Study On Soil-Water Characteristics And Hydraulic Conductivity Of Unsaturated Deformable Loess

Soil-water characteristics and hydraulic conductivity are the key elements of unsaturated soil mechanics research.Loess is a typical unsaturated soil that has the possibility of large deformation due to its large porosity and under-consolidation structure.The deformation may cause a change in porosity,and then significantly affect the unsaturated characteristics.The study is to accurately describe the soil-water characteristics and seepage properties of unsaturated loess,which includes the soilwater characteristic surface model,the indirect prediction model of unsaturated hydraulic conductivity,and the influence of deformation on soil-water characteristics and hydraulic conductivity.The main research contents and conclusions are as follows:(1)A modified unsaturated soil-water characteristic surface model,considering deformation,was constructed by deriving the relationship between the moisture content and the suction and void ratio,assuming a linear relationship under the assumption of constant suction conditions.The model can accurately describe the variation of water content with pore ratio and suction in the wetting and drying process of loess with different initial pore ratios.The experimental results of soilwater characteristics of two primary paths verified the rationality of the hypothesis of the model.(2)An indirect prediction model for the hydraulic conductivity of unsaturated deformed loess was developed by correcting the saturated hydraulic conductivity and relative hydraulic conductivity.The parameters of the model could all be obtained from the soil-water characteristics model as well as the correlation between saturated hydraulic conductivity and pore ratio.To overcome the defect of the Boltzmann transform method in the determination of the unsaturated hydraulic conductivity,the method was improved,and the experimental results verified the prediction effect of the model.(3)To study the influence of suction deformation on soil-water characteristics and unsaturated hydraulic conductivity,the state data of equal pore ratio obtained by the model and the measured data were compared and analyzed.It is found that the suction-induced deformation in the drying path could reduce the soil-water characteristic parameters such as the air-entry and residual values of the loess,inhibit the hysteresis effect,and weaken the unsaturated hydraulic conductivity.The results of confined compression tests were combined with the model to explore the effects of stress on soil-water characteristics and unsaturated hydraulic conductivity.It is found that stress has an indirect effect through changing the loess porosity,and the significance of the effect is related to the strength of the hydro-mechanical coupling.The study can improve the understanding of the unsaturated properties of loess,provide a more accurate and reliable model for the research of seepage and hydromechanical coupling model of unsaturated loess,and is of great significance to apply unsaturated soil mechanics to solve engineering and environmental problems in loess areas.