<p>Rigid and flexible boundary limits are two main types of boundary conditions used in subgrade construction, and they have significant effects on the deformation and settlement of foundation soil. In this paper, cube-triaxial compression tests were conducted on compacted loess under different compaction degrees using both rigid and flexible boundary conditions, and the resulting deformation differences of the compacted loess were studied. Additionally, the effects of lateral deformation of compacted loess under triaxial compression using these two boundary conditions on compaction degree, void ratio, and vertical strain and volume strain were analyzed. The relationship between vertical strain and volume strain was proposed, and the relationship between vertical strain and lateral strain was derived. The research results indicate that the deformation coordination ability of flexible constraints is greater than that of rigid constraints. These findings provide important theoretical reference and engineering application value for settlement calculation and maintenance of subgrade filling in loess areas.</p>