Abstract: To investigate the tensile-strength mechanical parameters of expansive soil and to clarify the mechanism governing tensile-strength variation under different compaction densities, a series of tensile tests was conducted on high and low-density compacted expansive soils using an improved strain-controlled triaxial apparatus. The mechanical characteristics of tensile strength were systematically examined. In addition, SEM testing was employed to analyze the microstructural mechanisms underlying the strength differences between high and low density expansive soils. The results indicate that, at a constant water content, the tensile strength of expansive soil first increases and then decreases with changing dry density. Under the same dry density, increasing water content produces a similar trend in tensile strength. Although high and low density expansive soils exhibit comparable patterns of tensile-strength variation, they differ significantly in strength magnitude and failure mode. High-density expansive soil predominantly undergoes brittle tensile failure, whereas low-density expansive soil exhibits ductile tensile failure. The observed variations in tensile-strength behavior arise from the combined effects of capillary pressure, cementation, seepage, shrink-swell behavior, and microscopic physical mechanisms.

Key words: Expansive Soils, Tensile Strength, Uniaxial Tensile Test, Mechanical Properties, Microstructure