Analyzing the Soil Water Characteristic Curve of an Unsaturated Soil under Low Matric Suction Ranges and Different Stress Conditions

This study aims to analyze the soil water characteristic curve of an unsaturated soil under low matric
suction ranges and different stress conditions. Accurate evaluation of unsaturated soil properties is
critical for the design of geotechnical and geo-environmental structures such as road pavements,
foundations, and earth dams. Water retention activity in soils which is used to predict the stability or
seepage problems in the ground is one of the key features in unsaturated soil mechanics. Thus, many
experimental works have reported on the unsaturated soil properties, and the soil-water characteristic
curve (SWCC) test has contributed significantly to the interpretation of matric suction. Since traditional
instruments cannot apply stress in SWCC tests, some researchers have developed suction controlled
triaxial apparatus, by which SWCC tests are performed under different stress states. Determination of
SWCCs under stress conditions like those in the field is key for interpretation of the hydro-mechanical
behavior of unsaturated soils. This study conducted SWCC tests of unsaturated silt soil in low matric
suction ranges under both drying and wetting conditions. The SWCCs were measured under onedimensional
and isotropic confining stresses ranging from 50 to 450 kPa. The micro porous
membrane method was used instead of high air entry ceramic disk for controlling relatively low matric
suction. The range of matric suction controlled was from 0 to 20 kPa. The study revealed that the
measured SWCC in low matric suction ranges seems to be affected by the in-fluence of stress
conditions. Isotropic confining stress caused the void structure of the specimen to become dense and
consequently, soil moisture flow movement also decreased. the obtained values of the R2 (0.99) for
both models clearly indicate that the fitted values and the experimental data sets are nearly located
around the line of perfect agreement. The water retention activity was obviously high, and the point
regard to air entry value was larger. The study further suggests that the current methods adopted for
estimating unsaturated soil properties require further development to consider the effect of different
stress conditions. The results of this research perhaps could be useful in providing relevant data for
understanding the coupled hydro-mechanical behavior of unsaturated silt soil in the geotechnical
engineering practice.