The article is devoted to studying the stress-strain state (SSS) and assessing the strength of the Gissarak, Sokh, and Pachkamar earth dams in a plane statement under the action of body forces and hydrostatic pressure. A mathematical model, algorithm, and computer program for studying the stress-strain state and assessing the strength of structures are developed in the article using the Lagrange variational equation. The finite element method was used in the problem solution. The adequacy of the model and the accuracy of the algorithm and program were verified by solving several test problems. It was revealed that the stress-strain state and strength of the studied earth dams significantly depend on the physical and mechanical properties of soils, the commensurability of geometric dimensions and slope coefficients of the dam retaining prisms, and on the level of water filling in reservoirs.