Effective Stress in Unsaturated Silt at Low Degrees of Saturation

Abstract

This paper presents an evaluation of the effective stress concept in unsaturated, compacted silt at low degrees of saturation. A set of isothermal, consolidated‐drained triaxial tests was performed on silt specimens under different combinations of total suction and net normal stress. The total suction was controlled using an automated humidity system, and variables monitored during equilibration and shearing include anisotropic volume change, axial displacement, temperature, relative humidity at the top and bottom of the specimen, and the gas pressure difference across the specimen. The results from the triaxial tests were analyzed to examine the applicability of predicting the suction stress characteristic curve (SSCC) using parameters from soil water retention curve (SWRC) models fitted to experimental data obtained at low suction magnitudes. The SSCC predicted from the SWRC at low suctions was found to overpredict the suction stress values at high suctions obtained from back‐extrapolation of the failure envelope to define the tensile strength. However, small adjustments in the fitting of the SWRC were found to provide a better fit between the SSCC and experimental suction stress data. The suction stress defined using the adjusted SWRC was found to provide a good interpretation of the critical state line in terms of mean effective stress over both high and low suction ranges.