Research On Soil-Water Characteristic Curve Of Unsaturated Soils

Practical applications of unsaturated soil mechanics still lag behind the state-of -the-art knowledge. The main stumbling block is the time-consuming processes in the measurement of the unsaturated soil parameters required for the constitutive models. Research has shown that the soil-water characteristic curve (SWCC) of a soil can be used in the establishment of a number of the unsaturated soil parameters. The research of the paper surrounds the SWCC. Firstly, the factors affected the shape of the SWCC are discussed based on the conception and measurement of the SWCC. Secondly, the fitting effect factors are analyzed based on the theoretical basis and classification of equations for the SWCC. Thirdly, the application of the SWCC in unsaturated soil mechanics was reviewed. Finally, in order to predict the unsaturated shear strength parameters with the SWCC and the saturated shear strength parameters, Luojiashan soil samples were selected for the unsaturated triaxial tests and SWCC tests. Based on the tests, the suitability of the previous procedures was contrasted and studied.The main research conclusions consist of:1. The SWCC of undisturbed soil have lower air-entry value and smaller slope than that of disturbed soil. The slope of disturbed soil's SWCC increases and finally equal to that of undisturbed soil's SWCC when air pressure exceeds air-entry value. The shape of undisturbed soil's SWCC is similar to that of disturbed soil. Some characteristic points, such as air-entry value and residual water content, vary differently.2. The hysteresis in the first drying and wetting cycle of undisturbed soil is obvious. There is no discernible change in the rates of desaturation and adsaturation of all drying and wetting cycles. The size of the hysteretic loop is the largest in the first cycle but it becomes smaller during the subsequent drying and wetting cycles.3. Generally speaking, the fitting effect of the SWCC equations with four parameters is much better than the SWCC equations with three parameters, especially the Fredlund and Xing equation.4. It can be concluded that the fitting effect of the SWCC equations is affected notably by the range in suction, which is covered by the actual measurements.5. The suitability of procedure, which uses a planar failure envelope for unsaturated soils in the range of low suction, is proved. The precision of the vanapalli equation is best in the equations to predict unsaturated soil shear strength.