| Water-retention and permeability characteristics are key points to the behavior of an unsaturated soil.On the basis of reviewing the literatures,this paper study evolutionary water retention model for pore size distribution of compacted clay,model of Bentonite hysteretic water retention,unsaturated permeability anisotropy and evolution of clay particles liquid bridge.The measured value and numerical calculation in the existing literature are carried out to study these five aspects,as follows:(1)A water retention model is presented accounting for the evolution of the aggregated structure of compacted clays along generalized hydro-mechanical stress paths.The water retention mechanisms of both micro-structural and macro-structural levels are described separately using an expression of typical water retention model.From this model,a theoretical pore diameter distribution can be derived.Experimental pore diameter distribution data on two compacted clays subjected to various wetting,drying and loading paths are exploited to provide a physical based calibration of the parameters of the water retention model.Not only they emphasize the evolution of the air-entry pressure,along generalized stress paths but they also provide a quantification of these processes.On this basis,simple evolution laws are proposed.Finally,the water retention model is validated against other experimental data on the same materials compacted at different dry densities.(2)After analyzing the water retention test results of high-swelling soils,a conceptual water retention model was developed to account for the change in the void ratio and the micro-structural evolutions during the hydration of the bentonite material.The model was based on an elasto-plasticity theory that used a linear anisotropic hardening rule.The model produced the water retention curves for the entire hydraulic domain under a constant void ratio.The scanning behavior at a given compaction state was analyzed by considering the micro-structural void ratio at different saturation stages.The developed formulation could be an essential contribution to the constitutive model of high-swelling soils.(3)On the basis of unsaturated permeability coefficient function proposed by Mualem,the expression of coefficient of anisotropy of effective saturation is derived through introducing connectivity-tortuosity parameters.Unsaturated permeability anisotropy is divided into nine different types according to the expression at the same time to study the applicability under different conditions,the validity of the expression is verified by the experimental result of unsaturated permeability coefficient values in the existing literature.In the end,combining with the Van Genuchten-Mualem function and using the expression to describe the effect of matric suction on unsaturated permeability anisotropy of 5 kinds of soil quantificationally.The results show that the expression can descrbie the change rule of anisotropy coefficient with matric suction.(4)Referencing the analogy procedure of coarse particle in the existing literature,clay particles are simplified as flaky grains that they are parallel to each other,with considering the influence of the surface roughness,and regard its moisture as fluid bridge,combined with geometrical parameters of liquid bridge between clay particles to deduce the expression that are about Dimensionless liquid bridge volume and solid-liquid contact angle of the dimensionless liquid bridge capillary force.By making the expression zero,the relationship between volume and solid-liquid contact angle of the dimensionless liquid bridge is plotted,and the curve is divided into three regions according to the formation of liquid bridges from the formation to the fracture process.In the end,settling the measured data in existing literature,and the relationship between capillary force and liquid bridge volume and solid-liquid contact angle was analyzed by the expression. |
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