Influence of the Silt Content on Mechanical Properties of Unsaturated Soil Under High Suction

The soil of subgrade slopes in areas with alternating cold and dry seasons throughout the year, where evaporation is much greater than precipitation, is in a unsaturated state with high suction most of the time. To study the influence of the silt content on soil-water characteristics and strength of unsaturated soil with high suction, the vapor equilibrium method of saturated salt solution was used to apply high suction to soil with different contents of silt, triaxial tests and splitting tensile tests were conducted on unsaturated soil. The test results indicated that:the silt content had a significant effect on the water intake value of unsaturated soil, there was a negative correlation between the two. The water-held capacity of the soil decreased with the increase of the silt content. Both the silt content and suction had a deteriorating effect on the tensile strength, and both factors simultaneously led to increase in the crack depth of soil. Suction had an inhibitory effect on the deformation of soil, the larger the suction was, the larger the cohesion provided by the suction was. The increase in the silt content had a significant effect on the degeneration of soil elastic moduli. The brittleness characteristics of unsaturated soil with high suction influenced by the silt content were evaluated by defining the brittleness index from a perspective of moduli. It was found that the brittleness of unsaturated soil with high suction was altered by the silt content mainly through the influence of the post-peak secant modulus.