HYSTERESIS OF CAPILLARY COHESION IN UNSATURATED SOILS

Abstract eng:
A theoretical analysis is conducted for modeling the constitutive relationships among water content, matric suction, and capillary cohesion in unsaturated granular soils (e.g., sands or silts). A rigorous series of equations is developed to describe the interparticle forces due to negative pore-water pressure for idealized spherical particles in simple-cubic and tetrahedral packing geometries. By considering changing meniscus geometry, matric suction and effective stress are evaluated as functions of water content for soil particles under the pendular (i.e., disconnected) pore-water regime. The contact angle at the interface between the pore-water menisci and the solid soil particles is considered as an arbitrary variable so that its effects on the hysteretic behavior of matric suction, effective stress, and capillary cohesion may be evaluated. The analysis provides a theoretical basis for describing several well-known phenomena in unsaturated soil behavior. Varying the contact angle from 0° to 40° to simulate drying and wetting processes respectively is shown to have an appreciable impact on hysteresis in the constitutive behavior of the modeled soils. The observations from the modeling effort are of practical importance in developing an improved understanding of the behavior of real unsaturated soils undergoing natural wetting and drying processes such as infiltration or drainage. This paper presents partial results of the described research.

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