Under low matric suction ranges and various stress conditions, this analysis aims to examine the soil water characteristic curve of an unsaturated soil. For the design of geotechnical and geo-environmental structures such as road pavements, foundations, and ground dams, accurate assessment of unsaturated soil properties is important. One of the main characteristics of unsaturated soil mechanics is water retention behaviour in soils that is used to predict stability or infiltration problems in the soil. Therefore, the unsaturated soil properties have been recorded by several experimental works, and the soil-water characteristic curve (SWCC) test has significantly contributed to the understanding of matric suction. Because conventional instruments in SWCC tests are unable to apply stress, some researchers have developed suction-controlled triaxial devices that conduct SWCC tests under different stress states. For the understanding of the hydro-mechanical behaviour of unsaturated soils, the determination of SWCCs under stress conditions such as those in the field is key. In both drying and wetting conditions, this study conducted SWCC tests of unsaturated silt soil in low matric suction ranges. Under one-dimensional and isotropic confining stresses varying from 50 to 450 kPa, the SWCCs were measured. Instead of the high air inlet ceramic disc, the micro porous membrane approach was used to control relatively low matric suction. The controlled matrix suction range was from 0 to 20 kPa. The research revealed that the measured SWCC seems to be influenced by the in-fluence of stress conditions in low matric suction ranges. Isotropic confining stress caused the specimen’s void structure to become dense and soil moisture flow movement also decreased as a result. For both models, the R2 (0.99) values obtained clearly show that the fitted values and the experimental data sets are almost located around the line of perfect agreement. Obviously, the water retention activity was high, and the point of reference to the air intake value was greater. Furthermore, the study indicates that the existing methods adopted to estimate unsaturated soil properties require further improvement to take into account the impact of different conditions of stress. Perhaps the findings of this study may be helpful in providing appropriate data to clarify the combined hydro-mechanical actions of unsaturated silt soil in the practise of geotechnical engineering.
Graduate School of Engineering, Ashikaga University, Omae Ashikaga Tochigi, Japan.
Prof. Tomoyoshi Nishimura
Department of Civil Engineering, Ashikaga University, Omae Ashikaga Tochigi, Japan.
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