| In recent years,with the continuous promotion of the great policy of the the Belt and Road,more and more engineering construction has occurred in the loess like saline land area in northwest China.However,due to the unique nature of loess like saline soil,a series of geotechnical engineering problems and natural disasters such as salt swelling,dissolution,and secondary salinization have seriously constrained local engineering construction and economic development.The emergence of these problems is closely related to the water retention and permeability characteristics of loess like saline soil.Therefore,based on previous research,this article takes artificially prepared loess-like saline soil as the research object,obtains soil water characteristic curves under different conditions using the filter paper method,analyzes the influence of initial salt content,salt type,initial dry density,and temperature on its water holding characteristics,and combines the measured soil water characteristic curves,The unsaturated permeability coefficients at different sodium sulfate salt contents and dry densities were obtained through the wet front advancement method.The main research results obtained are as follows:(1)The loess like saline soil is artificially prepared in the laboratory,and the compaction test,boundary moisture content test and direct shear test are carried out respectively.The test results show that with the increase of salt content,the maximum dry density of chloride saline soil first increases and then decreases,while the optimal water content always decreases.The maximum dry density of sulfate saline soil continuously decreases,while the optimal water content gradually increases.The maximum dry density of carbonate saline soil first increases and then decreases,while the optimal water content gradually increases.The liquid limit,plastic limit,and plastic index of chloride saline soil and sulfate saline soil gradually decrease with the increase of salt content,while the liquid limit,plastic limit,and plastic index of carbonate saline soil gradually increase with the increase of salt content.The shear strength indexes,cohesion,and internal friction angle of chloride saline soil,carbonate saline soil,and sulfate saline soil all show a trend of first increasing and then decreasing with the increase of salt content.(2)The water retention characteristics of loess-like saline soil are significantly affected by salt content,salt type,initial dry density,and temperature.As the initial salt content increases,the water retention capacity of the three types of loess shaped saline soils increases.At the same initial salt content,the matrix suction of sodium sulfate saline soil is the highest,followed by sodium carbonate saline soil,and sodium chloride saline soil is the smallest.As the initial dry density increases,the volumetric moisture content increases,and the water holding capacity of loess shaped saline soil increases.The influence of temperature on the water retention characteristics of loess shaped saline soil is mainly achieved through the occurrence of water and gas in the soil,the interaction between soil and water,and the solubility of salt.When the soil sample has the same moisture content,the lower the temperature,the greater the matrix suction,and this effect is more obvious at high moisture content.Based on the van Genuchten model,the soil water characteristic curve was fitted,and it was found that both the intake air value and the residual water content increased with the increase in dry density.This is because the larger the dry density,the less macropores,and the denser the soil.Temperature and salt content have little impact on the residual water content of soil.As the temperature decreases,the intake air value continuously increases,and the effect of salt content on the intake air value is opposite to that of temperature.(3)Based on a self-developed one-dimensional soil column infiltration device,a wetting front advancement method was used to conduct one-dimensional soil column infiltration tests on loess shaped sulfate saline soil under different dry densities and salt contents.The experimental results indicate that the wetting front rate exhibits a positive proportional relationship with time in the double logarithmic coordinate system.The higher the dry density and salt content,the slower the movement of the wetting front,and the longer it takes for the wetting front to move to the bottom of the soil column.The unsaturated permeability coefficient decreases with the increase of dry density,but it is mainly reflected in the low suction section.In the high suction section,the permeability coefficient of loess like sulfate saline soil under different dry densities is almost no difference.An increase in salt content also reduces the permeability coefficient,and the effect gradually weakens with the increase of matrix suction. |
