Effects of pore water surface tension and contact angle on dry-shrinkage cracking of expansive soils

The surface tensions of water, alcoholic solution and suds (surfactant) are measured by using the pendent drop method, and then their values are compared. The contact angle of soil samples is measured by means of the sessile drop method, and the samples are mixed with octadecylamine. Based on the results, the tests on dry-shrinkage cracking are conducted on expansive soil samples with different pore water surface tensions and contact angles. The results indicate that the surface tension and contact angle have a major impact on the dry-shrinkage cracking of expansive soils. The soil samples with a less surface tension have a less final crack ratio. In the phase of cracking development, the samples with a lower surface tension have a higher crack ratio during the same amount of drying time. Increasing the contact angle of soil particles and pore water can hold back the dry-shrinkage cracking in expansive soils. For the soil samples during the same drying time, a larger contact angle will cause a smaller crack ratio. Both decreasing the surface tension and increasing the contact angle lead to the increase of the radius of curvature in pore fluid, and the matric suction thus decreases. Meniscus may become convex because of the larger contact angle, and the matric suction will disappear in this situation.