Volume 35, Issue 1 (January 2012)
Influence of Hydraulic Hysteresis on the Shear Strength of Unsaturated Soils and Interfaces
The soil water characteristic curve (SWCC) portrays the relationship between soil suction and water content. This curve represents a fundamental behavior of unsaturated soils, from which many engineering properties (e.g., hydraulic conductivity, shear strength) can be estimated. However, the SWCC exhibits hysteretic behavior where a soil with different values of moisture content (e.g., due to seasonal variations) corresponding to drying and wetting paths can have the same suction. Hysteretic behavior (hydraulic hysteresis) can significantly influence the mechanical response of soils and soil-structure interfaces. This paper describes an investigation of the influence of hydraulic hysteresis during drying and wetting on the shearing response of unsaturated silty cohesionless soil alone and in contact with a rough steel counterface using a specially designed direct shear apparatus. For both soil and rough interface conditions, it was found that shear strength following a drying-wetting path was higher than for only the drying path, at similar suction and net normal stress. The magnitude of the difference in shear strength appears to correlate reasonably well with the difference in volumetric water content between the drying-wetting and drying paths at a given suction and net normal stress prior to shearing.