Soil Water Characteristic Surface (SWCS) Of Deformed Soils And Its Applications

ABSTRACT:Soil-Water Characteristic Curve is one of the most important constitutive equations in unsaturated soil mechanics, and plays an important role in both theory and application of unsaturated soil mechanics. Among the influencing factors of SWCC, soil deformation is very essential in geotechnical engineering, so that recent studies are particularly focusing on this aspect. In this thesis the void ratio is used as the deformation index to study the effect of deformation on SWCC, and hence the main work and achievements are summarized as follows:(1) The author summarized the existing studies on the impact of soil deformation on SWCC, and then classified them into different methods.(2) Using VJ tech consolidation apparatus, the author conducted SWCC test of silty sand in Beijing to study the influence of initial void ratio on SWCC. The result show that the influence of initial void ratio on SWCC is significant in low suction range, while in the high suction range the difference between SWCCs with different initial void ratio is not obvious.(3) According to the results file format of VJ tech consolidation apparatus, the author developed the software SWCCurver v1.0using the language of Python2.5. This software can provide user with many functions which includes reading and processing the raw data from VJ tech consolidation apparatus, fitting the result data with different model, visualizing the fitting result and finally export the result to Excel file.(4) The author modified the Fredlund-Xing model by introducing the void ratio to the model parameter which correlates to air entry value. Then came up with a new mathematical model which reflects the relationship between initial void ratio and SWCC. Using the new model, the author described a method to predict the coefficient of permeability after the soil deformation occurs.(5) Using the method described in (4), the author simulated seepage-proofing ability of the core wall with different void ratio, the result show that the section flow of core wall with different void ratio has a linear relationship with e3/(1+e).(6) Using the "qualitative method", the author compared the difference of seepage field and FOS of the slope between accounting and neglecting the soil deformation under the condition of rainfall infiltration, the analysis indicates that the evolution of unsaturated zone to saturated zone is faster under the same flux boundary condition when accounting for the soil deformation, thereby resulting in a smaller FOS of the slope. This analysis highlight the importance of soil deformation in engineering practice.