Abstract: Investigating the tensile strength of expansive soil helps clarify its crack-evolution behavior and holds significant value for road engineering applications. Using a newly developed tensile apparatus, tensile-strength tests were conducted on Ningming expansive soil at a constant dry density but with varying water contents to examine in depth how moisture conditions influence tensile behavior. To further elucidate the swelling mechanism of Ningming expansive soil, scanning electron microscopy (SEM) was employed to observe the microstructure of the specimens. Test results show that the tensile strength of the soil increases markedly with rising water content; however, when w>10.53%, the rate of strength increase diminishes. The clay minerals in the soil exhibit a plate-like morphology, which greatly enlarges the specific surface area of soil particles and enhances their hydrophilicity. In addition, water filling the pores between the larger structural units formed by the interbedding of plateshaped clay minerals affects both the matric suction and capillary suction of the specimens.

Key words: Expansive Soil, Tensile Strength, Moisture Content, Scanning Electron Microscope, Lamellar Structure