimental studies of determining the changes in the strength and deformability of clay soils under combined alternating long-term static and cyclic loading are necessary for the modernization of engineering methods for calculating sediments and the bearing capacity of foundations.