Study On Soil Water Characteristics And Freezing Characteristics Of Loess Containing Sodium Sulfate

Loess is concentrated in Northwest China.In dry region,the loess in large depth range is in unsaturated state.The moisture retention characteristics of unsaturated soil are often measured by the concepts of matrix suction and total suction.The change of suction in soil may affect the stability of structures such as slopes.Therefore,based on the remolded soil samples of the test loess,conducts the filter paper method test to explore the influence of salt content,dry density and other factors on the matrix suction and total suction of the test soil.In order to study the change rule of matrix suction during freezing,the unfrozen water content and matrix suction of specimens with different dry density and salt content during freezing and thawing were monitored.The main contents of this paper are as follows:(1)Loess in the suburb of Lanzhou City was selected for routine geotechnical test.The particle composition,maximum dry density,optimum moisture content and liquid-plastic limit of soil samples were measured;The influence of different sodium sulfate content on compaction characteristics was analyzed;The microstructure of the tested loess was observed by SEM.These provide references for the preparation of soil samples for further tests.(2)The filter paper method was used to measure the matrix suction and total suction of the test soil with different salt content and dry density at 25 ℃;The influence mechanism of salt content and dry density on matrix suction and osmotic suction was analyzed.Matrix suction characteristic curves and total suction characteristic curves of the test soil were drew,and used VG model to fit curves.The influence mechanism of salt content and dry density on the shape and parameters of soil-water characteristic curve were analyzed.(3)The COMSOL Multiphysics software was used to apply the measured VG model fitting parameters by the filter paper method directly to the finite element simulation.The saturation,plastic strain and displacement of soil in the unsaturated loess slope during rainfall were studied.(4)Conduct freezing and thawing test.Relying on pF-Meter sensor to dynamically monitor the changes of unfrozen water content and matrix suction during freezing and thawing.Analyze the influence of dry density and salt content on unfrozen water content and the hysteresis effect of unfrozen water content;The effects of dry density and salt content on temperature change,water and salt phase change and matrix suction change during freezing were investigated.