Stress State-dependent Soil-water Characteristic Curves And Strength Of Loess-like Backfill

The central and western regions in China are arid and semi-arid climate. In the construction of engineering, the overwhelming majority of foundation soil is unsaturated soil. The essential difference between unsaturated soil and saturated soil lies in the presence of matric suction in the unsaturated soil which affects the strength of unsaturated soil obviously. Changes in the environment and external loads will bring changes in the moisture content of soil, which will lead to changes in the matric suction, and thus changes in the strength of soil. Therefore, it is significant to research the relationships between moisture content of soil and matric suction, strength of unsaturated soil.The samples used in this program are loess-like backfill taken from two sites:Luliang High School and Pingyang highway in Shanxi Province. The test of Soil-Water Characteristic Curves(SWCC) of undisturbed and remolded soil are taken with Pressure-Plate of Stress State-Dependent SWCC. The data from the tests are fitted with empirical equation and the fitting results are evaluated. A group of undisturbed samples and two groups of remolded samples with different dry densities are tested with triaxial consolidation undrained test and the results are evaluated. The strength of unsaturated soil is predicted based on the result of SWCC and the strength parameters of saturated soil. The results are compared with the date obtained from the triaxial test.The conclusions of this program are as follows:(1)Through contrasting the fitting effect on the test results, the following results are drawn out:Van Genuchten equation of four parameters fits best; among three-parameters equations, the fitting of Gardner W R’s equation overmatches Fredlund and Xing equation and Brooks and Corey’s; however, Brooks and Corey equation’s form is simple and parameters with clear physical meaning. The test results show that:air entry values significantly increased with the decrease of void ratio; the sample with a smaller pore has a smaller soil storage coefficient.(2)A11stress-strain curves of undisturbed soil samples with different saturations show the pattern of "strain harden". The stress-strain curve pattern of remolded soil samples with different saturations are related to saturations of the samples; keeping dry density the same, when saturations are the same, larger confined pressure leads to larger peak of normal stress difference, and when confined pressures are the same, greater saturation leads to smaller peak of normal stress difference; while dry densities are different, when saturation and confined pressure are the same, the greater dry density is, the greater peak of normal stress difference is.(3)Triaxial consolidation undrained shear strengths of undisturbed and remolded soil decrease with the increasing of sample saturation, but they reduce in different ways, and the decrease of cohesion value is greater than internal friction angle values.(4)Through contrastive analysis on the test statistics result, the predicting method utilizing S WCC together with the strength parameters of saturated soil is convenient and effective, and forecast results is secure and the error is within the range allowed.