Study On Water Retention Characteristics And Hydraulic Conductivity Model Of Unsaturated Soil In The Entire Matric Suction Range

The soil-water characteristic curve is the relationship between the matric suction(or matric head)and the water content(or saturation)of the unsaturated soil.The relative hydraulic conductivity curve is the relationship between the matric suction(or matric head)and the relative hydraulic conductivity.They are the most basic constitutive relationship for describing the mechanical behavior of unsaturated soils.This paper analyzes the differences in the water-holding mechanism of unsaturated soils with different pore water components.Based on the fractal theory,the water-holding and hydraulic characteristics of unsaturated soils are studied.The major achievements are summarized as follows:1.Soil-water characteristic curve model for the entire matric suction range was proposedBased on the difference of the water-retention mechanism of unsaturated soils in different matric suction ranges,an extended capillary model was established according to the water transport process of unsaturated porous media.The molecular force component and the ionic electrostatic force component in the separation pressure were analyzed,and the concept of adsorbed water-specific thickness was proposed to describe the relationship between the pore size and the adsorbed film thickness,a soil-water characteristic curve for the entire suction range was established.Comparing the experimental data of different soil types with the prediction curves of the proposed model,the results show that the model can better describe the soil-water retention behavior in the entire suction rang.2.Hysteresis increment model of soil-water characteristic curve based on pore expansion and contraction was proposed for unsaturated soilThis paper this paper assumes that the expansion and contraction of pores can cause the hysteresis of SWCC.And axial translation technique is employed as an example to explain the expansion and contraction of soil pores under hydraulic loading.Then,an incremental equation for the soil-water characteristic curve that can describe the hysteresis effect and the pore expansion and contraction is obtained by reducing ?_d to a constant.Finally,the applicability of the model to different soil types is verified by five data sets,and the model can predict the high-order scanning curve.3.A fractal model of relative hydraulic conductivity curve account for irreducible water was proposedBased on the fractal theory and the Yang-Laplace equation,the influence of irreducible water on the hydraulic characteristics of unsaturated soil is considered,and then,a relative hydraulic conductivity model considering the irreducible water is established.The model was verified with 14 sets of test data of different soil types.Finally,the effects of fractal dimension D and r_min/r_max on the hydraulic characteristics of unsaturated soils are analyzed.4.A relative hydraulic conductivity curve of the entire matric suction range was proposed for unsaturated soilBased on the proposed concept of adsorbed water-specific thickness and extended capillary model,a generalized statistical equation of unsaturated soil water permeability coefficient was established.Then,the pore size distribution of porous media is used in the generalized statistical equation to obtain a fractal model of relative hydraulic conductivity equation that can describe the transport characteristics of adsorbed water.Eight data sets of relative hydraulic conductivity were used to validate the proposed model.The results show that the model can well describe the hydraulic characteristics of unsaturated soils in the whole matric suction range.Finally,the Monte Carlo simulation method was used to further analyze the applicability of the model to different soil types.